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Pressure induced speciation changes in the aqueous AL3+ system

Most of the work done on the linear response kernel χ(r,r′) has focussed on its atom–atom condensed form χAB. Our previous work [Boisdenghien et al., J. Chem. Theory Comput., 2013, 9, 1007] was the first effort to truly focus on the non-condensed form of this function for closed (sub)shell atoms in a systematic fashion. In this work, we extend our method to the open shell case. To simplify the plotting of our results, we average our results to a symmetrical quantity χ(r,r′). This allows us to plot the linear response kernel for all elements up to and including argon and to investigate the periodicity throughout the first three rows in the periodic table and in the different representations of χ(r,r′). Within the context of Spin Polarized Conceptual Density Functional Theory, the first two-dimensional plots of spin polarized linear response functions are presented and commented on for some selected cases on the basis of the atomic ground state electronic configurations. Using the relation between the linear response kernel and the polarizability we compare the values of the polarizability tensor calculated using our method to high-level values.

Exploring the structure aromaticity relationships in Hückel and Möbius N-fused pentaphyrins using DFT

Protein thiol/sulfenic acid oxidation potentials provide a tool to select specific oxidation agents, but are experimentally difficult to obtain. Here, insights into the thiol sulfenylation thermodynamics are obtained from model calculations on small systems and from a quantum mechanics/molecular mechanics (QM/MM) analysis on human 2-Cys peroxiredoxin thioredoxin peroxidase B (Tpx-B). To study thiol sulfenylation in Tpx-B, our recently developed computational method to determine reduction potentials relatively compared to a reference system and based on reaction energies reduction potential from electronic energies is updated. Tpx-B forms a sulfenic acid (R-SO−) on one of its active site cysteines during reactive oxygen scavenging. The observed effect of the conserved active site residues is consistent with the observed hydrogen bond interactions in the QM/MM optimized Tpx-B structures and with free energy calculations on small model systems. The ligand effect could be linked to the complexation energies of ligand L with CH3S− and CH3SO−. Compared to QM only calculations on Tpx-B’s active site, the QM/MM calculations give an improved understanding of sulfenylation thermodynamics by showing that other residues from the protein environment other than the active site residues can play an important role.

The photophysics of interstellar ices and condensed molecules adsorbed on grains is of primary importance for studies on the origin of the specific handedness of complex organic molecules delivered to the early Earth and of the homochirality of the building blocks of life. Here, we present quantum mechanical calculations based on time-dependent density functional theory for the absorption and circular dichroism (CD) of isovaline and its chiral precursor 5-ethyl-5-methylhydantoin, both observed in meteoritic findings. The systems are considered in their geometrical conformation as extracted from a full solid (icy)matrix, as a shortcut to understand the behaviour of molecules with fixed orientation, and/or taking into account the full solid matrix. In the context of a possible 'condensation-warming plus hydrolysis-recondensation' process, we obtain that: (i) for low-energy excitations, the 'condensed' precursor has a stronger CD with respect to the amino acid, suggesting that the handedness of the latter could be biased by asymmetric photolysis of the precursor in cold environments; (ii) enantiomeric excess could in principle be induced more efficiently in both systems for excitation at higher energies (VUV).X-ray absorption near-edge spectroscopy and related CDresults could serve as support for future experiments on ionization channels. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

International audience; To address the issue of the aggregation in second-order nonlinear optical (NLO) polymers we developed an approach based on the synthesis of a multifunctional macromolecular chain transfer agent. The controlled monomer insertion polymerization into the main chain by a 'reversible addition-fragmentation chain transfer' (RAFT) mechanism allows the spatial arrangement of the NLO chromophores along the polymeric chain in order to obtain sequence-ordered polymers. In a first step, a novel trithiocarbonate based macroinitiator containing the disperse red 19 (DR19) units in the main chain was synthesized by polycondensation; in a second step, this polymeric precursor was applied to the synthesis of a sequentially ordered polymer by controlled insertion radical polymerization of styrene. Size exclusion chromatography (SEC), nuclear magnetic resonance (NMR) data revealed that, (i) for the first time, polystyrenes (PS) bearing DR19 dyes covalently bounded were obtained, and (ii) both the insertion reaction and the length of the polystyrene segments were accurately controlled. Whatever the incorporated dye amount, all the copolymers were soluble in common solvents. Second-order optical nonlinearity in corona-poled thin films was evaluated, and second harmonic coefficients up to 80 pm/V were determined for loading ratio lower than 10 wt-% (DR19/PS). This approach opens up opportunities for the incorporation of more efficient chromophores even in apolar matrices.

The reactivity and complexation properties of dicoordinated Sn(II) and Sn(0) compounds are reviewed. The (dominant) electrophilicity of the stannylenes was confirmed and quantified through density functional theory (DFT) based reactivity indices. For these compounds, combining theoretical DFT calculations and experimental nuclear magnetic resonance (NMR) spectroscopic results has evidenced their potential to undergo π-complexation from aromatic π clouds in addition to significantly stronger σ-complexation. Moreover, their potential as Lewis bases was scrutinized in their interactions and reactions with iron and tungsten carbonyl Lewis acids. Finally, a prospective comparison of the reactivity of divalent stannylenes and stannylones, with a 0 oxidation state at the Sn atom, is presented.

