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Computational material design (CMD) employs quantum mechanical simulations, density functional theory, and machine learning techniques to correlate electronic structural attributes with physical and chemical properties of materials. Over the last decade, CMD has proven to be critical to the advancement of materials science and a variety of engineering fields. This contribution provides an overview of CMD's success in driving materials discovery for catalysis in the context of sustainable energy applications. Specifically, we discuss how CMD has enabled the development of catalysts for three electrochemical processes that are critical to sustainable energy applications, oxygen reduction reactions, water oxidation reactions, and CO2 reduction reactions. We illustrate how CMD provides a powerful and efficient method for understanding underlying reaction mechanisms as well as predicting and optimizing catalyst properties. Furthermore, we demonstrate how this strategic approach has enabled researchers to effectively navigate the vast chemical space of potential catalysts and rapidly identify novel materials possessing desirable electronic structures and catalytic activity. [ABSTRACT FROM AUTHOR]

We explore transfer learning models from a pre-trained graph convolutional neural network representation of molecules, obtained from SchNet, to predict 13C-NMR, pKa, and log S solubility. SchNet learns a graph representation of a molecule by associating each atom with an "embedding vector" and interacts the atom-embeddings with each other by leveraging graph convolutional filters on their interatomic distances. We pre-trained SchNet on molecular energy and demonstrate that the pre-trained atomistic embeddings can then be used as a transferable representation for a wide array of properties. On the one hand, for atomic properties such as micro-pK1 and 13C-NMR, we investigate two models, one linear and one neural net, that input pre-trained atom-embeddings of a particular atom (e.g. carbon) and predict a local property (e.g., 13C-NMR). On the other hand, for molecular properties such as solubility, a size-extensive graph model is built using the embeddings of all atoms in the molecule as input. For all cases, qualitatively correct predictions are made with relatively little training data (<1000 training points), showcasing the ease with which pre-trained embeddings pick up on important chemical patterns. The proposed models successfully capture well-understood trends of pK1 and solubility. This study advances our understanding of current neural net graph representations and their capacity for transfer learning applications in chemistry. [ABSTRACT FROM AUTHOR]

Computational chemistry approach based on density functional theory (DFT) was utilized to investigate the interaction, adsorption behaviour, electronic and structural properties of nanostructured complexes formed by 4-(4-(bis(2-chloroethyl)amino)phenyl)butanoic acid (CPB) and all carbon fullerene nanocage, (C24NC), boron functionalized carbon nanocage (C24NC@B@CPB), carboxylate functionalized (C24NC@COOH@CPB), amino functionalized (C24NC@NH2@CPB), and hydroxy functionalized (C24NC@OH@CPB) nanostructured materials. To understand effectively the interaction of the drug and surface, topological analysis was conducted via the atoms in molecule (quantum theory of atoms in molecules) and noncovalent interaction approach. Electronic properties such as quantum chemical descriptors, natural bond orbital and nonlinear optics are equally considered and reported. All computations were achieved at the B3LYP-D3 and ωB97XD levels of theory with the 6-311++G(d, p) basis set. The results indicate that the adsorption energy of CPB on C24NC and its functionalized derivatives are in the range of −0.52 to 2.89 eV indicating that physisorption and chemisorption mechanism are prevalent mechanisms of adsorption. C23B@CPB, C24OH@CPB, and C24NH2@CPB were observed to possess the best characteristics to be considered as transport vehicles for CPB due to their strong adsorption nature (chemisorption) and solubility in solution. [ABSTRACT FROM AUTHOR]

The article focuses on expanding uranyl dicyanoaurate coordination polymers into the second and third dimensions. Topics inlcude the uranyl dicyanoaurate coordination polymer of the form being structurally has characterized as a linear chain of dicyanoaurate units, and the materials exhibit emission arising the uranyl moiety and the gold(I) centre, and the first multidimensional uranyl–dicyanoaurate coordination polymers.

The article discusses a study on a two-step route, which is Mitsunobu followed by Schiff base reactions, to asymmetrically substituted pyridazinones from maleic hydrazide with 2-, 3-, or 4-pyridinecarboxaldehyde. Highlights include the reaction of maleic hydrazide with ethanolamine under Mitsunobu conditions, the use of ethanolamine when performing the Mitsunobu step, and hydrogen bonded dimers and close stacking of pyridazinone moieties.

The degree-based topological indices correlate certain physicochemical properties such as boiling point, strain energy, and stability, etc., of certain chemical compounds. Among the major classes of topological indices are the distance-based topological indices, degree-based topological indices, and counting-related polynomials and corresponding indices of graphs. Among all of the degree-based indices, namely the first general Zagreb index, general Rndić connectivity index, general sum-connectivity index, atom-bond connectivity index (ABC), and geometric-arithmetic index (GA), are most important due to their chemical significance. In this paper, we compute the first general Zagreb index, general Randić connectivity index, general sum-connectivity index, ABC, GA, ABC4, and GA5 indices of hexagonal parallelogram P( m, n) nanotubes, triangular benzenoid Gn, and zigzag-edge coronoid fused with starphene ZCS( k, l, m) nanotubes by using the line graphs of the subdivision of these chemical graphs. [ABSTRACT FROM AUTHOR]

Topological indices are numerical parameters of a graph that characterize its molecular topology and are usually graph invariant. In a QSAR/QSPR study, the physico-chemical properties and topological indices such as the Randić, atom-bond connectivity (ABC), and geometric-arithmetic (GA) indices are used to predict the bioactivity of chemical compounds. Graph theory has found a considerable use in this important area of research. All of the studied interconnection networks in this paper are constructed by the Star of David network. In this paper, we study the general Randić, first Zagreb, ABC, GA, ABC4 and GA5, indices for the first, second, and third types of dominating David derived networks and give closed formulas of these indices for these networks. These results are useful in network science to understand the underlying topologies of these networks. [ABSTRACT FROM AUTHOR]

Ab initio molecular-orbital calculations have been performed to investigate the reaction mechanisms of the HO*-initiated reactions of the α,β-unsaturated aldehydes: acrolein (ACR), methacrolein (MACR), and trans- crotonaldehyde (CROT). All geometries were fully optimized at the MP2(Full)/6-31G(d,p) level. The correlation energy corrections were introduced by carrying out single-point calculations using both spin-projected second-order Moller-Plesset perturbation theory (PMP2) and coupled-cluster theory (CCSD(T)) using basis sets of different sizes. All reaction pathways studied proceed via a barrierless formation of a loosely bound pre-reactive complex in the entrance channel. The transition-state structures of the HO* additions to the terminal (β) and to the central (α) carbon atoms of the C=C double bond are found to be reactant-like structures. The lowest-energy barrier pathways are found to be the aldehydic H-atom abstraction. The β-addition pathways are found to be energetically more favored than the a-addition pathways. The HO* addition and aldehydic H-atom abstraction pathways are found to be highly exoergic, with the H-atom abstraction pathway being more exoergic than the addition pathways. Although the methyl substitution at the C=C double bond of methacrolein and crotonaldehyde lowers the energies of the transition-state structures of both α- and β-addition pathways, it destabilizes the energies of the transition-state structures of the corresponding aldehydic H-atom abstraction pathways, compared with that of acrolein. Key words: ab initio, transition-state structures, acrolein, methacrolein, crotonaldehyde. On a effectue des calculs theoriques d'orbitales moleculaires ab initio afro d'etudier les mecanismes de reactions initiees par le radical HO* d'aldehydes α,β-insaturees, tel l'acroleine (ACR), la methacroleine (MACR) et le transcrotonaldehyde (CROT). Toutes les geometries ont ete completement optimisees an niveau MP2(full)/6-31G(d,p). Des corrections d'energie de correlation ont ete introduites en effectuant des calculs ponctuels a l'aide de la theorie des perturbations de Moller-Plesset du deuxieme ordre en projection de spin (PMP2) ainsi que la theorie des agregats couples [CCSD(T)], en faisant appel a des ensembles de bases de diverses tailles. Toutes les voies reactionnelles etudiees procedent, a l'entree du tunnel, par la formation sans barriere reactionnelle d'un complexe prereactif a interactions faibles. On a trouve que les structures des etats de transition resultant de l'addition du HO* aux atomes de carbone terminal (β) et central (α) de la double liaison C=C possedent des structures qui ressemblent aux reactifs. On a trouve que les voies reactionnelles impliquant la barriere d'energie la plus faible correspondent a l'enlevement de l'atome d'hydrogene aldehydique. On a trouve que les voies reactionnelles correspondant a l'addition du radical HO*et a l'enlevement de l'atome d'hydrogene sont fortement exoergiques; la voie impliquant l'enlevement de l'atome d'hydrogene est plus exoergique que les voies reactionnelles conduisant a une addition a. Meme si elle diminue les energies des structures de transition de chacune des deux voies reactionnelles des additions en a et en β, par comparaison avec celle de l'acroleine, la presence de substituants methyles sur la double liaison C=C de la methacroleine et du crotonaldehyde destabilise les energies des structures de l'etat de transition des voies reactionnelles correspondantes d'enlevement de l'atome d'hydrogene aldehydique. Mots-cles : ab initio, structure de l'etat de transition, acroleine, methacroleine, crotonaldehyde. [Traduit par la Redaction], Introduction Aldehydes play an important role in the chemistry of the polluted troposphere. They may be emitted as primary pollutants from partial oxidation of hydrocarbon fuels, industrial uses, and from [...]

Azide-terminated alkyl thiolate monolayer-protected gold nanoparticles (1-[C.sub.12]MPN) with a core size of 1.8 ± 0.2 nm were prepared. 1-[C.sub.12]MPN was modified in high yields via an uncatalyzed 1,3-dipolar cycloaddition (click-type reaction) with a variety of terminal acyl-alkynes under hyperbaric conditions at 11000 atm. The resulting 1,2,3- triazole modified MPNs (2-[C.sub.12]MPN) were characterized using ¹H NMR spectroscopy and were verified by comparison of the spectra to those obtained for the products of the model reactions of 1-azidododecane with the same alkynes. TEM analysis showed that the high-pressure conditions did not affect the size of the gold core, suggesting that the only effect is to facilitate the chemical reaction on the particles. Key words: nanoparticles, hyperbaric chemistry, 1,3-dipolar cycloaddition, monolayers. On a prepare des nanoparticules d'or protegees par une monocouche d'alkylthiol (1-[C.sub.12]MPN) portant une fonction azide en position terminale et dont le diametre principal est egal a 1,8 ± 0,2 nm. Le produit 1-[C.sub.12]MPN a ete modifie avec des rendements eleves par le biais d'une cycloaddition 1,3-dipolaire non catalysee (reaction de type par un clic) avec une variete d'acyl-alcynes terminales, dans des conditions hyperbariques, a 11,000 atmospheres. Les nanoparticules d'or modifiees, protegees par une monocouche d'alkylthiol (2-[C.sub.12]MPN) et portant un cycle 1,2,3-triazole ont ete caracterisees par spectroscopie RMN du 111 et ont ete verifiees par comparaison avec les spectres obtenus pour les produits des reaction' modeles du 1-azidodecane avec les memes alcynes. Une analyse par microscopie electronique a transmission (MET) a permis de montrer que les conditions de haute pression n'ont pas affecte la taille du diametre principal de l'or suggerant que le seul effet est de faciliter la reaction chimique sur les particules. Mots-cles : nanoparticules, chimie hyperbarique, cycloaddition 1, 3-dipolaire, monocouches. [Traduit par la Redaction], Introduction The Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition of azides to terminal alkynes to produce a triazole ring, the 'click' reaction, is a popular and powerful tool in organic synthesis and combinatorial [...]

The synthesis and properties of three ionic liquids based on 1-methyl-3-(2-phenethyl)imidazolium cation ([MPIm]) and the chloride, tetrafluoroborate, and hexafluorophosphate anions have been investigated. The proposed quaternization and anion exchange processes afforded quantitative amounts of the three ionic liquids, and very pure [MPIm][[BF.sub.4]] and [MPIm][[PF.sub.6]] were obtained after recrystallization from ethanol. [MPIm][[BF.sub.4]] showed low melting point and high electrical conductivity. These ionic liquids (immiscible with diethyl ether but miscible with water and DMSO) absorb air moisture, increasing their mass and decreasing their viscosity. The results of NMR spectroscopy ([sup.1.H], [13.sup.C], and [sup.19.F]) and X-ray structure determination confirm the possibility of ion-pair and hydrogen-bond formation in [MPIm][[BF.sub.4]]. Key words: ionic liquid, 1-methyl-3-(2-phenethylimidazolium), X-ray diffraction, tetrafluoroborate, hexafluorophosphate. La synthese et les proprietes de trois liquide ioniques bases sur le cation de 1-methyl-3-(2-phenethyl)imidazolium ([MPIm]) et des anions comme chlorude, tetrafluoroborate et hexafluorophosphate ont ete investigues. Le processus propose pour les reactions de quaternization et d'echange d'anion a offert les trois liquide ioniques de facon quantitative et tres pure [MPIm][[BF.sub.4]] et [MPIm][[PF.sub.6]] ont ete obtenus apres la cristallisation dans l'ethanol. [MPIm][[BF.sub.4]] a montre le point de fusion bas et la conductivite electrique elevee. Ces liquide ioniques (immiscibles dans l'ether mais miscibles dans l'eau et le DMSO) absorbent l'humidite de l'air qui augmente leur poids et diminue leur viscosite. Les resultats de spectroscopie RMN ([sup.1.H], [sup.13.C] et [sup.19.F]) et la determination de structure par rayon-X confirment la possibilite de la formation d'une paire d'ion et de la bande hydrogene dans [MPIm][[BF.sub.4]]. Mots-cles : liquide ionique, 1-methyl-3-(2-phenethyl)imidazolium, Diffraction du rayon X, tetrafluoroborate, hexafluorophosphate. [Traduit par la Redaction], Introduction Intense research activity in the field of ionic liquids is currently in progress. Because the properties of ionic liquids (miscibility with water and other solvents, solvation ability, polarity, viscosity, [...]

Water promotes hydrothiolation of unactivated alkynes efficiently without any catalyst or additive. The reaction at room temperature furnishes vinyl sulfides with high regioselectivity via anti-Markovnikov addition. The terminal alkynes provide dithiolanes at 80[degrees]C by bis-addition. The reactions are very clean and high yielding. Key words: alkynes, hydrothiolation, vinyl sulfides, regioselectivity, water. L'eau favorise l'hydrothiolation des alcynes non actives d'une facon efficace, sans catalyseur ou additif. A la temperature ambiante, la reaction conduit a la formation de sulfures de vinyle, avec une regioselectivite par le biais d'une addition anti-Markovnikov. Les additions a 80[grados]C sur des alcynes terminaux conduisent a des dithiolanes resultant d'une bis-addition. Les reactions sont tres propres et les rendements sont eleves. Mots-cles : alcynes, hydrothiolation, sulfures de vinyle, regioselectivite, eau. [Traduit par la Redaction], Introduction The hydrothiolation of alkynes by thiols is a very interesting and challenging reaction being associated with mono- and bis-condensation, Markovnikov and (or) anti-Markovnikov addition, and stereoselectivity. This reaction is [...]

