Activation of hydrogen peroxide by copper (II) complexes with some histidine-containing peptides and their SOD-like activities

Cu(II) complexes with peptides from FomA protein containing -His-Xaa-Yaa-Zaa-His and -His-His-motifs. ROS generation and DNA degradation

Mono- and dinuclear Cu(II) complexes with Ac-PTVHNEYH-NH₂ (L1) and Ac-NHHTLND-NH₂ (L2) peptides from FomA protein of Fusobacterium nucleatum were studied by potentiometry, spectroscopic methods (UV-Vis, CD, EPR) and MS technique. The dominant mononuclear complexes for L1 ligand are: CuHL (pH range 5.0-6.0) with 2N {2N_im}, CuH_-2L (pH range 8.0-8.5) and CuH_-3L species (above pH 9.0) with 4N {N_im, 3N^-} coordination modes. The complexes: CuH_-1L with 3N {2N_im, N^-}, CuH_-2L with 3N {N_im, 2N^-} and CuH_-3L with 4N {N_im, 3N^-} binding sites are proposed for the L2 ligand. Probably in the CuH_-2L complex for CuL2 system the second His residue in His-His sequence is bound to Cu(II) ion, while the first His residue may stabilize this complex by His-His and/or His-Cu(II) interactions. The dominant dinuclear Cu₂L1 complexes in the pH range 6.5-10.5 are: the Cu₂H_-4L and Cu₂H_-6L species with 3N{N_im, 2N^-}4N{N_im, 3N^-} and 4N{N_im, 3N^-}4N{N_im, 3N^-} binding sites, respectively. In the case of the Cu₂L2 complex in the pH range 7.2-10.5, the Cu₂H_-4L and Cu₂H_-7L species dominate with 2N{N_im, N^-}4N{N_im, 3N^-} and (Cu(OH)₄^2-4N{N_im, 3N^-}) coordination modes, respectively. The ability to generate reactive oxygen species (ROS) by uncomplexed Cu(II) ions, ligands and their complexes at pH 7.4 in the presence of hydrogen peroxide or ascorbic acid was studied. UV-Vis, luminescence, EPR spin trapping and gel electrophoresis methods were used. Both complexes produce higher level of ROS compared to those of their ligands. ROS produced by Cu(II) complexes are hydroxyl radical and singlet oxygen, which contribute to oxidative DNA cleavage.

Chemical synthesis of chitosan-mimetic polymers via ring-opening metathesis polymerization and their applications in Cu2+ adsorption and catalytic decomposition

Aiming at solving the uncontrollability in the properties of chitosan, we synthesized two chitosan-mimetic polymers, the homopolymer mimic PHNI and the copolymer mimic PHNI-PHNIA, by ring-opening metathesis polymerization (ROMP).

Tyrosinase mediated oxidative functionalization in the synthesis of DOPA-derived peptidomimetics with anti-Parkinson activity

DOPA-derived peptidomimetics are an attractive therapeutic tool for the treatment of Parkinson's disease.

Synthesis and antioxidant activity of DOPA peptidomimetics by a novel IBX mediated aromatic oxidative functionalization

DOPA peptidomimetics with stable O–C and N–C covalent bonds between amino acid residues have been prepared by aromatic oxidative functionalization of tyrosine with 2-iodoxybenzoic acid (IBX).

DNA-fiber EPR spectroscopy as a tool to study DNA-metal complex interactions: DNA binding of hydrated Cu(II) ions and Cu(II) complexes of amino acids and peptides

DNA-fiber EPR spectroscopy and its application to studies of the DNA binding orientation and dynamic properties of Cu(II) ions and their complexes with amino acids and peptides are reviewed. Cu(II) ions bind in at least two different binding modes; one mode was mobile while the other mode fixed the orientation of the coordination plane. The hydroxyl groups of L-Ser and L-Thr fixed the coordination plane of their respective Cu(II) complexes parallel to the DNA base pair plane, whereas Cu(II) complexes of Lys and Arg induced several binding modes, depending on the tertiary structure of the DNA and the chirality of the amino acids. Unusually broadened signals observed for the His complex were assigned to a mono-L-His complex stacked stereospecifically along the DNA double helix. In comparison, Cu(II). Xaa-Xaa' -His type complexes oriented in the minor groove with different affinities and extents of randomness depending on the Xaa-Xaa' sequence and the chirality of Xaa or Xaa' while the C-terminal Xaa residues in Cu(II).Arg-Gly-His-Xaa (Xaa=L-Leu or L-Glu) decreased the stereospecificity and the stability of the complexes bound to DNA. In contrast to Xaa-Xaa'- His complexes, the coordination planes of Cu(II).Gly-L-His-Gly and Cu(II).Gly-L-His-L-Lys complexes were found to lie parallel to the DNA-fiber axis. Dinuclear Cu(II).carnosine complexes were also shown to bind to DNA stereospecifically.