Insight into the key factors driving the competition of halogen and hydrogen bonds is obtained by studying the affinity of the Lewis bases trimethylamine (TMA), dimethyl ether (DME), and methyl fluoride (MF) towards difluoroiodomethane (CHF2I). Analysis of the infrared and Raman spectra of solutions in liquid krypton containing mixtures of TMA and CHF2I and of DME and CHF2I reveals that for these Lewis bases hydrogen and halogen-bonded complexes appear simultaneously. In contrast, only a hydrogen-bonded complex is formed for the mixtures of CHF2I and MF. The complexation enthalpies for the C-H center dot center dot center dot Y hydrogen-bonded complexes with TMA, DME, and MF are determined to be -14.7(2), -10.5(5) and -5.1(6) kJmol(-1), respectively. The values for the C-I center dot center dot center dot Y halogen-bonded isomers are -19.0(3) kJmol(-1) for TMA and -9.9(8) kJmol(-1) for DME. Generalization of the observed trends suggests that, at least for the bases studied here, softer Lewis bases such as TMA favor halogen bonding, whereas harder bases such as MF show a substantial preference for hydrogen bonding.

Noncovalent interactions involving aromatic rings, such as π-stacking and CH/π interactions, are central to many areas of modern chemistry. However, recent studies proved that aromaticity is not required for stacking interactions, since similar interaction energies were computed for several aromatic and aliphatic dimers. Herein, the nature and origin of π/π, σ/σ, and σ/π dispersion interactions has been investigated by using dispersion-corrected density functional theory, energy decomposition analysis, and the recently developed noncovalent interaction (NCI) method. Our analysis shows that π/π and σ/σ stacking interactions are equally important for the benzene and cyclohexane dimers, explaining why both compounds have similar boiling points. Also, similar dispersion forces are found in the benzene⋅⋅⋅methane and cyclohexane⋅⋅⋅methane complexes. However, for systems larger than naphthalene, there are enhanced stacking interactions in the aromatic dimers adopting a parallel-displaced configuration compared to the analogous saturated systems. Although dispersion plays a decisive role in stabilizing all the complexes, the origin of the π/π, σ/σ, and σ/π interactions is different. The NCI method reveals that the dispersion interactions between the hydrogen atoms are responsible for the surprisingly strong aliphatic interactions. Moreover, whereas σ/σ and σ/π interactions are local, the π/π stacking are inherently delocalized, which give rise to a non-additive effect. These new types of dispersion interactions between saturated groups can be exploited in the rational design of novel carbon materials.

Topics in Heterocyclic chemistry: Structure, bonding and reactivity of heterocyclic compounds

Evaluating interaction energies using the Buckingham-Hirshfeld method: Benchmark on the S22, S66, S22x5 and S66x8 data sets.

The mechanism of the decomposition of cyclopropenones and cyclopropenethiones giving acetylenes (R1–CC–R2 with R1 = R2 = H, F) plus carbon monoxide and carbon monothioxide, respectively (CX, X = O, S) has been probed using DFT (B3LYP/6-311G(d,p)) and MO (CCSD(T)/6-31G(d)) calculations. It turns out that the decomposition is stepwise, forming first an intermediate which has the properties of a semi-carbene, semi-zwitterion, whose structure is best described in both cases as a resonance hybrid between a carbene and a zwitterion. Using the PCM model, study of the solvent effect on the reactions in three continua (water, acetonitrile and benzene) shows that solvents do not affect the shape of the potential energy surfaces but tend to stabilize all the isomers. Estimation of the first vertical excited states by CIS and TD-B3LYP methods suggests that the photochemical reactions are likely to take place in the ground state rather than in an excited state. Hardness and polarizability profiles along the reaction paths show that there is a maximum in the polarizability profile besides an inverse relationship between hardness and polarizability. Fluorine substitution tends to stabilize the intermediate making it a genuinely detectable moiety.

"Ring currents and their origin in the modified all-metal aromatics, "

Trans Effect and Trans Influence: importance of metal mediated ligand-ligand repulsion.

We predict that electron attachment may be used with ESI-MS techniques to observe neutral Al metal aqua-oxo-hydroxo species and the complex polymerization and precipitation reactions in which they participate. Neutral aqueous metal species have, so far, been invisible to ESI-MS techniques.

