Copper(II) Complexes of Glycyl-l-histidine, Glycyl-l-histidylglycine, and Glycylglycyl-l-histidine in Aqueous Solution

Abstract

The complex formation of glycyl-l-histidine, glycyl-l-histidylglycine, and glycylglycyl-l-histidine with copper (II) ion in aqueous solutions containing equimolar amounts of copper(II) and the respective ligand was investigated by potentiometric and visible spectrophotometric methods. The presence of the following copper (II) complex species was assumed: CuLH2+, CuX, and CunYnn− for glycyl-l-histidine-copper(II) and glycyl-l-histidylglycine–copper(II) systems, and CuLH2+, CuY−, and CuZ2− for glycylglycyl-l-histidine-copper(II) system, where LH is the neutral species of the ligand and LH=XH2=YH3=ZH4. The formation and ionization constants were obtained graphically, and the distribution of copper(II) among the complex species was calculated for each system. The results indicate that copper(II) ions are bound to the imidazole and carboxyl (or carbonyl) groups in CuLH2+ and to the amino, imidazole, and deprotonated amide groups in CuX, CuY−, and CuZ2−. The spectral blue shift accompanying a deprotonation in the region from a=4 to 5 in the glycyl-l-histidine and glycyl-l-histidylglycine copper(II) systems indicates the formation of a polymer complex CunYnn− in which the imidazole ring acts as a bridge to connect copper atoms, where a represents moles of KOH added per completely protonated ligand.

Binding of copper(II) to thyrotropin-releasing hormone (TRH) and its analogs

“…It has been reported to occur at various pH values depending on the actual ligand structure, as low as pH 9.6 in some cases with TRH [35,36]. The deprotonated pyrrole nitrogen of imidazole may or may not coordinate with Cu(II) ion [34,37]. However, shown by Fig.…”

A multi-approach study of the interaction of the Cu(II) and Ni(II) ions with alanylglycylhistamine, a mimicking pseudopeptide of the serum albumine N-terminal residue

“…Cu(II) and Ni(II) cations are well known for their ability to interact with histidyl residues in peptides, particularly with those containing the N-terminal sequence X-Y-His that is encountered in serum albumine [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. This protein, the most abundant one in mammalian blood serum, is involved in the transport of these ions.…”

“…So the pseudopeptides X-Y-Ha (Ha: histamine) can be used to evaluate the complexing ability toward the Cu(II) and Ni(II) ions, although other models are possible, namely those using an histidine residue in the amide form [16]. This was previously made with Gly-Gly-Ha [17] that gives rise to the formation of the 4-N complex MLH À2 , as with Gly-Gly-His [7,8,[18][19][20][21][22], with a slightly lower formation constant. In order to see the influence of substituents on the coordinating ability of this kind of ligands we synthesized the pseudopeptide Ala-Gly-Ha, on which the Ala residue brings an asymmetric carbon allowing a CD study.…”

Structure of (L-alanyl-L-histidinato)copper(II) 3.5-hydrate, [Cu(C9H12N4O3)].3.5H2O

“…Histidine is frequently found as part of the active site of metalloproteins. The coordination mode of the metal with histidine-containing peptides has been investigated mainly in solution by potentiometric and spectroscopic methods (Wilson, Kasperian & Martin, 1970;Aiba, Yokoyama & Tanaka, 1974;Agarwal & Perrin, 1975, 1976Kruck & Sarkar, 1975;Lau & Sarkar, 1981;Ensuque, Demaret & Abello, 1982)and in some cases in the solid state by X-ray analyses (Freeman & Szymanski, 1965;Blount, Fraser, Freeman, Szymanski, Wang & Gurd, 1966;Blount, Fraser, Freeman, Szymanski & Wang, 1967;Osterberg, Sj6berg & S6derquist, 1972;Camerman, Careerman & Sarkar, 1976).…”