Decoding Aging: Understanding the Complex Relationship among Aging, Free Radicals, and GSH.

N-aryl maleimides can undergo a 1,4-Michael-type addition reaction with reduced glutathione (GSH), leading to a decreased concentration of GSH and an increased concentration of free radicals (FRs) in cells. GSH is a critical scavenging molecule responsible for protecting cells from oxidation and for maintaining redox homeostasis. N-aryl maleimides disturb redox homeostasis in cells because they scavenge thiol-containing molecules, especially GSH. This study aimed at measuring the concentrations of GSH and FRs by electronic paramagnetic resonance (EPR), in the brain and liver tissue of male Wistar rats (ex vivo) at different ages and after treatment with 3,5-dimaleimylbenzoic acid (3,5-DMB). Our results showed a relationship between age and the concentrations of GSH and FRs in cells. In young rats, the concentration of GSH was higher than in old rats, while the concentration of FRs was higher in adult rats than in young rats, suggesting an inverse relationship between GSH and FRs. On the other hand, the reaction of 3,5-DMB (an electrophilic maleimide) with cellular GSH increased the FR content. The results of this study contribute to the awareness that the process of aging implies not only a loss of tissue function but also essential changes in the molecular contents of cells, especially the concentrations of FRs and GSH.

CuICuII and AgIp-isocyanobenzoates as novel 1D semiconducting coordination oligomers.

Two novel semiconducting coordination oligomers with 1D chain structures, namely [H0.07 CuI0.65CuII0.14(µ-p-CNC6H4CO2)·0.9H2O]n and [Ag(µ-p-CNC6H4CO2)]n, were obtained and characterized by XRD powder patterns, and XPS, EPR, UV-vis-NIR, IR and Raman spectroscopy. According to XRD analysis, CuICuII-ICNBA is an amorphous solid, while AgI-ICNBA crystalizes with a monoclinic unit cell in the C2/c space group (Z = 4). The composition and further information of CuICuII-ICNBA were obtained from the spectroscopic data. In correspondence with the quantification of terminal groups from high-resolution XPS spectra, CuICuII-ICNBA and AgI-ICNBA are composed of an average of 9 and 7 monomer units, respectively, resulting in 1D-oligomers. The spectroscopic evidence indicates that CuICuII-ICNBA is better described as a non-stoichiometric coordination oligomer (where non-integer ratios of metal ions can be accommodated), while AgI-ICNBA is stoichiometric. In both materials, each metal center is linked by two µ-η1:η1-p-isocyanobenzoate ligands forming microfibers of around 120 nm (CuICuII-material) and 310 nm (AgI-material) in average diameters with optical band gaps of 2.60 eV and 2.17 eV, respectively.

Synthesis, Kinetic Study, and Spectroscopic Analysis of Peroxidase-like Pinch-Porphyrin Fe(III) Complexes.

In the present manuscript, we report the kinetic and spectroscopic analysis of six new pinch-porphyrins: protoporphyrin-picpenta 1, mesoporphyrin-picpenta 2, deuteroporphyrin-picpenta 3, protoporphyrin-picocta 4, mesoporphyrin-picocta 5, and deuteroporphyrin-picocta 6. The Michaelis-Menten enzymatic pathway and the guaiacol test confirmed the ability of the compounds to function like new peroxidase models. UV-vis, 1H NMR, and electron spin resonance studies are in accordance with porphyrin-Fe(III) molecules with the quantum phenomena called quantum mixed spin (qms, s = 3/2, s = 5/2). Importantly, the influence of the presence of the s = 3/2 spin state in the compounds and its critical role for the catalytic capacity is proven here, which was the original hypothesis in our research group. The compounds with higher populations of the s = 3/2 spin state have increased peroxidase activity.

Spectroscopic and Kinetic Characterization of Peroxidase-Like π-Cation Radical Pinch-Porphyrin-Iron(III) Reaction Intermediate Models of Peroxidase Enzymes.

The spectroscopic and kinetic characterization of two intermediates from the H2O2 oxidation of three dimethyl ester [(proto), (meso), (deuteroporphyrinato) (picdien)]Fe(III) complexes ([FePPPic], [FeMPPic] and [FeDPPic], respectively) pinch-porphyrin peroxidase enzyme models, with s = 5/2 and 3/2 Fe(III) quantum mixed spin (qms) ground states is described herein. The kinetic study by UV/Vis at λmax = 465 nm showed two different types of kinetics during the oxidation process in the guaiacol test for peroxidases (1-3 + guaiacol + H2O2 → oxidation guaiacol products). The first intermediate was observed during the first 24 s of the reaction. When the reaction conditions were changed to higher concentration of pinch-porphyrins and hydrogen peroxide only one type of kinetics was observed. Next, the reaction was performed only between pinch-porphyrins-Fe(III) and H2O2, resulting in only two types of kinetics that were developed during the first 0-4 s. After this time a self-oxidation process was observed. Our hypotheses state that the formation of the π-cation radicals, reaction intermediates of the pinch-porphyrin-Fe(III) family with the ligand picdien [N,N'-bis-pyridin-2-ylmethyl-propane-1,3-diamine], occurred with unique kinetics that are different from the overall process and was involved in the oxidation pathway. UV-Vis, ¹H-NMR and ESR spectra confirmed the formation of such intermediates. The results in this paper highlight the link between different spectroscopic techniques that positively depict the kinetic traits of artificial compounds with enzyme-like activity.

Inducing magnetic communication in caged dinuclear Co(II) systems.

