New insights on the mechanism of oxidation of D-galacturonic acid by hypervalent chromium.

The pollutant Cr(VI) is known to be very carcinogenic. In conditions of excess of Cr(VI), oxidation of D-galacturonic acid (Galur), the major metabolite of pectin, yields d-galactaric acid (Galar) and Cr(III). The redox reaction takes place through a multistep mechanism involving formation of intermediate Cr(II/IV) and Cr(V) species. The mechanism combines one- and two-electron pathways for the reduction of Cr(IV) by the organic substrate: Cr(VI)→ Cr(IV)→ Cr(II) and Cr(VI)→ Cr(IV)→ Cr(III). This is supported by the observation of the optical absorption spectra of Cr(VI) esters, free radicals, CrO(2)(2+) (superoxoCr(III) ion) and oxo-Cr(V) complexes. Cr(IV) cannot be directly detected; however, formation of CrO(2)(2+) provides indirect evidence for the intermediacy of Cr(II/IV). Cr(IV) reacts with Galur much faster than Cr(V) and Cr(VI) do. The analysis of the reaction kinetics via optical absorption spectroscopy shows that the Cr(IV)-Galur reaction rate inversely depends on [H(+)]. Nevertheless, high [H(+)] still does not facilitate accumulation of Cr(IV) in the Cr(VI)-Galur mixture. Cr(VI) and the intermediate Cr(V) react with Galur at comparable rates; therefore the build-up and decay of Cr(V) accompany the decay of Cr(VI). The complete rate laws for the Cr(VI), Cr(V) and Cr(IV)-Galur redox reaction are here derived in detail. Furthermore, the nature of the five-co-ordinated oxo-Cr(V) bischelate complexes formed in Cr(VI)-Galur mixtures at pH 1-5 is investigated using continuous-wave and pulsed electron paramagnetic resonance (EPR) and density functional theory (DFT).

Inhibition of superoxide dismutase from Ascaris suum by benzimidazoles and synthesized pyrimidine and glycine derivatives.

Copper-zinc superoxide dismutase was purified from Ascaris suum (Nematoda). Four benzimidazole derivatives, six recently synthesized pyrimidine derivatives and eleven recently synthesized glycine derivatives were shown to inhibit: (1) purified extracts of A. suum superoxide dismutase; (2) superoxide dismutase from host liver, and (3) purified extracts of superoxide dismutase from living A. suum incubated in the presence of these drugs. Thiabendazole compounds, with a documented effect against helminth parasites, were found to affect the superoxide dismutase. The inhibitory effects of some pyrimidine and glycine derivatives were higher than those of benzimidazoles, and the pyrimidine compounds failed to inhibit the host's enzyme. These derivatives are candidate anthelmintics, acting as inhibitors of certain metalloenzymes in parasites.

Palladium, platinum, cadmium, and mercury complexes with neutral isoorotic and 2-thioisoorotic acids: IR and NMR spectroscopies, thermal behavior and biological properties.

Seven complexes containing neutral isoorotic and 2-thioisoorotic acids, as well as thiocyanate and chloride anions as lignands, have been synthesized and characterized by means of both spectral (IR, 1H, and 13C NMR) and thermal (TG and DSC) methods, as well as conductivity measurements. Spectral data suggest that any binding metal-ligand mode for uracil derivatives is not easy to propose. Therefore, isoorotic ligands must link through some oxygen atom. Likewise, 2-thioisoorotic acid seems to be [N,S] bonded in Pd(II) and Pt(IV) complexes, whereas for Hg(II) complex a distorted tetrahedral HgCl2S2 structure has been proposed. In the cadmium complex, the metal ion exhibits a CdCl2O2 coordination sphere. Antimicrobial activities of the complexes against Pseudomonas sp, E. coli, Proteus sp, Salmonella sp, Micrococcus sp, Staphylococcus sp, Bacillus sp and Candida sp were performed as a previous step in the study of their biological activity.

Cu-Zn-superoxide dismutase activity in Moniezia expansa: inhibition by pyrimidine derivatives.

Copper-zinc, cyanide-sensitive superoxide dismutase (Cu-Zn-SOD) was detected in homogenates of Moniezia expansa. The enzyme was purified by a sequence of multiple differential centrifugations, ammonium sulphate precipitation, ion-exchange and G-75 Sephadex column chromatography. The final enzyme preparation had a specific activity of 623.00 +/- 9.97U per mg protein and, after isolation, a single-staining band on acrylamide-SDS gels was detected which coincided with enzyme activity. The inhibitory activities of several benzimidazoles and several novel pyrimidine derivatives were determined on purified extracts of the M. expansa Cu-Zn-SOD. The results indicated that the percentage inhibition of Cu-Zn-SOD by some pyrimidine derivatives (6-amino-1, 3-dimethyl-5-nitroso-uracil, 6-amino-5-methyl-5-nitroso-uracil and 5-amino-uracil) was markedly higher than inhibition with the benzimidazoles.

Malate dehydrogenase in helminth parasites. Inhibition by benzimidazoles and pyrimidine derivatives.

A study was performed of the activities of both cytoplasmic and mitochondrial, malate dehydrogenase (MDH) (E.C.1.1.1.37) in purified extracts of whole specimens of male and female nematodes of four species: T. canis, T. cati, T. leonina and A. suum (and tissues), two trematodes: F. hepatica and D. dendriticum, and four cestodes: M. expansa, M. benedeni, D. caninum and T. hydatigena. The results show that there exist species and sexual differences in the enzyme activities of both enzymes. The relative importance of this energy pathways of these helminth species is discussed. Determinations were made of the in vitro inhibitory activities of four benzimidazoles and six synthesised pyrimidine derivatives on MDH (soluble and mitochondrial) from helminth parasites. Several pyrimidine derivatives (6-amino-5-methyl-5-nitro-uracil, 4-amino-1-methyl-2-methylthio-5-nitro-6-oxo-1,2,3,4-tetrahydropyrimid ine and 4-amino-2-methylthio-5-nitro-6-oxo-1,2,3,4-tetrahidropyrimidine) produced double percent in vitro inhibitions of those shown by the benzimidazoles.

Superoxide dismutase in trematodes. Isoenzymatic characterization and studies of inhibition by a series of benzimidazoles and by pyrimidines of recent syntheses.

A comparative study was carried out of superoxide dismutase (E.C.1.15.1.1) (SOD) and catalase activities in purified extracts of two trematodes: Fasciola hepatica and Dicrocoelium dendriticum. The superoxide dismutase activity was very similar to that measured in other eukaryotic cells. As no catalase activity was detected, the possibility that SOD in these trematodes might have the particular importance of removing superoxide radicals is discussed. The SOD isoenzymes of each species were analysed by polyacrylamide gel electrophoresis and the patterns revealed a quantitative difference in the number of isoenzyme bands: F. hepatica showed three, and D. dendriticum only two. Determinations were made of the in vitro inhibitory activities of four benzimidazoles and six synthesised pyrimidine derivatives on SOD from trematodes. The present results confirm that the percentage inhibitions of the pyrimidine derivatives are markedly superior to those produced by the benzimidazoles.