镁(Ⅱ)-甘氨酸-水三元配合物结构和性质的理论研究

(Ⅱ)-甘氨酸-水三元配合物结构和性质的理论研究] 孟祥军*,石 瑾 (唐山师范学院化学系,河北 唐山 063000)

三元配合物; 甘氨酸; 金属离子; 水分子; 配位能力; 构型; 液相模型

Theoretical Study on Structure and Properties of Ternary Complexes [Mg(Gly)(H2O)n]2+
MENG Xiangjun*,SHI Jin

(Department of Chemistry,Tangshan Normal University,Tangshan 063000,China)

DOI: 10.6043/j.issn.0438-0479.201703003

备注

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/mol; 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/mol)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)(H2O)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.

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