Effect of vesicles of dimethyldioctadecylammonium chloride and phospholipids on the rate of decarboxylation of 6-nitrobenzisoxazole-3-carboxylate

Sonicated mixtures of dimethyldioctadecylammonium chloride (DODAC), egg pho sphatidylcholine (PC), dimyristoyl phosphatidylcholine (DMPC), and dipalmit oyl phosphatidylcholine (DPPC) were used to analyze vesicle effects on the rate of decarboxylation of 6-nitrobenzisoxazol-3-carboxylic acid (Nboc). El ectron microscopic images of the vesicles were obtained with trehalose, a k now cryoprotector. Phase diagrams and phase transitions temperatures of the vesicle bilayers were determined. Nboc decarboxylation rates increased in the presence of vesicles prepared with both phospholipids and DODAC/phospho lipid mixtures. Quantitative analysis of vesicular effects was done using p seudophase models. Phospholipids catalyzed up to 140-fold while the maximum catalysis by DODAC/lipid vesicles reached 800-fold. Acceleration depends o n alkyl chain length, fatty acid insaturation of the lipids, and the DODAC/ phospholipid molar ratio. Catalysis is not related to the liquid crystallin e-gel state of the bilayer and may be related to the relative position of N boc with respect to the interface.