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This paper aims to improve the aqueous stability and electrochemical activity of HKUST-1 (or Cu3(BTC)2, BTC = benzene 1,3,5-tricarboxylate; and HKUST from Hong Kong University of Science and Technology) by the incorporation of Graphene Oxide (GO). The synthesis was carried out in two steps; first, CuII ions were pre-adsorbed on the surface of GO, and then the BTC organic linker was added to form the HKUST-1 structure dispersed on GO sheets. Two concentrations of copper were used in the synthesis, 3.57 and 14.27 mmol, to obtain the samples: GO@HKUST-1low and GO@HKUST-1high, respectively. N2 adsorption properties of GO@HKUST-1high suggest an increase in surface area compared to HKUST-1 up to 1082.0 m2·g−1. In addition, the CO2 capture of GO@HKUST-1high increased from 5.34 (HKUST-1) to 6.92 mmol·g−1 at 273 K and 100 kPa. This improvement is associated with the dispersion of the HKUST-1 on the GO sheets achieved through the synthesis strategy used, which also increased the surface area, H2O adsorption capacity of the composite material, and electrochemical stability. After the H2O adsorption tests, XRD confirmed that the material was stable under aqueous conditions, showing that the material did not undergo any structural modification. [ABSTRACT FROM AUTHOR]

In this work, two polycrystalline samples were prepared using the solid-state reaction technique. The X-ray diffraction patterns revealed that the samples A and B are a mixture of the superconducting phases (Bi, Pb)-2212 (Bi1.6Pb0.4Sr2CaCu2O8) and (Bi, Pb)-2223 (Bi1.6Pb0.4Sr2Ca2Cu3O10). The T c was measured using electron paramagnetic resonance (EPR) in absorption mode: 97 K for the sample A and 101 K for sample B. The EPR spectra were measured (derivative of the absorption) and showed a signal in the low-field region only present in the superconducting state. The study of this signal revealed the coexistence of antiferromagnetism and diamagnetism in the sample A, for T < T c . The same was observed in sample B after a light grinding. The effective penetration depth was estimated from the peak-to-peak linewidth of the EPR signal (at T = 92 K): λ (92 K) = 479 nm for sample A, and 440 nm for sample B. These results are in agreement with the values obtained using techniques such as μ -spin rotation and magnetization measurements. With the aid of the two-fluid model and the BCS approximation λ was also estimated at 0 K. Using these values and the Ginzburg-Landau theory, the lower critical field was calculated at T = 92 K and 0 K. [ABSTRACT FROM AUTHOR]

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 (HO), which reacts with metals (Fe, Cu, Cr, Zn, and Cd) 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, Cu, Cr, Zn, and Cd), HO (without Aβ42), and OH radicals produced from FR and FLR. The results showed that the HO and the metals do not modify the AChE catalytic activity, but the OH radical causes a decrease in it. On the other hand, metals, HO and OH radicals, increase the ACh hydrolysis. This finding suggests that when HO, 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 HO is produced directly from Aβ42. [ABSTRACT FROM AUTHOR]

Septic shock is characterized by an excess of reactive oxygen and nitrogen species. The induction of nitric oxide (NO) synthesis has been related to vasoplegia, myocardial depression, and decompensated shock. Decompensation cannot be diagnosed in its early phases and is associated with high mortality. The goal of this study was to detect the NO radical, by electron paramagnetic resonance (EPR), in organs isolated from septic male Wistar rats to establish a time course of septic shock and to detect the onset of decompensation. The heme-nitrosyl (HbNO) adduct was detected in hearts and livers 1 h after lipopolysaccharide (LPS) administration. Advantage was taken of the heme group which acts as endogenous spin-trap. Three hours after the LPS dosing, HbNO was evident in the lung and ileum. The early increase of HbNO in the heart, a new finding, could indicate that cardiovascular dysfunction begins earlier that it was thought before. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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-(3 H-imidazol-4-ylmethyl)- N′-{2-[(3 H-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. [ABSTRACT FROM AUTHOR]

In this work, SiO2 samples with silver, prepared using the sol-gel method, were analyzed after being thermally treated in air in the range of 100 to 800°C. The sol-gel starting solutions were prepared by mixing tetra-ethyl-orthosilicate (TEOS), water and ethanol. Samples with 4 different H2O/TEOS molar ratios (3.3, 5, 7.5 and 11.7 respectively) and with different nominal Ag concentrations were prepared (1, 2 and 4%vol. of Ag). It was found that upon annealing, different silver spices were formed, such as Ag2 +, Ag+, Ag°, and metallic silver aggregates. The identification of these spices was carried out by means of X-ray diffraction, Electron Paramagnetic Resonance (EPR), optical emission and optical absorption. It was also found that the specific type of silver spices observed depends on the structure of the SiO2 matrix and on the annealing temperatures. It was found that samples prepared from precursor solutions with a low H2O/TEOS ratio have a more open structure, and therefore silver diffuses faster and forms agglomerates at lower temperatures. Samples prepared from solutions with larger H2O/TEOS ratios have a more dense structure, which allows the formation of atomic or molecular spices in addition to silver particles. A systematic study of this system was carried out using EPR on samples prepared from solutions having different H2O/TEOS molar ratios, various Ag concentrations and subjected to different thermal treatments. [ABSTRACT FROM AUTHOR]