Formation Constants of Copper(II) Complexes with Tripeptides Containing Glu, Gly, and His: Potentiometric Measurements and Modeling by Generalized Multiplicative Analysis of Variance

详细信息    查看全文

• 作者：Rima Raffoul Khoury ; Gordon J. Sutton ; Diako Ebrahimi ; D. Brynn Hibbert
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：February 3, 2014
• 年：2014
• 卷：53
• 期：3
• 页码：1278-1287
• 全文大小：445K
• ISSN：1520-510X

文摘

We report a systematic study of the effects of types and positions of amino acid residues of tripeptides on the formation constants log尾, acid dissociation constants pK_a, and the copper coordination modes of the copper(II) complexes with 27 tripeptides formed from the amino acids glutamic acid, glycine, and histidine. log尾 values were calculated from pH titrations with l mmol L^鈥?:1 mmol L^鈥? solutions of the metal and ligand and previously reported ligand pK_a values. Generalized multiplicative analysis of variance (GEMANOVA) was used to model the log尾 values of the saturated, most protonated, monoprotonated, log尾(CuL) 鈥?log尾(HL), and pK_a of the amide group. The resulting model of the saturated copper species has a two-term model describing an interaction between the central and the C-terminal residues plus a smaller, main effect of the N-terminal residue. The model supports the conclusion that two copper coordination modes exist depending on the absence or presence of His at the central position, giving species in which copper is coordinated via two or three fused chelate rings, respectively. The GEMANOVA model for pK_amide, which is the same as that for the saturated complex, showed that Gly-Gly-His has the lowest pK_amide values among the 27 tripeptides. Visible spectroscopy indicated the formation of metal鈥搇igand dimers for tripeptides His-His-Gly and His-His-Glu, but not for His-His-His, and the formation of multiple ligand bis compexes CuL₂ and Cu(HL)₂ for tripeptides (Glu/Gly)-His-(Glu/Gly) and His-(Glu/Gly)-(Glu/Gly), respectively.