Daniel Ramírez-Rosales

Electron paramagnetic resonance analyses of biotransformation reactions with cytochrome P-450 immobilized on mesoporous molecular sieves

Mobil Crystalline Material (MCM-41) can be used for the immobilization of enzymes and the investigation of electron transfer in biological systems. Electron transfer between MCM-41 with aluminum (Al-MCM-41) and cytochrome P-450 (CYP2B4) was observed using electron paramagnetic resonance (EPR). When CYP2B4 was immobilized by adsorption, it catalyzed the conversion of aniline to p-aminophenol. The electron transfer was evidenced when the signal with a g value (also called g-factor or spectroscopic manifestation of the magnetic moment) of 1.98 increased at the same time that the signal with a g value 2.24 decreased due to the addition of NADPH to CYP2B4 immobilized on Al-MCM-41, indicating that FeIII was reduced to FeII. Therefore, it is possible that Al-MCM-41 participates in the electron transfer process in biological systems.

In Vitro Effect of H2O2, Some Transition Metals and Hydroxyl Radical Produced Via Fenton and Fenton-Like Reactions, on the Catalytic Activity of AChE and the Hydrolysis of ACh

It is well known that the principal biomolecules involved in Alzheimer’s disease (AD) are acetylcholinesterase (AChE), acetylcholine (ACh) and the amyloid beta peptide of 42 amino acid residues (Aβ42). ACh plays an important role in human memory and learning, but it is susceptible to hydrolysis by AChE, while the aggregation of Aβ42 forms oligomers and fibrils, which form senile plaques in the brain. The Aβ42 oligomers are able to produce hydrogen peroxide (H2O2), which reacts with metals (Fe2+, Cu2+, Cr3+, Zn2+, and Cd2+) present at high concentrations in the brain of AD patients, generating the hydroxyl radical (·OH) via Fenton (FR) and Fenton-like (FLR) reactions. This mechanism generates high levels of free radicals and, hence, oxidative stress, which has been correlated with the generation and progression of AD. Therefore, we have studied in vitro how AChE catalytic activity and ACh levels are affected by the presence of metals (Fe3+, Cu2+, Cr3+, Zn2+, and Cd2+), H2O2 (without Aβ42), and ·OH radicals produced from FR and FLR. The results showed that the H2O2 and the metals do not modify the AChE catalytic activity, but the ·OH radical causes a decrease in it. On the other hand, metals, H2O2 and ·OH radicals, increase the ACh hydrolysis. This finding suggests that when H2O2, the metals and the ·OH radicals are present, both, the AChE catalytic activity and ACh levels diminish. Furthermore, in the future it may be interesting to study whether these effects are observed when H2O2 is produced directly from Aβ42.

Comparison of the effect of chronic cadmium exposure on the antioxidant defense systems of kidney and brain in rat

Abstract Cadmium (Cd2+) produces toxic effects on various tissues as kidney and liver, so several studies have focused to explore the effect produced by different doses and exposure times of this metal. However, little has been reported about the effect that Cd2+ shows in the brain in vivo. Hence, this study aimed at comparing the effect of chronic Cd2+ exposure on antioxidant defense systems of kidney and brain in rats. Six groups of male rats were employed; five were administered for 45 days with different doses of cadmium chloride (0.187, 0.375, 0.562, 0.937 and 1.125 mg/kg; i.p.) and the other was used as control. Free radicals (FRs) were directly quantified by electron paramagnetic resonance (EPR) spectroscopy; malondialdehyde (MDA), reduced glutathione (GSH) and the activity expression of superoxide dismutase (SOD2) and catalase (CAT) were also measured. The EPR results showed that there was no increase in FR content in kidney or brain. MDA and GSH levels increased in kidney but not in the brain. The SOD2 activity was not altered, but its expression decreased in both tissues. On the other hand, CAT activity and expression tended to increase at low doses and decrease at high doses in both tissues. Therefore, these results suggest that there exist compensatory mechanisms in both kidney and brain that are capable of avoiding the toxic effects exerted by Cd2+ at these doses and exposure time.