[Champagne, Benoit] Univ Namur, Dept Chem, Unit Phys Chem, Lab Theoret Chem, B-5000 Namur, Belgium. [Deleuze, Michael S.] Hasselt Univ, Res Grp Theoret Chem & Mol Modeling, B-3590 Diepenbeek, Belgium. [De Proft, Frank] Vrije Univ Brussel, Fac Wetenschappen, Eenheid Algemene Chem ALGC, B-1050 Brussels, Belgium. [Leyssens, Tom] Catholic Univ Louvain, Lab Crystal Engn, Inst Condensed Matter & Nanosci, B-1348 Louvain, Belgium. benoit.champagne@unamur.be; michael.deleuze@uhasselt.be; fdeproft@vub.ac.be; tom.leyssens@uclouvain.be

We present results showing that our recently developed density functional theory (DFT)-based speciation model of the aqueous Al(3+) system has the potential to improve the interpretations of ESI-MS studies of aqueous metal cation hydrolytic speciation. The main advantages of our method are that (1) it allows for the calculation of the relative abundance of a given species which may be directly assigned to the signal intensity in a mass spectrum; (2) in cases where species with identical m⁄z ratios may coexist, the assignment can be unambiguously assigned based on their theoretical relative abundances. As a demonstration of its application, we study four pairs of monomer and dimer aqueous Al(3+) species, each with identical m/z ratio. For some of these pairs our method predicts that the dominant species changes from the monomer to the dimer species under varying pH conditions.

Although a lot of work has been done on the chemical relevance of the atom-condensed linear response kernel chi(AB) regarding inductive, mesomeric, and hyperconjugative effects as well as (anti)aromaticity of molecules, the same cannot be said about its not condensed form chi(r,r'). Using a single Slater determinant KS type ansatz involving second order perturbation theory, we set out to investigate the linear response kernel for a number of judiciously chosen closed (sub)shell atoms throughout the periodic table and its relevance, e.g., in relation to the shell structure and polarizability. The numerical results are to the best of our knowledge the first systematic study on this noncondensed linear response function, the results for He and Be being in line with earlier work by Savin. Different graphical representations of the kernel are presented and discussed. Moreover, a frontier orbital approach has been tested illustrating the sensitivity of the nonintegrated kernel to the nodal structure of the orbitals. As a test of our method, a numerical integration of the linear response kernel was performed, yielding an accuracy of 10(-4). We also compare calculated values of the polarizability tensor and their evolution throughout the periodic table to high-level values found in the literature.

Halogen bonds between the trifluoromethyl halides CF3Cl, CF3Br and CF3I, and dimethyl ether, dimethyl sulfide, trimethylamine and trimethyl phosphine were investigated using Pearson's hard and soft acids and bases (HSAB) concept with conceptual DFT reactivity indices, the Ziegler-Rauk-type energy-decomposition analysis, the natural orbital for chemical valence (NOCV) framework and the non-covalent interaction (NCI) index. It is found that the relative importance of electrostatic and orbital (charge transfer) interactions varies as a function of both the donor and acceptor molecules. Hard and soft interactions were distinguished and characterised by atomic charges, electrophilicity and local softness indices. Dual-descriptor plots indicate an orbital sigma hole on the halogen similar to the electrostatic s hole manifested in the molecular electrostatic potential. The predicted high halogen-bond-acceptor affinity of N-heterocyclic carbenes was evidenced in the highest complexation energy for the hitherto unknown CF3I center dot NHC complex. The dominant NOCV orbital represents an electron-density deformation according to a n ->sigma*-type interaction. The characteristic signal found in the reduced density gradient versus electron-density diagram corresponds to the non-covalent interaction between contact atoms in the NCI plots, which is the manifestation of halogen bonding within the NCI theory. The unexpected C-X bond strengthening observed in several cases was rationalised within the molecular orbital framework.

Periodic DFT calculations are used to simulate the early stages of hydration of dehydrated high-loading vanadia/titania catalysts. The hydration of molecularly dispersed vanadia is studied by successive additions of water molecules to initially dehydrated models. Special attention is paid to the formation and transformation between different surface species, monovanadates and polyvanadates, and the role of V-OH in the hydration process. It is found that two physical surface processes occur at high vanadia coverage and that their importance depends on the surface water content. First, under mild hydration conditions, a polymerization process increases the number of polyvanadates chains. Polyvanadates formation is preceded by an initial generation of monomers with OV(OH)O2 and OVO3 pyramidal structures. Second, with higher number of water molecules, a solvation process increases the coordination number of vanadium. The interconversion between different surface vanadium oxide species occurs through a fast hydrogen transfer mechanism and depends on water content. Theoretical results are combined with in situ Raman spectra acquired at several temperatures in dry and humid environment during stepwise dehydration. The experimental data indicate that the redshift of the vanadyl band upon exposure to increasing humidity and decreasing temperature is associated to such progressive interaction with water molecules, which weakens the vanadyl V=O bond. © 2013 American Chemical Society., The authors thank Spanish Ministry project PRO-CTQ2011-25517 and ESF COST Action D36, COST CM1104. A.E.L. acknowledges the European Commission, Capacities Area, Research Infrastructures for HPC-EUROPA2 project (nr: 228398) and Spanish Ministry of Education and Science for ″Juan de la Cierva″ postdoctoral contract. M.C. and F.T. thank HPC resources from GENCI-CINES/IDRIS (Grants 2010-x2010082131 and 2011-x2011082022), the CCRE-DSI of Université P. M. Curie, and Institut Universitaire de France for a junior position.