Temperature- and pressure-dependent Raman and luminescence spectra of four crystalline complexes of palladium(II) and platinum(II) with chelating diethyldithiocarbamate (EDTC) and pyrrolidine-N-dithiocarbamate (PDTC) ligands are reported. The crystal structure of [Pd[(PDTC).sub.2]] was resolved at 120 K. Luminescence band maxima are observed at approximately 14 500 [cm.sup.-1] and 16 000 [cm.sup.-1] for the palladium(II) and platinum(II) complexes, respectively. Pressure leads to blue shifts of the band maxima by +9 and +13 [cm.sup.-1]/kbar for [Pd[(EDTC).sub.2]] and [Pd[(PDTC).sub.2]], and +15 [cm.sup.-1]/kbar for [Pt[(EDTC).sub.2]]. These spin-forbidden d-d luminescence transitions have lifetimes of approximately 600 ms at temperatures below 20 K. Luminescence intensities at room temperature are low, but they increase significantly with external pressure. The experimental results show that strong increases of luminescence intensities caused by pressure are not limited to complexes with monodentate ligands, a result providing insight on the coordinates with emitting-state distortions responsible for this effect. Key words: palladium(II) complexes, platinum(II) complexes, high-pressure luminescence spectroscopy, high-pressure Raman spectroscopy. Cet article porte sur les proprietes spectroscopiques d'une serie de quatre composes du palladium(II) et du platine(II) avec les ligands chelatants diethyldithiocarbamate (EDTC) et pyrrolidine-N-dithiocarbamate (PDTC). La structure cristalline du complexe [Pd[(PDTC).sub.2]] a 120 K a en outre ete resolue. Les spectres Raman et de luminescence a temperature et pression variable ont ete mesures pour les quatre composes. Les maxima des bandes de luminescence se trouvent a environ 14 500 [cm.sup.-1] et 16 000 [cm.sup.-1] pour les complexes de palladium(II) et platine(II). La pression induit un decalage vers le bleu des maxima de luminescence de +9 [cm.sub.-1]/kbar pour [Pd[(EDTC).sub.2]], de +13 [cm.sup.-1]/kbar pour [Pd[(PDTC).sub.2]] et de +15 [cm.sup.-1/kbar] pour [Pt[(EDTC).sub.2]]. Ces transitions d-d interdites de spin ont des durees de vie de l'ordre de 600 ms a basse temperature. Les bandes de luminescence ont une faible intensite a temperature ambiante, mais celle-ci augmente de maniere importante avec la pression. Les resultats experimentaux montrent que l'augmentation de l'intensite de luminescence a haute pression n'est pas limitee aux complexes avec ligands monodentates. Mots-cles : complexes du palladium(II), complexes du platine(II), spectroscopie de luminescence a basse temperature et a haute pression, spectroscopie Raman a haute pression., Introduction Square-planar complexes of [d.sup.8]-configured metal ions such as platinum(II) and palladium(II) have a rich variety of electronic excited states, which has made them attractive systems for studies of electronic [...]

Weakly interacting ligands including three Gemini surfactants, didodecyldimethylammonium bromide (DDAB), and amines ([RNH.sub.2], [R.sub.2]NH, and [R.sub.3]N) were used to prepare Au nanoparticles (NPs). Aqueous Au NPs capped with DDAB and Gemini surfactants showed similar sizes (3-4 nm), whereas toluene-based NPs stabilized with DDAB, amines, and their mixtures range from 2.5 to 9.3 nm. Ligand effect on Au-Pd NP structure was also studied with EXAFS. These findings were consistently accounted for by considering the ligand's electronic/steric effects and mixed ligands coadsorption, and suggest useful ways to control NP structure by manipulating the two effects and using mixed capping ligands. Key words: metal nanoparticles, capping ligands, electronic effect, steric effect, EXAFS. On a utilise des ligands interagissant faiblement, dont trois agents de surface Gemini, le bromure de didodecyldimethylammonium (BDDA) et des amines ([RNH.sub.2]), [R.sub.2]NH et [R.sub.3]N) pour preparer des nanoparticules (NP) d'or (Au). Les tailles des nanoparticules d'or aqueuses, fermees avec du BDDA ou des agents de surfaces Gemini sont assez semblables (3-4 nm) alors que celles des nanoparticules a base de toluene et stabilisees par du BDDA, des amines ou leurs melanges varient de 2,5 a 9,3 nm. On a aussi examine l'effet de ligand sur la structure des nanoparticules Au--Pd par la technique de structure fine d'absorption des rayons-X etendue (SFAXE). Les observations peuvent etre expliquees d'une facon coherente en considerant les effets sterique/electronique du ligand et la coadsorption des ligands mixtes et ceci suggere des facons utiles de controler la structure des nanoparticules en manipulant les deux effets et en utilisant des ligands mixtes pour les fermer. Mots-cles : nanoparticules metalliques, ligands de fermeture, effet electronique, effet sterique, structure fine d'absorption des rayons X etendue (SFAXE). [Traduit par la Redaction], Introduction Selection of capping ligands for the synthesis of metal nanoparticles (NPs) is of fundamental and technological importance. (1-6) Capping the NP surface with alkanethiols and their derivatives has become [...]

A new tetraoxygenated xanthone, cowaxanthone F (1), as well as four known compounds, morelloflavone (2), volkensiflavone (3), morelloflavone-7'-O-glucoside (fukugiside, 4), and 1,6-dihydroxyxanthone (5), were isolated from the crude acetone extract of the twigs of Garcinia cowa (Guttiferae). All compounds (1-5) were tested for antioxidant activity against DPPH (diphenylpicrylhydrazyl), hydroxyl, and superoxide radicals; only morelloflavone (2) and morelloflavone-7'O-glucoside (4) exhibited high potency. Eight tetraoxygenated xanthones from the fruits of G. cowa, cowaxanthones A-D (6-9), cowanin (15), °-mangostin (16), mangostanin (17), and cowanol (18), were also investigated for anti-inflammatory activity using ethyl phenylpropiolate (EPP)-induced ear edema. Assessment at 30, 60, and 120 min revealed that cowaxanthones B-D (7-9), cowanin (15), and °-mangostin (16) exhibited significant anti-inflammatory activity when compared to phenylbutazone, while cowaxanthone A (6), mangostanin (17), and cowanol (18) showed less activity. Key words: Guttiferae, Garcinia cowa, cowaxanthone F, anti-inflammatory activity, antioxidant activity. On a isole une nouvelle xanthone tetraoxygenee, la cowaxanthone F (1) ainsi que quatre composes connus : morelloflavone (2), volkensiflavone (3), morellosflavone-7'-O-glucoside (fukugiside, 4), et la 1,6-dihydroxyxanthone (5) a partir de l'extrait brut a l'acetone des rameaux de Garcinia cowa (Guttiferae). On a teste tous les produits pour leurs proprietes antioxydantes contre les radicaux DPPH, hydroxyles et superoxydes et seuls la morelloflavone (2) et le morellosflavone-7'-O-glucoside presentent des potentiels eleves. On a aussi examine huit xanthones tetraoxygenees extraites des fruits de G. cowa : cowaxanthones (A-D) (6-9), cowanine (15), α-mangostine (16), mangostanine (17) et cowanol (18) pour determiner leur activite anti-inflammatoire a l'aide de l'oedeme de l'oreille induite par EPP. L'evaluation a 30, 60 et 120 minutes revele que, par comparaison avec la phenylbutazone, les cowaxanthones (B-D) (7-9), cowanine (15) et α-mangostine (16) presentent une activite anti-inflammatoire significative alors que la cowaxanthones (A) (6), la mangostanine (17) et le cowanol (18) en possede moins. Mots-cles: Guttiferae, Garcinia cowa, cowaxanthone F, activite anti-inflammatoire, activite antioxydante. [Traduit par la Redaction], Introduction Garcinia cowa Roxb. (Guttiferae, Clusiaceae), commonly known as 'Cha-muang', is a small to medium sized tree found widely distributed in Thailand. The fruits and leaves are used for the [...]

This paper considers the degree to which branched hydrocarbons obey a group additivity scheme for energy and population, extending the study of the known experimental and theoretical transferability of the methyl and methylene groups of the linear hydrocarbons. The chemical groups are defined and their properties are determined using the quantum theory of atoms in molecules (QTAIM). The calculations are carried out with a large basis set at the restricted Hartree--Fock and MP2(full) levels of theory. The deviations from additivity, noted for small ring hydrocarbons leading to the definition of strain energy, are also investigated, showing that the QTAIM energies recover the experimental values. The particular delocalization of the electron density over the surface of the cyclopropane ring, responsible for its 'homoaromatic' properties, is discussed in some detail. The calculations reported here satisfy the virial theorem as required for the atomic definition of energy. The problems associated with the use of DFT theory arising from its failure to satisfy the virial theorem are discussed with reference to the study of group transferability. Key words: atoms in molecules, group additivity, transferability, strain energy. Dans ce travail, on considere le degre auquel des hydrocarbures ramifies obeissent a un schema d'additivite de groupe pour l'energie et la population, etendant ainsi l'etude de la transferabilite experimentale et theorique connue des groupes methyle et methylene des hydrocarbures lineaires. Les groupes chimiques sont definis et leurs proprietes sont determinees en faisant appel a la theorie quantique des atomes dans les molecules (TQADM). Les calculs sont effectues avec un grand ensemble de base aux niveaux de Hartree-Fock et MP2(complet) de la theorie. On a aussi examine les deviations par rapport a l'additivite notes pour les petits cycles hydrocarbones, ce qui a conduit a la definition de l'energie de tension et qui a permis de montrer que les energies de la TQADM recuperent les valeurs experimentales. On discute en detail de la delocalisation particuliere de la densite electronique sur la surface du noyau cyclopropane, responsable de ses proprietes homoaromatiques. Les calculs rapportes ici satisfont le theoreme du viriel, tel que requis pour la definition atomique de l'energie. En reference avec l'etude sur la transferabilite de groupe, on discute aussi des problemes associes avec l'utilisation de la theorie de la fonctionnelle de la densite decoulent de son incapacite a satisfaire le theoreme du viriel. Mots-cles : atomes dans les molecules, additivite de groupe, transferabilite, energie de tension. [Traduit par la Redaction], Experimental additivity schemes It is nearly 80 years since Rossini and co-workers demonstrated that the heats of formation of the homologous series of linear saturated hydrocarbons obey a group additivity [...]

Polyyne glycosides are a class of natural products that have been found in terrestrial plants, fungi, and marine algae. Many display interesting and potentially useful biological activities, which in some cases has initiated synthetic efforts toward their formation. This review provides a comprehensive report of polyyne glycosides isolated from natural sources, as well as the synthesis of these molecules and their analogues. Key words: polyynes, polyacetylenes, carbohydrates, natural products. Les glycosides de polyyne correspondent a une classe de produits naturels qu'on retrouve dans les plantes terrestres, les champignons et les algues marines. Plusieurs presentent des activites biologiques interessantes et potentiellement utiles qui, dans certains cas, ont conduit a l'initiation d'efforts de synthese orientes vers leur formation. Cette revue fournit un rapport approfondi sur les glycosides de polyyne isoles de sources naturelles et sur les efforts de synthese de ces molecules et de leurs analogues. Mots-cles : polyynes, polyacetylenes, hydrates de carbone, produits naturels. [Traduit par la Redaction], Introduction Polyynes (1) have long been known to exist in natural sources, and thousands have been isolated in the past century from a wide range of terrestrial plant species, fungi, [...]

When the anisotropy of a harmonic ion trap is increased, the ions eventually collapse into a two-dimensional structure consisting of concentric shells of ions. This collapse generally behaves like a second-order phase transition. A graph of the critical value of the anisotropy parameter vs. the number of ions displays substructure closely related to the inner-shell configurations of the clusters. The critical exponent for the order parameter of this phase transition (maximum extent in the z direction) was found computationally to have the value β = 1/2. A second critical exponent related to displacements perpendicular to the z axis was found to have the value δ = 1. Using these estimates of the critical exponents, we derive an equation that relates the amplitudes of the displacements of the ions parallel to the x-y plane to the amplitudes along the z axis during the flattening process. Key words: ion trap, flattening, phase transition, critical exponent. Quand on augmente l'anisotropie d'un piege ionique, les ions adoptent tot ou tard une structure aplatie formee de couches concentriques d'ions. Cet aplatissement se comporte comme une transition de phase du deuxieme ordre. Un graphe de l'anisotropie critique contre le nombre d'ions demontre une organisation reliee a la configuration de la couche interne de l'amas. Nos calculs numeriques demontrent que l'exposant critique associe au parametre d'ordre de cette transition de phase (l'etendue maximale le long de l'axe z) a la valeur β = 1/2. Un deuxieme exposant critique associe aux deplacements des ions perpendiculairement a l'axe z a la valeur δ = 1. Ces estimations numeriques des exposants critiques nous permettent d'obtenir une equation qui relie les amplitudes des deplacements des ions paralleles au plan x-y aux deplacements paralleles a l'axe z durant l'aplatissement. Mots-cles : piege ionique, aplatissement, transition de phase, exposant critique., Introduction The potential energy of a system of N identically charged ions in a harmonic trap, expressed in dimensionless form, is (1,2) [1] [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] where [...]