New copper-based complexes with quinoxaline N1,N4-dioxide derivatives, potential antitumoral agents

Taking into account our previous studies on cytotoxic metal compounds, new copper complexes with 3-aminoquinoxaline-2-carbonitrile N1,N4-dioxide derivatives as ligands were synthesized and characterized by different spectroscopic methods. The hypoxic selective cytotoxicity towards V79 cells and the superoxide dismutase-like activity of the complexes were determined and related to physicochemical properties of the compounds. In particular, the copper(II) complex with 3-amino-6-chloro-7-fluoroquinoxaline-2-carbonitrile N1,N4-dioxide showed cytotoxic selectivity in hypoxia being the most lipophilic compound of the series. On the contrary, the complex with 3-aminoquinoxaline-2-carbonitrile N1,N4-dioxide was cytotoxic but not selective and that with 3-amino-7-chloro-6-methoxy-quinoxaline-2-carbonitrile N1,N4-dioxide was not cytotoxic towards V79 cells neither in oxia nor in hypoxia in the assayed conditions. The sigmam Hammett substituent electronic descriptor was related to the effect in hypoxic conditions and the SOD-like activity was correlated to the effect in normoxia.

Body- or tip-controlled reactivity of gold nanorods and their conversion to particles through other anisotropic structures

We report the shape transformation of gold nanorods to spherical nanoparticles, assisted by cupric ions. The reaction proceeds through a series of structures and could be arrested at any stage to produce particles of desired shape. In the presence of a larger concentration of cetyltrimethylammonium bromide (CTAB), selective etching of the tips of the nanorods occurs to a greater extent. The subsequent transformation is driven by the surface reconstruction of nanorods to generate more stable surfaces. As the stability of various surfaces depends on the protecting agent used, the reactivity is modified by controlling its presence at the surface. We show that the body of the rods is more susceptible for reaction at reduced CTAB concentrations. During the conversion to particles, several anisotropic transient structures were observed and were imaged using high-resolution transmission electron microscopy (HRTEM). The transformation occurs due to the hydroxyl radicals produced by Cu2+ in the presence of ascorbic acid (AA). A mechanism has been proposed and several control experiments were conducted to test it. The cupric ion induced shape transformations can be extended to other ions, and knowing the mechanism allows the control of the process to stabilize various anisotropic structures.

Extended polymorphism in copper(II) imidazolate polymers: a spectroscopic and XRPD structural study

Copper(II) bisimidazolate affords five different polymorphs; of these, one was structurally characterized 40 years ago by standard single-crystal X-ray diffraction (Jarvis, J. A. J.; Wells, A. F. Acta Crystallogr. 1960, 13, 1027), while the remaining four, selectively prepared as pure polycrystalline phases, have been now studied by X-ray powder diffraction (XRPD) methods. Of the four new (blue, green, olive-green, and pink) phases, three were solved by the ab initio XRPD technique and refined by the Rietveld method, and the fourth phase (pink) could not be structurally characterized. Crystal data for [Cu(imidazolate)(2)](n): blue phase, a = 27.559(3) A, c = 5.3870(9) A, trigonal, R3 macro, Z = 54; green phase, a = 21.139(1) A, b = 19.080(1) A, c = 9.2842(8) A, orthorhombic, Ccca, Z = 20; olive-green phase, a = 11.7556(8) A, b = 23.422(2) A, c = 9.0727(9) A, beta = 104.993(5) degrees, monoclinic, C2/c, Z = 12. All polymorphs contain four-coordinate CuN(4) chromophores and (N,N')-exobidentate imidazolate ligands, but show different spectroscopic and structural properties, the latter ranging from 2D to different 3D networks of the PtS, sodalite, and moganite archetypes. The intermediacy of the [Cu(imidazole)(2)CO(3)]-H(2)O species in the synthesis of the blue polymorph has been confirmed by spectroscopic and thermal analyses. FTIR, Raman, and electronic spectra were correlated with the structural features revealed in the present work, and used to gain insight into the coordination geometry of copper(II) ions of the pink polymorph. In addition, the correct Raman spectrum for copper(II) bisimidazolate, common for all polymorphs, has been definitely determined.

