Henry Chermette

Assessment of the exchange-correlation functionals for the physical description of spin transition phenomena by density functional theory methods: all the same?

This study aims to assess present day density functionals in the description of spin crossover iron(II) complexes. Two recently synthesized spin crossover complexes were considered. Theoretical calculations were made using 53 of the most popular exchange-correlation density functionals with triple zeta plus polarization quality basis sets. The present work shows that even though different density functionals can lead to different energy gaps between spin states, most of them are very similar for these two compounds when a comparison between energy gaps is sought. The present work shows that even though different exchange correlations can lead to different energy gaps between spin states, the difference between these gaps calculated at different geometries and that calculated at a given reference geometry is surprisingly independent of the choice of functional. The reasons for the similarities and the differences among exchange and correlation functional combinations are discussed.

Electronic structure of the Cu+ impurity center in sodium chloride

The multiple‐scattering Xα method is used to describe the electronic structure of Cu+ in sodium chloride. Several improvements are brought to the conventional Xα calculation. In particular, the cluster approximation is used by taking into account external lattice potential. The ’’transition state’’ procedure is applied in order to get the various multiplet levels. The fine electronic structure of the impurity centers is obtained after a calculation of the spin–orbit interactions. These results are compared with those given by a modified charge‐consistent extended Huckel method (Fenske‐type calculation) and the merit of each method is discussed. The present calculation produces good quantitative agreement with experiment concerning mainly the optical excitations and the emission mechanism of the Cu+ luminescent centers in NaCl.

A proposal for an extended dual descriptor: a possible solution when Frontier Molecular Orbital Theory fails

In this paper, we introduce new local descriptors in the framework of Conceptual Density Functional Theory. They can be considered as an extension of the dual descriptor [Morell et al., J. Phys. Chem. A, 2005, 109, 205]. These indices are particularly suited for the discrimination between electrophilic and nucleophilic sites inside a molecule. They are computed using the densities of the electronic excited states, giving a picture of the polarization of the electron density induced by the approach of a reactant. Links with the linear-response function are discussed, and the first examples of applications are given, highlighting how these new descriptors can be used in practice for reactivity studies. It has been found that this extension of the dual descriptor can handle tricky cases, such as nitrobenzene or isoquinoline, for which Frontier Molecular Orbital Theory fails.

Minimum electrophilicity principle: an analysis based upon the variation of both chemical potential and absolute hardness.

In this work, the minimum electrophilicity principle (MEP), assessed by either the electrophilicity power or the DeltaNmax, is mathematically analysed through the variation of both chemical potential and chemical hardness. It appears that the decrease of the electrophilicity power and the decrease of the DeltaNmax are ruled by similar expressions in which both the chemical potential and the absolute hardness should increase. A reduced expression at constant chemical potential shows that the MEP and the maximum hardness principle are equivalent. However it pops up from the monitoring of chemical processes such as bond formation and redox reactions that the variation of the chemical potential is the most important term.

From discrete [Y(DMF)8][Cu4(µ3-I)2(µ-I)3I2] ion pairs to extended [Y(DMF)6(H2O)2][Cu7(µ4-I)3(µ3-I)2(µ-I)4(I)]1∞ and [Y(DMF)6(H2O)3][CuI7CuII2(µ3-I)8(µ-I)6]2∞ arrays by H-bond templating in a confined solvent-free environment

An ionic heterometallic species [Y(DMF)(8)][Cu(4)(micro(3)-I)(2)(micro-I)(3)I(2)](1) was isolated from a solution of CuI, NH(4)I and YI(3)(Pr(i)OH)(4) in DMF-isopropoxyethanol, and was converted in a confined environment by progressive substitution of the DMF ligands with water molecules first into a 1D zig-zag structure [Y(DMF)(6)(H(2)O)(2)][Cu(7)(micro(4)-I)(3)(micro(3)-I)(2)(micro-I)(4)(I)](1infinity)(2) and finally into a 2D sheet [Y(DMF)(6)(H(2)O)(3)][Cu(I)(7)Cu(II)(2)(micro(3)-I)(8)(micro-I)(6)](2infinity)(3) by H-bond templating.

Electronic structure and chemical bonding in metallic clusters of binary and ternary transition metal chalcogenides. I. SCF MS Xα study including relativistic effect of PbMo6S8

Cluster calculations of the electronic structure and charge distribution of PbMo6S8 have been performed using the SCF Xα scattered‐wave method. These results compare fairly well with those obtained with solid state methods and ionization energies are in agreement with XPS experimental spectra. Moreover, the chemical bonding, particulary the interactions between the Mo6 metallic clusters with its chalcogenide neighboring, is discussed by comparing the results obtained for the Mo6 and (Mo6S8)2− units. These main features are also illustrated by using both the partial wave population analysis and contour map of some bonding molecular orbitals of the valence band. The importance of relativistic effects on such metal 4d compounds is discussed.

