Monique Riviere

Chemical and photechemical reactivity in micellar media and microemulsions IV: concentration effects on isophorone dimerization

Abstract A study of concentration effects in isophorone photodimerization shows the importance not only of interfacial processes but also of selective extraction of the reactants and products. From this work, another feature can be pointed out: microemulsification is a general phenomenon and microemulsions containing a polar component as the “oil” can be prepared.

Chemical and photochemical reactivity in micellar media and microemulsions VII- Effect of the interface on the reactivity of excited states

Abstract Study of the photodimerization of coumarin in micellar media and microemulsions shows that the orientation and the concentration of molecu- les in the interfacial film can favor reactions involving just one of the excited states (the singlet state in this case).

CI (CIPSI) calculations of the vertical ionization and excitation energies of the formamide molecule

Abstract The vertical excited and ionized states of the formamide molecule are calculated in a (double-zeta + diffuse) AO basis ·set using the CIPSI algorithm. The correct ordering of the ionization potential is obtained (despite a 0.6 eV underestimation of the calculated IPs). The calculated vertical excitation energies of the “valence” excited states are good, especially for the 1 ππ* excited state (7.6 eV), but several Rydberg states are calculated to lie below this value.

Single-run analysis of retinal isomers, retinol and photooxidation products by high-performance liquid chromatography

Abstract A high-performance liquid chromatographic (HPLC) procedure was developed to allow the rapid separation, in a single run, of a mixture of the main retinal isomers (all-trans, 13-cis, 9-cis), all-trans-retinol, and of the two major photooxygenated photoproducts (5,8-peroxyretinal and 5,6-epoxyretinal). The mixture was separated by HPLC on an octadecyl (ODS) column with 16% (v/v) diethyl ether in hexane as mobile phase and anthracene as the internal standard. A commercial type cosmetic formulation containing 0.05% all-trans-retinal was analyzed successfully for this analyte.

Amphiphilic urocanic acid derivatives as catalysts of ester hydrolysis

The hydrolysis of p-nitrophenyl acetate at pH 8 and 25°C is demonstrated to be a good test reaction to study the influence of the structure of several long-chain derivatives of urocanic acid on the imidazole ring reactivity in organized media. Cetyltrimethylammonium bromide micelles including (E)-dodecyl urocanate gave an approximately 7-fold rate enhancement over (Z)-dodecyl urocanate, 30-fold over (E)-urocanic acid and 4790-fold over CTABr. The behavior of (E)-dodecyl urocanate in the presence of excess substrate was also been investigated. The value of kobs decreased by 37% as the substrate:catalyst ratio was increased from 1:10 to 10:1. Under the same conditions, the total activity was restored when one equivalent of chloral was added to one equivalent of (E)-dodecyl urocanate. Chloral significantly enhanced the deacylation rate of N-acetyl dodecyl urocanate, giving a good reaction turnover.

Effect of Microemulsions on Photochemical Reactions

Three photochemical reactions have been studied in both anionic and cationic microemulsions. E ⇄ Z isomerization of O-methyl oxime ethers of aromatic ketones; photocycloaddition of α-cyclenones; photodimerization of cinnamic derivatives. Our results showed that the magnitude of the microemulsion effect depends on: the substrate localization; the reaction mechanism and more specially the involvement of an excimer; the structure of the microemulsion.

Réaction d’isomérisation de l’acide urocanique et de ses dérivés: stabilité comparée des isomères Z et E‡

Resume L’etude de la photo-isomerisation de l’acide urocanique E (photoprotecteur naturel de la peau) et de certains de ses derives a permis de montrer l’importance du coefficient d’extinction molaire des deux isomeres a la longueur d’onde d’irradiation. L’isomerisation thermique des memes composes a lieu difficilement et uniquement dans le sens Z → E. Les isomeres E sont thermodynamiquement les plus stables. Dans les derives non N-alkyles, en milieu basique, le passage par l’ion amidure delocalise abaisse la barriere energetique sans changer le sens de l’isomerisation.