Topology Switching in [32]Heptaphyrins controlled by Solvent, Protonation and meso-Substituents

How the Conical Intersection Seam Controls Regioselectivity in the Photocycloaddition of Ethylene and Benzene

s,p-Aromaticity and anti-aromaticity as retrieved by the linear responde kernel

N-> As intramolecularly coordinated organoarsenic5III) chalcogenides: Isolation of terminal As-S and As-Se bonds.

Due to its unique mechanical properties, graphene can be applied for reinforcement in nanocomposites. We analyse the Young’s modulus of graphene at the semi-empirical PM6 level of theory. The internal forces are calculated and the Young’s modulus is predicted for a finite graphene sheet when external strain is applied on the system. These results are in a good agreement with theoretical and experimental results from the literature giving values of about 1 TPa for the Young’s modulus. Stress–strain curves are computed for elongation up to 20%. In addition, the influence of the presence of a single vacancy, as well as for oxygenation of a vacancy, on the mechanical properties of graphene has been analysed. Our results indicate that when applying the deformation locally onto the system, higher local stress can be induced, as confirmed by Finite Element Analysis. Also, the presence of structural defects in the system will stiffen the system upon low strain, but reduces the elastic limit from more than 20% strain for pristine graphene to less than 10% strain when defects are present.

Tuning the band gap of graphene nanoribbons by chemical edge functionalisation is a promising approach towards future electronic devices based on graphene. The band gap is closely related to the aromaticity distribution and therefore tailoring the aromaticity patterns is a rational way for controlling the band gap. In the present work, it is shown how the three distinct classes of aromaticity patterns already found for armchair graphene nanoribbons can be rationally tuned by chemical edge functionalisation to modify their electronic arrangement and band gap. The electronic structure and the aromaticity distribution are studied using DFT calculations and through a series of delocalisation and geometry analysis methods, like the six-centre index (SCI) and the mean bond length (MBL) geometry descriptor. Novel aromaticity patterns are found for fluorine and nitrogen functionalisation characterised as inverted incomplete-Clar, and broken-Kekulé classes, while oxygen and nitrogen functionalisation is found to cut and extend the aromatic system, respectively. All these different arrangements of aromatic rings along the structure of graphene nanoribbons are explained using Clar's sextet theory, and a mesomeric effect mechanism for fluorine and nitrogen. In all cases, the changes in the aromaticity patterns are related to changes in the band gap. The energy and stability of the different edge functionalised graphene nanoribbons are also studied. An overall picture of edge effects, aromaticity patterns, and band gap tuning is provided.

International audience; Densities and specific heat capacities of aqueous solutions: 1-methylcytosine; 1-methyl-N4-hydroxycytosine; 1,5-dimethylcytosine; I,N4-dimethylcytosine; 1,5-dimethyl-N4-hydroxycytosine; 1-methyl-N4-methoxycytosine; 1,N4,N4-trimethylcytosine, 1,5-dimethyl-N4-methoxycytosine were determined using flow calorimetry and flow densimetry at 25°C. Apparent molar volumes and heat capacities were then determined. Molecular excluded volumes were evaluated. A relationship was found between the values of the increments in partial molar values and the kind of groups substituted. Four types of contributions were distinguished: substitution of hydrogen on C, N, and O (in OH group on N4) atoms by CH3 group and replacement of hydrogen on N4 atom by OH group. The correlation between the experimental partial molar volumes and calculated molecular excluded volumes was also elaborated.

The effect of electron correlation on the Fukui function f− (r) is studied for three closed shell molecules of the ambident nucleophile type using the Configuration Interaction with Single and Double excitations (CISD) method. These effects are shown to be of relatively small importance, thereby stressing the reliability of Hartree-Fock type calculations.

A study is made on the influence of the electronegativity and hardness of a group X on the gas-phase acidities of the first- and second-row hydrides HX. It is shown that these two density functional theory (DFT)-based global properties are sufficient for the correct description of the gas-phase acidity sequences, the group hardness being the more important factor and describing the influence of polarizability effects in the charged forms of the acid-base equilibrium. Various calculated properties effects in the charged forms of the acid-base equilibrium. Various calculated properties of the traditional quantum chemical type (Mulliken charges and the MEP) and DFT-based (local softness), associated with the neutral form of the acid, were found to contain a certain periodicity in their description of the gas-phases acidities. The gas-phase acidities ({Delta}H{sub acid} and {Delta}G{sub acid} values) were also obtained theoretically via quantum statistical thermodynamical calculations at the Hartree-Fock level with the 6-31 + G* basis set; these calculated acidities were in fair agreement with the experimental ones. 43 refs., 7 figs., 4 tabs.

The electronegativity equalization principle, originally formulated by Sanderson and proven quantum mechanically by Parr et al., within the framework of density functional theory, is studied numerically. A first order expression for the electronegativity x of an atom A in a molecule is derived, based on the change, upon molecule formation, of the number of electrons N A and the external potential v A ( r ) of this atom with respect to the isolated atom case. The relative importance of the two corrections to the isolated atom electronegativity is discussed. Furthermore, the expression was identified with other density functional theory based electronegativity equalization formalisms and was applied to small molecular systems: the resulting charge distributions and molecular electronegativities showed a fair correlation with other estimations for these quantities. The importance of second order terms is also discussed, together with an extension, permitting the use of functional group electronegativities and hardnesses.

