Coenzyme Models. II. Effect of Micellar Environments on the Acid-Catalyzed Hydration of 1,4-Dihydropyridine Derivatives

An effect of micelles on the acid-catalyzed modification reaction of two dihydropyridines is reported in connection with the NADH function bound to alcohol dehydrogenase, and the hydration equilibrium of dihydronicotinamides was found to be quite susceptible to the ionic environment. The absorption maximum at 357 nm of 1-benzyl-1,4-dihydronicotinamide(NBzNH) was not affected by the presence of cationic micelles, while that of 1-lauryl-1,4-dihydronicotinamide(NLaNH) shifted by 5–6 nm to shorter wavelengths, probably due to the neighboring cationic charge. The hydration rates for dihydronicotinamides were prompted by NaLS micelle and retarded by CTAB micelle. The rate augmentation in the NaLS micelle, compared with the non-micellar system, was 1.7-fold for NBzNH and 33-fold for NLaNH. On the other hand, CTAB micelle pronouncedly depressed the hydration rate of NLaNH, which is 414-fold slower than in NaLS. The micelle of 1-lauryl-3-carbamoylpyridinium(NLaN), which forms the charge transfer complex with NLaNH, was found to inhibit the acid-catalyzed hydration more efficiently (1400-fold slower). Thus, it is suggested that the ammonium ion adjacent to the dihydronicotinamide group in alcohol dehydrogenase–NADH complex performs some biological functions.