Hay R W, Hassan M M, You-Quan C
Chemistry Department, University of St. Andrews, U.K.
J Inorg Biochem. 1993 Oct 1;52(1):17-25. doi: 10.1016/0162-0134(93)85619-j.
The protonation constants of the tripeptide glycylglycyl-L-histidine (L-) have been determined at 25 degrees C and I = 0.1 mol dm-3 as log K 8.06, 6.82, and 2.80. Complexation with copper(II) can be represented by the series of equilibria [formula: see text] in the case of nickel(II) only the species [NiLH]2+, [NiL]+, and [NiLH-2]- are of importance with log beta 111 = 11.33(2); log beta 110 = 4.74(6), and log beta 11-2 = -6.93(1). The tripeptide acts as a quadridentate ligand to give complexes with copper and nickel with an amino group, two deprotonated amide groups and an imidazole pyridine nitrogen (Im-N3) as donors. At 1:1 ligand-to-metal ratios the purple copper(II) complex [CuLH-2]- is essentially 100% abundant above pH 7 and the planar yellow [NiLH-2]- above pH 8. The displacement of the tripeptide ligand from the nickel(II) complex by L-histidine has been studied kinetically over the pH range 7-8. There is a small solvolytic reaction and a reaction which is first-order in the hydrogen ion concentration. Under the experimental conditions employed, the reaction is essentially independent of the L-His concentration and displacement occurs by a proton-assisted nucleophilic pathway with rate-determining cleavage of the first nickel(II)-N(peptide) bond.
在25℃和离子强度I = 0.1 mol dm⁻³条件下，测定了三肽甘氨酰甘氨酰-L-组氨酸（L-）的质子化常数，其log K分别为8.06、6.82和2.80。与铜（II）的络合作用可由一系列平衡反应表示[化学式：见原文]；对于镍（II），只有物种[NiLH]²⁺、[NiL]⁺和[NiLH⁻²]⁻是重要的，其log β₁₁₁ = 11.33(2)；log β₁₁₀ = 4.74(6)，log β₁₁⁻² = -6.93(1)。该三肽作为四齿配体，以一个氨基、两个去质子化的酰胺基团和一个咪唑吡啶氮（Im-N3）作为供体，与铜和镍形成络合物。在配体与金属的比例为1:1时，紫色的铜（II）络合物[CuLH⁻²]⁻在pH 7以上基本上100%存在，而平面黄色的[NiLH⁻²]⁻在pH 8以上存在。已经在pH范围7 - 8内对L-组氨酸从镍（II）络合物中取代三肽配体的过程进行了动力学研究。存在一个小的溶剂解反应和一个对氢离子浓度为一级的反应。在所采用的实验条件下，该反应基本上与L-组氨酸的浓度无关，取代反应通过质子辅助的亲核途径发生，速率决定步骤是第一个镍（II）-N（肽）键的断裂。