The O-H σ-bond activation of methanol, the Si-H σ-bond activation of silane, and the Si-C σ-bond activation of methylsilane by titanium(IV)-imido complex [([Me.sub.3]SiO).sub.2] Ti(NSi[Me.sub.3]) were theoretically investigated with DFT and MP2 to MP4(SDQ) methods. The O-H σ-bond activation of methanol occurs with small activation barrier ([E.sub.a]) of 7.1 (14.6) kcal/mol and large exothermicity ([E.sub.exo]) of 65.8 (61.4) kcal/mol to afford [([Me.sub.3]SiO).sub.2]Ti(O[CH.sub.3])[NH(Si[Me.sub.3])], indicating that the O-H σ-bond activation occurs easier than the C-H σ-bond activation ([E.sub.a] = 14.6 (21.5) kcal/mol and [E.sub.exo] = 22.7 (16.5) kcal/mol), where DFT- and MP4(SDQ)-calculated values are presented without and in parenthesis hereafter. Though the O[CH.sub.3] group becomes anionic and the H atom becomes proton-like in this activation reaction, population changes more moderately occur than those of the C-H σ-bond activation. This is because the H-O[CH.sub.3] bond is already polarized in methanol. In the Si-H σ-bond activation, two reaction courses were investigated; in one course, the product is [([Me.sub.3]SiO).sub.2]Ti(Si[H.sub.3])[NH(Si[Me.sub.3])] in which the H atom and the Si[H.sub.3] group are bound to the N atom and the Ti center, respectively, while in the other course the product is [([Me.sub.3]SiO).sub.2]Ti(H)[N(Si[H.sub.3])(Si[Me.sub.3])] in which the H atom and the Si[H.sub.3] group are bound to the Ti center and the imido N atom, respectively. Though the former reaction occurs with small Ea value and large exothermicity, the latter reaction occurs easier with further smaller [E.sub.a] value of 2.6 (4.3) kcal/mol and larger [E.sub.exo] value of 32.5 (34.1) kcal/mol than those of the former reaction. This is because the Ti-H bond energy is much larger than the Ti-Si[H.sub.3] one. The Si-C σ-bond activation occurs with moderate activation barrier of 19.1 (18.6) kcal/mol and considerably large exothermicity of 33.9 (37.7) kcal/mol. Based on these results, we wish to propose the theoretical prediction that the titanium(IV)-imido complex is useful for O-H, Si-H, and Si-C σ-bond activation reactions. Key words: σ-bond activation, titanium(IV)-imido complex, heterolytic σ-bond activation, density functional theory (DFT), bond energy. Faisant appel aux methode de la theorie de la fonctionnelle de la densite (TFD) et aux methodes MP2 et MP4(SDQ), on a etudie d'une facon theorique l'activation de la liaison σ du O-H du methanol, lactivation de la liaison s du Si-H du silane et l'activation de la liaison s Si-C du methylsilane par le complexe titane(IV)-imido [([Me.sub.3]Si).sub.2]Ti(NSi[Me.sub.3]). L'activation de la liaison s du OH du methanol donne lieu a une faible barriere d'activation ([E.sub.a]) de 7,1 (14,6) kcal/mol et une grande exothermicite ([E.sub.exo]) de 65,8 (61,4) kcal/mol qui conduit a la formation de [([Me.sub.3]Si).sup.2]Ti(O[CH.sub.3])[NH(Si[Me.sub.3])] indiquant que l'activation de la liaison σ du O-H se produit plus facilement que celle de la liaison σ C-H [([E.sub.a]) de 14,6 (21,5) kcal/mol et ([E.sub.exo]) de 22,7 (16,5) kcal/mol] dans lesquelles les valeurs obtenues par la methode TFD sont rapportees sans parenthe ses alors que celles calculees par la methode MP4(SDQ) sont rapportees entre parentheses. Meme si le groupe O[CH.sub.3] devient ionique et que l'atome H prend une forme semblable a celle d'un proton dans cette reaction d'activation, les changements de population sont plus moderes que ceux observes lors de l'activation s de la liaison C-H. Ceci resulte du fait que la liaison H-O[CH.sub.3] est deja polarisee dans le methanol. Dans la reaction d'activation s de la liaison Si-H, on a etudie deux voies reactionnelles; dans l'une, le produit est [([Me.sub.3]Si).sup.2]Ti(Si[H.sub.3])[NH(Si[Me.sub.3])] dans lequel l'atome H et le groupe Si[H.sub.3] sont lies respectivement a l'atome N et au centre Ti alors que dans l'autre voie reactionnelle le produit est [([Me.sub.3]Si).sup.2]Ti(H)[NH(Si[CH.sub.3])(Si[Me.sub.3])] dans lequel l'atome H et le groupe Si[H.sub.3] sont lies respectivement au centre Ti et a l'atome N imido. Meme si la premiere reaction se produit avec une valeur de Ea faible et une grande exothermicite, la derniere reaction se produit plus facilement avec une valeur de Ea encore plus faible 2,6 (4,3) kcal/mol et une valeur de Eexo plus elevee de 32,5 (34,1) kcal/mol que celle de la reaction precedente. Ceci resulte du fait que l'energie de liaison du Ti-H est beaucoup plus elevee que celle de la liaison Ti-Si[H.sub.3]. L'activation s de la liaison Si-C se produit avec une barriere d'activation moderee de 19,1 (18,6) kcal/mol et une exothermicite beaucoup plus elevee de 33,9 (37,7) kcal/mol. Sur la base de ces resultats, on desire proposer une prediction theorique que le complexe titane(IV)-imido [([Me.sub.3]Si).sup.2]Ti(NSi[Me.sub.3]) s'averera utile pour l'activation des liaisons s O-H, Si-H et Si-C. Mots-cles : activation dune liaison s, complexe titane(IV)-imido, activation d'une liaison σ heterocyclique, theorie de la fonctionnelle de la densite (TFD), energie de liaison. [Traduit par la Redaction], Introduction The σ-bond activation of a saturated molecule by a transition-metal complex is one of the important reactions in organometallic chemistry, inorganic chemistry, and catalytic chemistry, because active species is [...]

The β scission (cracking) of branched carbenium ions have been observed in molecular dynamics simulations, possibly for the first time. Simulations were performed with molecular dynamics based on PW91 density functional theory, and which included three-dimensional periodic boundary replication of the unit cell to mimic long-range bulk effects. A rising-temperature algorithm was used to encourage reaction within the narrow time windows (~10 ps) of the simulations. Twenty-eight simulations were performed, featuring alkyl ions in three different catalytic systems: the ionic liquid, [[([C.sub.5][H.sub.5][NH.sup.+]).sub.5][([Al.sub.2] [Cl.sub.7.sup.-]).sub.6.sup.-]], the chabazite zeolite, [[Al[Si.sub.23][O.sub.48]].sup.-], and the chabazite zeolite, [[[Al.sub.4][Si.sub.20][O.sub.45] [(OH).sub.3]].sup.-]. Twenty-four runs began with unbranched sec-n-alkyl ions, but only one exhibited β scission, and only after branching to a tertiary ion and under extreme heating. In contrast, the four simulations that began with branched alkyl ions were all successful in demonstrating β scission at lower temperatures: 2,4,4-trimethyl-2-pentyl ion and 2,4-dimethyl-2-hexyl ion in each of the first two catalysts. The lifetimes of desorbed alkyl ions in the chabazite models were < 5 ps at 1000-1500 K. The β scission results support the classical Weitkamp et al. (Appl. Catal. 1983, 8, 123) mechanism over the nonclassical Sie (Ind. Eng. Chem. Res. 1992, 31, 1881) and the chemisorping Kazansky et al. (J. Catal. 1989, 119, 108) mechanisms. Key words: C-C bond fission, cationic b scission, carbenium ions, alkyl ions, protonated cyclopropane ([PCP.sup.+]), catalysis, chloroaluminate, catalytic cracking mechanism. On a observe, peut etre pour la premiere fois, une scission β (craquage) d'ions carbenium ramifies dans des simulations de dynamique moleculaire. Les simulations ont ete effectuees a l'aide de la dynamique moleculaire basee sur la theorie de la fonctionnelle de densite PW91 qui inclut une replication tridimensionnelle de la frontiere periodique de la cellule unitaire pour representer les effets globaux a long terme. On a utilise un algorithme avec temperature croissante pour encourager la reaction vers des fenetres etroites de temps (~10 ps) des simulations. On a effectue vingt-huit simulations mettant en evidence des ions alkyles dans trois systemes catalytiques differents, un liquide ionique, [[[[C.sub.5][H.sub.5] [NH.sup.+]).sub.5][([Al.sub.2][Cl.sub.7-]).sup.6]].sup.-], la chabazite zeolithe, [[Al[Si.sub.23][O.sub.48]].sup.-] et la zeolithe chabazite, [[[Al.sub.4][Si.sub.20][O.sub.45] [(OH).sub.3]].sup.-]. Vingt-quatre de ces simulations commencaient avec des ions lineaires alkyles secondaires, mais seulement un a presente une scission β et uniquement apres avoir ramifie la chaine vers un ion tertiaire, avec un chauffage intense. Par ailleurs, les quatre simulations lancees avec des ions ramifies ont toutes conduit a des scissions β, a des temperatures plus basses, dont l'ion 2,4,4-trimethylpent-2-yle et l'ion 2,4-dimethylhex2-yle dans chacun des deux premiers catalyseurs. Les temps de vie des ions alkyles desorbes dans les modeles de la chabazite sont de < 5 ps a 1000-1500 K. Les resultats de scission b sont en accord avec le mecanisme classique de Weitkamp et al. (Appl. Catal. 1983, 8, 123) concernant le mecanisme non classique de Sie (Ind. Eng. Chem. Res. 1992, 31, 1881) et celui de chimisorption de Kazansky et al. (J. Catal. 1989, 119, 108). Mots-cles : fission d'une liaison C-C, scission cationique b, ions carbenium, ions alkyles, [PCP.sup.+], catalyse, chloroaluminate, mecanisme de craquage catalytique. [Traduit par la Redaction], Introduction In petroleum cracking of aliphatic hydrocarbon feedstock, the dominant C--C-bond scission step is β scission of carbocations (carbenium ions). The 1949 mechanisms of Thomas (1) and Greensfelder et al. [...]

Density functional theory (DFT) is used to explore the competitive C--H and C--Cl oxidative additions (OA) of chlorobenzene to the cationic Ir(I) complex: [[(PNP*)[Ir.sup.I]].sup.+] [PNP* = 2,6- bis((dimethylphosphino)methyl)pyridine]. Consistent with [...]

A preliminary study involving solid-state [sup.77.Se] NMR spectroscopy and first principles calculations of [sup.77.Se] NMR parameters in Se--N heterocycles is reported. [sup.77.Se] CP/MAS NMR spectra of the ring systems reveal expansive selenium chemical shift (CS) tensors, which are extremely sensitive to molecular geometry, symmetry, ligand substitution, and intermolecular contacts. For systems with known crystal structures, hybrid density functional theory (DFT) calculations of selenium nuclear magnetic shielding (NMS) tensors were carried out, and tensor orientations in the molecular frames examined. Additional DFT calculations of selenium NMS tensors are presented, along with a detailed analysis of pairs of occupied and virtual molecular orbitals that give rise to the Se NMS tensors. A new naturalized local molecular orbital (NLMO) analysis under the same DFT framework is also discussed. Collectively, the NMR data and first principles calculations provide understanding of the influences of electronic structure, bonding, and intermolecular interactions on the selenium NMS tensors, allowing for (i) prediction of unknown molecular structures and (ii) insight into the positions of the stereochemically active selenium lone pairs. Key words: solid-state NMR, [sup.77.Se] NMR, ab initio calculations, chemical shielding, main-group inorganic chemistry, heterocycles, DFT calculations, MO analysis, Gaussian 03, ADF. On rapporte les resultats d'une etude preliminaire de spectroscopie RMN du [sup.77.Se] a l'etat solide et de calculs a partir de principes fondamentaux des parametres RMN du [sup.77.Se] dans des heterocycles Se-N. Les spectres RMN des systemes cycliques par la technique de la rotation a l'angle magique avec polarisation croisee (RAMPC) mettent en evidence l'existence d'un large eventail de tenseurs du deplacement chimique (DC) du selenium qui sont extremement sensibles a la geometrie moleculaire, a la substitution par des ligands et aux contacts intermoleculaires. Pour les systemes dont on connait les structures cristallines, on a effectue des calculs des tenseurs de blindage magnetique nucleaire (BMN) du selenium avec la theorie de la fonctionnelle de la densite (TFD) hybride et on a examine les orientations des tenseurs dans des cadres moleculaires. On rapporte les resultats de calculs effectues sur la base de la TFD des tenseurs de blindage magnetique nucleaire ainsi qu'une analyse detaillee des paires d'orbitales moleculaires occupees et virtuelles qui donnent lieu aux tenseurs de blindage magnetique nucleaire du selenium. On discute aussi d'une nouvelle analyse de l'orbitale moleculaire naturalisee (OMLN) dans le meme cadre de la TFD. Pris collectivement, les donnees de la RMN et les calculs a partir de principes fondamentaux permettent de comprendre les influences de la structure electronique, des liaisons et des interactions intermoleculaires sur les tenseurs de BMN et aussi (i) de faire des predictions pour 15 structures moleculaires inconnues et (ii) de se faire une idee sur les positions des paires d'electrons libres du selenium qui sont actives d'un point de vue stereochimique. Mots-cles : RMN a l'etat solide, RMN du [sup.77.Se], calculs ab initio, blindage chimique, chimie inorganique du groupe principal, heterocycles, calculs TFD, analyse des OM, gaussienne 03, fonctionnelle de la densite d'Amsterdam (FDA). [Traduit par la Redaction], Introduction Carbenes are known to be important reaction intermediates, and there is an enormous amount of literature reporting their syntheses, structures, and reactivities. (1-7) Since the first report of the [...]

A computational investigation about the Lewis acid-base adducts between bases [Cp.sub.2]M[H.sub.2] (M = Mo, W) and acids B[X.sub.3] (X = F, Cl) and [Al([CH.sub.3].sub.3] is presented. Density functional methods based on pure and hybrid correlation-exchange functionals and relativistic corrections based on the zero order relativistic approximation (ZORA) have been applied. A comparison with experimental data has been addressed to give insights about the nature of the acid-base interaction with the aim to evaluate the role of the transition metal in charge donation toward the acid centre. In this respect, the likelihood of proposed criteria for recognizing the presence of transition-metal direct charge donation has been discussed. Key words: metallocenes, Lewis basicity, density functional theory (DFT), atoms in molecules (AIM), zero order relativistic approximation (ZORA). On a effectue une etude theorique des adduits acide-base de Lewis entre les bases [Cp.sub.2]M[H.sub.2] (M = Mo, W) et les acides B[X.sub.3] (X = F, Cl) et [Al([CH.sub.3].sub.3]. On a utilise les methodes de la fonctionnelle de la densite en faisant appel a des fonctionnelles de correlation-echange pures ainsi qu'hybrides et on a applique des corrections relativistes basees sur l'approximation relativiste d'ordre zero (AROZ). Une comparaison avec les donnees experimentales a ete realisee afin d'obtenir des informations sur la nature de l'interaction acide-base qui permettraient d'evaluer le role du metal de transition dans le transfert de charge vers le centre acide. Dans cette optique, on discute du potentiel d'utilite des criteres proposes pour reconnay tre la presence d'un transfert de charge direct de la part du metal de transition. Mots-cles : metallocenes, basicite de Lewis, theorie de la fonctionnelle de la densite (TFD), atomes dans une molecule << AIM >>, approximation relativiste d'ordre zero (AROZ). [Traduit par la Redaction], Introduction The acid-base adduct between bis(cyclopentadienyl)dihydridotungsten ([Cp.sub.2]W[H.sub.2]) and B[F.sub.3] was firstly communicated by Shriver (1) in 1963. It represented one of the first (and representative) examples of Lewis base behaviour [...]

