Abstract
Copper(II) complexes of amino acids and peptides containing the chelating bis(imidazolyl) residues have been reviewed. The results reveal that bis(imidazolyl) analogues of these biomolecules are very effective ligands for metal binding. The nitrogen donor atoms of the chelating agent are the major metal binding sites under acidic conditions. In the presence of terminal amino group the multidentate character of the ligands results in the formation of various polynuclear complexes including the ligand and the imidazole bridged dimeric species. The most intriguing feature of the coordination chemistry of these ligands is that the deprotonation of the coordinated imidazole-N(1)H groups results in the appearance of a new chelating site in the molecules. It leads to the formation of stable trinuclear complexes via negatively charged imidazolato bridges.
Highlights
Imidazole nitrogen donor atoms are among the most common metal binding sites in metalloenzymes
Taking into account the fact that the coordination ability of amino acids and peptides is significantly influenced by the presence of the terminal hm’e Sovago et al Bioinorganic Chem&tr), and Applications amino group and the coordinating side chain residues the synthetic analogues of the original biomolecules can be classified into four different categories: N- and C-terminally protected tripeptides with non-coordinating side chains/9/: Ac-ProLeuGIy-BIMA and BIP-IleAlaGly-OEt (Scheme 2), N- and C-terminally protected tripeptides containing histidyl residues in all possible locations/11/: BOCProLeuHis-BIMA, BOC-ProHisGIy-BIMA, BOC-HisLeuGly-BIMA, BIP-HisAlaGly-OEt, BIPIleHisGly-OEt and BIP-IieAlaHis-OMe (Scheme 3), amino acid derivatives of BIMA containing free amino groups/10,14/: GIy-BIMA, Phe-BIMA and HisBIMA (Scheme 4), dipeptide derivatives of BIMA containing free amino terminus /15/: LeuGly-BIMA, GIyLeu-BIMA, PheGIy-BIMA and AlaPro-BIMA (Scheme 5)
The results obtained for the copper(ll) complexes of amino acids and peptides reveal that bis(imidazolyl) analogues of these biomolecules are very effective ligands for metal binding
Summary
Imidazole nitrogen donor atoms are among the most common metal binding sites in metalloenzymes. The metal ion coordination generally takes place via the N(1) or N(3) atoms of imidazole residues as it is represented by a great variety of iron, zinc and copper proteins including myoglobin and other heme proteins, carbonic anhydrase, carboxypeptidase and blue copper proteins. Another group of metalloenzymes, contains the imidazole moiety as a bridging ligand; e.g. in CuZn-superoxide dismutase (CuZnSOD), where both nitrogen atoms of the negatively charged imidazolato residue take part in metal binding. The applications of these experimental techniques are discussed in the original publications/9-15/
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