Studies Of The Zn²⁺-H₂O Systems By ABEEM/MM Model As Well As Quantum Chemistry And Preliminary Study Of Zinc-Containing Proteins

Metal ions are indispensable for maintaining the structural stability and catalytic activityof metalloproteins. Molecular modeling studies of such proteins with force fields, however,are often hampered by the missing of accurate potential function. In order to describeaccurately the effect of coordination of Zinc-containing proteins in aqueous. Based on the QMresults, an accurate potential function for Zn²⁺-Water was constructed by the atom-bondelectronegativity equalization fluctuating charge model（ABEEM/MM）, then calculated chargedistribution of Zn²⁺（H₂O）n（n=1¹2） by ABEEM. A chemical bonding sites between the Zincand oxygen of the first hydration was introduced to well describe the ligand effect of Zn²⁺with water. The related parameters were successfully transferred to calculate the chargedistributions of Zn²⁺-containing proteins.High-level quantum chemistry methods were employed to investigate theZn²⁺（H₂O）n（n=1¹2） clusters. The geometries were optimized and the vibration frequencywere calculated by MP2/6-31++G（d,p） method (and for Zn²⁺, the LANL2DZ basis setemployed). The energies were calculated at the MP2/6-311++G（2d,2p） level with BSSEcorrection. Results show that: when n=1⁶, the most stable conformation corresponds to thatZn²⁺interacts directly with water, rather than the formation of intermolecular hydrogenbonding between water molecules, and the average distance between Zn²⁺and oxygen atomsof the first hydration layer, R_Zn-O,is lengthened gradually, when n=7¹2, the most stableconformation is5+x configuration, and R_Zn-Ois shortened gradually. Compared to isolatedwater molecule, the HO stretching vibration of water molecules moved towards the directionof lower wave number, while the vibration frequency of∠HOH did not change obviously inthe hydrated clusters. With the increase number of coordinated water molecules, thesuccessive binding energy decreases gradually, the positive charges of Zn2+and the hydrogenatoms of the first hydration layer reduced gradually, while the negative charges of oxygenatoms in the first hydration layer did not change much. The ABEEM/MM potential was usedto calculated the structures and binding energy of Zn²⁺（H₂O）n（n=1¹2）, and the results areconsistent with the QM results.