Organic photovoltaics (OPVs) are considered a promising energy source for the future, owing to interesting properties such as easy processing and flexibility. Their main drawback however, is the low efficiencies that can be obtained so far. So far the highest OPV efficiencies have been found for so-called bulk-heterojunction (BHJ) solar cells, where the active layer is a bicontinuous composite of donor and acceptor phases. Due to their high electron affinity and ability to transport charge, fullerene derivatives are the most widespread type of acceptor. As a donor phase a conjugated, light-excitable polymer is required. In this study a poly(3-hexyl thiophene) (P3HT) and [6,6]-phenyl C61 - butyric acid methyl ester (PCBM) blend, the most widespread OPV system, is investigated by both experimental and theoretical means. An important technological challenge for BHJ OPV's is the morphology of the active layer. Due to the limited lifetime of generated excitons, a nm-size phase separated morphology is requiredfor efficient charge generation at the interface between donor and acceptor. A more crystalline material will also lead to more efficient charge transfer, and post-production annealing plays an important role in optimising these two factors. In this work, post production annealing is therefore studied using several fast-scanning calorimetry techniques, such as Rapid Heat-Cool Calorimetry (RHC) and Fast Scanning Differential Chip Calorimetry (FSDCC. By applying the Avrami model on the isothermal crystallisation of a P3HT/PCBM 1:1 blend, it is found that the crystallisation rate goes through 2 maxima, making it possible to improve the annealing procedure. Next to the morphology of the active layer, the mechanism of charge transfer and exciton dissociation at the donor/acceptor interface is just as important. This charge transfer is modelled using ab initio DFT calculations under periodic boundary conditions (PBC).

In this paper, a combined experimental and theoretical study was performed on the P3HT:PCBM system used in organic photovoltaics. Fast-scanning differential chip calorimetry, an advanced thermal analysis technique, was used to simulate the thermal annealing used in the production of P3HT:PCBM solar cells to increase the degree of crystallinity, and thus efficiency. The main advantage of this technique for stuying the thermal annealing are the very high rates of heating and cooling that can be used, up to 10 6 K.s -1 , permitting one to avoid crystallization during cooling. In parallel with the experimental study, the charge transfer between donor (P3HT) and acceptor (PCBM) at the interface is studied using density functional theory. The charge separation between donor and acceptor present for the ground state of the combined system, diminished when the first triplet was investigated. This was explained by the formation of a bridge state, formed after population by the LUMO with one electron. Such a molecular orbital can facilitate charge transfer.

A density functional theory (DFT) study is performed to determine the stability of the complexes formed between either the N or O site of 3-methyl-4-pyrimidone and 1-methyl-2-pyrimidone molecules and different ligands. The studied ligands are boron and alkali Lewis acids, namely, B(CH(3))(3), HB(CH(3))(2), H(2)B(CH(3)), BH(3), H(2)BF, HBF(2), BF(3), Li(+), Na(+), and K(+). The acids are divided into two groups according to their hardness. The reactivity predictions, according to the molecular electrostatic potential (MEP) map and the natural bond orbital (NBO) analysis, are in agreement with the calculated relative stabilities. Our findings reveal a strong regioselectivity with borane and its derivatives preferring the nitrogen site in both pyrimidone isomers, while a preference for oxygen is observed for the alkali acids in the 3-methyl-4-pyrimidone molecule. The complexation of 1-methyl-2-pyrimidone with these hard alkali acids does not show any discrimination between the two sites due to the presence of a continuous delocalized density region between the nitrogen and the oxygen atoms. The preference of boron Lewis acids toward the N site is due to the stronger B-N bond as compared to the B-O bond. The influence of fluorine or methyl substitution on the boron atom is discussed through natural orbital analysis (NBO) concentrating on the overlap of the boron empty p-orbital with the F lone pairs and methyl hyperconjugation, respectively. The electrophilicity of the boron acids gives a good overall picture of the interaction capabilities with the Lewis base.

Recently, hexaphyrins have emerged as a promising class of π-conjugated molecules that display a range of interesting electronic, optical, and conformational properties, including the formation of stable Mobius aromatic systems. Besides the Mobius topology, hexaphyrins can adopt a variety of conformations with Huckel and twisted Huckel topologies, which can be interconverted under certain conditions. To determine the optimum conditions for viable Mobius topologies, the conformational preferences of [26]- and [28]hexaphyrins and the dynamic interconversion between the Mobius and Huckel topologies were investigated by density functional calculations. In the absence of meso substituents, [26]hexaphyrin prefers a planar dumbbell conformation, strongly aromatic and relatively strain free. The Mobius topology is highly improbable: the most stable tautomer is 33 kcal mol(-1) higher in energy than the global minimum. On the other hand, the Mobius conformer of [28]hexaphyrin is only 6.5 kcal mol(-1) higher in energy than the most stable dumbbell conformation. This marked difference is due to aromatic stabilization in the Mobius 4n electron macrocycle as opposed to antiaromatic destabilization in the 4n+2 electron system, as revealed by several energetic, magnetic, structural, and reactivity indices of aromaticity. For [28]hexaphyrins, the computed activation barrier for interconversion between the Mobius aromatic and Huckel antiaromatic conformers ranges from 7.2 to 10.2 kcal mol(-1), in very good agreement with the available experimental data. The conformation of the hexaphyrin macrocycle is strongly dependent on oxidation state and solvent, and this feature creates a promising platform for the development of molecular switches.

