Claude Loucheux

Circular dichroism study

SummaryN methacryloyl-S-methyl-L-cysteine (SMC) homopolymer along with a copolymer with methacrylic acid were prepared in the purpose of studying their complexation with Pd(II). The circular dichroism study showed that the binding of SMC residue to a polymeric chain does not change the coordination donor set of Pd complexation, i.e. ¦N, s ¦. The number of side chains per metal ion involved in the complexation depends on the molar fraction of SMC in the case of the copolymer and on the SMC/Pd ratio for both homopolymer anc copolymer. The variation of viscosity when adding Pd(II) suggests the formation of intramolecular loops.

Transition metal complexes of L-cysteine containing di- and tripeptides.

Nickel(II), cobalt(II), zinc(II), and cadmium(II) complexes of Ala-Cys, Phe-Cys, and Ala-Ala-Cys were studied by potentiometric and spectroscopic methods. Ni(II) induces deprotonation and coordination of the amide nitrogens, and the stable monomeric or oligomeric complexes are formed, depending on the metal to ligand molar ratios. Formation of the stable bis-complexes with [S,O] coordination mode is characteristic for cobalt(II), zinc(II), and cadmium(II) ions.

NMR and CD studies of sulfur chirality center in Pd(II) complexes with S-benzyl-cysteine and glycyl-S-benzyl-L-cysteine

Abstract 1 H NMR and CD spectra have shown the creation of chirality centers on thioether sulfur atoms when bound to metal ions in Pd(II) complexes with S-benzyl-L-cysteine and glycyl-S-benzyl-L-cysteine. Two diastereomers are formed with R or S configuration on the sulfur. The 1 H NMR and CD spectra as well as the molecular model considerations were used to suggest the absolution configuration of the respective diastereomers in the series of Pd(II) complexes with S-methyl, S-ethyl and S-benzyl-L-cysteine derivatives. The S-substituent was also found to have a critical influence on the absolute configuration of sulfur atom in the studied complexes.

NMR and CD studies of palladium(II) complexes with S-methyl-L-cysteine containing peptides

Abstract The studies on Pd(II) complexes with Gly-SMC, SMC-Gly and SMC-SMC have shown that S-methyl-L-cysteine as a residue in dipeptide ligands binds palladium ions by {N,S} donor set, creating a new chirality center on sulfur atom. The conformation of SMC in the formed complexes seems to be different when it acts as a dipeptide residue, as compared to that found in PdSMC complex. The presence of vicinal N-Terminal residue ( e.g. Gly in PdGly-SMC) stablizes the δ conformer of the SMC chelate ring, as well as changing the kinetics of the sulfur inversion in palladium complexes. The formation of the metal thioether sulfur bond enriches considerably the UV region of the CD spectra where the S → Pd(II) charge transfer (as well as intra sulfur transition) could be observed.

Synthesis and properties of photoreactive polysiloxanes containing pendant functional groups

Functional polysiloxanes containing photo-reactive pendant groups were prepared by multi-step modification of silicone copolymers containing methylhydrosiloxanes units. A first method based on the platinum Catalyzed hydrosilylation of vinylsilyl terminated photoreactive esters allowed to prepare liquid silicone polymers containing photo-dimerizable esters. Another method based of the esterification of pendant epoxy groups previously grafted on the silicone main chain was found as a general and very powerful alternative route to prepare photo-reactive polysiloxanes. The method has been applied to synthesize polysiloxanes containing various functional side-groups such as dimerizable esters, aromatic carbonyl compounds or dyes which possess properties of photochemical interest. The reactivity, the ability to be photosensitized as well as some practical properties of different photo-crosslinkable polysiloxanes modified either by cinnamic, furacrylic or a cyano p styrylacrylic ester groups were examined. A kinetic investigation of the reactivity of the polysiloxane-bound dimerizable chromophores allows to point out the effect of the silicone matrix in comparison with more classical hydrocarbon pho topolymer 8.

Polymethacrylic acid derivatives: 6. Hydrodynamic behavior of poly(N methacryloyl-l-alanine-co-N-phenyl-methacrylamide)

SummaryThe viscosimetric titrations of poly(N methacryloyl-l-alanine) and of a series of poly(N methacryloyl-l-alanine-co-N phenylmethacrylamide) have been studied. The stability of the compact conformation at low degree of neutralization ¯α depends on the hydrophobic nature of the copolymer. When titrating with tetraalkylammonium hydroxides instead of sodium hydroxyde, the tetraalkylammonium ion has been found to increase the molecular dimensions of PNMA and in opposite, to decrease those of the copolymers. This has been explained by the existence of intermolecular hydrophobic interactions.The titration of one of the copolymers in the presence of calcium ions, has shown that this divalent cation strongly depresses the electrostatic repulsions, giving to the copolymer a marked hydrophobic character.