The density functional theory (DFT) method has been employed to unravel mechanistic intricacies of the 1,4- polymerization of 1,3-butadiene mediated by the [[([η.sup.3]-R[C.sub.3][H.sub.4]) [Fe.sup.II]([C.sub.15][H.sub.11][N.sub.3])([η.sup.2]-[C.sub.4] [H.sub.6])].sup.+] terpyridine--iron(II) active catalyst species. The π-allyl-insertion mechanism is operative for chain growth, whilst the alternative σ-allyl- insertion mechanism has been explicitly demonstrated as being inoperable. This study elucidates the mechanism of cis--trans regulation and unveils the factors that govern the observed high trans-1,4 stereoselectivity, in particular, the discriminative role of allylic isomerization. An atactic trans-1,4-polydiene is expected from polymerization of a terminally monosubstituted butadiene, the experimental results of which have not been reported thus far. Key words: 1,3-diene polymerization, reaction mechanisms, structure-reactivity relationships, iron complexes, density functional calculations. La methode DFT a ete employee afin d'eclaircir les subtilites de la 1,4-polymerisation du 1,3-butadiene assistee par les especes terpyridine-fer(II) [([([η.sup.3]-R[C.sub.3][H.sub.4]) [Fe.sup.II]([C.sub.15][H.sub.11][N.sub.3])([η.sup.2]-[C.sub.4] [H.sub.6])].sup.+]) catalytiquement actives. Le mecanisme selon l'insertion π-allylique se deroule pour la croissance de chaine tandis que le mecanisme alternatif selon l'insertion s-allylique a ete explicitement demontre comme inoperable. Cette etude elucide le mecanisme de la regulation cis-trans et devoile les facteurs gouvernant la haute stereoselectivite trans-1,4 observee, en particulier le role discriminatoire de l'isomerisation allylique. Un trans-1,4-polydiene atactique est attendu a partir de la polymerisation d'un butadiene monosubstitue en position terminale. Ces resultats experimentaux n'ont pas ete reportes jusque-la. Mots-cles : polymerisation du 1,3-diene, mecanismes reactionnels, relations structure-reactivite, complexes de fer, calculs de la fonctionnelle de la densite. [Traduit par la Redaction], Introduction The metal-catalyzed polymerization of 1,3-dienes is a key process in the chemical industry and as such has triggered considerable research efforts in both academia and industry. (1-5) Structurally defined [...]

Quantum chemical calculations using BP86 with TZ2P basis sets were carried out to elucidate the structures and the bond-bond dissociation energies of the donor-acceptor complexes [[(P[Me.sub.3]).sub.2][M-EX.sub.3]] with X = H, F, Cl, Br, I; E = B, Al, Ga, In, Tl; and M = Ni, Pd, Pt. The nature of the metal-ligand bond was investigated with an energy decomposition analysis. The geometry optimizations gave for most compounds T-shaped structures with nearly linear P-M-P angles where the [EX.sub.3] ligand has either a staggered or eclipsed conformation with respect to the PMP plane. The energy differences between the conformations are very small which means that there is nearly free rotation about the [M-EX.sub.3] axis. The equilibrium structures of eight nickel compounds have a distorted geometry where one E-X bond is engaged in attractive interactions with the metal atom which yields a distorted square-planar arrangement of the metal atom. The complex [[(P[Me.sub.3]).sub.2]Ni-Tl[I.sub.3]] exhibits two attractive interactions between Tl-I bonds and the metal which features a five-coordinated metal atom. The calculated bond dissociation energies show that the boron complexes exhibit a different trend for the [D.sub.e] values than the heavier group-13 homologues. The results for the Pd and Pt complexes suggest that the [[(P[Me.sub.3]).sub.2][M-BX.sub.3]] bond strength increases with F < Cl < Br < I < H which means that the [BH.sub.3] ligands are the most strongly bonded Lewis acids and [BF.sub.3] is the most weakly bonded species . The trend for the heavier group-13 complexes [[(P[Me.sub.3]).sub.2][M-EX.sub.3]] where E = Al, Ga, In, Tl follows the opposite order F > Cl > Br > I > H. The energy decomposition analysis of the [M-EX.sub.3] bonds indicates a substantial π contribution of between 12.7% and 30.3% to the total orbital interactions. There is no direct correlation between the strength of the orbital interactions or any of the other energy terms Δ[E.sub.elstat] or Δ[E.sub.Pauli] which correlates with the total interaction energy. The bond dissociation energy of the [EX.sub.3] ligands after breaking the [M-EX.sub.3] bonds is quite large. It is shown that the intrinsic strength of the [M-EX.sub.3] bonds is much larger than the BDEs and that the trends of Δ[E.sub.int] and [D.sub.e] are not always the same. The [EX.sub.3] ligands in [[(P[Me.sub.3]).sub.2][M-BX.sub.3]] always carry a large negative charge. Key words: density functional calculations, bonding analysis, Lewis acids, transition metal complexes, reversed DCD model. On a effectue des calculs de mecanique quantique BP86 a l'aide d'ensembles de base TZ2P dans le but d'elucider les structures et les energies de dissociation de liaison des complexes donneur-accepteur [[(P[Me.sub.3]).sub.2][M-EX.sub.3]] dans lesquels X = H, F, Cl, Br, et I; E = B, Al, et Ga, In, Tl; et M = Ni, Pd, et Pt. On a etudie la nature de la liaison metal-ligand par le biais d'une analyse de l'energie de decomposition. Les optimisations de la geometrie conduisent, pour la plupart des composes, a des structures en forme de T avec des angles P-M-P pratiquement lineaires, dans lesquels le ligand [EX.sub.3] se trouve dans une conformation decalee ou eclipsee par rapport au plan PMP. Les differences d'energie entre les conformations sont tres faibles, ce qui implique qu'il existe une rotation pratiquement libre autour de l'axe [M-EX.sub.3]. Les structures a l'equilibre dans les neuf composes du nickel comportent toutes une geometrie deformee dans laquelle une liaison E-X est engagee dans des interactions attractives avec l'atome metallique ce qui conduit a un arrangement plan carre deforme de l'atome metallique. Le complexe [[(P[Me.sub.3]).sub.2]Ni-Tl[I.sub.3]] presente meme deux interactions attractives entre les liaisons Tl-I et le metal qui comporte un atome de metal pentacoordonne. Les energies de dissociation de liaison calculees montrent que les complexes de bore presentent une tendance differente pour les valeurs [D.sub.e] que les homologues plus lourds du groupe 13. Les resultats pour les complexes du Pd et du Pt suggerent que la force de la liaison [[(P[Me.sub.3]).sub.2][M-EX.sub.3]] augmente avec F < Cl < Br < I < H, ce qui signifie que les ligands [BH.sub.3] sont les acides de Lewis les plus fortement lies et que les especes [BF.sub.3] participent aux liaisons les plus faibles. La tendance pour les complexes plus lourds du groupe 13 [[(P[Me.sub.3]).sub.2][M-EX.sub.3]] dans lesquels E = Al, Ga, In et Tl conduit a l'ordre inverse F > Cl > Br > I > H. L'analyse de l'energie de decomposition des liaisons [M-EX.sub.3] met en evidence la presence d'une contribution π importante, allant de 12,7 % a 30,3 % des interactions or bitalaires totales. Il n'existe aucune correlation directe entre la force des interactions orbitalaires ou l'un des autres termes d'energie, tel Δ[E.sub.elstat] ou Δ[E.sub.Pauli] et l'energie totale d'interaction. L'energie de dissociation de la liaison des ligands [EX.sub.3] apres le bris des liaisons [M-EX.sub.3] est tres elevee. On a demontre que la force intrinseque des liaisons [M-EX.sub.3] est beaucoup plus elevee que les BDE et que les tendances des Δ[E.sub.int] et [D.sub.e] ne sont pas toujours les memes. Les ligands [EX.sub.3] dans les complexes [[(P[Me.sub.3]).sub.2][M-EX.sub.3]] portent toujours une forte charge negative. Mots-cles : calculs de la fonctionnellle de la densite, analyse de liaison, acides de Lewis, complexes de metaux de transition, modele DCD inverse. [Traduit par la Redaction], Introduction The chemical bonds in donor-acceptor complexes of transition metals with main-group ligands are usually described using the Dewar-Chatt-Duncanson (DCD) model (1) where the ligand, being a Lewis base, serves [...]

Density functional theory and the polarized continuum model are used to derive the electronic structures of some open-shell, bis(bipyridine)ruthenium complexes bound to noninnocent quinonoid or thiolosulfinato ligands formally in the semiquinone oxidation state. The noninnocent properties of the o-thiolosulfinato ligand are explored and compared with those of the more conventional o-semiquinones with nitrogen, oxygen, and sulfur donor atoms. Spin densities are shown to be fairly localized in the metallocycle ring. It is demonstrated that oxidation of the parent [[Ru.sup.II][(bpy).sub.2] (1,2-(S,[SO.sub.2])-[C.sub.6][H.sub.4]] species occurs primarily in the metallocycle ring and is localized in the Ru-[S.sup.0] bond. Key words: ruthenium, sulfenate, sulfinate, thiol, optical spectrum, density functional theory (DFT), infrared, noninnocent ligand. On a fait appel a la theorie de la fonctionnelle de densite et du modele du continuum polarise pour deriver les structures electroniques de quelques complexes a couches ouvertes du bis(bipyridine)ruthenium lie a des ligands quinonoides ou thiolosulfinato non innocents formellement dans l'etat d'oxydation semiquinone. On a etudie les proprietes non innocentes du ligand o-thiolosulfinato et on les a comparees avec celles de o-semiquinones plus conventionnelles portant des atomes d'azote, d'oxygene et de soufre donneurs. On a montre que les densites de spin sont assez localisees dans le noyau metallocyclique. On demontre que l'oxydation de l'espece parente [[Ru.sup.II][(bpy).sub.2](1,2-(S,[SO.sub.2])-[C.sub.6][H.sub.4)]] se produit principalement dans le noyau metallocyclique et qu'elle est localisee dans la liaison Ru-[S.sup.0]. Mots-cles : ruthenium, sulfenate, sulfinate, thiol, spectre optique, theorie de la fonctionnelle de la densite (TFD), infra-rouge, ligand non innocent. [Traduit par la Redaction], Introduction We have recently reported (1) the physical properties and electronic structures of bis(bipyridine)ruthenium complexes of o-thiolosulfinatobenzene 1 [Ru[(bpy).sub.2](1,2-(S,[SO.sub.2])-[C.sub.6][H.sub.4])] and o-disulfinatobenzene 2 [Ru[(bpy).sub.2](1,2-([SO.sub.2],[SO.sub.2])-[C.sub.6][H.sub.4])], which are of interest, in part, because [...]

Relativistic density functional theory (ZORA-PBE, COSMO solvation) is used to address the title question, based on comparison with recent experimental data (1). Structural data (bond lengths), vibrational frequencies, and [sup.17.O] NMR chemical shifts are used to prove that [[Np[O.sub.4][(OH).sub.2]].sup.3-] is the predominant species in high-ionic-strength alkaline solutions of [Np.sup.VII]. Neptunium(VII) complexes have stronger bonds than their formally isoelectronic uranium(VI) analogues. The experimentally observed 300 ppm shift in [sup.17.O] chemical shifts between the known [[U[O.sub.2][(OH).sub.4]].sup.2-] and [Np.sup.VII] solution is shown to be partly a function of the central metal ([Np.sup.VII] vs. [U.sup.VI]) and not of the coordination environment (tetraoxo vs. dioxo). Comparing, for a given An ([U.sup.VI] or [Np.sup.VII]), actinyl complexes [[An[O.sub.2][X.sub.4]].sup.2-/1-], X = Cl, F, OH, a decreasing strength of the axial actinyl bond is observed that is traced to electronic factors (equatorial π-competition). Key words: neptunium, density functional theory, relativity, NMR chemical shifts, alkaline solution. En se basant sur une comparaison avec des donnees experimentales recentes (1), on a utilise la theorie de la fonctionnelle de la densite relativiste << ZORA-PBE, solvatation COSMO >> pour etudier la question mentionnee dans le titre. On a utilise les donnees de structure (longueurs de liaison), les frequences de vibration et les deplacements chimiques en RMN du [sup.17.O] pour prouver que le cation [[Np[O.sub.4][(OH).sub.2].sup.3-] est l'espece predominante dans les solutions alcalines de force ionique elevee du [Np.sup.VII]. Les complexes du [Np.sup.VII] possedent des liaisons plus fortes que leurs analogues formellement isoelectroniques de l'uranium(VI). On a demontre que les deplacements chimiques de 300 ppm observes experimentalement pour les [sup.17.O] du cation connu [[U[O.sub.2][(OH).sub.4]].sup.2-] et de la solution de [Np.sup.VII] sont partiellement fonction de l'atome metallique central [[Np.sup.VII] vs. [U.sup.VI]] et non pas de l'environnement de coordination (tetraoxo vs. dioxo). Pour un actinyle, An, donne, lorsqu'on compare des complexes d'actinyle d'uranium(VI) et de neptunium(VII) de formule generale [[An[O.sub.2][X.sub.4]].sup.2-/1-] dans lesquels X = Cl, F, OH, on observe une diminution de la force de la liaison axiale de l'actinyle qui peut etre attribuee a des facteurs electroniques (competition equatoriale/π). Mots-cles : neptunium, theorie de la fonctionnelle de la densite, relativite, deplacements chimiques en RMN, solution alcaline. [Traduit par la Redaction], Introduction The purpose of this paper is to provide a definite answer to the title question: Is neptunium(VII) in high-ionic-strength alkaline solution present as [[Np[O.sub.2][(OH).sub.4].sup.1-] or as [[Np[O.sub.4][(OH).sub.2].sup.3-]? We address [...]

Density functional theory (DFT) calculations for M--([C.sub.10][H.sub.12][N.sub.2][O.sub.8.sup.4-]) and M--[([H.sub.2]O).sub.6], where M = [Na.sup.+], [K.sup.+], [Rb.sup.+], [Mg.sup.2+], [Ca.sup.2+], and [Sr.sup.2+], and ([C.sub.10][H.sub.12][N.sub.2][O.sub.8.sup.4-]) = [EDTA.sup.4-], were carried out at both all-electron and pseudopotential levels. Results from these four methods were compared, and it was found that the ions bind to [EDTA.sup.4-] with selectivity of [Mg.sup.2+] > [Ca.sup.2+] > [Sr.sup.2+] > [Na.sup.+] > [K.sup.+] > [Rb.sup.+.] Key words: ethylenediamine tetraacetic acid (EDTA), alkali metal ions, alkaline earth metal ions, binding affinity. Faisant appel a la theorie de la fonctionnelle de la densite et operant aux niveaux de tous les electrons ainsi que du pseudopotentiel, on a effectue des calculs sur les cations M--([C.sub.10][H.sub.12][N.sub.2][O.sub.8.sup.4-])] et M--[([H.sub.2]O).sub.6] dans lesquels M = [Na.sup.+], [K.sup.+], [Rb.sup.+], [Mg.sup.2+], [Ca.sup.2+], et [Sr.sup.2+] et [C.sub.10][H.sub.12][N.sub.2][O.sub.8.sup.4-] = [EDTA.sup.4-]. Les resultats obtenus avec ces methodes ont ete compares entre eux et on a trouve que les ions se lient avec [EDTA.sup.4-] avec la selectivite suivante : [Mg.sup.2+] > [Ca.sup.2+] > [Sr.sup.2+] > [Na.sup.+] > [K.sup.+] > [Rb.sup.+]. Mots-cles : acide ethylenediaminetetraacetique, ions de metaux alcalins, ions de metaux alcalinoterreux, affinite de fixation. [Traduit par la Redaction], Introduction Ethylenediamine tetraacetic acid ([H.sub.4]EDTA) is a polyprotic acid that has been widely used, together with its associated anion ethylenediamine tetraacetate ([EDTA.sup.4-]), since the pioneering work on [H.sub.4]EDTA was done [...]