We have investigated aqueous Al-dimer complexes using density functional theory methods (e.g. the B3LYP exchange-correlation functional and the 6-311++G(d,p) basis set). In these calculations interactions between the Al(3+) cations and the H(2)O or OH(-) coordinating ligands are considered explicitly while the second hydration shell and remaining solvent are treated as a continuum under the IEF-PCM formalism. The Al-dimer chemical reactivity is discussed by analysis of changes in geometry, electronic structure and Gibbs free energy of formation, relative to two independent Al(H(2)O) monomers, as a function of water and hydroxide coordination. Our results indicate that the mechanism of cooperativity, i.e. decreased Al-water bond stability with increasing OH(-) coordination and increased water ligand hydrolysis as complex CN decreases, is operating on the dimer species and that, therefore, a wide variety of dimer species are available. While the stability of these species is observed to be dependent on the number of water and hydroxide ligands, the hydroxide bridging structure (singly, doubly and triply bridged species are considered) does not appear to correlate with dimer stability. Interestingly, intra-molecular H-bonds (in the form of the well known H(3)O bridge as well as two bridging structures, H(4)O(2) and H(2)O, that have not, to our knowledge, been previously considered) are observed to influence dimer stability. The evaluation of the equilibrium mole fraction of the dimer species in equilibrium with the aqueous Al(3+) monomer species of our previous study displays the qualitatively correct trend of solution composition as pH increases, namely monomeric aqueous Al(3+) and Al(OH) complexes dominate at low and high pH, respectively, and all remaining monomer and dimer species exist at intermediate pH. Further refinement of our data set by eliminating dimer complexes with OH/Al ratios greater than 2.6 brings our predicted equilibrium mole fraction distributions into excellent agreement with experimental observations. The triply bridged dimer is observed in low amounts while the singly and doubly bridged dimers dominate our model system at pH = ∼4-7.

Reactions of bis[bis(trimethylsilyl)amino]tin and the dimer of [bis(trimethylsilyl)amino]tin chloride with various carbodiimides give pure corresponding tin(II) guanidinates in essentially quantitative yields. Heteroleptic bis(trimethylsilyl)amido ({R-NC[N(SiMe3)2]N-R}SnN(SiMe3)2)- and chloro-substituted ({R-NC[N(SiMe3)2]N-R}SnCl) tin(II) guanidinates were obtained from reactions of N,N′-diisopropyl-, N,N′-dicyclohexyl-, N,N′-bis(4-methylphenyl)-, and N-[3-(dimethylamino)propyl]-N′-ethylcarbodiimides, respectively. Homoleptic tin(II) guanidinates {R-NC[N(SiMe3)2]N-R}2Sn were obtained from the N,N′-bis(4-methylphenyl)- and N-[3-(dimethylamino)propyl]-N′-ethyl-substituted carbodiimides. Similar reactions of N,N′-bis(2,6-diisopropylphenyl)- and N,N′-bis(trimethylsilyl)carbodiimide, respectively, having the bulkiest substituents of the series, failed to take place under various conditions. The complexes prepared were characterized as monomers in solution by 1H, 13C, and 119Sn NMR spectroscopy in C6D6 and THF-...

Organic photovoltaics (OPVs) can still only achieve efficiencies below those of conventional silicon photovoltaics. To date the highest OPV efficiencies have been found for so-called bulk-heterojunction (BHJ) solar cells, where the active layer is a bi-continuous composite of donor (a conjugated polymer) and acceptor (a small molecule) phases. As in conventional polymer blend systems, the morphology formed will strongly influence the material characteristics, and post-production annealing has been shown to increase device efficiencies. In this study, the active layer of BHJ devices is analysed using fast-scanning calorimetry techniques in order to investigate the transitions that play a role in stability and morphology development. In particular, Rapid Heat-Cool Calorimetry (RHC) [1], and fast scanning differential chip calorimetry (FSDCC) were used. FSDCC especially shows great potential for these systems due to the very high scanning rates and the ability to study thin layer samples, like in actual BHJ devices.

