Detailed equilibrium and spectroscopic characterization of the complex formation processes of the nickel binding loop in NiSOD and its related fragments is reported in the slightly acidic–alkaline pH range. The N-terminally free and protected nonapeptides HCDLPCGVY-NH2 (NiSODM 1 ), HCDLACGVY-NH2 (NiSODM 3 ), and Ac-HCDLPCGVY-NH2 (NiSODM 2 ) and the N-terminally shortened analogues HCDL-NH2 and HCA-NH2 were synthesized, and their nickel­(II) complexes were studied by potentiometric and several spectroscopic techniques. EPR spectroscopy was also used to assign the coordinating donor sites after the in situ oxidation of nickel­(II) complexes. The terminal amino groups are the primary metal binding sites for nickel­(II) ion in NiSODM 1 and NiSODM 3 , resulting in the high nickel­(II) binding affinity of this peptide via the formation of a square-planar, (NH2,N–,S–,S–) or (NH2,NImN–,S–) coordinated species in a wide pH range. The latter coordination sphere prevents the formation of the active structure of NiSOD under physiological pH, reflecting the crucial role of proline in nickel­(II) binding. In situ oxidation of the Ni­(II) complexes yielded Ni­(III) transient species in the case of nonapeptides. The square-pyramidal coordination environment with axial imidazole ligation provides the active structure of the oxidized form of NiSOD in the case of N-terminally free peptides. Consequently, these ligands are promising candidates for modeling NiSOD. The acylation of the amino terminus significantly reduces the nickel­(II) binding affinity of the nonapeptide, while the oxidation results in coordination isomers.

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This diagnostic study aims to shed light on the catalytic activity of a library of Cu(ii) based coordination compounds with benzotriazole-based ligands. We report herein the synthesis and characterization of five new coordination compounds formulated as [Cu(L)(MeCN)(CFSO)] (1), [Cu(L)(CFSO)] (2), [Cu(L)(MeCN)(CFSO)]·(CFSO) (3), [Cu(L)(HO)(CFSO)]·(CFSO)·2(MeCO) (4), and [Cu(L)(L)(CFSO)]·4(CFSO)·8(MeCO) (5), derived from similar nitrogen-based ligands. The homogeneous catalytic activity of these compounds along with our previously reported coordination compounds (6-13), derived from similar ligands, is tested against the well-known Cu(i)-catalysed azide-alkyne cycloaddition reaction. The optimal catalyst [Cu(L)(CFSO)] (10) activates the reaction to afford 1,4-disubstituted 1,2,3-triazoles with yields up to 98% and without requiring a reducing agent. Various control experiments are performed to optimize the method and examine parameters such as ligand variation, metal coordination geometry and environment, in order to elucidate the behaviour of the catalytic system.

The prion protein (PrP) is a membrane-anchored cell surface glycoprotein containing 231 amino acids. It has been associated with a group of neurodegenerative disorders. Copper(II) interaction with the Human Prion 103-112 fragment and its mutants has been studied with various techniques. The studied human prion fragment contains both histidine and methionine residues, while methionine residues are systematically replaced or displaced in the studied mutants. pH-potentiometric, UV-Vis and circular dicroism spectroscopic techniques were applied to study the stoichiometry, stability and structure of the copper(II) complexes, while HPLC-MS and MS/MS were used for identifying the products of copper(II) catalyzed oxidation. The complex formation reactions of the studied ligands are rather similar; only 1:1 complexes are formed, where the imidazole nitrogen of the histidine residue is the main binding site beside the amide nitrogens of the peptide chain. The only difference is, that in the peptides which contain methionine in position 109, in addition to the (N,N,N) coordination mode, a weak interaction of thioether sulfur atoms can be supposed. The mutant peptide which does not contain methionine did not undergo oxidation, only the fragmentation of the peptide chain was perceived. However, in the case of methionine containing peptides, the peptide chain was not cleaved; but the oxidation of methionine to methionine sulfoxide occurred.

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The very first Fe(iii)-peptide chelators exhibiting antioxidant properties thanks to an unprecedented dual direct/indirect mode of action.

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The systematic studies of copper(II), nickel(II) and zinc(II) ion complexes of protected multihistidine peptides containing amino acids with different side chains (Ac-SarHAH-NH2, Ac-HADH-NH2, Ac-HDAH-NH2, Ac-HXHYH-NH2 X, Y = A, F, D or K, Ac-HXHAHXH-NH2, X = F or D) have provided information about the metal ion and protein interaction and have made it possible to draw conclusions regarding general trends in the coordination of metal complexes of multihistidine peptides. The stability of the metal complexes significantly depends on the position of the histidines and amino acids, which are present in the neighbourhood of the histidine amino acids as well. The most significant effect was observed on peptides containing aspartic acid or phenylalanine. The redox parameters of complexes, however, depend on the number and position of histidines, and the other side chain donor atoms have practically no effect on the electrochemical properties of imidazole-coordinated species. However, the presence of aspartic acid side chains results in a more distorted geometry of amide-coordinated species and increases the reducibility of these complexes.