The synthesis, structural, electronic and magnetic characterization of five dinuclear Co(II) azacryptand compounds (1-5) bridged through different ions are reported. The magnetic exchange interactions, 2J values, obtained from theoretical computations show that the variation of the intermetallic angles and distances lead to antiferromagnetic behaviours. Magneto-structural correlations show a trend, where the angles Co(II)-bridge-Co(II) closer to 180° favour an increase in the superexchange pathway leading to higher AF interaction values.

In vitro effect of H2O 2, 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 (Aß42). ACh plays an important role in human memory and learning, but it is susceptible to hydrolysis by AChE, while the aggregation of Aß42 forms oligomers and fibrils, which form senile plaques in the brain. The Aß42 oligomers are able to produce hydrogen peroxide (H2O2), which reacts with metals (Fe(2+), Cu(2+), Cr(3+), Zn(2+), and Cd(2+)) 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 (Fe(3+), Cu(2+), Cr(3+), Zn(2+), and Cd(2+)), H2O2 (without Aß42), 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 Aß42.

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

Cadmium (Cd(2+)) 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 Cd(2+) shows in the brain in vivo. Hence, this study aimed at comparing the effect of chronic Cd(2+) 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 Cd(2+) at these doses and exposure time.

Caloric restriction increases free radicals and inducible nitric oxide synthase expression in mice infected with Salmonella Typhimurium.

It is well known that CR (caloric restriction) reduces oxidative damage to proteins, lipids and DNA, although the underlying mechanism is unclear. However, information concerning the effect of CR on the host response to infection is sparse. In this study, 6-month-old mice that were fed AL (ad libitum) or with a CR diet were infected with Salmonella serovar Typhimurium. EPR (electron paramagnetic resonance; also known as ESR (electron spin resonance)) was used to identify FRs (free radicals). These results were subsequently correlated with SOD (superoxide dismutase) catalytic activity, iNOS [inducible NOS (nitric oxide synthase) or NOSII] expression and NO (nitric oxide) content. EPR analysis of liver samples demonstrated that there was a higher quantity of FRs and iron-nitrosyl complex in infected mice provided with a CR diet as compared with those on an AL diet, indicating that CR was beneficial by increasing the host response to Salmonella Typhimurium. Furthermore, in infected mice on the CR diet, NOSII expression was higher, NO content was greater and spleen colonization was lower, compared with mice on the AL diet. No changes in SOD activity were detected, indicating that the NO produced participated more in the formation of iron-nitrosyl complexes than peroxynitrite. These results suggest that CR exerts a protective effect against Salmonella Typhimurium infection by increasing NO production.

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.

Magnetic properties and crystal structure of a one-dimensional phase of tetrakis(mu2-benzoato-O,O')-bis(dimethyl sulfoxide)dicopper(II).

A new crystalline polymorphic phase of tetrakis(mu2-benzoato-O,O')-bis(dimethyl sulfoxide)dicopper(II) was obtained by direct synthesis, in space group P2(1)/n. The copper coordination is in a slightly distorted square pyramidal geometry with an intramolecular Cu...Cu distance of 2.6494(8) angstroms. The Cu-O distances of the two copper in a dimer are different, giving different chemical environments for each Cu ion. The crystal structure is built up of well-separated stacking columns oriented along the b-axis, with units uniformly spaced, producing a one-dimensional (1-D) zigzag chain through Cu(II)-S...S-Cu(II) interdimer interactions [S...S separation: 3.975(2) angstroms]. Magnetization measurements in the range 2-300 K indicate two magnetic orderings, at low temperature (T < 10 K) a weak ferromagnetic ordering is observed, and above this temperature an antiferromagnetic behavior takes place. ESR spectra at 300 and 77 K of a polycrystalline sample show the characteristic signal of zero-field with D = 0.354 cm(-1), consistent with a ferromagnetic Cu...Cu exchange interaction at low temperature.

New pinch-porphyrin complexes with quantum mixed spin ground state S=3/2,5/2 of iron (III) and their catalytic activity as peroxidase.

New complexes of the pinch-porphyrin family were obtained from the dimethylester of (proto-, meso-, and deutero-porphyrinato)iron(III) with the ligand [N,N'-bis-pyridin-2-ylmethyl-propane-1,3-diamine] 1-3 and with the ligand [N-pyridin-2-ylmethyl-N'-[3-[(pyridin-2-ylmethyl)-amino]-propyl]-propane-1,3-diamine] 4-6. The UV/VIS studies of 1-6 indicate an increase in the distortion of the ligand field excited state. The 1H NMR spectra of 1-6 at RT and over the range 223-328 K show iron(III)-complexes with quantum mixed spin state (qms) S=5/2, S=3/2. The chemical shifts of the meso protons are consistent with qms state S=3/2, S=5/2, where the S=3/2 spin state is lowest in energy. For methyl-heme the chemical shifts are also consistent with a qms state but now the S=5/2 ground state is lowest in energy. ESR spectra of 1-6 show two different species, B and C, of iron(III) with qms, S=5/2, S=3/2 consistent with the 1H NMR results. Species B with 70% of S=5/2 and species C with 72.5% of S=3/2. The catalytic activity as peroxidase of 1-6 was quantified by guaiacol test; their theoretical maximum rate constants were k(cat) approximately 10(2)-10(3) M(-1) s(-1). A quantitative empirical correlation is found: the higher the 32 spin contribution to the qms state and the higher proportion of this species into the samples, the higher the peroxidase activity. Such a correlation was also obtained for pinch-porphyrins already reported.