In this manuscript, we provide a theoretical rationalization of the mechanisms that control double H2 addition to an unsaturated 14 e cationic Ir(III) complex to yield a dihydride Ir(III) complex. Further, we also present two mechanisms that can explain the experimentally observed incorporation of deuterium into the tert-Butyl ([sup.t.Bu]) groups of the N-heterocyclic I[sup.t.Bu] ligands. Key words: homogeneous catalysis, hydrogenation, deuteration, N-heterocyclic carbene, density functional calculations. Dans ce travail, on rapporte une rationalisation theorique des mecanismes qui controlent la double addition de [H.sub.2] sur le complexe cationique insature de Ir(III) conduisant a la formation d'un dihydrure complexe de Ir(III). De plus, on presente deux mecanismes qui pourraient expliquer l'incorporation observee experimentalement de deuterium dans les groupes tert-butyles des ligands I[sup.t.Bu] de l'heterocycle azote. Mots-cles: catalyse homogene, hydrogenation, deuteration, carbene N-heterocyclique, calculs de la fonctionnelle de la densite. [Traduit par la Redaction], Introduction Coordinatively unsaturated transition-metal complexes containing hydride ligands are of remarkable interest because of their potential role in catalysis. (1-6) Due to their unsaturated nature, the structural characterization and a [...]

This study is aimed at developing an explicit solvent model for highly charged species such as polyoxometalates. The model includes solvent molecules in the first solvation shell explicitly, and long-range bulk effects and counterions as a set of single point charges. The model strongly stabilizes the electronic structure of the Keggin anion. The energies of the Kohn-Sham orbitals obtained using our model lie very close to those computed using the COSMO continuum solvent model; moreover, the total solvation energy evaluated with our model compares well to the value calculated by COSMO. Key words: polyoxometalates, solvation, DFT, MD, discrete models. Cette etude a ete realisee dans le but de developper un modele de solvant explicite pour les especes fortement chargees, tels les polyoxometalates. Le modele comprend explicitement des molecules de solvant dans la premiere couche de solvatation et les effets globaux a longue distance ainsi que les contre-ions sous la forme de charges ponctuelles. Le mode le stabilise fortement la structure electronique de l'anion Keggin. Les energies des orbitales Kohn-Sham obtenues a l'aide de notre modele sont tres proches de celles calculees a l'aide du modele de solvant continu COSMO; de plus, l'energie totale de solvatation evaluee a l'aide de notre modele se compare bien avec celle calcule a l'aide du modele COSMO. Mots-cles : polyoxometalates, solvatation, theorie de la fonctionnelle de la densite, modeles discrets, MD. [Traduit par la Redaction], Introduction The introduction of solvent effects in quantum chemical studies is nowadays an almost standard procedure thanks to the development of several continuum solvent models, which efficiently introduce the effect [...]

The characterization of the stability of the fused aromatic region (FAR) in oil asphaltenes in terms of kinetic and thermodynamic stability is primary. Such an understanding is important if we are to get the optimal use from the heavy fraction of any crude oil. The FAR region is composed of pericondensed cyclopenta-fused polycyclic aromatic hydrocarbon compounds (CPPAHs) with N, S, and O heteroatoms. The Clar model, which states that the most important representation of a PAH is one having the maximum number of disjoint π-sextets, depicted by inscribed circles, and a minimum number of fixed double bonds, captures the essence of the kinetic and thermodynamic stability arguments. This model is readily employed for complex aromatics of the sort to be considered for asphaltenes. In the present research we prove that the aromaticity of CPPAHs can be assessed by using the qualitative easy-to-apply Y-rule. In the literature, it is proven that the Y-rule is applicable to elucidate the aromaticity of benzenoid PAHs and it has been validated for pericondensed benzenoid PAHs but not for pericondensed CPPAHs. Here, we verify that it is applicable for CPPAHs. The applicability of the Y-rule has been theoretically proven by comparing the π-electronic distribution obtained with it with the one obtained from nucleus-independent chemical shift (NICS) calculations at the density functional theory (DFT) level. The importance of doing this is that due to the polydispersity in the composition of the oil asphaltenes, and to understand their aromatic core structure, it is necessary to be able to asses the aromaticity of many cyclopenta-fused PAHs (possibly more than 500), of different sizes (up to 15 rings between hexagons and pentagons), and different spatial rearrangements in a quick but realistic and effective way. To try to do this with NICS will be very time consuming and computationally expensive, especially in the case of big systems. Key words: aromaticity, nucleus-independent chemical shifts (NICS), Y-rule, cyclopenta-fused PAHs, asphaltenes. En termes de stabilite cinetique et thermodynamique, la caracterisation de la stabilite de la region aromatique condensee (RAC) des asphaltenes d'huile est primaire. Une telle comprehension est important si on veut pouvoir faire un usage optimal de la fraction lourde des huiles brutes. La region aromatique condensee est formee d'hydrocarbures aromatiques polycycliques cyclopentaniques peri-condenses (HAP-CP) dans lesquels on retrouve des atomes d'azote, de soufre ou d'oxygene comme heteroatomes. Le modele de Clar qui specifie que la representation la plus importante d'un HAP est de posseder un nombre maximal de sextets π decrits par des cercles inseres et un nombre minimal de doubles liaisons fixes decrit l'essence des arguments de stabilite cinetique et thermodynamique. Ce modele est facilement utilisable pour les produits aromatiques complexes de la sorte retrouvee dans les asphaltenes. Dans le present travail, on montre que l'aromaticite des HAP-CP peut etre evaluee en utilisant la regle-Y qui est facile a appliquer d'un point de vue qualitatif. Dans la litterature, il est prouve que la regle-Y peut etre utilisee pour elucider l'aromaticite de HAP benzenoides et elle a aussi ete validee pour les HAP benzenoides pericondenses, mais pas pour les HAP-CP pericondenses. On verifie donc ici qu'elle est aussi applicable a ces derives. L'applicabilite de la regle-Y a ete demontree d'une facon theorique en comparant la distribution electronique obtenue grace a elle avec celle obtenue a partir de calculs de deplacements chimiques independants des noyaux (DCIN) au niveau de la theorie de la fonctionnelle de la densite. L'importance de cette demarche est que, en raison de la polydispersite dans la composition des asphaltenes de l'huile et afin de mieux comprendre leur structure aromatique fondamentale, il est necessaire d'etre capable d'evaluer l'aromaticite de plusieurs HAP-CP (possible plus de cinq cents), de tailles differentes (allant jusqu'a 15 noyaux hexagonaux ou pentagonaux) et d'arrangement spatial different d'une facon rapide, mais realiste et efficace. Il serait tres long et d'un point de vue de temps de calcul tres couteux d'essayer de faire ces evaluations a l'aide de calculs DCIN. Mots-cles : aromaticite, calculs de deplacements chimiques independants des noyaux (DCIN), regle-Y, HAP condenses a des cyclopentanes, asphaltenes. [Traduit par la Redaction], Introduction Polycyclic aromatic hydrocarbons (PAHs) containing, by periannulation, at least one unsaturated five-membered ring, cyclopenta (CP) moiety, and fused to six-membered ring perimeters (CPPAHs) are important in several contexts. (1), [...]

The structures and stabilities of the glycerol (G) and glycerol 3-phosphate (G3P) isomers have been calculated in the gas phase, using an ab initio density functional theory (DFT) method. The different conformational structures are shown to be at the origin of the various phospholipid conformers, except, obviously, for the alkyl chain torsions. The G3P conformations have been examined taking into account the experimental structures of the complexation sites in the glycerol kinase (GK) and glycerol 3-phosphate acyl transferase (G3PAT) enzymes, which correspond to the first and second steps of the 'de novo' phospholipid biogenesis, respectively. The conformational analysis of the glycerophosphate skeleton is shown to determine most of the structural characteristics of the phosphatidyl choline lipids, which differ by the length of their diacyl chains, i.e., dilauroyl (DL), dimyristoyl (DM), and dipalmitoyl (DP) phosphatidylcholines (PC). Higher energy conformers with kinks in the acyl chains have been found, in preparation for molecular dynamics studies of the chain melting phase transformation. Key words: glycerol, glycerol 3-phosphate, phosphatidylcholines, DLPC, DMPC, DPPC, conformational analysis, density functional theory, DFT-D. Les structures et stabilites relatives du glycerol (G) et du glycerol 3-phosphate (G3P) ont ete calculees en phase gaseuze avec une methode ab initio, basee sur la theorie de la fonctionnelle de la densite (TFD). A l'exception des formes gauches des chaines alkyles, les differentes conformations de ces molecules sont effectivement a l'origine des conformeres possibles des phospholipides. Les conformations de G3P ont ete analysees en considerant les structures experimentales des sites de complexation des enzymes glycerol kinase (GK) et glycerol 3-phosphate acyl transferase (G3PAT) qui correspondent, respectivement, aux deux premieres etapes de la biosynthese << de novo >> des phospholipides. L'analyse conformationnelle du squelette glycerophosphate montre qu'il determine la plupart des caracteristiques structurales des lipides phosphatidylcholines qui different par la longueur de leurs chaines alkyles, c.-a-d. dilauroyl (DL), dimyristoyl (DM) et dipalmitoyl (DP) phosphatidylcholines (PC). Des conformeres d'energie plus elevee, presentant des formes gauches dans les chaines alkyles, ont ete etudies en relation avec les simulations par dynamique moleculaire des transformations structurales des chaines, au cours de la transition principale de phase. Mots-cles : glycerol, glycerol 3-phosphate, phosphatidylcholine, DLPC, DMPC, DPPC, analyse conformationnelle, theorie de la fonctionnelle de la densite, TFD-D., Introduction Phospholipids and proteins are the main components of biological membranes, separating the cell and its various constituents from their environment. Cell membranes also have different functional roles, including protein [...]

Reactions of [[RhCl(COE)(IPr)].sub.2] (1) and [[RhCl(COE)(IMes)].sub.2] (2) (COE = cyclooctene; IPr = N,N'-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene; IMes = N,N'-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene) with the diphosphines [Ph.sub.2]P[(C[H.sub.2]).sub.n]P[Ph.sub.2] and 1,2-bis(diphenylphosphino)benzene (dppbz) give the N-heterocyclic carbene (NHC)-diphosphine-rhodium(I) complexes: RhCl(NHC)[[Ph.sub.2]P[(C[H.sub.2]).sub.n]P[Ph.sub.2]] [NHC = IPr, n = 1 (3); NHC = IMes, n = 1 (4); NHC = IPr, n = 2 (5); NHC = IMes, n = 2 (6); NHC = IPr, n = 4 (7); NHC = IMes, n = 4 (8)] and RhCl(NHC)(dppbz) [NHC = IPr (9); NHC = IMes (10)]. All the complexes are characterized by ¹H, [sup.31]P(¹H}, and [sup.13]C{¹H} NMR spectroscopy, elemental analysis, and mass spectrometry. Complexes 3, 7, and 9 are also characterized crystallographically. In benzene solution, the complexes decompose in the presence of [O.sub.2] with formation of the diphosphine dioxide, whereas reaction with CO leads to replacement of the NHC ligand to give known carbonyl-diphosphine complexes. Key words: rhodium, N-heterocyclic carbenes, bis(diphenylphosphino) ligands, crystallography. Resume : Les reactions du [[RhCl(COE)(IPr)].sub.2] (1) et du [[RhCl(COE)(IMes)].sub.2] (2) [COE = cyclooctene; IPr = N,N'-bis(2,6-diisopropylphenyl)imidazoline-2-ylidene; IMes = N,N'-bis(2,4,6-trimethylphenyl)imidazoline-2-ylidene] avec les diphosphines [Ph.sub.2]P[(C[H.sub.2]).sub.n]P[Ph.sub.2] et 1,2-bis(diphenylphosphino)benzene (dppbz) conduisent a la formation de complexes carbene N-heterocyclique (NHC)-diphosphine-rhodium(I): RhCl(NHC)[[Ph.sub.2]P[(C[H.sub.2]).sub.n]P[Ph.sub.2]] [NHC = IPr, n = 1 (3); NHC = IMes, n = 1 (4); NHC = IPr, n = 2 (5); NHC = IMes, n = 2 (6); NHC = IPr, n = 4 (7); NHC = IMes, n = 4 (8)] et RhCl(NHC)(dppbz) [NHC = IPr (9); NHC = IMes (10)]. Tous les complexes ont ete caracterises par des analyses elementaires, par spectroscopie RMN du ¹H, du [sup.31]P{¹H} et du [sup.13]C{¹H} et par spectrometrie de masse. Les complexes 3, 7 et 9 ont aussi ete caracterises par diffraction des rayons X. En solution dans le benzene, les complexes se decomposent en presence de [O.sub.2] avec formation d'oxyde de diphosphine, alors qu'une reaction avec le CO conduit au remplacement du ligand NHC pour conduire aux complexes carbonyl-diphosphines connus. Mots-cles : rhodium, carbenes N-heterocycliques, ligands bis (diphenylphosphino), cristallographie. [Traduit par la Redaction], Introduction A just-published special issue of European Journal of Inorganic Chemistry demonstrates the growing interest in transition-metal N-heterocyclic carbene (NHC) complexes. (1) Seven of the papers in the issue are [...]

