Alicia Diaz

EPR characterization of mono(thiosemicarbazones) copper(II) complexes. Note II

Copper(II) complexes with thiosemicarbazones have been shown to be more active in cell destruction, in the inhibition of DNA synthesis than the uncomplexed ligand. Several derivatives of thiosemicarbazones and their iron and copper complexes have been studied for their cytotoxicity and inhibiting activity against DNA synthesis. In the present work complexes formed in H2O-DMSO solution between copper(II) and the acetophenone thiosemicarbazone (ATSC) and the o-aminobenzaldehyde thiosemicarbazone (o-NH2TSC) have been studied. EPR studies have been performed at different pH values and metal-to-ligand ratios. The spectra have been recorded at both room (298 K) and low temperatures (120 K). A possible relationship between structure and activity is attempted on the basis of the EPR data.

EPR characterization of a series of mono- and bis-thiosemicarbazone copper(II) complexes

Abstract EPR studies at room and low temperatures of cooper(II) complexes of acetaldehyde thiosemicarbazone (AlTSC), pyruvic acid thiosemicarbazone (PTSC) and ribose bis-thiosemicarbazone (RibTSC) have been undertaken. Computer simulation of the EPR spectra has revealed differences in the magnetic parameters of the compound. Two species with different metal-ligand ratios were found to be present in PTSC. The higher degree of tetrahedral distortion displayed by the two mono-thiosemicarbazones with respect to RibTSC suggests that monothiosemicarbazone copper(II) complexes may be more effective superoxide dismutase-like mimics than bis-thiosemicarbazone complexes are.

Interpretation of the sod-like activity of a series of copper(II) complexes with thiosemicarbazones

Abstract In the present paper we report the SOD-like activity of a series of copper(II) complexes with acetaldehyde, acetophenone, 2-oxo-glutaric acid, methyl-furfural, piruvic acid, salicylaldehyde, 2-acetylpyridine thiosemicarbazones and ribose bis(thiosemicarbazone). The complexes were studied by EPR spectroscopy. A linear correlation between f=g‖/A‖ and the SOD-like activity was observed. The higher f values correspond to copper(II) complexes with enhanced tetrahedral distortion.

Interactions of nitric oxide with copper(II) dithiocarbamates in aqueous solution.

This is the first report on the formation of air-stable copper nitrosyl complexes. The interaction of nitric oxide, NO, with Cu(DTC)(2).3H(2)O (DTC: dithiocarbamate) and was studied in aqueous solution at pH 7.4 and 293 K. The stability constants were determined from UV-Vis data, using LETAGROP program. The high values obtained, log beta(1)=9.743(5) and log beta(2)=15.44(2) for Cu(ProDTC)(2)-NO, (ProDTC=L-prolinedithiocarbamate) and log beta(1)=8.723(5) and log beta(2)=11.45(2) for Cu(MorDTC)(2)-NO system, (MorDTC=morpholyldithiocarbamate), indicate the formation of two stable nitrosyl complexes, Cu(DTC)(2)NO and Cu(DTC)(2)(NO)(2). Coordinated NO is neither affected by the presence of air nor when the solution is purged with Ar. Cu(MorDTC)(2)NO.3H(2)O was isolated in the solid state and its nuNO (IR) band at 1682 cm(-1), but affected by temperature variations over 333 K.

Determination of SOD-Like activity of Copper(II) complexes with α-Amino acid dithiocarbamates

Abstract The SOD-like activity of the copper(II) complexes of five amino acid (Gly, Ala, Ser, Asn, Glu) dithiocarbamates was determined. The concentration of the complexes that inhibit by 50% (IC 50 ) the reduction of nitroblue tetrazolium by superoxide radical (generated by xanthine oxidase) lies between 1.2 μM (Glu) and 20 μM (Gly). Quantitative structure-activity relationships, QSAR, were established between pIC 50 (-log IC 50 ) and the molar refraction values of the amino acid substituents, as well as Cu(I) / Cu(II) oxidation potentials (determined by cyclic voltammetry). The high SOD-like activity of the Glu dithiocarbamate complex is interpreted to be due to its distorted geometry based on EPR spectra and conductimetric titration data.

