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The surface and self-assembly properties of a family of multiheaded, multitailed surfactants based on a tripentaerythritol backbone are described. Critical aggregation concentrations of these unusual surfactant systems have been determined from surface tension measurements; aggregate sizes in the presence and absence of a small amount of added electrolyte have been obtained via dynamic light scattering, and the morphologies of the aggregates were examined from electron microscopy measurements. In general, when compared to conventional ionic and two-headed surfactants (and other recently synthesized pentaerythritol derived surfactants from this group), these multiheaded surfactants exhibited some unusual trends in their aggregation behaviour and interesting aggregate structures in aqueous solution, as a function of alkyl chain length. Key words: tripentaerythritol, surfactants, aggregates, critical aggregation concentration, light scattering. Le present article decrit la surface et les proprietes d'auto-assemblage d'une famille de surfactants a tetes et queues multiples, formes d'une chaine principale de tripentaerythritol. Les concentrations d'agregation critique de ces types de surfactant inhabituels ont ete determinees a partir des mesures de tension superficielle. La taille des agregats en presence ou en absence de petites quantites d'electrolytes ajoutes a ete mesuree par diffusion dynamique de la lumiere et leur morphologie a ete analysee a l'aide de mesures au microscope electronique. D'une maniere generale, lorsqu'on les compare aux surfactants habituels ioniques ou a deux tetes (ou a d'autres surfactants recemment synthetises, derives du pentaerythritol et issus de ce meme groupe), on constate que ces surfactants a tetes multiples donnent lieu a quelques phenomenes d'agregation inhabituels et a la formation de structures d'agregats interessantes en solution aqueuse, qui dependent de la longueur de la chaine alkyle. [Traduit par la Redaction] Mots-cles: tripentaerythritol, surfactants, agregats, concentration d'agregation critique, diffusion de la lumiere., Introduction We have recently described the extremely flexible synthesis of cationic, (1-3) zwitterionic, and anionic (4) two-headed surfactants based on the pentaerythritol moiety. In previous publications, these compounds have been [...]

Efficient syntheses of three series of anionic gemini surfactants based on pentaerythritol are described. A series of disulfates was prepared by the double displacement of the two cyclic sulfates in the S4-symmetric compound pentaerythritol spirobicyclic sulfate (1) with linear alkoxides. A second series of disulfates was prepared by reaction of the dialkoxides of di-O-alkylpentaerythritols with ethylene sulfate. The di-O-alkylpentaerythritols can be prepared as previously reported by us or by the acid-catalyzed hydrolysis of the first series of disulfates. A series of disulfonates was prepared by reaction of the dialkoxides of di-O-alkylpentaerythritols with 1,3-propanesultone. This last set of reactions was complicated by the formation of oxetanes, which probably arose from initial reversible displacement on sulfur of the sultone alkoxide by the pentaerythritol alkoxide followed by a second intramolecular displacement of the resulting sulfonate. Changing the order of addition to keep the reaction medium from containing excess base as well as lowering the reaction temperature minimized the amounts of these byproducts. All three series had excellent surfactant properties. Key words: gemini surfactants, anionic surfactants, pentaerythritol, cyclic sulfates, disulfates, sulfonates, 1,3- propanesultone. On decrit les syntheses efficaces de trois series de tensioactifs gemines anioniques a partir de pentaerythritol. Une serie de disulfates a ete preparee par double deplacement de deux sulfates cycliques dans le compose de symetrie S4 sulfate spirobicyclique de pentaerythritol (1) par des alkoxydes lineaires. Une deuxieme serie de disulfates a ete obtenue par reaction des dialkoxydes de di-O-alkylpentaerythritols avec du sulfate d'ethylene. Les di-O-alkylpentaerythritols peuvent etre prepares comme nous l'avons decrit anterieurement ou par hydrolyse de la premiere serie de disulfates catalysee par un acide. Une serie de disulfonates a ete preparee par reaction des dialkoxydes de di-O-alkylpentaerythritols avec la 1,3-propanesultone. Ce dernier ensemble de reactions a ete complique par la formation d'oxetanes qui ont probablement ete produits par le deplacement reversible initial du soufre de l'alkoxyde de sultone par l'alkoxyde de pentaerythritol, suivi par un deuxieme deplacement intramoleculaire du sulfonate resultant. La modification de l'ordre d'addition afin d'eviter que le milieu de reaction ne contienne un exces de base, de meme que la reduction de la temperature de reaction ont minimise les quantites de ces sous- produits. Les series ont toutes les trois d'excellentes proprietes tensioactives. [Traduit par la Redaction] Mots-cles: tensioactifs gemines, tensioactifs anioniques, pentaerythritol, sulfates cycliques, disulfates, sulfonates, 1,3-propanesultone., Introduction Gemini surfactants display critical micellization concentrations that are one to two orders of magnitude lower than those of the corresponding conventional surfactants with only a single head group and [...]

