Characterization of Copper(III)-Tetrapeptide Complexes with Histidine as the Third Residue.
Characterization of Copper(III)-Tetrapeptide Complexes with Histidine as the Third Residue.
复制标题
以组氨酸为第三个残基的铜 (III)-四肽复合物的表征。
作者：
M. R. Mcdonald;F. Fredericks;D. W. Margerum
表征了Gly（2）HisGly和Aib（2）HisGly的铜（III）络合物，其中Gly是甘氨酸，His是L-组氨酸，Aib是α-氨基异丁酸。它们各自的还原电位（V vs NHE）为0.978和0.826。两个Cu（III）配合物进行胺去质子化与pK（a）值分别为8.79和8.81。相对于具有5 -5-6、5-6-5、6-5-5和5-5-5元连接的连续环的不含组氨酸的Cu（III）-三肽络合物，检查5-5-6元螯合环对E度和pK（a）值的影响。第三个肽残基中存在六元环，导致相对于5-5-5元环系统降低约1.0 pK（a）单位。与羧酸盐配位相比，来自组氨酸的咪唑配位导致额外减少1.3 pK（a）单位。在0.3-4.7的pH范围内测量Cu（III）（H（-2）Gly（2）HisGly）和Cu（III）（H（-2）Aib（2）HisGly）络合物的分解。动力学和反应产物表明，在组氨酰残基的α碳上的质子的提取是速率决定步骤。Gly（2）HisGly的初始分解产物是具有α-羟基组氨酰残基的四肽，其脱水得到具有α，β-脱氢组氨酰残基的烯烃。报道了烯烃以及Gly（2）HisGly和Aib（2）HisGly的Cu（III）络合物的紫外-可见光谱性质。
Copper(III) complexes of Gly(2)HisGly and Aib(2)HisGly are characterized, where Gly is glycine, His is L-histidine, and Aib is alpha-aminoisobutyric acid. Their respective reduction potentials (V vs NHE) are 0.978 and 0.826. Both Cu(III) complexes undergo amine deprotonation with pK(a) values of 8.79 and 8.81, respectively. The influence of the 5-5-6 membered chelate rings on the E degrees ' and pK(a) values is examined relative to the Cu(III)-tripeptide complexes without histidine that have 5-5-6, 5-6-5, 6-5-5, and 5-5-5 membered linked-consecutive rings. The presence of a six-membered ring in the third peptide residue causes a decrease of approximately 1.0 pK(a) unit relative to a 5-5-5 membered ring system. Imidazole coordination from histidine compared to carboxylate coordination causes an additional decrease of 1.3 pK(a) units. Decompositions of Cu(III)(H(-2)Gly(2)HisGly) and Cu(III)(H(-2)Aib(2)HisGly) complexes are measured over the pH range 0.3-4.7. The kinetics and the reaction products show that abstraction of a proton at the alpha carbon of the histidyl residue is the rate-determining step. The initial decomposition product of Gly(2)HisGly is a tetrapeptide with an alpha-hydroxyhistidyl residue that dehydrates to give an alkene with an alpha,beta-dehydrohistidyl residue. UV-vis spectral properties are reported for the alkene as well as the Cu(III) complexes of Gly(2)HisGly and Aib(2)HisGly.