Contribution of trans -aconitic acid to DPPH scavenging ability in different media

The antioxidant properties of trans-aconitic acid (TAA) alone or in the presence of usual antioxidants were assessed by DPPH assay. The IC50 value equal to 70mM was very high compared to usual antioxidants (vitamin C and trolox). A joint experimental/theoretical study suggested that hydrogen atom abstraction in TAA by DPPH was located on –CH2– methylene bridge because the corresponding radical was more stabilized than COO· and CC· radicals. In combination with antioxidants (vitamin C, gallic acid, caffeic acid, trolox), synergy or additivity effects were noticed. The magnitude of the synergistic effect varied between 1.06 and 1.24 depending on the type and concentration of antioxidant for a concentration of TAA equal to 22.3mM. Especially, the addition of TAA at a concentration below 32mM to a solution containing 20μM of vitamin C had a synergy effect. Beyond this concentration, TAA showed an additive effect

Molar Mass, Radius of Gyration and Second Virial Coefficient from new Static Light Scattering Equations for Dilute Solutions: Application to 21 (Macro)molecules

International audienceNew equations for static light scattering of dil. binary solns. allow molar mass detn. of macromols. from measurements of scattered intensity ratios between soln. and solvent (Ir). In contrast to the std. Carr-Zimm equations, they do not rely on the exptl. abs. value of the Rayleigh ratio of a ref. liq. The picture shows a typical plot for the surfactant BRIJ72 in CH2Cl2 (MSupplier=0.359 kg mol-1). New static light scattering (SLS) equations for dil. binary solns. are derived. Contrarily to the usual SLS equations [Carr-Zimm (CZ)], the new equations have no need for the exptl. abs. Rayleigh ratio of a ref. liq. and solely rely on the ratio of scattered intensities of solns. and solvent. The new equations, which are based on polarizability equations, take into account the usual refractive index increment .vdelta.n/.vdelta.Ï2 complemented by the solvent specific polarizability and a term proportional to the slope of the soln. d. Ï vs. the solute mass concn. Ï2 (d. increment). Then all the equations are applied to 21 (macro)mols. with a wide range of molar mass (0.2\textlessM\textless8000 kg mol-1). On the studied dataset with M\textless200 kg mol-1, the new equations clearly achieve a better agreement with supplier M values. For macromols. (M\textgreater500 kg mol-1), for which the scattered intensity is no longer independent of the scattering angle, the new equations give the same value of the radius of gyration as the CZ equation and consistent values of the second virial coeff. [on SciFinder(R)

Étude théorique de sites de protonation et d'enthalpies de liaison hydrogène (application à des molécules d'intérêt neurobiologique)

Le site de protonation (azote pyridinique sp2 ou azote amino sp3) de 14 ligands nicotiniques se fixant sous leur forme monoprotonée sur les récepteurs nicotiniques du système nerveux central a été calculé ab initio. Le site de ligands à fonction amine secondaire (azote pyridinique) est très robuste tandis que celui de ligands à fonction amine tertiaire dépend plus des modulations structurales. Les énergies de liaison hydrogène de complexes du méthanol avec les bases de Lewis sont bien reproduites (+- 2 kJ mol-1 au niveau MP2/aug-cc-pVTZ à l état gazeux. En solution l accord entre calculs et expérience est plus difficile à atteindre à cause d une solvatation variable (de 7 kJ mol-1 en moyenne avec CCl4). L application de ces calculs au chlorure de galanthaminium, un médicament anti-Alzheimer, permet de comprendre comment cette molécule se fixe par liaison hydrogène à son récepteur, l acétylcholinestérase.The site of protonation (sp2 or sp3 nitrogen atom) of 14 nicotinic ligands which bind under their monoprotonated form to the nicotinic receptors of the central nervous system has been calculated at the ab initio level. The site of ligands with a secondary amine function (sp2 nitrogen) is found very robust while that of ligands with a tertiary amine function is more depending on structural variations. The hydrogen bond energies of the complexes of methanol with Lewis bases are obtained within +- 2 kJ mol-1 at the MP2/aug-cc-pVTZ level in the gas state. In solution the agreement between experimental and calculated energy values is less satisfactory because of a variable solvation (a mean of 7 kJ mol-1 is observed in CCl4). The application of these calculations to galanthaminium chloride, an Anti-Alzheimer drug, allows to understand how this molecule binds through hydrogen bonding to its acetylcholinesterase receptor.NANTES-BU Sciences (441092104) / SudocSudocFranceF

Can Quantum-Mechanical Calculations Yield Reasonable Estimates of Hydrogen-Bonding Acceptor Strength? The Case of Hydrogen-Bonded Complexes of Methanol

International audienceThe thermodynamics and some vibrational properties of hydrogen-bonded complexes of methanol with 23 hydrogen-bond acceptors (HBAs) have been determined in CCl4 by FTIR spectrometry. The experimental sample contains carbon, nitrogen, oxygen, sulfur, fluorine, and chlorine organic bases and covers an energetic range of 13 kJ mol?1 in the basicity scale (??G), 22 kJ mol?1 in the affinity scale (??H), and 400 cm?1 in the spectroscopic scale (??(OH)) (from benzene to trimethylphosphane oxide and amines). The experimental results in CCl4 are compared to those computed in the gas phase at various levels of theory. Ninety five percent of the variance of the red shift and 89% of the variance of the intensification of the OH stretching upon hydrogen bonding are explained by gas-phase B3LYP/6-31+G(d,p) calculations. However, this level does not satisfactorily explain the thermodynamic properties. Only 68% of the variance of the methanol affinity (??H) is taken into account. MP2/aug-cc-pVTZ//B3LYP/6-31+G(d,p) affinity calculations raise the explanation to 77% for all HBAs and to 93% when three outliers (Me2SO, Me3PO, and tetrahydrothiophene) are excluded. Discrepancies are analyzed in terms of experimental errors, calculation approximations, and solvation

Study of the cross-linking mechanism of a copolymer containing an electrooptic chromophore

9 pagesThe mechanism of the cross-linking reaction occuring between an NLO chromophore copolymerized with a glycidyl epoxide unit (polymer PIII) was rationalized using magic angle spinning (MAS) NMR spectroscopy. A first study conducted on a system composed of a model chromophore and a simple epoxy molecule enabled us to attribute the NMR changes that accompany the epoxy ring opening. Further, the use of a guest-host system made of an azo chromophore dispersed in an MMA-GMA copolymer matrix indicated a quantitative yield of the carboxyl/epoxy anchorage reaction after 30 min of heating at 140°C. The 13C cross polarization (CP)/MAS NMR spectroscopic study showed unambiguously that the cross-linking reaction in polymer PIII is due to a nucleophilic opening of the epoxy rings by the carboxylic groups of the chromophores resulting in carboxylic ester bond formation. Finally, the blue shift of the ca 500 nm absorption band was modeled with a computational study. It is concluded that the esterification of the acid carboxylic group of the chromophore causes the torsion of the azo molecule

Are nicotinoids protonated on the pyridine or the amino nitrogen in the gas phase?

0894-323

Des parcours et des hommes - enssib 2012

Série d\u27entretiens filmés ou enregistrés dans le cadre du volet audiovisuel de l\u27exposition "Mémoire de l\u27enssib - acte 2 : des parcours et des hommes", à l\u27occasion des vingt ans de l\u27école