A family of polymer stars has been prepared from early generation dendritic cores with four, six, and eight arms. Four dendritic cores were prepared from the sequential reaction of a multifunctional alcohol with a protected anhydride, followed by deprotection to afford two or three new alcohol functionalities per reactive site. These cores were used as initiators for the tin-catalyzed ring-opening polymerization of L-lactide and raolactide to afford isotactic and atactic degradable stars, respectively. Two series of stars were prepared for each monomer, either maintaining total molecular weight or number of monomer units per arm. The polymers were characterized by NMR spectroscopy, light-scattering gel-permeation chromatography, differential scanning calorimetry, and thermogravimetric analysis. Our results support previous work that suggests that the length of the arms dictates thermal properties rather than the total molecular weight of the star. Little effect was noted between aromatic and aliphatic cores, presumably due to the flexibility of the rest of the core molecule. We have shown that early generation dendrimers can serve as excellent core structures for building core-first polymer stars via the ring-opening of cyclic esters. Key words: poly(lactic acid), dendrimer, biodegradable polymer, synthesis, star polymer, thermal properties, DSC, TGA. On a prepare une famille de polymeres en etoile a partir de cceurs dendritiques de premieres generations possedant quatre, six ou huit branches. On a produit quatre cceurs dendritiques en partant de la reaction sequentielle d'un alcool multifonctionnel avec un anhydride protege, suivie d'une deprotection de maniere a donner deux ou trois nouvelles fonctions alcool par site de reaction. Ces coeurs ont servi d'initiateurs de polymerisation par ouverture de cycle, catalysee par l'etain, du L-lactide et du rac-lactide pour obtenir des etoiles degradables de formes isotactique et atactique, respectivement. Pour chaque monomere, on a prepare deux series d'etoiles, en maintenant le meme poids moleculaire total ou le meme nombre d'unites monomeriques par branche. On a caracterise les polymeres par spectrometrie RMN, par chromatographie par permeation de gel associee a un detecteur a diffusion de lumiere, par calorimetrie differentielle a balayage (DSC) et par analyse thermogravimetrique (ATG). Nos resultats corroborent ceux de travaux anterieurs donnant a penser que la longueur des branches dicte les proprietes thermiques plutot que le poids moleculaire total de l'etoile. Nous n'avons constate que peu de difference entre les coeurs aromatiques et aliphatiques, probablement en raison de la flexibilite du reste de la molecule centrale. Nous avons montre que les dendrimeres de premieres generations peuvent constituer d'excellentes structures de base pour la construction de polymeres en etoile a partir du coeur par ouverture d'esters cycliques. [Traduit par la Redaction] Mots-cles : acide polylactique, dendrimere, polymere biodegradable, synthese, polymere en etoile, proprietes thermiques, DSC, ATG., Introduction Control over polymer macrostructure, especially over polymer topology, is an increasingly important method to modify polymer properties. These branched structures include graft, comb, brush, cross-linked, dendritic, and star polymer [...]

