三元配合物Zn(L-tyr)(Aa)分子内配体间疏水作用

Intramolecular ligand-ligand hydrophobic interactions of ternary complexes of Zn(Ⅱ)ion with amino acids

应用pH电位滴定法研究了三元配合物Zn(L tyr)(Aa)[L tyr(酪氨酸根),Aa =L val(缬氨酸根),L php(苯丙氨酸根)],L trp(色氨酸根)]在水和x=0 20、0 40及0 60二氧六环 水混合溶剂中的稳定性[t=25℃,I=0 1mol/LNaClO4]。三元配合物相对稳定性用δK=ΔlogK[=logβZnZn(L tyr)-logKZnZn(Aa)]-ΔlogK(s)Zn(L tyr)(Aa)-logKZn[=1/2ΔlogK(L tyr)+ΔlogK(Aa)+log2]表示。结果表明:与L 丙氨酸(L ala)配合物Zn(L tyr)(L ala)相比,所有这些配合物均具有相对较高的δK值,表明配合物分子内存在着额外的稳定化作用。这种稳定性化作用可能主要归因于三元配合物分子内氨基酸侧链之间的疏水作用,并且这种作用随着氨基酸侧链结构及溶剂极性变化而变化。

Stability constants of ternary complexes Zn(Ltyr)(Aa)were determined by pH potentiometric titrations in water,φ=020?040and 060 dioxanewater solvents,where Ltyr-=Ltyrosinate,Aa-=Lvalinate,Ltryptophanate and Lphenylalaninate (t=25℃,I=01mol/L NaClO4).The relative stability of the ternary complexes is defined by δK {=ΔlogKZnZn(Ltyr)(Aa)-logKZnZn(Ltyr)-logKZn-ΔlogK(s)}.The results show that,compared with the complex Zn(Ltyr)(Lala) with Lalaninate,the complexes with the amino acids have larger δK values,indicating that there are extra stabilizing effects in the ternary complexes.This may be mainly attributed to the intramolecular hydrophobic or stacking interactions between the phenyl group of Ltyr and the side chains of other amion acids in the complexes,and the interactions vary with the side chains of the amino acids or solvent polarity.