Ney V. Vugman

On the pro-oxidant effects of haemozoin

Haemozoin (Hz) is a haem aggregate produced in some blood‐feeding organisms. There is a general belief that Hz formation would be a protective mechanism against haem toxicity. Here we show that when aggregated into Hz, haem is less deleterious than its free form. When haem was added to phosphatidylcholine (PC) liposomes, there was an intense stimulation of oxygen consumption, which did not occur when Hz was incubated with the same preparation. Evaluation of oxygen radical attack to lipids, by measurement of thiobarbituric acid reactive substances (TBARS), showed significantly lower levels of lipid peroxidation in samples containing PC liposomes incubated with Hz than with haem. However, TBARS production induced by Hz was much higher when using 2‐deoxyribose (2‐DR) as substrate, than with PC liposomes. Spin‐trapping analysis by electron paramagnetic resonance (EPR) of Hz and tert‐butylhydroperoxide (tert‐BuOOH) showed that production of methoxyl and tert‐butoxyl radicals was only slightly reduced compared to what was observed with haem. Interestingly, when large Hz crystals were used in 2‐DR TBARS assays and tert‐BuOOH EPR experiments, the pro‐oxidant effects of Hz were strongly reduced. Moreover, increasing concentrations of Hz did not induce erythrocyte lysis, as occurred with haem. Thus, the reduced capacity of Hz to impose radical damage seems to result from steric hindrance of substrates to access the aggregated haem, that becomes less available to participate in redox reactions.

Melanin in Fonsecaea pedrosoi: a trap for oxidative radicals

BackgroundThe pathogenic fungus Fonsecaea pedrosoi constitutively produces the pigment melanin, an important virulence factor in fungi. Melanin is incorporated in the cell wall structure and provides chemical and physical protection for the fungus.We evaluated the production of nitric oxide (NO) in macrophages, the oxidative burst and the inducible nitric oxide synthase (i-NOS) activity in interactions between activated murine macrophages and F. pedrosoi. Experiments were carried out with or without tricyclazole (TC) treatment, a selective inhibitor of the dihydroxynaphthalene (DHN)-melanin biosynthesis pathway in F. pedrosoi. The paramagnetisms of melanin and the TC-melanin were analysed by electron spin resonance. The fungal growth responses to H2O2 and to S-nitroso-N-acetylpenicillamine (SNAP), a nitric oxide donor, were also evaluated.ResultsMelanised F. pedrosoi cells were more resistant to both H2O2 and NO. Nitrite was not detected in the supernatant of macrophages incubated with melanised fungal cells. However, i-NOS expression was unaffected by the presence of either untreated control F. pedrosoi or TC-treated F. pedrosoi. In addition, the inhibition of the DHN-melanin pathway by TC improved the oxidative burst capability of the macrophages.ConclusionThe NO-trapping ability of F. pedrosoi melanin is an important mechanism to escape the oxidative burst of macrophages.

Bonding parameters of vanadyl ion in humic acid from the Jucu river estuarine region, Brazil

Abstract Natural and synthetized complexes of vanadyl ion with humic acid from a sediment of Rio Jucus estuarine region have been studied by electron spin resonance (ESR) spectroscopy. ESR spectra of natural samples show, besides the VO2+ ion in an axially symmetric environment, lines attributed to Mn2+ and Fe3+. Photoacoustic and ESR spectroscopies data and a LCAO-MO ligand field calculation were used to evaluate the bonding parameters for the synthesized vanadyl-humic acid complex. The values of the parameters suggest that VO2+ groups in the humic acid molecules are at salycilate-type sites. A comparison of the position of the lines in the ESR spectra of natural and synthesized complexes suggests that the binding sites for vanadyl ions in the natural complex may also be of the salycilate type.