Characterization of the Chemical Behavior of the Low Excited States through a Local Chemical Potential.

Exploiting the locality of the chemical potential of an excited state when it is evaluated using the ground-state density functional theory (DFT), a new descriptor for excited states has been proposed. This index is based on the assumption that the relaxation of the electronic density drives the chemical reactivity of excited states. The sign of the descriptor characterizes the electrophilic or nucleophilic behavior of the atomic regions. A relation between the new descriptor and the dual descriptor is derived and provides a posteriori justification of its use to rationalize the Woodward-Hoffmann rules for photochemical reactions within the conceptual DFT. Finally, the descriptor is successfully applied to some [2 + 2] photocycloadditions, like Paterno-Büchi reactions.

Quantitative structure–activity relationship to predict acute fish toxicity of organic solvents

REACH regulation requires ecotoxicological data to characterize industrial chemicals. To limit in vivo testing, Quantitative Structure-Activity Relationships (QSARs) are advocated to predict toxicity of a molecule. In this context, the topic of this work was to develop a reliable QSAR explaining the experimental acute toxicity of organic solvents for fish trophic level. Toxicity was expressed as log(LC50), the concentration in mmol.L(-1) producing the 50% death of fish. The 141 chemically heterogeneous solvents of the dataset were described by physico-chemical descriptors and quantum theoretical parameters calculated via Density Functional Theory. The best subsets of solvent descriptors for LC50 prediction were chosen both through the Kubinyi function associated with Enhanced Replacement Method and a stepwise forward multiple linear regressions. The 4-parameters selected in the model were the octanol-water partition coefficient, LUMO energy, dielectric constant and surface tension. The predictive power and robustness of the QSAR developed were assessed by internal and external validations. Several techniques for training sets selection were evaluated: a random selection, a LC50-based selection, a balanced selection in terms of toxic and non-toxic solvents, a solvent profile-based selection with a space filling technique and a D-optimality onions-based selection. A comparison with fish LC50 predicted by ECOSAR model validated for neutral organics confirmed the interest of the QSAR developed for the prediction of organic solvent aquatic toxicity regardless of the mechanism of toxic action involved.

Epimerase activity of the human 11β-hydroxysteroid dehydrogenase type 1 on 7-hydroxylated C19-steroids☆

Cytochrome P4507B1 7alpha-hydroxylates dehydroepiandrosterone (DHEA), epiandrosterone (EpiA) and 5alpha-androstane-3beta,17beta-diol (Adiol). 11beta-Hydroxysteroid dehydrogenase type 1 (11beta-HSD1) interconverts 7alpha- and 7beta-forms. Whether the interconversion proceeds through oxido-reductive steps or epimerase activity was investigated. Experiments using [(3)H]-labelled 7beta-hydroxy-DHEA, 7beta-hydroxy-EpiA and 7beta-hydroxy-Adiol showed the (3)H-label to accumulate in the 7-oxo-DHEA trap but not in 7-oxo-EpiA or 7-oxo-Adiol traps. Computed models of 7-oxygenated steroids docked in the active site of 11beta-HSD1 either in a flipped or turned form relative to cortisone and cortisol. 7-Oxo-steroid reduction in 7alpha- or 7beta-hydroxylated derivatives resulted from either turned or flipped forms. 11beta-HSD1 incubation in H(2)(18)O medium with each 7-hydroxysteroid did not incorporate (18)O in 7-hydroxylated derivatives of EpiA and Adiol independently of the cofactor used. Thus oxido-reductive steps apply for the interconversion of 7alpha- and 7beta-hydroxy-DHEA through 7-oxo-DHEA. Epimerization may proceed on the 7-hydroxylated derivatives of EpiA and Adiol through a mechanism involving the cofactor and Ser(170). The physiopathological importance of this epimerization process is related to 7beta-hydroxy-EpiA production and its effects in triggering the resolution of inflammation.

Relativistic calculation of the electronic structure of IrCl63

Abstract Relativistic MSXα calculations have been performed on a IrCl63− cluster and compared with non-relativistic MSXα results obtained with identical sets of parameters. The impact of the relativistic effects on the photoionization energies is demonstrated; better agreement with the experimental spectrum is obtained. The variation of the spin—orbit parameters with the eigenvalues is discussed and the absorption spectrum is compared with both experimental results and ligand field calculations.