X-ray crystallographic studies of two axial glycosyl sulfoxides having [R.sub.S] configurations (derivatives of phenyl 2-azido-2-deoxy-1-thio-α-D-galactopyranoside S-oxide) show that they adopt anti conformations in the solid state, in contrast to previous observations and assumptions. Density functional theory (DFT) calculations at the B3lYP6-311G+(d,p)/ 6-31G(d) level confirm that anti conformations of both phenyl and methyl [R.sub.S] glycosyl sulfoxides of 2-azido-2-deoxy-α-D-pyranosides are more stable than exo-anomeric conformations in the gas phase. 1D NOE measurements indicate that the more polar exo-anomeric conformers are only populated to a slight extent in solution. The anti conformations are distorted so that the glycosyl substituents are closer to being eclipsed with H1. This distortion allows S n → [σ.sup.*] overlap if the sulfur lone pair is a p-type lone pair. Evidence for this overlap comes from short C1-S bond distances, as short as the comparable bond distances in the X-ray crystal structure and in the results from DFT calculations for the [S.sub.S] glycoside, which does adopt the expected exo-anomeric conformation, both in the solid state and in solution, and has normal n → [σ.sup.*] overlap. For 2-deoxy derivatives not bearing a 2-azido group, gas-phase DFT calculations at the same level indicate that the anti- and exo-anomeric conformers have comparable stabilities. Comparison of the results of the two series shows that electronegative substituents in equatorial orientations at C2 destabilize conformations with parallel S-O arrangements, the conformation favored by having an endocyclic C-O dipole antiparallel to the S-O dipole, by about 2.5 kcal [mol.sup.-1] (1 cal = 4.184 J). An equatorial glycosyl sulfoxide, ([S.sub.S]) phenyl 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-1-thio-β- D-glucopyranoside S-oxide, also adopts an anti conformation in the solid state as shown by X-ray diffraction. It also adopts this conformation in solution, in contrast to studies of other equatorial glycosyl sulfoxides. Key words: sulfoxide configurations, glycosyl sulfoxides, conformational analysis, density functional theory (DFT) calculations, 1D NOE measurements, X-ray crystallography. Des etudes de cristallographie par diffraction des rayons-X de deux glycosyles sulfoxydes axiaux de configurations [R.sub.S], des derives du S-oxyde de 2-azido-2-desoxy-1-thio-a-galactopyranoside de phenyle, montrent qu'ils adoptent des conformations anti a l'etat solide, contrairement aux observations anterieures et aux hypotheses. Des calculs selon la theorie de la fonctionnelle de la densite; (TFD) au niveau B31YP6-311G+(d,p)/6-31G(d) confirment que les conformations anti que, en phase gazeuse, chacun des [R.sub.S] glycosyles sulfoxydes, 2-azido-2-desoxy-1-thio-α- galactopyranoside tant de methyle que de phenyle sont plus stable dans les conformations anomeres exo. Des mesures d'effet Overhauser nucleaire (eOn) 1D indiquent que, en solution, les conformeres anomeres les plus polaires ne forment qu'une faible partie de la population. Les conformations anti sont deformees de facon a ce que les substituants glycolyses soient dans une position pratiquement eclipsee avec le H1. Cette distorsion permet un recouvrement S n → [σ.sup.*] sur la paire libre du soufre est une paire libre de type p. Un support pour ce recouvrement vient des courtes longueurs de liaison C1-S, pratiquement aussi courtes que les longueurs mesurees par diffraction des rayons-X dans la structure cristalline et en accord avec les resultats des calculs TFD pour le [S.sub.S] glycoside qui adopte la conformation anomere exo attendue, tant a l'etat solide qu'en solution, et pour le recouvrement n → [σ.sup.*] normal. Pour les derives 2-desoxy ne portant pas de groupe azido, les calculs de TFD en phase gazeuse, au meme niveau, indiquent que les conformeres anomeres anti et exo ont des stabilites comparables. Une comparaison des resultats des deux series montre que les substituants electronegatifs en orientations equatoriales en C2 destabilisent les conformations avec des arrangements S-O paralleles, la conformation favorisee par un dipole C-O endocyclique antiparallele au dipole S-O par environ 2,5 kcal [mol.sup.-1] (1 cal = 4.184 J). La diffraction des rayons-X montre aussi que, a l'etat solide, un glycosyle sulfoxyde equatorial, le S-oxyde du [S.sub.S] 3,4,6-tri-O-acetyl-2-desoxy-2- phtalimido-1-thio-β-D-glucopyranoside de phenyle, adopte aussi une conformation anti. Il adopte aussi cette conformation en solution, en opposition a ce qui a ete observe dans les etudes sur glycosyles sulfoxydes equatoriaux. Mots-cles: configurations de sulfoxydes, glycosyles sulfoxydes, analyse conformationnelle, calculs selon la theorie de la fonctionnelle de la densite (TFD), mesures d'effet Overhauser nucleaire (eOn) 1D, cristallographie., Introduction One of the most important techniques for the formation of glycosides employs glycosyl sulfoxides activated by electrophiles as leaving groups. (1) This method has been used to form glycosides [...]

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 [...]