ZnO nanostructures have been synthesized by thermal evaporation on Si substrates. It is found that the morphologies of the nanostructures are governed by growth conditions such as temperature, carrier-gas flow rate, and the nature of the substrate (with and without a catalyst). We report X-ray excited optical luminescence from ZnO nanostructures of distinctly different morphologies in the energy and time domain using excitation photon energies across the Zn K-edge. X-ray excited optical luminescence (XEOL) and X-ray absorption near edge structure (XANES) study has clearly shown the morphology dependence of the ZnO optical properties. A correlation of luminescence with morphology, size, and crystallinity emerges. Key words: ZnO nanostructures, XEOL, TRXEOL, XANES, vapour deposition. Resume : On a synthetise des nanostructures de ZnO par evaporation thermique de substrats contenant de l'etain. On a trouve que les morphologies des nanostructures sont gouvernees par les conditions de croissance, la vitesse d'ecoulement du gaz porteur et la nature du substrat, avec ou sans catalyseur. Utilisant des energies photoniques d'excitation sur l'arete K du zinc, on a pu observer de la luminescence optique excitee par les rayons X a partir de nanostructures de ZnO de morphologies comportant des differences importantes dans le domaine du temps et de l'energie. Des etudes de luminescence optique excitee par les rayons X << XEOL >> et par la spectroscopie de la structure fine d'absorption des rayons X pres du seuil << XANES >> ont clairement demontre l'importance de la morphologie sur les proprietes optiques du ZnO. Il en emerge une correlation entre la luminescence et la morphologie, la taille et la cristallinite. Mots-cles : nanostructures de ZnO, luminescence optique excitee par les rayons X << XEOL >>, spectroscopie de la structure fine d'absorption des rayons X pres du seuil << XANES >>, depot de vapeur. [Traduit par la Redaction], Introduction Zinc oxide, a wide-band-gap semiconductor ([E.sub.g] = 3.37 eV at room temperature), ranks high among oxide semiconductors for its unique properties. With suitable doping, the band gap of ZnO [...]

Pressure-induced structural transformations of the ammonia borane complex ([NH.sub.3] x [BH.sub.3]) were investigated in diamond anvil cells by Raman spectroscopy and synchrotron IR spectroscopy up to 14 GPa at room temperature. Starting with a disordered tetragonal structure, [NH.sub.3] x [BH.sub.3] is found to undergo several transformations upon compression as monitored by in situ Raman measurements. These transformations are indicated by the sequential changes of characteristic Raman modes as well as by the pressure dependence of these modes. Synchrotron IR absorption spectroscopy provided supplementary and consistent information about the structural evolution of [NH.sub.3] x [BH.sub.3] under compression. Decompression measurements on [NH.sub.3] x [BH.sub.3] suggest the pressure-induced transformations are reversible in the entire pressure region. The combined Raman and IR data allowed analysis of possible high-pressure structures of [NH.sub.3] x [BH.sub.3]. Our study significantly complements previous high-pressure Raman studies by providing new information on the structures and stabilities of [NH.sub.3] x [BH.sub.3]. Key words: ammonia borane, hydrogen storage, high pressure, Raman spectroscopy, IR spectroscopy, diamond anvil cell. Operant a la temperature et a des pressions allant jusqu'a 14 GPa et faisant appel a la spectroscopie Raman et a la spectroscopie infrarouge (IR) synchrotron avec une cellule avec contre-partie de diamant, on a etudie les transformations induites par la pression du complexe ammoniac-borane ([NH.sub.3] x [BH.sub.3]). Tel qu'on a pu l'observer par des mesures Raman in situ, on a trouve que, par compression, le [NH.sub.3] x [BH.sub.3] subit plusieurs transformations a partir de sa structure tetragonale desordonnee initiale. Ces transformations sont caracterisees par des changements sequentiels des modes Raman caracteristiques ainsi que par l'influence de la pression sur ces modes. La spectroscopie d'absorption IR synchrotron fournit des informations supplementaires et consistantes au sujet de l'evolution structurale du [NH.sub.3] x [BH.sub.3] soumis a une compression. Des mesures de decompression sur le [NH.sub.3] x [BH.sub.3] suggerent que les transformations induites par la pression sont reversibles sur l'ensemble de la region de pression. Les donnees combinees des spectroscopies Raman et IR permettent de faire une analyse des structures du [NH.sub.3] x [BH.sub.3] a haute pression. Ce travail apporte des complements aux etudes anterieures par spectroscopie Raman en fournissant de nouvelles informations sur les structures et les stabilites du [NH.sub.3] x [BH.sub.3]. Mots-cles: ammoniac-borane, emmagasinage de l'hydrogene, haute pression, spectroscopie Raman, spectroscopie infrarouge, cellule avec contre-partie de diamant. [Traduit par la Redaction], Introduction The ammonia borane complex ([NH.sub.3] x [BH.sub.3]) has received intensive investigation in recent years because of its promising potential as a hydrogen storage material. (1,2) Ammonia borane is a [...]

The synthesis and advanced characterization of a series of extended dithieno[2,3-b:3',2'-e][1,4-dihydro-1,4]phosphasilins is reported, and their suitability as new building blocks for organic electronics is evaluated. Synthesis of basic, as well as benzo-extended dithienophosphasilins, can be achieved using appropriate 2,3-dibromothiophene precursors in a two-step protocol introducing the silicon and phosphorus centers subsequently. Both ladder-type materials show the typical reactivity of trivalent phosphorus species and can quantitatively be converted into the corresponding oxides or gold complexes, the latter exemplified with the basic dithienophosphasilin. Their optoelectronic properties were found to be inferior to those of related dithieno[3,2-b:2',3'-d]phospholes, indicating a disruption of the π-conjugation in the molecular scaffold. X-ray crystallographic studies revealed that the molecular scaffold is planar in the oxidized benzo-extended material, whereas the basic dithieno materials show some small deviation from planarity. Density functional theory calculations suggest all materials to be planar, with the exception of the benzo-extended trivalent phosphasilin. This structure-property study illustrates that the disruption of the π-conjugation in the molecular scaffold of the extended phosphasilins is exclusively due to the presence of the silicon center and its electronic effects, rather than structural features. Key words: phosphorus heterocycles, silicon heterocycles, organic electronics, thiophene, π-conjugation. Resume : On a effectue la synthese et la caracterisation avancee d'une serie etendue de dithieno[2,3-b:3',2'-e][1,4-dihydro-1,4-]phosphasilines et on a evalue la possibilite de les utiliser dans la synthese de composes organiques electroniques. On peut realiser la synthese du produit de base ainsi que de diverses benzodithienophosphasilines en utilisant comme precurseurs des 2,3-dibromothiophenes appropries dans un protocole en deux etapes au cours desquelles on introduit les centres silicies et phosphores ulterieurement. Les deux types de materiaux en echelle presentent la reactivite type des especes contenant du phosphore trivalent et ils peuvent etre transformes quantitativement en oxydes correspondants ou en complexes d'or, un exemple de ce dernier ayant ete prepare avec la dithienophosphasiline basique. On a trouve que leurs proprietes optoelectroniques sont inferieures a celles des dithieno[2,3-b:3',2'-d]phospholes, ce qui indique qu'il se produit une interruption dans la conjugaison π dans l'echafaudage moleculaire. Les etudes cristallographiques par diffusion des rayons X revelent que l'echafaudage moleculaire est plan dans les derives benzo-condenses oxydes alors que les materiaux dithieno de base presentent de faibles deviations par rapport a la planeite. Des calculs a base de la theorie de la fonctionnelle de la densite suggerent que tous les materiaux doivent etre plans, a l'exception de la benzophosphasiline trivalente. L'etude structure propriete illustre le fait que la disruption de la conjugaison π dans l'echafaudage moleculaire de phosphasilines etendues est exclusivement due a la presence du centre silicium et de ses effets electroniques et n'a rien a voir avec ses caracteristiques structurales. Mots-cles : heterocycles du phosphore, heterocycles du silicium, electroniques organiques, thiophene, conjugaison π. [Traduit par la Redaction], Introduction Organic π-conjugated materials have received significant attention in recent years owing to their beneficial photophysical and electronic properties that provide intriguing opportunities for the field of organic electronics. Their [...]

Bacopa monnieri is a well-known Ayurvedic Indian medicinal plant traditionally used as a memory enhancer. Its memory-enhancing effect is mainly attributed to dammarane triterpenoid saponins. In the present study, two new dammarane-type triterpenoid saponins, bacopaside-XI (1) and bacopaside-XII (2), together with known compounds, bacopaside IV, bacopaside V, and apigenin, were isolated from the aerial parts of the B. monnieri. The structures of the new saponins were elucidated as 3-O-[α-L-arabinofuranosyl (1 → 3)]-6-O-sulfonyl-β-D-glucopyranosyl pseudojujubogenin (1) and 3-O-{β-D-glucopyranosyl(1 → 3)[α-L-arabinofuranosyl(1 → 2)] -β-D-glucopyranosyl}-20-O-α-L-arabinopyranosyl pseudojujubogenin (2) on the basis of extensive investigations of 1D and 2D NMR (HMQC and HMBC), ESI-QTOF-MS/MS spectroscopic methods, and chemical evidences. Key words: scrophulariaceae, Bacopa monnieri, triterpenoid saponins, bacopaside-XI, bacopaside-XII. Le Bacopa monnieri est un plante medicinale bien connue chez les indiens ayurvediques ou elle est utilisee pour amelioree la memoire. Cet effet est generalement attribue aux saponines triterpenoides dammarane. Dans la presente etude sur les parties aeriennes du B. monnieri, on a isole deux nouvelles saponines triterpenoides du type dammarane, le bacopaside-XI (1) et le bacopaside-XII (2) aux cotes de composes connus, dont le bacopaside-IV, le bacopaside-V et l'apigenie. Faisant appel a des etudes extensives de donnees chimiques, de RMN mono- et bidimensionnelles (<< HMQC >> et << HMBC >>) et de spectrometrie de masse (<< ESI-QTOF-MS/MS >>), on a elucide les structures des nouvelles saponines, la 3-O-[α-L-arabinopyranosyl-(1 → 3)-6-O-sulfonyl-β-D-glucopyranosylpseudojujubogenine (1) et la 3-O-{β-D-glucopyranosyl(1 → 3)[α-L-rabinofuranosyl(1 → 2)]-β-D-glucopyranosyl}-20-O-L-arabinopyranosylpseudojujubogenine (2). Mots-cles : scrofulariacee, Bacopa monnieri, sapogenines triterpenoides, bacopaside-XI, bacopaside-XII. [Traduit par la Redaction], Introduction Bacopa monnieri (L) WETTST. (Scrophulariaceae) (commonly known as 'Brahmi') is a reputed medicinal herb, found throughout the Indian subcontinent in wet and marshy places. (1) It is used in [...]

Chalcones are useful intermediates in organic synthesis and exhibit a large number of different biological activities. Chalcones have been synthesized in high yields by Claisen--Schmidt condensation of substituted acetophenones with various aromatic aldehydes in the presence of 10 mol% of iodine at room temperature by grinding under solvent-free conditions. Key words: iodine, chalcones, Claisen--Schmidt condensation, grinding, solvent-free. Les chalcones sont des intermediaires importants en synthe'se organique et elles presentent un grand nombre d'activite s biologiques diverses. On a realise la synthe'se de chalcones avec des rendements eleves, par le biais d'une condensation de Claisen--Schmidt d'acetophenones substituees avec divers aldehydes aromatiques, en presence de 10 moles % d'iode, a la temperature ambiante, par simple broyage dans des conditions sans solvant. Mots-cles: iode, chalcones, condensation de Claisen--Schmidt, broyage, sans solvant. [Traduit par la Redaction], Introduction Chalcones and their derivatives are useful intermediates in organic synthesis. (1) Many chalcone derivatives display interesting pharmacological and biological activities. (2) Therefore, much attention has been paid to the [...]

Ruthenium-catalyzed preparation of oxindoles from one-pot trimerization of indoles under oxidative conditions and from electrophilic substitution reaction of indoles with isatins or isatin-derived imines under very mild reaction conditions is reported. Key words: ruthenium, oxindoles, isatins, indoles, oxidative conditions. On a realise la preparation d'oxindoles par la reaction de trimerisation monotope d'indoles dans des conditions oxydantes et catalysee par le ruthenium ainsi que par la reaction de substitution electrophile d'indoles avec des isatines ou des imines derivees de l'isatine, dans des conditions reactionnelles tres douces. Mots-cles : ruthenium, oxindoles, isatines, indoles, conditions oxydantes. [Traduit par la Redaction], Introduction Various indole derivatives occur in many pharmacologically and biologically active compounds, (1) and the chemistry of indoles has been and continues to be one of the most active areas [...]

Conjugated polymers have received a lot of attention, since they combine the best features of metals or semi-conductors with those of synthetic polymers. For instance, solar cells based on poly(2,7-carbazole) derivatives have revealed power-conversion efficiencies up to 6%. This class of materials could lead to printable and flexible photovoltaic devices. Moreover, water-soluble luminescent polythiophenes have allowed the specific, rapid, and ultra-sensitive detection of unlabelled DNA, RNA, or proteins. This new optical detection mechanism is based on electrostatic interactions between a cationic polythiophene derivative and negatively charged oligonucleotides. This method makes now possible the rapid assessment of the identity of single nucleotide polymorphisms (SNPs), genes, and pathogens without the need for nucleic acid amplification. Key words: conjugated polymers, plastic electronics, biosensors, polyfluorenes, polythiophenes, polycarbazoles. Les polymeres conjugues suscitent beaucoup d'interet puisqu'ils combinent les proprietes des metaux ou des semiconducteurs a celles des polymeres synthetiques. Par exemple, des piles solaires fabriquees a l'aide de derives du poly(2,7-carbazole) ont montre des efficacites de conversion energetique de l'ordre de 6 %. Cette classe de materiaux pourrait donc conduire a la mise en place de dispositifs photovoltaiques flexibles et imprimables. Par ailleurs, des polythiophenes luminescents et solubles dans l'eau ont permis une detection rapide, specifique, ultra-sensible et directe d'ADN, d'ARN ou de proteines. Ce nouveau mecanisme de detection optique utilise les interactions electrostatiques entre un derive cationique du polythiophene et les charges negatives de sondes a base d'oligonucleotides. Cette methode rend maintenant possible l'identification rapide de mutations genetiques, de genes specifiques ou de pathogenes sans le recours d'amplification du materiel genomique. Mots-cles : polymeres conjugues, electronique plastique, biocapteurs, polyfluorenes, polythiophenes, polycarbazoles., Introduction In the field of micro-electronics and medicine, polymeric materials were traditionally used in applications such as packaging and electrical insulators. However, new opportunities emerged with the discovery of conducting [...]

Commercially available zirconia (Zr[O.sub.2]) is reported as an extremely efficient catalyst for the synthesis of quinolines. A one-step reaction of 2-aminoarylketones and a carbonyl compound (Friedlander reaction) took place under solvent-free conditions to afford the corresponding quinolines in good-to-high yields in the presence of Zr[O.sub.2]. Furthermore, the catalyst is reused several times without any significant loss of its catalytic activity. Key words: Zr[O.sub.2], Quinoline, Friedlander reaction, solvent-free, 2-aminoarylketones. On a observe que la zircone commercialement disponible est un catalyseur extremement efficace pour la synthese des quinoleines. En presence de Zr[O.sub.2], la reaction de Friedlander, une reaction en une etape entre une 2-aminoarylcetones et un compose carbonyle, se produit dans des conditions sans solvant pour conduire aux quinoleines correspondantes avec des rendements allant de bons a excellents. De plus, on peut reutiliser le catalyseur a plusieurs reprises sans perte significative de son activite catalytique. Mots-cles : Zr[O.sub.2], reaction de Friedlander, sans solvant, 2-aminoarylcetones. [Traduit par la Redaction], Introduction Quinolines are well-known for a wide range of medicinal properties and for being used as antimalarial, antiasthmatic, antihypertensive, antibacterial, and tyrosine-kinase-inhibiting agents. (1) They also undergo hierarchical self-assembly into [...]