Solid-state structural studies on amorphous platinum–fullerene[60] compounds [PtnC60] (n=1,2)

Abstract Homoleptic amorphous platinum–fullerene compounds were synthesized from low-valent platinum precursors. Both variation of precursor and temperature of synthesis lead to different phases. Simultaneous observation of symmetric and antisymmetric fullerene vibrational modes in the platinum–fullerene IR and resonant Raman spectra support evidence for dimer and oligomer formations. Doublet splitting of fullerene ( I h point group symmetry) F 1u modes and observation of previously IR silent modes also indicate substantial local disorder at the fullerene moiety. X-band CW-EPR measurements, using the microwave power saturation technique, allows observation of at least two different relaxation behaviours, that are attributed to activation of efficient relaxation pathways in the compounds synthesized at 25°C. These processes are absent in fullerene[60] and much less effective in the platinum compound obtained at −45°C.

The first hetero-binuclear alkoxide of iron and vanadium: structural and spectroscopic features

Abstract The immediate reaction between [V2(μ-OPri)2(OPri)6] (A) and [Fe2(μ-I)2I2(HOPri)4] (B) in toluene/propan-2-ol gives the novel mixed-metal [FeI2(μ-OPri)2V(OPri)2(HOPri)] (C). Structural, spectroscopic and magnetochemical characterisation are all consistent with a non-oxo vanadium(IV)/high-spin iron(II) formulation; variable-temperature X-band EPR spectra reveal an S=1/2↔S=1 equilibrium involving the vanadium centres in propan-2-ol solution.

On the origin of 13C and 14N hyperfine interactions in [Co(CN)6]4− and [Rh(CN)6]4− complexes in KCl host lattice

Abstract Ab-initio ROHF, PUHF and PUHF-MP2 calculations of 13 C and 14 N hyperfine interactions for the [Co(CN)6]4− and [Rh(CN)6]4− complexes in the KCl host lattice were performed and compared to experimental results. The host lattice was represented by a set of 80 potentials located at the ion positions, leading to a consistent picture of the complex electronic structure. A detailed analysis of each molecular orbital contribution shows that collective effects are very important and must be considered to achieve a realistic description of this property.

EPR of palladium(I) and palladium(III) cyanide complexes in NaCl and KCl single crystals

Abstract The EPR spectra of X-ray-irradiated single crystals of NaCl and KCl doped with cyanide complexes of Pd have been studied at 77 K. The measured g and A values indicate the formation of [Pd(CN) 4 Cl 2 ] n− ( n = 3, 5) complexes. Ligand field parameters and spin densities have been estimated for the oxidized d 7 species.

Pseudomonas fluorescens dynamics in the soil surface to subsurface transect.

Microbial displacement in the soil is an important process for bioremediation and dispersal of wastewater pathogens. We evaluated cell movement in surface and subsurface red-yellow podzolic soil driven by advection and microbial motility and also survival of a microbial population at high pressure as is prevalent in deep soil layers. Pseudomonas fluorescens Br 12, resistant to rifampycin and kanamycin, was used as a model organism traceable in non-sterile soil. Our results showed that more than 40% of the P. fluorescens population survived under high pressure, and that microbial motility was not a major factor for its displacement in the soil. Cells were adsorbed in similar amounts to surface and subsurface soils, but more viable cells were present in the leachate of surface than in subsurface soils. The nature of this unexpected cell binding to the subsurface soil was studied by EPR, Mossbauer, NMR, and infrared techniques, suggesting iron had a weak interaction with microbes in soil. P. fluorescens movement in soil resulted mainly from convection forces rather than microbial motility. The transport of this bacterium along the transept toward groundwater encountered restricted viability, although it survived under high pressure conditions simulating those in deep soil layers.

Hyperfine interactions and lattice distortion of the F center in KCl, NaCl and LiCl crystals

Detailed embedded-cluster quantum-chemistry (ROHF, UHF and UMP2) calculations of hyperfine interactions for the F center in KCl, NaCl and LiCl are presented. Our values for the isotropic hyperfine interaction show a good general agreement with experiments. We show that a careful treatment of the lattice environment, local lattice distortion, spin polarization and correlation are important for this good agreement.

Dynamic effects in Ni (III) and Pd (III) cyanides in KCl and NaCl studied by EPR spectroscopy

Abstract The temperature dependence of the spin Hamiltonian parameters for the trivalent nickel and palladium tetracyanides in KCl and NaCl host lattices have been measured by electron paramagnetic resonance spectroscopy in the range 12–300 K and attributed to the effect of localized anharmonic vibration modes. A recently published theory is used to interpret the experimental data.