Hydrophobic vitamin B₁₂. III. Incorporation of hydrophobic vitamin B₁₂ derivatives into single-compartment vesicles and their alkylation in various molecular aggregates

The incorporation of hydrophobic vitamin B₁₂ derivatives into the single-compartment vesicles of N'N,-didodecyl-N(α)-[6-(tyimethylammonio)hexanoyl]-L-alaninamide bromide (N⁺C₅Ala2C₁₂) was found to be primarily concerned with the extent of insolubility of the cobalt complexes in the aqueous bulk phase, while such incorporation into the single-walled vesicles of N,N-ditetradecyl-N(α)-[6-(trimethylammonio)hexanoyl]-L-histidinamide bromide (N⁺C₅His2C₁₄) was enhanced by the coordination interaction between the cobalt complex and the imidazolyl group of the lipid. In molecular aggregates formed with hexadecyltrimethylammonium bromide, α-[4-(1,1,3,3-tetramethylbutyl)phenyl]-ω-hydroxypoly(oxyethylene), or N⁺C₅Ala2C₁₂, the alkylation rates of a hydrophobic vitamin B₁₂ with 1-bromo-2-methylpropane and methyl 2-methyl-3-bromopropanoate were much enhanced relative to those in methanol. In the N⁺C₅Ala2C₁₂ vesicle, a two-step mechanism was observed for the alkylation with the latter reagent. The possible origin of such rate enhancement was discussed.