The stability of the fused chelate-ring structures of Cu(H−2L) concerning dynamic aspects was evaluated based on the rate constant (k1+) for the formation of ternary complexes, Cu(H−1L)(Cys−), from Cu(H−2L) and cysteine (Cys), where L denotes tripeptides composed of various combinations of α-, β-, and γ-amino-acid residues. The ligand-exchange reaction was examined by the stopped-flow spectrophotometric method. The Cu(H−2L) species, having 5–6–5- and 6–5–5-membered fused-chelate rings, were kinetically fairly stable; k1+ = 2–3 × 104 M−1 s−1. Other Cu(H−2L) species, having 5–5–5-, 5–5–6-, 5–5–7-, 5–6–6-, and 6–5–6-membered rings, reacted rapidly with Cys to form the Cu(H−1L)(Cys−) species; k1+ ≥ 1 × 105 M−1 s−1. The Cu(H−1L)(Cys−) species, upon forming, successively reacted with Cys to afford a binary complex, Cu(Cys−)2. The Cu(H−1L)(Cys−) species, with the β-Ala residue at the N-terminus, were kinetically labile to be rapidly transformed to Cu(Cys−)2.
根据 Cu(H-2L)和半胱
氨酸(Cys)形成三元复合物 Cu(H-1L)(Cys-)的速率常数(k1+),评估了 Cu(H-2L)融合螯合环结构在动态方面的稳定性。
配体交换反应采用停流分光光度法进行检测。具有 5-6-5 元和 6-5-5 元融合螯合环的 Cu(H-2L) 物种在动力学上相当稳定;k1+ = 2-3 × 104 M-1 s-1。其他具有 5-5-5-、5-5-6-、5-5-7-、5-6-6-和 6-5-6 元环的 Cu(H-2L) 物种会迅速与 Cys 反应生成 Cu(H-1L)(Cys-) 物种;k1+ ≥ 1 × 105 M-1 s-1。Cu(H-1L)(Cys-) 物种形成后,又先后与 Cys 反应生成二元复合物 Cu(Cys-)2。N 端含有 β-Ala 残基的 Cu(H-1L)(Cys-) 物种具有动力学易变性,可迅速转化为 Cu(Cys-)2。