Antioxidative properties of copper(II) complexes

Eleven copper(II) complexes with amino acids, salicylate, 2, 2′-phenanthroline, ethylenediamine, ethylenediaminetetraacetic acid, dithiocarbamates, and thiosemicarbazones were studied as scavengers of superoxide and hydroxyl radicals. These two radicals exist in biological systems and play an important role in oxidative stress. The complexes with the first three ligands are pro-oxidants. On the contrary, the bis(dithiocarbamato)copper(II) complexes are the most active against the studied radicals. ¶ This article is dedicated to Professor Alfredo Mederos who dedicate his life to develop Chemistry in Canary Islands, Spain.

Synthesis and SOD-Like Activity of Monosaccharide Derived Thiosemicarbazones

Abstract The synthesis of new O-β-D-glucopyranosyl- and O-β-D-galactopyranosyl-2-hydroxyacetaldehyde thiosemicarbazones (5a,b) is reported. Oxidation of allyl glycoside 1 with KMnO4 followed by NaIO4 cleavage of the resulting diol 2 afforded aldehyde 3, which was then condensed with thiosemicarbazide and deprotected to give the target compounds (5a,b). Compounds 5a,b showed hydrolytic stability in neutral solution with half-life periods greater than 70 h. The SOD-mimetic activity was determined for the Cu(II) and Mn(II) complexes of 5a,b (IC50 = 0.2–0.8 mM). This activity is higher by two orders of magnitude than copper (II) bisthiosemicarbazones. The ESR and UV-Vis data of Cu(II)-5a suggest a tetrahedral distortion of the coordination sphere around the central copper atom which could be the reason for their high SOD-mimetic activity.

Electron paramagnetic resonance studies on copper(II)-cyclodextrin systems

Three copper(II) complexes containing beta-cyclodextrin (betaCD) derivatives as ligands [mono-6-methylamino-6-deoxy-betaCD dithiocarbamate (CDTC), mono-6-histamino-6-deoxy-betaCD (CDHM) and mono-6-Nalpha-arginyl-6-deoxy-betaCD (CDARG)] have been studied by electron paramagnetic resonance. The spectra have been recorded at X- and S-bands and different temperatures and simulated to obtain the best set of magnetic parameters. In particular, the 300 K spectra are typical of the slow motion regime, as expected considering the high molecular weight of the ligands. Some structural characteristics of the complexes are proposed on the basis of dynamic and covalency parameters obtained from simulation.

Association Capacity of Ribose Bis(Thiosemicarbazonato)Copper(II) with Nitric Oxide

The stability constant for copper(II) complex with ribose bis(thiosemicarbazone) (log K=18.46±0.15) was determined from UV-Vis data using LETAGROP program. Its interaction with nitric oxide was studied by spectroscopic and electrochemical techniques. This interaction was observed in the UV-Vis spectra as a shoulder around 350 nm and an isosbestic point at 420 nm. The corresponding equilibrium constant was calculated and the obtained value (log K=8.68±0.12), indicates the formation of a stable nitrosyl complex. Copper(II) bis(thiosemicarbazonato) complex was immobilized on a gold electrode, as demonstrated by cyclic voltammetric studies and used for NO recognition. The reduction of NO coordinated to the copper centre was observed at a potential around −700 mV.

Computer-aided electron paramagnetic resonance spectroscopy in the speciation of pH-dependent equilibria for copper {[2,2′-[1-(1-ethoxyethyl)-1,2-ethanediylidene]bis[N,N-dimethylhydrazinecarbothioamidato]](2-)N2,N2′,S,S′} complex

An extensive reinvestigation of EPR spectra of [{2,2′-[1-(1-ethoxyethyl)-1,2-ethanediylidene]bis[N,N-dimethyl-hydrazinecarbothioamidato]}(2-)N2,N2′,S,S′]copper(II)(CuKTSM2) was performed over a large pH range at room temperature. A thorough speciation was possible only by massive use of computer simulation of spectra at room temperature and careful exploration of linewidth details. EPR data vs. pH for CuKTSM2 clearly establishes the existence in solution of two distinguishable forms, at pH = 1.7 and at pH = 6.4. Spin Hamiltonian parameters and the correlation time were precisely discriminated by a new strategy based on computer-aided EPR spectroscopy and the choice of a suitable microwave frequency.