摘要：
为认识金属离子的生物功能,采用CCSD/6-31++G**∥M06/6-31++G**理论方法系统研究了三元配合物[Mg(Gly) (H2O)n]2+的结构和性质.气相模型下得到的结果为:1)O,O双啮型两性甘氨酸的配位能力最强,比N,O双啮型中性甘氨酸的配位能力强37.6 kJ/mol,比2个水分子强约60 kJ/mol;2)与Mg2-配位时,O,O双啮型两性甘氨酸优先,结合能达到-669.1 kJ/mo[;随后4个水分子依次配位,结合能变化值递减,平均为159.1 kJ/mol,此时配位键达到饱和数6,体系的结合能达到-1 305.4 kJ/mol;3)第5个水分子可通过强氢键(键能为85.5 kJ/rnol)作用于体系得到次稳定构型,结合能为-1 390.9 kJ/mol;也能插入到甘氨酸的O原子与Mg2+之间,取代甘氨酸的1个O原子与Mg2+形成配位键,导致甘氨酸变为单啮配体,这样得到的构型最稳定,结合能达到-1 393.1 kJ/mol.液相模型下的构型结构与气相模型相比变化微小,能量次序与气相结果相同.%CCSD// M06/6-31+ + G** method was applied to investigate the structure and properties of ternary complexes [Mg(Gly) (H2 O)n]2+ systematically.The results based on a gas-phase model show that:1) Coordination ability of the zwitterion glycine molecule (coordination sites are two O atoms) is stronger by 37.6 kJ/mol than that of the neutral glycine molecule (coordination sites are the N atom and one O atom),and is stronger by 60 kJ/mol than that of two water molecules.2) Bidentate glycine ligand with O and O coordination sites is prior to be coordinated to Mg2+,with the binding energy of-669.1 kJ/mol;subsequently,the water molecule is coordinated to Mg2+ successively from 1 to 4 with the variation of binding energy decreasing (the average value is 159.1 kJ/mol);at this time coordination bonds are saturated at the number of 6,and the binding energy of the system is-1 305.4 kJ/mol.3) The fifth water molecule can be combined with the above system by a strong hydrogen bond (the bonding energy is 85.5 kJ/mol),and the total binding energy is-1 390.9 kJ/mol;it also can be inserted into the O atom of zwitterion glycine and Mg2+,combined with Mg2+ by a coordination bond;in this case,glycine changed into a mono-dentate ligand,but the stability of this conformation is the best,and the binding energy reached-1 393.1 kJ/mol.The structure of each conformation of liquid-phase model changes a little in comparison with the corresponding gas-phase model conformation,but the order of conformation stability has no change.
