Nickel(iii) oxidation of its glycylglycylhistamine complex

Abstract

The doubly-deprotonated Ni(III) complex of Gly(2)Ha (where Ha is histamine) undergoes base-assisted oxidative self-decomposition of the peptide. At </= p[H(+)] 7.0, a major pathway is a two-electron oxidation at the alpha-carbon of the N-terminal glycyl residue. Major products (up to 73%) of this two-electron oxidation are glyoxylglycylhistamine and ammonia. Glyoxylglycylhistamine will decay to give isocyanatoacetylhistamine and formaldehyde. Two-electron oxidations of the second glycyl and histamine residues occur as minor pathways (12% of the total possible reaction). Above p[H(+)] 8.5, two Ni(III)-peptide complexes form an oxo bridge in the axial positions to give a reactive dimer species. This proximity allows the resulting Ni(II)-peptide radical intermediates to undergo peptide-peptide cross-linking at the N-terminal glycyl residues. The products found below p[H(+)] 7.0 are observed above p[H(+)] 8.5 as well, although in lower yields. In contrast to this work, Ni(III)(H(-2)Gly(2)HisGly) undergoes a four-electron oxidation at the N-terminal glycyl residue. Oxidation at the internal glycyl and histidyl residues are not observed. The reactivity of Ni(III)(H(-2)Gly(2)Ha)(+) is also different than Cu(III)(H(-2)Gly(2)Ha)(+), which undergoes a two-electron oxidation at the histamine group with no peptide-peptide cross-linking in basic solution.

Nickel Ion Complexes of Amino Acids and Peptides

“…A [(Ni III salen) 2 O] species has been isolated and its crystal structure determined [209]. The self-decomposition reaction of [Ni III (H Ϫ2 Gly 2 Hm)] ϩ at pH 5 to 7.0 is a two-electron oxidation at the N-terminal glycyl residue to give [Ni II (H Ϫ2 glyoxylglycylhistamine)] [210]. By contrast, the [Ni III (H Ϫ2 Gly 2 HisGly)] complex undergoes a four-electron oxidation at the same site.…”

Zinc(ii) coordination polymers with pseudopeptidic ligands

“…Thus, it is not surprising that many efforts have been devoted to developing different catalytic systems based on the coordination of pseudopeptidic ligands to different metals. [1][2][3][4] In this regard, we have recently studied the Cu 2+ and Zn 2+ coordination properties of simple C 2 symmetric pseudopeptides such as 1 (see Scheme 1) in which two valine fragments are connected by an aliphatic spacer (-(CH 2 ) n -). [5][6][7][8][9][10][11][12] Spectroscopic, mass spectrometric and X-ray crystallographic studies revealed that the corresponding complexes can adopt a variety of coordination geometries depending on several factors such as the nature of the cation, pH of the medium and the length of the central aliphatic spacer.…”

Metal assisted peptide bond hydrolysis: Chemistry, biotechnology and toxicological implications

“…Stable 4N Ni(II) complexes with C-terminal reaction products may produce oxidative damage when exposed to hydrogen peroxide, which is an endogenous molecule. Such reactivity, proceeding via Ni(III) intermediates, was demonstrated for a range of synthetic complexes and for naturally occurring peptides bearing analogous N-terminal His-3 sequences [124][125][126][127]. It is very likely to contribute to molecular processes underlying Ni(II) carcinogenesis [118,119,128], and perhaps also to nickel allergy [129].…”