Ab initio molecular orbital method has been empolyed, in this paper, to study the mechanism of the hydrolysis of acetylcholine. First of all, the optential energy surface of the reaction system has been investigated at HF/6-31G level, and two transition states and and intermediate linking the two transition states have been found. The optimized geometries have been used to perform further single point energy calculatios at RHF/6-31G** level. It has been shown that there existed different intramolecular hydrogen bonding in two four-center cycles of the two transition states, and that during the hydrolysis of acetylcholine, the fission took places at the bond between the carbonyl carbon and the ester oxygen. Finally, the self-consistent-reaction-field (SCRF) procedure based on the Quantum Onsager model has been applied to the energy calculations on all the reactions, transition states, intermediate and products at the RHF/6-31G** level in order to work out the energy barriers and the total reaction heat involving the solvent effect.

Key words: REACTION MECHANISM, HYDROLYSIS, ACETYLCHOLINE, AB INITIO CALCULATION, POTENTIAL ENERGY SURFACES, TRANSITION STATE