Reinvestigation of the copper(II)-carcinine equilibrium system: "Two-dimensional" EPR simulation and NMR relaxation studies for determining the formation constants and coordination modes

Zsuzsanna Árkosi, Zoltán Paksi, László Korecz, Tamás Gajda, Bernard Henry, Antal Rockenbauer

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7 Citations (Scopus)

Abstract

The equilibria and solution structure of complexes formed between copper(II) and carcinine (β-alanyl-histamine) at 2 ≤ pH ≤ 11.2 have been studied by EPR and NMR relaxation methods. Beside the species that have already been described in the literature from pH-potentiometric measurements, several new complexes have been identified and/or structurally characterized. The singlet on the EPR spectrum detected in equimolar solutions at pH 7, indicates the formation of an oligomerized (CuL)n2n+ complex, with {NH 2, N im} coordination. The oligomerization is probably associated with the low stability of the ten-membered macrochelate ring, which would form in the mononuclear complex CuL 2+. In presence of moderate excess of ligand the formation of four new bis-complexes (CuL2Hn2+n, n = 2,1 and 0/-1) was detected with {N im}{N im}, {NH 2, N im}{N im} and {NH 2, N -, N im}{N im} type co-ordination modes, respectively. At higher excess of ligand ([L]/[Cu 2+] > 10) and at pH ∼ 7, the predominant species is CuL4H24+. The 1H and 13C relaxation measurements of carcinine solutions (0.6 M) in presence of 0 mM ≤ [Cu 2+] tot ≤ 5 mM at pH = 6.8, allowed us to extract the carbon-to-metal distances, the electronic relaxation and tumbling correlation times, as well as the ligand exchange rate for the species CuL4H24+. According to these results, the metal ion is {4N im} co-ordinated in the equatorial plane, while the neutral amino groups are unbounded. Since naturally occurring carcinine shows in vivo antioxidant property, the SOD-like activity of the copper(II)-carcinine system has also been investigated and the complex CuLH -1 was found to be highly active.

Original languageEnglish
Pages (from-to)1995-2005
Number of pages11
JournalJournal of Inorganic Biochemistry
Volume98
Issue number12
DOIs
Publication statusPublished - Dec 1 2004

ASJC Scopus subject areas

  • Biochemistry
  • Inorganic Chemistry

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