Eduardo Muñoz

Captopril does not scavenge superoxide: captopril prevents O2-. production by chelating copper.

The purpose of this study was to use a direct method, that of electron spin resonance spectroscopy, to evaluate the ability of captopril, an angiotensin-converting enzyme inhibitor, to prevent the superoxide-mediated formation of phenyl radicals. Results indicate that, under certain conditions, captopril is a potent inhibitor of the generation of phenyl radicals, produced by the autoxidation of phenylhydrazine. The inhibitory effect of captopril, however, was better understood as a direct interaction of the drug with the metals that catalyze the autoxidation process rather than as a reaction of captopril with the free radicals generated. This last conclusion was supported by the finding that captopril was not able to inhibit the superoxide anion-mediated reduction of nitroblue tetrazolium.

Dehydroxylation and the Crystalline Phases in Sol-Gel Zirconia

The formation and evolution with temperature of the crystalline phases in sol-gel ZrO2 was analyzed by using X-ray powder diffraction, refinement of the crystalline structures, ESR, and UV-Vis spectroscopy. The precursor phase of crystalline zirconia was amorphous Zr(OH)4 with the same local order as the tetragonal crystalline phase. This amorphous phase dehydroxylated with temperature, generating nanocrystalline tetragonal zirconia, and producing point defects that stabilized the tetragonal structure, generated a paramagetic ESR signal with g values like the free electron, and had a light absorption band at 310 nm. When the sample was annealed at higher temperatures, it continued dehydroxilating, and the point defects disappeared, causing the transformation of the nanocrystalline tetragonal phase into nanocrystalline monoclinic zirconia. The two crystalline nanophases coexisted since the beginning of crystallization.

Study of the interaction of cadmium with membrane-bound succinate dehydrogenase

Cadmium ions inhibit membrane-bound succinate dehydrogenase with a second-order rate constant of 10.42 mM−1s−1 at pH 7.35 and 25°C. Succinate and malonate protect the enzyme against cadmium ion inhibition. The protection pattern exerted by succinate and malonate suggests that the group modified by cadmium is located at the active site. The pH curve of inactivation by Cd2+ indicates the involvement of an amino acid residue with pKa of 7.23.

Coke formation on an industrial reforming Pt–Sn/γ‐Al2O3 catalyst

The characterization of the coke deposited on an industrial Pt–Sn/γ‐Al2O3 catalyst, used in a continuous reforming process, was performed with AFM, XRD, FTIR, EPR, NMR, TG‐DTG and DTA techniques. Composition, structure and location of the coke on the catalyst were investigated. The coke was predominantly deposited on the catalyst surface and in the interstices between the catalyst particles. Its content increased along the reactor from top to bottom. Coke was deposited in the form of uniform films and clusters of three‐dimensional disks with diameters between 0.12 and 0.18 μm. It had a pseudo‐graphite structure produced by the dehydrogenation and polymerization of the aromatic precursor compounds. The coked catalyst showed a good combustion behavior; it was regenerated below 550°C. These results are important to elucidate the coke formation mechanism, to generate new continuous reforming catalysts, and to optimize the reactor operation parameters.

Construction of acetate-bridged dicopper(II) hybrid organic–inorganic networks with calix[4]arene-derived nitrogenous ligands

The reactions of mono-, bis- and tetrapicolyl-p-tert-butylcalix[4]arene derivatives functionalised in the phenolic positions (L 1 –L 4 ) with copper(II) acetate resulted in the formation of discrete complexes or extended coordination polymers. The centrosymmetric dimer [Cu2(μ-O2CCH3)4(L 1 )2] 1, obtained with monodentate L 1 , has square pyramidal coordination around the copper centres and a cone conformer of monopicolyl-calix[4]arene acting as an axial ligand, with a molecule of acetonitrile hosted within its cavity. The potentially bidentate L 2 acts as a monodentate ligand, affording the complex [Cu2(μ-O2CCH3)4(L 2 )2] 2, which based on spectroscopic and combustion analysis data has a similar coordination sphere around Cu(II). Compound L 3 bridges two dicopper units in the coordination polymer [Cu2(μ-O2CCH3)4(μ-L 3 )] n 3, with the calixarene hosting a molecule of tetrahydrofuran. Finally, compound L 4 reacts with 4 equivalents of copper(II) acetate, presumably generating a two-dimensional coordination polymer formulated as [{Cu2(μ-O2CCH3)4}2(L 4 )] 4.

Polymerization of Diphenylbutadiyne by Gamma Rays Irradiation in the Molten State

Diphenylbutadiyne was irradiated with Gamma ray in the molten state (90°C), and its polymerization process was studied. The amorphous product has a number average molecular weight of around 1300. The yield reached around 20% with a dose of 3000 kGy, which is far greater than that in the case of irradiation in the solid state at room temperature. From the number of spins and molecular weights the product is thought to be mainly composed of cyclic oligomers. The third order nonlinear optical susceptibility of the products was found to be 3–6 × 10−10 esu determined by the Z-scan technique.

Thermal Reactions of Aromatic Diacetylenes: An Insight to Amorphous State Polymerization of Diacetylenes

Several aromatic diacetylenes were heated in molten state, and the formation of diradicals was studied by ESR spectroscopy. Intense ESR signals were observed even at temperatures as high as 180°C. The formation of radical species at such low temperatures was explained by the formation of oligomeric species. The numbers of unpaired electrons in the molten state reached to 1021 electrons per mole of diacetylene, when heated to 180°C, and deep red materials were obtained. Surprisingly the radicals did not disappear when exposed to air showing that the radicals are stable in air.

Correlation of ESR with lyoluminescence dosimetry using some sugars

Abstract Most applications involving ESR dosimetry currently center on aminoacids because of their relative tissue equivalence. Sugars, however, in addition to possessing high sensitivity and stability in their ESR and LL responses, are widely available as chemical reagents and as commercial sugar. In the present study, dosimetric characteristics of mannose, trehalose, sucrose and commercial sugar obtained by means of ESR and LL techniques are reported. Doses measured by both methods showed agreement within 5%.

Study of a Fenton type reaction: effect of captopril and chelating reagents.

The purpose of this study was to determine if captopril, an angiotensin-converting enzyme inhibitor, could interact with iron ions and so modify a Fenton type reaction. Results indicate that different degrees of thiobarbituric acid-reactive substance from deoxyribose are obtained in an ascorbate-driven Fenton system depending on the order of addition of captopril and iron to the incubation medium. Similar results were obtained with the chelating reagents ethylenediaminetetraacetic acid and diethylenetriaminepentaacetic acid, indicating that the buffer solution plays a relevant role when a particular iron complex is formed with a chelating agent. These metal complexes produce oxidizing species in a Fenton type system whose nature is discussed.

Hydrolysis, Condensation, and Tetragonal Phase Formation in Sol-Gel Zirconia Prepared with Electron-Irradiated Alkoxide Solutions

Sol-gel zirconia precursor, zirconium n-butoxide in ter-butanol, was irradiated with 1.3 MeV electrons to a dose of 330 KGy. Gelling was instantaneously produced when an aqueous solution of sulfuric, hydrochloric or acetic acid was added to the irradiated solution; no hydrolysis catalyst was required. Samples were characterized with X-ray powder diffraction, infrared spectroscopy, and electron paramagnetic resonance. The electron irradiation accelerated hydrolysis and condensation, which avoided the stabilization of the tetragonal phase via carboxyls, and decreased the capability of sulfate ions to stabilize it. These results suggest that the stabilization of the tetragonal phase of sol-gel zirconia via carboxyl and sulfate ions depends on their diffusion in the sol.