Density functional theory and second-order Moller-Plesset perturbation theory with effective core potentials have been used to calculate homolytic bond-dissociation enthalpies, D(Sn-X), of organotin compounds, and their performance has been assessed by comparison with available experimental bond enthalpies. The SDB-aug-cc-pVTZ basis set with its effective core potential was used to calculate the D(Sn-X) of a series of trimethyltin(IV) species, [Me.sub.3] Sn- X, where X = H, C[H.sub.3], C[H.sub.2]C[H.sub.3], N[H.sub.2], OH, Cl, and F. This is the most comprehensive report to date of homolytic Sn-X bond-dissociation enthalpies (BDEs). Effective core potentials are then used to calculate thermodynamic parameters including donoracceptor bond enthalpies, [bar.D](Sn-X), for a series of tin-ligand complexes, [L.sub.2]Sn[X.sub.4] (X = Br or Cl, L = py, dmf, or dmtf), which are compared with previous experimental and nonrelativistic computational results. Based on computational efficiency and accuracy, it is concluded that effective core potentials are appropriate computational methods to examine bonding in organotin systems. Key words: bond-dissociation enthalpy, trimethyltin bond-dissociation enthalpies, donor-acceptor bond enthalpy, density functional theory, effective core potential, tetrahalotin complexes. On a fait appel a la theorie de la fonctionnelle de la densite et a la theorie des perturbations du deuxieme ordre de Moller-Plesset avec des potentiels de coeur effectifs pour calculer les enthalpies de dissociation homolytique des liaisons, D(Sn-X), de composes organiques de l'etain et on a evalue leurs performances par comparaison avec les enthalpies experimentales de liaison disponibles. On a utilise l'ensemble de base SDB-aug-cc-pVTZ avec son potentiel de coeur effectif pour calculer les valeurs des D(Sn-X) d'une serie d'especes organiques de l'etain, [Me.sub.3]Sn-X dans lequel X = H, C[H.sub.3], C[H.sub.2] C[H.sub.3], N[H.sub.2], OH, Cl et F. Il s'agit de l'etude la plus complete a date sur les enthalpies de dissociation homolytique de liaisons Sn-X (ENL). On a ensuite utilise les potentiels de coeur effectifs pour calculer des parametres thermodynamiques, dont les enthalpies de liaison donneur-accepteur, [bar.D]Sn - X, pour une serie de complexes de l'etain, [L.sub.2]Sn[X.sub.4] (X = Br ou Cl, L = py, dmf ou dmtf), qui ont ete comparees avec les resultats anterieurs obtenus d'une facon experimentale ou par des calculs non relativistes. En se basant sur l'efficacite des calculs et leur exactitude, on peut conclure que les potentiels de coeurs sont des methodes appropriees de calcul pour examiner les systemes organiques de l'etain. Mots-cles : enthalpie de dissociation de liaison, enthalpies de dissociation de liaison du trimethyletain, enthalpie de liaison donneur accepteur, theorie de la fonctionnelle de densite, potentiel de coeur efficace, complexes tetrahalogenes de l'etain. [Traduit par la Redaction], Introduction The importance of tin chemistry is attributed to the prevalence of organotin compounds in organic synthesis and materials science, as well as the industrial, agricultural, and biological applications of [...]

A systematic comparison of the optimized geometries of five organotin compounds with the available gas-phase electron diffraction results is reported. It is concluded that the combination of SDB-aug-cc-pVTZ basis set and the Los Alamos National Laboratory 2 have effective core potential for tin, together with 6-31G(d,p) basis set for other atoms.

Tripentaerythritol was converted efficiently into 2',2':6',6':10', 10'-tri-O-cyclohexylidene-2,2,6,6,10, 10-hexakis(hydroxymethyl)-4,8-dioxa-1,11-undecandiol (4) by the toluenesulfonic acid catalysed reaction with cyclohexanone in a mixture of N,N-dimethylformamide and benzene. Reaction of tripentaerythritol with benzaldehyde under similar conditions gave an easily separated mixture of the four possible stereoisomers. Structures of these stereoisomers were assigned based on ¹H and [sup.13]C NMR chemical shifts using trends previously observed for the dibenzylidene acetals of dipentaerythritol, whose structures had been established unambiguously by X-ray crystallography. It was found that reduction of the mixture of benzylidene acetals to 2,6,10-tris(benzyloxymethyl)-4,8-dioxa-1,11-undecanediol could be accomplished using triethylsilane with ethylaluminium dichloride as the Lewis acid after a number of commonly used conditions for this transformation failed. Key words: pentaerythritol, tripentaerythritol, dipentaerythritol, acetals, benzylidene acetals, reduction. La reaction du tripentaerythritol avec la cyclohexanone, en solution dans un melange de N,N-dimethylformaroide et de benzene et catalysee par l'acide toluenesulfonique, conduit a la formation de 2',2':6',6':10',10'-tri-O-cyclohexylidene-2,2,6,6,10,10-hexakis(hydroxymethyl) -4,8-dioxaundecane-1,11-diol (4). La reaction du tripentaerythritol avec le benzaldehyde dans des conditions semblables conduit a un melange des quatre stereoisomeres possibles qui ont pu etre separes facilement. Les structures de ces stereoisomeres ont ete attribuees sur la base de deplacements chimiques dans les spectres RMN du ¹H et du [sup.13]C et en faisant appel aux tendances observees anterieurement pour les acetals dibenzylidenes du pentaerythritol dont les structures avaient ete determinees sans ambiguite par diffraction des rayons X. Apres avoir essaye en vain de le faire en utilisant un certain nombre de conditions regulierement a cette fin, on a trouve qu'il est possible de realiser la reduction du melange d'acetals dibenzylidenes en 2,6,10-tris-(benzoloxymethyl)-4,8-dioxaundecane-1,11-diol en utilisant le triethylsilane en presence de dichlorure d'ethylaluminium utilise comme acide de Lewis. Mots cles : pentaerythritol, tripentaerythritol, dipentaerytrhitol, acetals, acetals dibenzylidene, reduction. [Traduit par la Redaction], Introduction Dendrimers have become the subject of intense interest in the last few years (1-7). One of the molecules that has attracted the most attention as either the central core [...]

