配位化合物分子内配体间的疏水缔合作用——Ⅲ.镉(Ⅱ)/ATP/氨基酸体系

Intramolecular Ligand-Ligand Hydrophobic Interaction in Coordination Compounds 3.Systems of Cadmium(Ⅱ)-ATP-Amino Acids

应用 pH-电位滴定法测定了水溶液中 Cd(ATP)(Aa)^(3-)(ATP^(4-)为腺苷三磷酸根,Aa^-分别为丙氨酸 ala^-、蛋氮酸 met^-、苯丙氨酸 phe^-和色氨酸 trp^-)型混合配体配合物及相应的单配体配合物在离子强度为 KNO_30.10 mol/L,温度为37℃时的稳定常数.混配配合物的稳定性与氨基酸配体的关系为 trp^->met^->phe^->ala^-.从分子内配体间的弱相互作用角度对促成上述序列规律进行了讨论.

The stability constants of ternary complexes of Cd(ATP)(Aa)and of correspond- ing binary complexes have been determined by potentiometric pH titration in solution at 37℃ and at 0.10 mol/L ionic strength(ATP=adenosine triphosphate,Aa=alanine(ala),methio- nine(met),phenylalanine(phe)or tryptophan(trp)respectively).The relative stabilities of the ternary complexes in the amino acid ligand order are trp^->met^->phe^->ala^-.The pos- sible reasons have been discussed in terms of intramolecular ligand-ligand interactions spe- cially the hydrophobic association including aromatic ring stacking.In order to characterize the intramolecular ligand-ligand interaction quantitatively,the equilibrium constants,K_1,of transfer between opened species(in the absense of the ligand-ligand interaction)and closed species(with ligand-ligand interaction)have been calculated.The results show that the closed species of ternary complexes containing trp,met or phe as one of ligands are the major components in solution.