A series of estradiol (EZ) derivatives were designed to interact with both the substrate- and the cofactor-binding sites of 17β-hydroxysteroid dehydrogenase type 1 (17P-HSD1). These analogues of potent [E.sub.2]--adenosine hybrid inhibitor EM-1745, where the adenosine moiety was replaced by a more stable benzene derivative, were synthesized from estrone using alkene cross-metathesis and Sonogashira coupling reactions as key steps. In vitro biological evaluation of these steroid derivatives revealed that a spacer of 13 methylenes, between the 16β-position of [E.sub.2] and the adenosine mimic bearing a carboxylic acid group, gave the best inhibition of 17β-HSD1. Key words: 17p-hydroxysteroid dehydrogenase, enzyme, inhibitor, steroid, metathesis, Sonogashira coupling. Plusieurs derives de l'estradiol ([E.sub.2]) ont ete prepares pour interagir avec le site de liaison du substrat et le site de liaison du cofacteur de la 17β-hydroxysteroide deshydrogenase type 1 (17β-HSD1). Ces analogues du puissant inhibiteur EM-1745, un hybride [E.sub.2]--adenosine dont la partie adenosine a ete remplacee par un derive benzylique plus stable, ont ete obtenus a partir de l'estrone en utilisant la metathese de Grubbs et le couplage de Sonogashira comme etapes cle. L'evaluation biologique in vitro de ces derives steroidiens a montre qu'une chaine ayant 13 groupes methylenes, entre la position 16P du steroide [E.sub.2] et le noyau benzylique porteur d'un acide carboxylique, provoquait la meilleure inhibition de l'enzyme 17β-HSD1. Mots-cles : 17β-hydroxysteroide deshydrogenase, enzyme, inhibiteur, steroide, metathese, couplage de Sonogashira., Introduction 17β-Hydroxysteroid dehydrogenase type 1 (17β-HSD1) or human estradiol dehydrogenase [E.C.1.1.1.62] was partially purified from human placenta by Langer and Engel in 1958. (1) It is a 327-amino-acids protein that [...]

The ionization and excitation spectra of valence and core electrons of s-triazine in the gas phase are studied with ab initio, density functional, and semi-empirical methods. The results are compared with available experimental data and previous calculations. New estimates are proposed for the ionization energies of both valence and core electrons. The calculated excitation energies are consistent with experiment. Key words: ionizations, photoelectron spectra, excitations, UV absorption, electron spectra, s-triazine, core-electron binding energies, ESCA, DFT. Faisant appel a des methodes de calculs semi-empiriques, ab initio et selon la theorie de la fonctionnelle de la densite, on a etudie les spectres d'excitation et d'ionisation des electrons de coeur et de valence de la s-triazine en phase gazeuse. On compare les resultats de ces calculs avec les donnees experimentales disponibles et les resultats de calculs anterieurs. On propose de nouvelles evaluations pour les energies d'ionisation des electrons de valence et de coeur. Les energies d'excitation calculees sont coherentes avec les resultats experimentaux. Mots-cles: ionisations, spectres photoelectroniques, excitations, absorption UV, spectres electroniques, s-triazine, energies de liaison des electrons de coeur, spectroscopie electronique pour l'analyse chimique (SEAC), theorie de la fonctionnelle de densite (TFD). [Traduit par la Redaction], Introduction The photoelectron spectra of 1,3,5-(sym)-triazine ([C.sub.3][N.sub.3][H.sub.3]) vapour were reported by several workers in 1972.1-4 The assignments of some of the bands were somewhat tentative, since the interpretation of the [...]

A short and efficient route is described for both isomers of aziridine derived from the commercially available 1:1 mixture of limonene oxides. The process is amenable to scale-up and allows easy access to multigram quantities of these useful chiral building blocks. Key words: cis- and trans-limonene oxide, β-amino alcohol, o-tosylation, limonene aziridine. On a decrit une methode courte et efficace d'obtention des deux isomeres de l'aziridine qui peut etre obtenue a partir d'un melange 1 :1 commercialement disponible d'oxydes de limonene. Le processus pourrait etre amener a produire de grandes quantites et il permet d'acceder facilement a des quantites multigrammes de ces importants intermediaires chiraux. Mots-cles: oxydes des cis- et trans-limonene, P-amino alcool, o-tosylation, aziridine du limonene. [Traduit par la Redaction], Terpenes, particularly limonenes, are an important class of naturally occurring chiral compounds widely used in organic synthesis either as starting materials in the synthesis of optically pure molecules (1) or [...]

A series of phosphinimide complexes of Hf are prepared and characterized. Reaction of the phosphinimine t-[Bu.sub.3]PNH with Hf[(NE[t.sub.2]).sub.2] gave [(t-[Bu.sub.3]PN)Hf(NE[t.sub.2]).sub.3] (1) but this species was not readily converted to the corresponding Hf[Cl.sub.3]-derivative. The reaction of 2 equiv. of t-[Bu.sub.3]PNH with Hf[(NE[t.sub.2]).sub.2], however, gave [(t-[Bu.sub.3]PN).sub.2]Hf[(NE[t.sub.2]).sub.2] (2), which was readily converted to [(t-[Bu.sub.3]PN).sub.2]Hf[Cl.sub.2] (3) and [(t-[Bu.sub.3]PN).sub.2]Hf[Me.sub.2] (4). Employing t-[Bu.sub.3]PNLi and Hf[Cl.sub.4] afforded [(t-[Bu.sub.3]PN).sub.3]HfCl (5) while reaction with CpHf[Cl.sub.3] gave rise to ligand redistribution reactions affording (t-[Bu.sub.3]PN)2Hf[Cl.sub.2] and [Cp.sub.2]Hf[Cl.sub.2]. However, Cp[(t-[Bu.sub.3]PN).sub.2]HfCl (7) was prepared by treating [(t-[Bu.sub.3]PN).sub.2]Hf[Cl.sub.2] with CpNa. The related species of [Cp.sub.2](t-[Bu.sub.3]PN)HfCl (8) was synthesized by the reaction of [Cp.sub.2]Hf[Cl.sub.2] and t-[Bu.sub.3]PNLi. Ligand redistribution was avoided in the reaction of [Cp.sup.*]Hf[Cl.sub.3] as [Cp.sup.*](t-[Bu.sub.3]PN)Hf[Cl.sub.2] (9) and [Cp.sup.*](i-[Pr.sub.3]PN)Hf[Cl.sub.2] (10) were readily obtained and derivatized as [Cp.sup.*](t-[Bu.sub.3]PN)Hf(N[Me.sub.2])2 (11) and [Cp.sup.*](t-[Bu.sub.3]PN)Hf[Me.sub.2] (12), respectively. Similarly, ((Me3Si)2C5H3)(t-[Bu.sub.3]PN)Hf[Cl.sub.2] (13) was converted to ((Me3Si)2C5H3)(t-[Bu.sub.3]PN)Hf[Me.sub.2] (14). Reactions with Lewis acid activators were used to prepare [Cp.sup.*](t-[Bu.sub.3]PN)HfMe(THF)MeB([C.sub.6][F.sub.5])3 (15), ([Cp.sup.*][(t-[Bu.sub.3]PN)Hfme)[(B([C.sub.6][F.sub.5]).sub.4]) (16), and [(t-[Bu.sub.3]PN)2Hf(H2B([C.sub.6][F.sub.5])2).sub.2] (17). Preliminary testing of 3, 9, and 13 in ethylene polymerization is reported. Compounds 3, 4, 7, 9, and 17 are characterized crystallographically. Key words: hafnium, phosphinimide, ligand redistribution, cyclopentadienyl ligands, ethylene polymerization. On a prepare et caracterise une serie de complexes de Hf avec le phosphinimide. La reaction de la phosphinimine t-[Bu.sub.3]PNH avec le Hf[(NE[t.sub.2]).sub.4] conduit a la formation du compose [(t-[Bu.sub.3]PN)Hf(NE[t.sub.2]).sub.3] (1); toutefois, cette espece ne se transforme pas facilement en derive Hf[Cl.sub.3] corrrespondant. Toutefois, la reaction de 2 equiv. de t-[Bu.sub.3]PNH avec du Hf[(NE[t.sub.2]).sub.2] conduit a la formation de [(t-BuPN)2Hf(NE[t.sub.2]).sub.2] (2) qu'on peut facilement transformer en (t-[Bu.sub.3]PN)2Hf[Cl.sub.2] (3) et en [(t-[Bu.sub.3]PN).sub.2]Hf[Ne.sub.2] (4). L'utilisation de (t-BuPNLi) et de Hf[Cl.sub.4] conduit a la formation de (t-[Bu.sub.3]PN)2HfC1 (5) alors que la reaction avec du CpHf[Cl.sub.3] conduit a une reaction de redistribution de ligand conduisant au (t-[Bu.sub.3]PN)2Hf[Cl.sub.2] et au [Cp.sub.2]Hf[Cl.sub.2]. Toutefois, on a pu preparer le [(t-[Bu.sub.3]PN).sub.2]HfCl (7) par traitement du (t-[Bu.sub.3]PN)2Hf[Cl.sub.2] avec du CpNa. On a effectue la synthese de l'espece apparentee [Cp.sub.2](t-[Bu.sub.3]PN)HfCI (8) par reaction du [Cp.sub.2]Hf[Cl.sub.2] avec le t-[Bu.sub.3]PNLi. La reaction de redistribution des ligands a ete evitee dans la reaction du [Cp.sup.*]Hf[Cl.sub.3] et il a ete possible d'obtenir facilement de [Cp.sup.*](t-[Bu.sub.3]PN)Hf[Cl.sub.2] (9) et [Cp.sup.*](t-BuPN)Hf[Cl.sub.2] (10) et de les transformer en derives [Cp.sup.*][(t-[Bu.sub.3]PN)Hf(N[Me.sub.2]).sub.2] (11) et [Cp.sup.*](t-BuPN)Hf(N[Me.sub.2])2 (12) respectivement. De la meme maniere, on a pu transformer le produit [([Me.sub.3]Si)2[C.sub.5][H.sub.3]](t-[Bu.sub.3]PN)Hf[Cl.sub.2] (13) en [([Me.sub.3]Si)2[C.sub.5][H.sub.3]](t-[Bu.sub.3]PN)Hf[Cl.sub.2][Me.sub.2] (1 a des reactions avec des activateurs d'acide de Lewis pour preparer les produits [Cp.sup.*](t-BuPH)HgMe(THF)MeB[([C.sub.6][F.sub.5]).sub.3] (15), ([Cp.sup.*](t-[Bu.sub.3]PN)HfMe)[(B([C.sub.6][F.sub.5]).sub.4]) (16) et (t-[Bu.sub.3]PN)Hf([H.sub.2]B([C.sub.6][F.sub.5])2)2 (17). On rapporte les resultats preliminaires de l'evaluation des composes 3, 9 et 13 dans des polymerisations de l'ethylene. Les structures des composes 3, 4, 7, 9 et 17 ont ete caracterisees par cristallographie. Mots-cles : hafnium, phosphonimide, redistribution de ligand, ligands cyclopentadienyles, polymerisation de l'ethylene. [Traduit par la Redaction], Introduction The drive to discover new homogeneous catalysts for olefin polymerization has stimulated much research over the last 25 years. Several reviews have described such studies. (1-9) While synthetic routes [...]

A variety of phenol derivatives were successfully nitrated via combination of Al[(N[O.sub.3]).sub.3]*9[H.sub.2]O and silica sulfuric acid in the presence of wet Si[O.sub.2] (50% w/w) in dichloromethane at room temperature with moderate-to-good yields. Key words: nitration, phenol, heterogeneous conditions, aluminum nitrate [Al(N03)3-9H20], silica sulfuric acid (Si[O.sub.2]-OS[O.sub.3]H). Operant a la temperature ambiante, dans le dichloromethane et faisant appel a une combinaison de Al[(N[O.sub.3]).sub.2]*9[H.sub.2]O et d'acide sulfurique lie a de la silice, en presence de Si[O.sub.2] humide (50 % w/w), on a realise avec succes la nitration des derives du phenol, avec des rendements allant de moderes a bons. Mots-cles : nitration, phenol, conditions heterogenes, nitrate d'aluminium [Al[(N[O.sub.3]).sub.2]*9[H.sub.2]O], acide sulfurique lie a de la silice (Si[O.sub.2]-OS[O.sub.3]H). [Traduit par la Redaction], Introduction Nitrophenols have been identified in the atmospheric gas phase and in cloud and rainwater. (1) Nitration of organic substrates is a widely studied reaction of great industrial significance, as [...]

Kinetic studies of the Wallach rearrangements of four azoxypyridines, four azoxypyridine N-oxides, and one azoxypyridine N-methiodide have been carried out in the 100% [H.sub.2]S[O.sub.4] acidity region. For all of the β-isomers in the study the reactions proceeded at a spectrally measurable rate, and the log observed rate constants were found to be linear functions of the log [H.sub.3]S[O.sub.4.sup.+] concentration, as previously found for azoxybenzene itself, suggesting that the reaction mechanism for these substrates is the same as that previously deduced for axozybenzene, i.e., a general-acid-catalysis A-[S.sub.E]2 process. For the a-azoxypyridines no reaction could be observed at all. The two a-azoxypyridine N-oxides in the study did react, albeit very slowly, but for these two compounds the log observed rate constants were not linear functions of the log [H.sub.3]S[O.sub.4.sup.+] concentration, but were instead found to be linear in the [H.sub.o] acidity function, which is known for the 100% [H.sub.2]S[O.sub.4] acidity region. It follows that the reaction mechanism for these α-isomers is a different one, presumably an Al process. This mechanism was proposed back in 1963 for azoxybenzene, but has never actually been observed for any substrate before the work reported in this study. Thus, the Wallach rearrangement story can be said to have come full circle. Key words: azoxypyridines, azoxypyridine N-oxides, Wallach rearrangement, reactivities, mechanisms. Operant dans la region d'acidite du [H.sub.2]S[O.sub.4] α 100 %, on a effectue des etudes cinetiques sur les rearrangements de Wallach de quatre azoxypyridines, de quatre N-oxydes d'azoxypyridines et d'un N-methiodure d'azoxypyridine. Pour tous les isomeres β de l'etude, les reactions procedent a des vitesses spectroscopiquement mesurables et on a trouve que le log des constantes de vitesse observees sont lineaires avec le log de la concentration en [H.sub.3]S[O.sub.4.sup.+], tel qu'on l'avait observe anterieurement avec l'azoxybenzene lui-meme, ce qui suggere que le mecanisme de la reaction pour ces substrats est le meme que celui deduit anterieurement pour l'azoxybenzene, c'est-a-dire un processus de catalyse acide generale, A-[S.sub.E]2. Pour les a-azoxypyridines, on n'a observe aucune reaction. Les deux N-oxydes de la a-azoxypyridne reagissent, mais la reaction est toutefois tres lente et les log des constantes de vitesses de ces deux produits ne donnent pas de relation lineaire avec le log de la concentration en [H.sub.3]S[O.sub.4.sup.+]; elles sont toutefois lineaires avec une fonction d'acidite [H.sub.o] qui est connue pour la reaction d'acidite du [H.sub.2]S[O.sub.4] α 100 %. On peut donc en conclure que le mecanisme de la reaction pour les isomeres a est different, probablement un processus Al. Ce mecanisme avait deja ete propose en 1963 pour l'azoxybenzene, mais il n'avait jamais ete observe avec un substrat avant celui rapporte dans ce travail. On peut donc dire que l'histoire du rearrangement de Wallach a retrouve son point de depart. Mots-cles : azoxypyridines, N-oxydes d'azoxypyridines, rearrangement de Wallach, reactivites, mecanismes. [Traduit par la Redaction], Introduction Many of the kinetic and other studies of the Wallach rearrangement, discovered in 1880 (2) and shown below for azoxybenzene 1, have been extensively reviewed, along with other aromatic [...]