Methods were developed to convert dipentaerythritol efficiently into di-[OMICRON]-benzylidene, di-[OMICRON]-cyclohexylidene, di-[OMICRON]-l-ethylpropylidene, and di-[OMICRON]-methylene diacetals. The known di-[OMICRON]-benzylidene acetal, considered to be a single isomer, was shown to be close to a statistical mixture of the cis, cis-,cis,trans-, and trans,trans-isomers. Structures were established by a combination of NMR spectroscopy and X-ray crystallography. Reaction of the di-[OMICRON]-benzylidene acetals with benzyl chloride and potassium hydroxide surprisingly gave good to excellent yields of the monobenzyl ethers. An explanation for this observation was advanced. The dibenzyl derivatives of the di-[OMICRON]-benzylidene acetals were formed by reaction of their dianions with benzyl bromide in DMF. Selective reduction of the di-[OMICRON]-benzylidene acetals with triethylsilane and boron trifluoride etherate gave 2',6'-di-[OMICRON]-benzyldipentaerythritol. A crown ether was formed in modest yield (12%) by reaction of the dianion of the di-[OMICRON]-methylene acetal with [alpha],[alpha]'-dibromo-m-xylene in DMF. Key words: dipentaerythritol, pentaerythritol, acetals, dendrimer, selective benzylation, crown ether.

The conformations of a series of derivatives of the disaccharide [alpha]-L-fucopyranosyl-(1 [right arrow] 3)-2-acetamido-2-deoxy-D-glucopyranoside, part of the [Le.sup.x] determinant, were studied by molecular modelling using the MM[3.sup.*] forcefield and by [sup.1]H NMR spectroscopy. Unusually shielded O-benzyl protons were observed in the [sup.1]H NMR spectrum of phenyl 2,3,4-tri-O-benzyl-[alpha]-L-fucopyranosyl-(1 [right arrow] 3)-2-deoxy-2-phthalimido-1-thio-[alpha]-D-glucopyranoside and assigned to the 2-O-benzyl group. This observation was explained by a shift in the population of the conformational mixture present about the glycosidic linkage from the positive [PSI] region in the unsubstituted disaccharide to the negative [PSI] region induced by [pi]-stacking between the phthalimide and the 2-O-benzyl phenyl ring. The experimental nuclear Overhauser enhancements confirm the accuracy of the calculations. Key words: disaccharide, conformation, [pi]-stacking, [Le.sup.x] determinant, NOE measurements, MM3 calculations.

Crown thioethers by differential scanning calorimetry form -90 degrees celsius, or lower, up to their melting points are examined. New solid-solid phase transitions above room temperature in 12S3, in the alpha-phase of 14S4, in 15S5 and in both the alpha-phase and beta-phase of 16S4 is identified.

The article explains several different strategies that can be employed for the synthesis of five series of cationic germini surfactants based on pentaerythritol. The superior surfactant properties of the members of these series are also discussed.

The application of dibutylstannylene acetal intermediates for the semisynthesis of long-chain alkyl ether derivatives of sulfated oligosaccharides is discussed.

A convergent approach is used to synthesize a nonavalent glycodendrimer bearing terminal alpha-D-mannopyranoside units and the terminal trivalent dendrons bearing p-halophenyl ethers are prepared by glycosylation of pentaerythritol derivates having three 2-hydroxyethyl ether substituents. The product was deprotected and it and its precursors were characterized by NMR spectroscopy and FT-ICR mass spectroscopy.