Establishment of a Kinetic Model for the Intramolecular Catalyzed Hydrolysis of [18 F]- Benzylfluoride Containing Amino Acid Analoques by Linking Experimental and DFT Studies

Electronic Activity in Chelotropic and Cycloaddition Reactions

International audience; A combined experimental and ab initio periodic DFT calculation on the structure and stability of different chromium-substituted zeolite models are presented. Experimental investigation by XRD, FT-IR and UV-vis show the presence of chromium in SiBEA zeolite. The favorable chromium sites are characterized by their calculated geometrical parameters, energetics, vibrational frequencies and protonation/deprotonation energies. The theoretical vibrational frequencies are compared with experimental FT-IR measurements. A phase diagram was constructed on the basis of calculated total energies of the optimized structures. Cr(III) is stabilized in the zeolite framework as a tri-coordinated site. Cr sites are predicted to be more acidic than group V containing zeolites. Dehydration of the site leads to the formation of a Cr(VI) containing a Crdouble bond; length as m-dashO group. These results are fully consistent with experimental data and allow the identification of the molecular structure of chromium sites in a zeolite framework.

Zeolites exchanged with metal cations can be considered as solid Lewis acid–base materials. Lewis acidity is associated with the exchangeable cations and Lewis basicity with the lattice oxygens. This Lewis basicity can be probed by following the spectral changes of adsorbed molecules such as CO2, pyrrole, methanol, methyl iodide and N2O4 and by DFT modeling. The best molecules are those which disproportionate into cations and anions. The anions immobilize the exchangeable cations. The cations adsorb onto the lattice oxygens of the zeolitic framework and probe the basicity of these oxygens. Basicity of zeolites can be described in the frame of conceptual DFT. Local hardness is not sensitive enough to describe basicity trends in zeolites. Local softness, approximated by the ratio of the local and global density of states, is found to be a good descriptor of framework basicity, but it has only been calculated on a cluster model. Also the Fukui function of the framework oxygens is a good basicity descriptor, but it is only calculated at the semi-empirical EEM level. Of the other parameters that have been proposed in the literature the minimum of the molecular electrostatic potential at the oxygen atoms describes the basicity trends correctly, whereas the charge on the oxygens is not a good basicity descriptor.

We analyse the electronic structure and aromaticity of graphene nanoribbons and carbon nanotubes through a series of delocalisation and geometry analysis methods. In particular, the six-centre index (SCI) is found to be in good agreement with the mean bond length (MBL) and ring bond dispersion (RBD) geometry descriptors. Based on DFT periodic calculations, three distinct classes of aromaticity patterns have been found for armchair graphene nanoribbons, appearing periodically as the width of the ribbon is increased. The periodicity in the band gap is found to be related to these aromaticity patterns. Also, the appearance of such distinct aromaticity distribution is explained within the framework of the Clar’s sextet theory. Both delocalisation and geometry analysis methods are shown to be very fast and reliable tools for easily analysing the aromaticity in carbon nanosystems.

Using DFT in search for support-effects during methanol oxidation on supported molybdenum oxides

A set of four pincer ligands, either the OCO type ligands L(1-3) [2,6-(ROCH(2))(2)C(6)H(3)](-), where R = Me (L(1)), mesityl (L(2)), t-Bu (L(3)) or novel NCO ligand [2-(Me(2)NCH(2))-6-(t-BuOCH(2))C(6)H(3)](-) was studied. The reaction of L(4)Li with PCl(3) resulted in isolation of [2-(OCH(2))-6-(Me(2)NCH(2))C(6)H(3)]PCl (1) as a result of intramolecular ether bond cleavage and elimination of t-BuCl. The conversion between the organolithium compounds L(1,2,4)Li and AsCl(3) led to the desired chlorides, i.e. (L(1))(2)AsCl (2), L(2)AsCl(2) (3), L(4)AsCl(2) (5), but an analogous reaction using the L(3)Li compound gave [2-(OCH(2))-6-(t-BuOCH(2))C(6)H(3)]AsCl (4) as a result of intramolecular cyclization. The organoantimony chloride L(3)SbCl(2) was shown to undergo very slow cyclization in CDCl(3) again via elimination of t-BuCl giving [2-(OCH(2))-6-(t-BuOCH(2))C(6)H(3)]SbCl (6) and it was demonstrated that this reaction may be accelerated by preparation of L(3)Sb(Cl)(OTf) (7) with more Lewis acidic central atom. On the contrary, both antimony derivatives of the NCO ligand L(4), not only the chloride L(4)SbCl(2) (8) but also the ionic pair containing highly Lewis acidic cation [L(4)SbCl](+)[CB(11)H(12)](-) (9), are stable without any indication for etheral bond cleavage. The situation is rather similar in the case of organobismuth derivatives of L(4), which allowed isolation of compounds L(4)BiCl(2) (10), L(4)Bi(Cl)(OTf) (11) and [L(4)BiCl](+)[CB(11)H(12)](-) (12). All studied compounds were characterized by the help of (1)H and (13)C NMR spectroscopy, ESI mass spectrometry, elemental analysis and (except 1) by single-crystal X-ray diffraction.