The compound 2-APPy [1-(2-aminophenyl)pyrrole] as an organic phase in an inorganic-organic semiconductor interface (101) assembly was the subject of photoelectrochemical studies in aqueous solutions. Results show that thin films of poly(2-APPy) can be prepared using oxidative electropolymerization. Furthermore, absorption spectroscopic studies indicate that the protonated 2-APPy polymer's ionization potential (IP) is 4.7 eV, the electron affinity (EA) is 1.90 eV, and a gap of 2.80 eV separates the higher occupied molecular orbital's (HOMO) and lower unoccupied molecular orbital's (LUMO) energy levels of this polymer. Impedance measurements under illumination show an increase in the film charge capacitance compared with those measured under darkened conditions. The behavior of the poly(2-APPy) film as a host for redox-active dopants was also explored. The results show that the film did not alter the redox potentials of a large dopant such as P[Mo.sub.12][O.sub.40.sup.3-]. The photoactivities of the 101 assemblies consisting of 2-APPy and nanoparticles of ZnO, and of [Fe.sub.2][O.sub.3] were investigated using fluorescence emissions. Results show that the fluorescence emissions generated by 2-APPy were quenched by 5% and 55% on ZnO and on [Fe.sub.2][O.sub.3], respectively. The charge injection rate constants, [k.sub.et], at the inorganic metal oxide-2-APPy interface, were calculated. Key words: poly[ 1-(2-aminophenyl)pyrrole], photoelectrochemistry, semiconductors, material, charge transfer. Operant en solutions aqueuses, on a effectue des etudes photoelectrochimiques sur un assemblage du 1-(2-aminophenyl)pyrrole (2-APPy)dans une interface inorganique/organique semiconductrice (110). Les resultats obtenus montrent qu'il est possible de preparer le poly(2-APPy) par electropolymerisation oxydante. De plus les etudes spectroscopiques d'absorption indiquent que le potentiel d'ionisation (PI) du polymere 2-APPy protone est egal a 4,7 eV; l'affinite electronique (AE) est de 1,90 eV et que 2,80 eV separent les niveaux d'energie de l'orbitale moleculaire haute occupee (HO) et de l'orbitale moleculaire basse vacante (BV) de ce polymere. Des mesures d'impedance sous illumination mettent en evidence une augmentation dans la capacitance de la charge du film par comparaison avec celles mesurees en l'absence d'illumination. On a aussi examine le comportement du film de poly-2-APPy comme hite pour des dopants redox actifs. Les resultats montrent que le film n'altere pas les potentiels redox d'un dopant volumineux, tel le P[Mo.sub.12][O.sub.40.sup.3-]. Les photoactivites des assemblages d'interfaces inorganique/organique semi-conductrices formees de 2APPy et de nanoparticules de ZnO et de [Fe.sub.2][O.sub.3] ont aussi ete examinees a l'aide d'emission de fluorescence. Les resultats montrent que les emissions de fluorescence generees par le 2-APPy sont piegees respectivement par 5% et 55% de ZnO et de [Fe.sub.2][O.sub.3]. On a calcule les constantes d'injection de charge, [k.sub.et], a l'interface oxyde metallique inorganique/2-APPy. Mots-cles : poly[l-(2-aminophenyl)pyrrole], photoelectrochimie, semiconducteurs, materiau, transfert de charge. [Traduit par la Redaction], Introduction The interest in developing sensitizers that improve interfacial charge transfer and suppress charge recombination substantiates the need for a wider investigation of organic semiconductors. Organic compounds with semiconducting character [...]

Various dielectric continuum models in Gaussian 03, based on the SCRF approach, PCM, CPCM, DPCM, IEFPCM, IPCM, and SCIPCM, have been tested on a set of 54 highly polar, generally polyfunctional compounds for which experimental solvation energies are available. These compounds span a range of 13 kcal/mol in Δ[G.sub.t] The rootmean-square (RMS) errors for the full set of compounds range from 2.48 for DPCM to 1.77 for IPCM. For each method, classes of compounds which were not handled well could be identified. If these classes of compounds were omitted, the performance improved, and ranged from 1.58 (PCM, 39 compounds) to 1.02 (IPCM, 42 compounds). Models in the PCM family (PCM, CPCM, DPCM, and IEFPCM) with the recommended UAHF or UAKS sets of radii rely on a highly parameterized definition of the solvent cavity. Where this parameterization was inadequate, the calculated solvation energies were less reliable. This has been demonstrated by devising a new parameterization for PCM and halogen compounds, which markedly improves performance for polyhalogen compounds. The effective radius for the portion of the cavity centered on a halogen atom was assumed to be linear in the electron-withdrawing or -donating properties of the rest of the molecule as measured by Hammett a (for halogens on aromatic rings) or Taft 6* (for halogens on aliphatic carbons). This new parameterization for PCM was tested on a set of 45 aliphatic and 22 aromatic polyhalogen compounds and shown to do well. IPCM, which was already the best of the methods in Gaussian, can be considerably improved by a parameterization to allow for cavitation, dispersion, and hydrogen bonding. A large set of compounds was used for the parameterization to have multiple examples for each parameter and as far as possible to have molecules with multiple instances of each structural feature. In the end, 15 parameters were found to be defined by the data for 241 compounds. With this parameter set, the RMS error for the set used for fitting was 0.81 kcal/mol, and the RMS error for the original set of 54 compounds was 0.85. With this new parameterization, IPCM is clearly the best of the methods available in Gaussian 03. Key words: solvation energy, polyfunctional molecules, computational chemistry, parameterization, IPCM. Utilisant un ensemble de 54 composes hautement polaires et generalement polyfonctionnels pour lesquels des donnees experimentales sur les energies de solvatation sont disponibles, on a evalue divers modeles dielectriques continus dans la gaussienne 03, basee sur l'approche du champ reactionnel autocoherent (CRAC), dans des modeles du continuum polarisable divers, tel le modele apparente a un conducteur << CPCM >>, le modele dielectrique << DPCM >>, le modele dans un formalisme d'equation integrale << IEFPCM >>, le modele avec surface d'isodensite << IPCM >> ou son equivalente en champ autocoherent << SPICM >>. Les valeurs du Δ[G.sub.t] pour ces composes s'etalent sur une plage de 13 kcal mol. La valeur quadratique moyenne (VQM) des erreurs pour l'ensemble des composes varie de 2,48 pour la methode << DPCM >> a 1,77 pour l' << IPCM >>. Pour chacune des methodes, il a ete possible de bien identifier des classes de produits qui ne pouvaient pas etre examines. Si on omet ces classes de produits, la performance s'ameliore et elle varie de 1,58 (<< PCM >>, 39 composes) a 1,02 (<< IPCM >>, 42 composes). Les modeles de la famille << PCM >> << PCM, CPCM, DPCM, IEFPCM >> utilises avec les ensembles recommandes de rayons atomiques d'atome unis de Hartree-Fock << UAHF >> ou de 'UAKS' reposent sur une definition hautement parametrisee de la cavite du solvant. Lorsque cette parametrisation n'etait pas adequate, les energies de solvatation etaient moins fiables. On a demontre ce point en mettant au point une nouvelle parametrisation pour la methode 'PCM' et les composes halogenes qui a permis d'ameliorer grandement la performance pour les derives polyhalogenes. On fait l'hypothese que le rayon effectif de la portion de la cavite centree sur un atome d'halogene est lineaire dans le caractere electroaffinitaire ou electrodonneur du reste de la molecule, tel que mesure par les valeurs 6 de Hammett (pour les atomes d'hydrogene sur les noyaux aromatiques) et 6* de Taf (pour les atomes d'halogene sur les carbones aliphatiques). On a teste cette nouvelle parametrisation dans le modele << PCM >> sur un ensemble de 45 composes polyhalogenes aliphatiques et 22 aromatiques et on a montre qu'elle donne de bons resultats. La methode << IPCM >> qui etait deja la meilleure des methodes gaussiennes peut etre considerablement amelioree par une parametrisation qui tient compte de la cavitation de la dispersion et des liaisons hydrogenes. Afin de couvrir plusieurs exemples de chacun des parametres et pour avoir des molecules comportant de multiples instances de chacune des caracteristiques structurales, on a utilise un large ensemble de composes pour effectuer la parametrisation. On a trouve que les parametres sont definis par les donnees relatives a 241 composes. Avec cet ensemble de parametres, l'erreur quadratique moyenne pour l'ensemble utilise est de 0,81 kcal/mol alors qu'elle etait de 0,85 pour l'ensemble original de 54 composes. Avec cette nouvelle parametrisation, la methode 'IPCM' est nettement la meilleure disponible dans la gaussienne 03. Mots-cles : energie de solvatation, molecules polyfonctionnelles, chimie theorique, parametrisation, modele du continum polarisable avec surface d'isodensite << IPCM >>. [Traduit par la Redaction], Introduction Reading the literature might leave one with the impression that the problem of calculating solvation energies with precision similar to experiment, i.e., errors less than 1 kcal/mol, had been [...]

Chemical analysis of the acetone extract of Commiphora holtziana gum resin has led to the isolation of triterpenes characterized as methyl 3-oxo-1α,19α,28-trihydroxyurs-12-en-24-oate (1), methyl 3β-acetyl-2α11α,19α,28-tetrahydroxyurs-12-en-24-oate (2), methyl 3β,11α-diacetyl-1α,2α,28-trihydroxyurs-12-ene-24-oate (3), and 3P,28-diacetyl-1α,2α,25-trihydroxydammar-23-ene (4). The known compounds isolated from the same extract included cabraleadiol monoacetate (5), mansumbinol (6), 3β-acetylamyrin (7), 3α-acetylboswellic acid (8), 2-methoxy-8,12-epoxygermacra-1(10),7,11-trien-6-one (9), 2-methoxy-5-acetylfuranogermacra-1(10),7,11-tri en-6-one (10), furadienone (11), 2-methoxy-5-acetyl-4-furanogermacra-1(10)Z-en-6-one (12), α-amyrin (13), sistosterol (14) and stigmasterol 3-0-acetate (15). Structural elucidation was carried out using spectroscopic and physical methods as well as by comparison with the literature data. Key words: Commiphora holtziana, Burseraceae, triterpenes, gum-oleo-resin exudate. L'analyse chimique des produits extraits a l'acetone a partir de la gomme resine Commiphora hostziana a permis d'extraire des triterpenes caracterises comme le 3-oxo-1α,19a,28-trihydroxyurs-12-en-24-oate de methyle (1), le 3βp-acetyl2α,11α,19α,28-tetrahydroxyurs-12-en-24-oate de methyle (2), le 3β,11α-diacetyl-1α,2α,28-trihydroxyurs-12-en-24-oate de methyle (3) et le 3β,28-diacetyl-1α,2α,25-trihydroxydamma-23-ene (4). On a aussi isole les produits connus suivants: monoacetate de cabraleadiol (5), mansumbinol (6), 3β-amyrine (7), acide 3-a-acetylboswellique (8), 2-methoxy-8,12epoxy-germ acra-1(10),7,11-trie n-6-one (9), 2-methoxy-5-acetylfuranogermacra-1(10),7,11-tri en-6-one (10), furadienone (11), 2-methoxy-5-acetyl-4-furanogermacra-1(10)Z-en-6-one (12), a-amyrine (13), sistosterol (14) et 3-0-acetate du stigmasterol (15). L'elucidation des structures a ete realisee a l'aide de methodes physiques et spectroscopiques ainsi que par comparaison avec des donnees tirees de la litterature. Mots-cles : Commiphora holtziana, Burseraceae, triterpenes, exsudate de gomme-oleo-resine. [Traduit par la Redaction], Introduction The genus Commiphora (Burseraceae) is widely distributed in the tropics and subtropics, particularly in Africa, Asia, and Australia. (1) Over 46 Commiphora species are acclimatized in the northeastern province [...]

Sulfinyltoluquinones (2a-2c) were submitted to thermal or catalyzed [4+2] cycloaddition reactions with cyclopentadiene. For p-tolylsulfmyltoluquinones (2b) and (2c), almost complete C2-C3-chemo- and unlike-diastereoselectivity was achieved by catalysis with ZnBr2, yielding adducts 6. Under thermal conditions, Diels-Alder reaction took place at the C5-C6 double bonds of quinones 2a-2c, generating mixtures of diastereoisomeric like- and unlike-adducts 4. Key words: Diels-Alder reaction, sulfinyltoluquinones, sulfinyl group, stereochemical control, Ti-facial selectivity. On a soumis les sulfinyltoluquinones (2a-2c) a des reactions de cycloaddition thermiques ou catalysees avec le cyclopentadiene. Avec le ZnBr2 comme catalyseur, les p-tolylsulfmyltoluquinones (2b) et (2c) conduisent a 1a formation des adduits 6 et al diastereoselectivite chimique et dissemblable au niveau de 1a liaison C2-C3 est pratiquement complete. Dans des conditions thermiques, 1a reaction de Diels-Alder se produit au niveau des doubles liaisons C5-C6 des quinones 2a-2c qui conduit a 1a formation d'adduits 4 sous 1a forme de melanges diastereomeres semblables et dissemblables. Mots-cles : reaction de Diels-Alder, sulfinyltoluquinones, groupe sulfinyle, controle stereochimique, selectivite de 1a face n. [Traduit par 1a Redaction], Introduction The Diels-Alder (DA) reaction remains as one of the most powerful methods for the construction of cyclic systems with potential for stereochemical control of up to four stereogenic centers [...]