Spectroscopic studies of novel porphyrin-copper(II) and zinc(II) complexes that share the pinch-porphyrin family structure of iron(III) complex models of peroxidases

Six novel pinch-porphyrin complexes [(picdien)(protoporphyrinate dimethyl ester)]copper(II) (7), [(picdien)(mesoporphyrinate dimethyl ester)]copper(II) (8) and [(picdien)(deuteroporphyrinate dimethyl ester)]copper(II) (9), [(picdien)(protoporphyrinate dimethyl ester)]zinc(II) (13), [(picdien)(mesoporphyrinate dimethyl ester)]zinc(II) (14) and [(picdien)(deuteroporphyrinate dimethyl ester)]zinc(II) (15), were prepared from the corresponding free copper(II)-porphyrins (4–6), and zinc(II)-porphyrins (10–12) and picdien (N-(3H-imidazol-4-ylmethyl)-N′-{2-[(3H-imidazol-4-ylmethyl)-amino]-ethyl}-ethane-2,3-diamine). Spectroscopic studies show that complexes (7–9) and (13–15) have the pinch-porphyrin type structure previously found in iron(III) complex models of peroxidases. Complexes (7–9), were characterized by u.v.–vis., m.c.d., and e.s.r. spectroscopy. E.s.r. spectra of the copper parent compounds (4–6) at ca. 10−2–10−4 M concentrations were typical of copper(II)-dimers. The addition of the picdien ligand broke up the dimers as detected by e.s.r. Compounds (7–9) are predominantly monomeric at ca. 10−3 M concentration. The presence of picdien in (7–9) distorts the porphyrin internal portion of the plane so as to make these four internal nitrogen atoms, coordinated to copper(II), e.s.r.-distinguishable. MO and ligand field theories were used to characterize and to evaluate the directional covalence parameters of compounds (7–9). A non-fully axial, out-of-the-porphyrin-plane bonding was found for (7–9), similar to the bonding of the pinch-porphyrins-iron(III). However the in-plane distortion produced by the presence of the picdien ligand on copper(II) is significantly larger than in pinch-porphyrin-iron(III). The n.m.r. data show that the porphyrin-zinc(II) is the less strained and has the weakest bonded structure. The coordination number of the pinch-porphyrin with iron(III), copper(II) and zinc(II), is in all cases six.

Crystal structure, spectroscopy and ferromagnetostructural behavior of the complex [CuII(L)(Cl)(L´)]•H2O (L = 2-aminomethylbenzimidazole, L´= L-isoleucinate)

Cu(L)(Cl)(L ́)]·H2O 1 (L = 2-aminomethylbenzimidazole, L ́ = L-isoleucinate) compound crystallizes in the orthorhombic space group P212121. A short Cu—O...Cu contact is observed between neighboring molecules in the crystal structure, with a O...Cu separation of 4.214(3) Ǻ. Molecular structure of 1 shows that L and L ́ act as bidentate ligands, forming the base of the square pyramidal geometry environment of the Cu ion, while the chloro is the fifth apical ligand. UV/VIS spectrum of 1 shows d-d transitions with λmax = 603 nm, characteristic of a low symmetry. Far IR spectrum shows νCu-N at 493, 404 cm, νCu-O at 446 cm, and at 302 cm νCuCl. ESR X-band of polycrystalline 1 at 77, 300 K show axial spectra with the ratio A77/A300 = 4.51, and a linewidth increase by 14.5 % on going from 300 K to 77 K, suggesting a incipient ferromagnetic exchange interaction. ESR axial spectrum of 1 in solution shows abundant hfs and shfc interactions. Susceptibility vs Temperature data measured from 2-300 K range, show that the magnetic ordering may be due to Cu ions linking by oxygen bridges given place to a weak ferromagnetic interaction. The very weak exchange interaction, J = 0.103 cm, is in agreement with the ESR spectra results and with a Cu—O...Cu direct interaction. Issue in Honor of Prof Rosalinda Contreras Theurel ARKIVOC 2008 (v) 31-42 ISSN 1424-6376 Page 32 ARKAT USA, Inc.