Coenzyme Models. VII. Micellar Catalysis of Acid-Catalyzed Hydration of 1-Dodecyl-1,4-Dihydronicotinamide

The acid-catalyzed hydration reaction of 1-dodecyl-1,4-dihydronicotinamide was examined in cationic(CTAB) and anionic (SDS) micelles. The H3O+-catalysis(kH was negligibly small in the presence of the CTAB micelle and 225–521 M−1 s−1 in the presence of the SDS micelle, the difference being about 107-fold. The catalysis by carboxylic acids (kHA) was considerably suppressed in the CTAB micelle, but was promoted in the SDS micelle, suggesting the development of a cationic charge on a nitrogen atom of dihydropyridine at the rate-determining step. Brönsted plots for logkHA in the CTAB and SDS micelles vs. pKa of carboxylic acids gave straight lines with the slope of −0.8, the line for SDS being higher by two orders of magnitude than that for CTAB. These results indicate that a cationic charge (e.g., the lysine residue of alcohol dehydrogenase located very close to the bound NADH) may protect the NADH from hydration decay.