DANIEL COSSETTE and DANIEL VOCELLE. Can. J. Chem. 65. 1576 (1987). . .I3c and 1 5~ nuclear magnetic resonance spectra of mixtures of all-trans-retinylidene tert-butylamine (RtBA) and substituted acetic acids in equimolar concentrations in both CDC13 and CD30D were studied in relation to two questions: the nature of the state of protonation of a retinal Schiff base in the presence of carboxylic and mineral acids in solvents of different polarities, and secondly, to determine the nature of the interactions (if any) between the polar groups located on the acids and the polyenic chain of the retinal derivative. Using carboxylic acids of different pK,s and three mineral acids, we present results that indicate that, in solvents of low polarity, weak acids can only partially protonate RtBA while, in a more polar milieu, the protonation percentages are higher. With polar groups such as NO2, CI, Br, I, and CN, no specific interaction could be found between the polyenic chain of the imine and these groups. Variations in the intensity of certain peaks of RtBA were noted and these could possibly be related to the presence of the polar groups on the acids. Comparisons of our results with those obtained on rhodopsin and bacteriorhodopsin indicate that the milieu surrounding the chromophore must be polar if protonation is complete, while in a less polar environment partial protonation can be expected.DANIEL COSSETTE et DANIEL VOCELLE. Can. J. Chem. 65, 1576Chem. 65, (1987. Les spectres de rCsonance magnitique nuclkaire de I3C et de 1 5~ de mClanges de tout-trans-ritinylidkne tert-butylamine (RtBA) et d'acides acitiques substituis, en concentrations Cquimolaires dans des solvants comme CDCI3 et CD30D, ont itC ttudiis relativement deux questions : la nature de l'itat de protonation d'une base de Schiff du rCtinal en prisence d'acides carboxyliques dans des solvants de polaritis diffkrentes, et deuxiemement, de diterminer la nature des interactions (si elles existent) entre les groupes polaires localisks sur les acides et la chaine polyinique. Par l'utilisation d'acides carboxyliques ayant des pK,s variis et Cgalement de trois acides minCraux, nous montrons des resultats qui indiquent que dans des solvants de faibles polaritCs, les acides faibles ne peuvent protoner RtBA que partiellement tandis qu'en des milieux plus polaires, la protonation peut &tre complkte. Avec des groupes comme NO2, Cl, Br, I et CN, aucune interaction spicifique n'a pu &tre trouvke entre la chaine polyCnique de I'imine et ces groupes. Des variations dans l'intensiti de certains pics de RtBA ont CtC aperques qui peuvent possiblement &tre reliCes i i la presence des groupes polaires des acides. Des cornparaisons de nos rksultats avec ceux obtenus a partir de rhodopsine et de bactCriorhodopsine indiquent que le milieu entourant le chromophore doit &tre polaire pour une protonation complkte tandis qu'en milieu rnoins polaire une protonation partielle est probable.
DANIEL COSSETTE and DANIEL VOCELLE. Can. J. Chem. 65, 661 (1987).The interactions (mostly protonation) between several carboxylic and mineral acids and trans,trans-2,4-heptadienylidene tert-butylamine (HBA) were determined by I3c and I5N nuclear magnetic resonance spectroscopies. Results indicate that protonation is only partial with weak acids in both polar and nonpolar solvents. No interaction between polar groups located on the acids and the polyenic chain of HBA seems to occur. The chemical shifts of all carbon atoms and also of the Schiff base nitrogen are linearly correlated with the acidity strength of the carboxylic acids.DANIEL COSSETTE et DANIEL VOCELLE. Can. J. Chem. 65, 661 (1987).Les interactions (surtout la protonation) entre plusieurs acides carboxyliques et minCraux avec la trans,trans-heptadiknylidkne-2,4 tert-butylamine (HBA) ont Ct C dCterminCes par la rCsonance magnCtique nuclCaire du I3C et du I5N. Les rCsultats indiquent que la protonation est partielle pour les acides faibles aussi bien pour les solvants polaires que non-polaires. Aucune interactionentre les groupes polaires des acides et la chaine polyCnique de HBA n'a pu &tre dCcelCe. Les dkplacements chimiques de tous les atomes de carbone et aussi de l'azote de la base de Schiff sont IinCairement correles avec la force de l'aciditk des acides carboxyliques.
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