Reaction of 2-[(dimethylamino)methyl]aniline with butyllithium, followed by conversion with triinethylsilyl, triphenylsilyl, triphenylgermyl, trimethylstannyl, or tri-n-butyl-stannyl chloride, gives the corresponding substituted aniline. These compounds were further deprotonated by butyllithium and reacted with germanium, tin, and lead dichlorides, respectively, in both stoichiometric ratios 2:1 and 1:1, providing the target homo- ([2-(Me(2)NCH(2))C(6)H(4)(YR(3))N](2)M) and heteroleptic ([2-(Me(2)NCH(2))C(6)H(4)(YR(3))N]MCl) germylenes and stannylenes, where M = Ge, Sn, Y = Si, Ge, and R = Me, Ph. Unlike all of these cases, the heteroleptic plumbylene can only be obtained with this reaction when the amide is substituted by a trimethylsilyl moiety. Anilines substituted by trimethyltin or tri-n-butyltin moieties gave transmetalation products after the second deprotonation by butyllithium. The trimethyltin-substituted stannylenes could likewise not be obtained by hexamethyldisilazane elimination of (trimethylstannyl)-2-[(dimethylamino)methyl]aniline with 0.5 mol equiv of either bis[bis(trimethylsilyl)amido]tin or bis[bis(trimethylsilyl)amido]tin chloride}. Products of these reactions are heterocubanes with compositions {[2-(Me(2)NCH(2))C(6)H(4)N]Sn}(4) and [2-(Me(2)NCH(2))C(6)H(4)N](2)-(mu(2)-SnMe(2))(2), respectively, and Me(4)Sn or Me(3)SnCl. The structures of trimethylsilyl- and triphenylgermyl-substituted germylenes, stannylenes, and plumbylenes, as well as a number of their precursors, in the crystalline state, were investigated by X-ray diffraction and NMR spectroscopy in solution. Density functional theory methods were used for evaluation of the structures of several compounds.

An experimental and theoretical DFT study was carried out on the solution behavior in [D(7)]DMF for bis-chelate complex [Pd(L)(2)](BF(4))(2)center dot 2CH(3)CN (L = 4-phenyl-1-(2-picolyl)-1,2,3-triazole). In structure of [Pd(L)(2)](2+), the central square-planar palladium(II) cation is trans-chelated by two L substrates, each through the pyridine and the triazole N2 nitrogen atoms, forming two six-membered metallacycles. These can adopt boat-like conformations anti-trans-[Pd(L)(2)](2+) and syn-trans-[Pd(L)(2)](2+) in which the picolyl methylene carbons are anti or syn, respectively, relative to the palladium coordination plane. In solution, the boat-to-boat inversion at both metallacycles takes place. The conformers are in a dynamic equilibrium, which was monitored by variable-temperature (VT) (1)H NMR spectroscopy in the temperature range of 223-353 K. The equilibrium lies on the side of the anti-trans-[Pd(L)(2)](2+) conformer and the corresponding reaction enthalpy and entropy is estimated to be 0.6 +/- 0.5kcal mol(-1) and 0.8 +/- 1 cal mol(-1) K(-1), respectively. From the full-line-shape analysis of resonances in the VT (1)H NMR spectra, the activation enthalpy and activation entropy was determined to be 13.0 +/- 0.4 kcal mol(-1) and 2.7 +/- 1.6 cal mol(-1) K(-1), respectively. The activation entropy close to zero suggests a nondissociative mechanism for the isomerisation. DFT investigation revealed that the isomerisation proceeds through a one step mechanism with a barrier of 11.40 kcal mol(-1). The structures of the syn and anti conformers as well as that of the transition state were characterized. Energy decomposition analysis was carried out in order to explore the origins of the stability difference between the syn and anti isomers. (C) 2011 Elsevier Ltd. All rights reserved.

Carbon nanotube (CNT) based nanocomposites have attracted much interest, owing to the conductive properties and mechanical reinforcement CNTs may transfer to the complete material. When using CNTs as a filler material for the development of (polymer) nanocomposites, a key element is the dispersion of the CNTs. This will strongly influence at what point a 3D percolating CNT network is formed, also know as the percolation threshold. For various reasons, the percolation threshold should be as low as possible. However, due to the strong interactions between CNTs, achieving good dispersion in the matrix can be problematic. For this purpose, specialized dispersion techniques are used in the preparation of CNT nanocomposites, such as latex technology, where surfactants are used to form aqueous polymer and nanotube emulsions, which are subsequently mixed, freeze-dried and compression-moulded. A complementary approach for lowering the percolation threshold is limiting the volume of the material that is accessible to CNTs. Here a phase separated morphology is desired, with CNTs ideally only found in one of the phases, leading to volume exclusion or double percolation. In this work a polystyrene (PS) / polymethylphenylsiloxane (PMPS) blend system was studied as a matrix for CNT nanocomposites. The study of these polymer blend nanocomposites was performed using thermal analysis techniques, such as DSC, as well as surface characterization and rheology. While an excellent dispersion of CNTs by polydimethylsiloxane (PDMS) was reported before, this is to our knowledge the first study on the related PMPS, which seems to show similar CNT-dispersing properties Unlike the strongly immiscible behaviour known for PS/PDMS blends however, the PS/PMPS system showed partial miscibility. While this means that phase separated morphologies can still be attained, which can be used for volume exclusion, this also makes it possible to develop homogeneous blends where PMPS seems to act more as a CNT compatibiliser. Clear proof of mechanical percolation was found for such systems, and conductivity studies are underway.