金属离子(Na~+、K~+、Ca~(2+)、Mg~(2+)、Zn~(2+))与鸟嘌呤异构体配合物的稳定性

在B3LYP/6-311++G**水平上用极化连续介质模型(PCM)系统研究了金属离子(M+/2+=Na+,K+,Ca2+,Mg2+,Zn2+)和十三种鸟嘌呤异构体形成的配合物GnxM+/2+(n为鸟嘌呤异构体的编号,x表示M+/2+与鸟嘌呤异构体的结合位点)在气(g)液(a)两相中的稳定性顺序.着重探讨了液相中配合物的稳定性差异,并且从溶质-溶剂效应、结合能、形变能及异构体的相对能量等几个方面分析了造成稳定顺序发生变化的原因.报道了溶液中这五种金属离子与鸟嘌呤异构体结合形成的六种基态配合物:aG1N2,N3Na+,aG1N2,N3K+,aG1O6,N7Ca2+,aG1N2,N3Mg2+(aG1O6,N7Mg2+),aG2N3,N9Zn2+.可以看出,除了在Zn2+配合物中鸟嘌呤异构体为G2外,构成其余四种金属离子配合物的鸟嘌呤异构体都是G1,但结合位点不同.同时对气相中各类配合物稳定性也进行了系统的排序,并报道了几种较稳定的配合物,如:gG3N1,O6K+,gG5N1,O6K+,gG3N1,O6Ca2+/Mg2+,gG4O6,N7Ca2+/Mg2+.

Stability of Complexes Combined by Metal Ions(Na+,K+,Ca2+,Mg2+,Zn2+)and Guanine Isomers

The order of stability for complexes of differently coordinated metal ions (M^+/2+=Na⁺, K⁺, Ca²⁺, Mg²⁺, Zn²⁺) with thirteen guanine isomers in gas (g) and aqueous (a) phases was systematically investigated at the B3LYP/6-311++G^** level in combination with the polarized continuum model (PCM). Special effort was devoted to differences in the order of stability for aGn_xM^+/2+ (n is the label of guanine isomers, x denotes binding site of M^+/2+ and guanine isomers) complexes that were obtained in aqueous solutions. An analysis was also performed to determine the reason for these differences with respect to the solute-solvent effect, binding energy, deformation energy, and relative free energy of the guanine isomers. The most stable complexes generated by the five metal ions were: aG1_N2,N3Na⁺ , aG1_N2,N3K⁺ , aG1_O6,N7Ca²⁺ , aG1_N2,N3Mg²⁺ (aG1_O6,N7Mg²⁺), and aG2_N3,N9Zn²⁺. The isomer of guanine in the most stable Zn²⁺ complex in the aqueous solution was G2 whereas in the other four most stable complexes it was G1, i.e., the different active sites in G1 generate the four most stable complexes. Additionally, we report on stable complexes in the gas phase such as gG3_N1,O6K⁺, gG5_N1,O6K⁺, gG3_N1,O6Ca²⁺/Mg²⁺, and gG4_O6,N7Ca²⁺/Mg²⁺.