How amino acids control the binding of Cu(II) ions to DNA. Part III. A novel interaction of a histidine complex with DNA

L-Histidine Cu(II) complex bound to DNA showed broad EPR signals characteristic of the aggregated Cu(II) species, which could be observed even when the molar ratio of L-histidine to Cu(II) ion was smaller than unity. The signal for the DNA fibers changed with the orientation of the fibers in the static magnetic field. Based on these results, the signal was assigned to a mono-histidine Cu(II) complex stereospecifically aggregated in a groove or along a phosphodiester chain of the double helical DNA. In contrast to the L-histidine complex, the D-histidine complex bound to DNA did not show such broad signals and the observed spectra for the complex on B-form DNA fibers at -150 degrees C were simulated assuming that the g1 axis of the mono-D-histidine complex tilts by about 55 degrees from the DNA-fiber axis. Addition of some deoxy-nucleotides, but not deoxy-nucleosides, to a solution of a mono-histidine complex resulted in the formation of a dinuclear ternary complex with different structures for L- or D-histidine, suggesting the possibility that the stereospecific aggregation of the L-histidine complex on a double helical DNA was mediated by the phosphodiester backbones.

Models for superoxide dismutases: characterization of mononuclear Cu(II), Fe(III), and Mn(II) complexes with 4',5'-bis(salicylideneimino)benzo-15-crown-5

Mononuclear Cu(II), Fe(III), and Mn(II) complexes with 4',5'-bis (salicylideneimino)benzo-15-crown-5, (SALH2), were characterized by elemental analysis, IR and UV-Vis spectroscopy and tested spectrometrically as catalysts for superoxide disproportionation by utilizing xanthine-xanthine oxidase (XXO) assays. The results indicate that the examined mononuclear complexes are speculative potent superoxide dismutase mimics.

Structural and biological aspects of copper (II) complexes with 2-methyl-3-amino-(3H)-quinazolin-4-one

A series of new copper (II) complexes with 2-methyl-3-amino(3H)-quinazolin-4-one (MAQ) and various anions (Cl-, Br-, ClO(-)4, NO(-)3, SCN-, and SO(2-)4 was prepared. Their structures and properties were characterized by elemental analysis, IR, UV-Vis and ESR spectroscopy, molar conductivity, and magnetic moment measurements. The square-planar complex was only obtained in the presence of perchlorate anion, whereas the five coordinate species, which have a square-pyramidal structure, were obtained for chloro and bromo complexes. In the case of hexa coordinate complexes, in which nitrate, sulphate, or thiocyanate is attached to a copper(II) ion in a 1:2 (metal:ligand) ratio, a distorted octahedral geometry around copper(II) is proposed. The antimicrobial activity of the free ligand and its copper(II) complexes clearly illustrates that the compounds have both an antibacterial and antifungal potency against the organisms tested. In most cases, the complexes were found to be more active than the free ligand, but in some cases, an equal activity was displayed. To further elucidate the biological activity of the complexes, their activities towards active oxygen species, such as H2O2 and O(-)2, were investigated. A probable mechanism for the cytotoxic reaction with the different organisms is proposed.

Study of H2O2 interaction with copper(II) complexes with diamino-diamide type ligands, diastereoisomeric dipeptides, and tripeptides

Copper(II) complexes with LL or LD dipeptides, tripeptides, L-aminoacylamides, or N,N'-bis(aminoacyl)alcanediamine were studied in their reaction with hydrogen peroxide by ESR spectroscopy. Shifts in the magnetic parameters g parallel and A parallel or differences in the quenching percentages of the ESR signal intensity, due to the formation of copper(I) species, suggested that the decomposition mechanism of H2O2 proceeds through the formation of a five-coordinated adduct and a subsequent electron transfer. This last process gave rise to a decomposition process which involved not only H2O2, but also the ligand coordinated to copper. It was surprising to find that, at the longest interaction time, this decomposition reaction always produced a similar copper(II) complex with g = 2.330 +/- 0.005 and A = 164 +/- 4 x 10(-4) cm-1 in spite of the different ligands. Voltammetric measurements confirmed what had been seen by ESR spectroscopy, and suggested that the decomposition mechanism did not involve the formation of copper(III) species. Furthermore, the only copper(II) complex with diastereoisomeric dipeptides, which was able to promote the copper oxidation, was that formed by LL- or LD- Ala-Trp, thus suggesting that d-pi interaction plays a favorable role in the oxidation process. The complexes which showed catalytic activity in the hydrogen peroxide decomposition were those obtained from LL- or LD- Ala-Ala or Ala-Leu, i.e., copper(II) complexes with dipeptides having aliphatic side chains. This fact strongly supports the hypothesis of the formation of a ligand radical species due to the breakage of the weak copper(I)-peptide nitrogen bond, radical starting the degradation of the ligand itself.

Reactions of copper(II)-oligopeptide complexes with hydrogen peroxide: effects of biological reductants

Cu(II) complexes with oligopeptides containing histidyl residue in the second or third position could scarcely activate hydrogen peroxide (H2O2), but they could activate H2O2 to yield hydroxyl radical (.OH) in the presence of biological reductants such as cysteine and ascorbic acid. Further, DNA single strand breakage was also observed during the reactions of Cu(II)-glycylglycylhistidylglycine (GGHG) with H2O2 in the presence of same biological reductants.