Study of the carbon dioxide chemical fixation-activation by guanidines

Fixation of CO(2) is one of the most important priorities of the scientific community dedicated to reduce global warming. In this work, we propose new methods for the fixation of CO2 using the guanidine bases tetramethylguanidine (TMG) and 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]-pyrimidine (TBD). In order to understand the reactions occurring during the CO(2) fixation and release processes, we employed several experimental methods, including solution and solid-state NMR, FTIR, and coupled TGA-FTIR. Quantum mechanical NMR calculations were also carried out. Based on the results obtained, we concluded that CO(2) fixation with both TMG and TBD guanidines is a kinetically reversible process, and the corresponding fixation products have proved to be useful as transcarboxylating compounds. Afterward, CO(2) thermal releasing from this fixation product with TBD was found to be an interesting process for CO(2) capture and isolation purposes. (C) 2008 Elsevier Ltd. All rights reserved.

Cathepsin X cleaves the beta 2 cytoplasmic tail of LFA-1 inducing the intermediate affinity form of LFA-1 and alpha-actinin-1 binding

The motility of T cells depends on the dynamic spatial regulation of integrin-mediated adhesion and de-adhesion. Cathepsin X, a cysteine protease, has been shown to regulate T-cell migration by interaction with lymphocyte function associated antigen-1 (LFA-1). LFA-1 adhesion to the ICAM-1 is controlled by the association of actin-binding proteins with the cytoplasmic tail of the beta(2) chain of LFA-1. Cleavage by cathepsin X of the amino acid residues S(769), E(768) and A(767) from the C-terminal of the beta(2) cytoplasmic tail of LFA-1 is shown to promote binding of the actin-binding protein alpha-actinin-1. Furthermore, cathepsin X overexpression reduced LFA-1 clustering and induced an intermediate affinity LFA-1 conformation that is known to associate with a-actinin-1. increased levels of intermediate affinity LFA-1 resulted in augmented cell spreading due to reduced attachment of T cells to the ICAM-1-coated surface. Gradual cleavage of LFA-1 by cathepsin X enables the transition between intermediate and high affinity LFA-1, an event that is crucial for effective T-cell migration.

Melatonin triggers PKA activation in the rodent malaria parasite Plasmodium chabaudi

Calcium (Ca2+) is a critical regulator of many aspects of the Plasmodium reproductive cycle. In particular, intra-erythrocyte Plasmodium parasites respond to circulating levels of the melatonin in a process mediated partly by intracellular Ca2+. Melatonin promotes the development and synchronicity of parasites, thereby enhancing their spread and worsening the clinical implications. The signalling mechanisms underlying the effects of melatonin are not fully established, although both Ca2+ and cyclic AMP (cAMP) have been implicated. Furthermore, it is not clear whether different strains of Plasmodium use the same, or divergent, signals to control their development. The aim of this study was to explore the signalling mechanisms engaged by melatonin in P. chabaudi, a virulent rodent parasite. Using parasites at the throphozoite stage acutely isolated from mice erythrocytes, we demonstrate that melatonin triggers cAMP production and protein kinase A (PKA) activation. Interestingly, the stimulation of cAMP/PKA signalling by melatonin was dependent on elevation of Ca2+ within the parasite, because buffering Ca2+ changes using the chelator BAPTA prevented cAMP production in response to melatonin. Incubation with melatonin evoked robust Ca2+ signals within the parasite, as did the application of a membrane-permeant analogue of cAMP. Our data suggest that P. chabaudi engages both Ca2+ and cAMP signalling systems when stimulated by melatonin. Furthermore, there is positive feedback between these messengers, because Ca2+ evokes cAMP elevation and vice versa. Melatonin more than doubled the observed extent of parasitemia, and the increase in cAMP concentration and PKA activation was essential for this effect. These data support the possibility to use melatonin antagonists or derivates in therapeutic approach.

Increased SOD1 association with chromatin, DNA damage, p53 activation, and apoptosis in a cellular model of SOD1-linked ALS

Mutations in the gene encoding cytosolic Cu,Zn-superoxide dismutase (SOD1) have been linked to familial amyotrophic lateral sclerosis (FALS). However the molecular mechanisms of motor neuron death are multifactorial and remain unclear. Here we examined DNA damage;p53 activity and apoptosis in SH-SY5Y human neuroblastoma cells transfected to achieve low-level expression of either wild-type or mutant Gly(93) --> Ala (G93A) SOD1, typical of FALS. DNA damage was investigated by evaluating the levels of 8-oxo-7,8-dihydro-2`-deoxyguanosine (8-oxodGuo) and DNA strand breaks. Significantly higher levels of DNA damage, increased p53 activity, and a greater percentage of apoptotic cells were observed in SH-SY5Y cells transfected with G93A SOD1 when compared to cells overexpressing wild-type SOD1 and untransfected cells. Western blot, FACS, and confocal microscopy analysis demonstrated that G93A SOD1 is present in the nucleus in association with DNA. Nuclear G93A SOD1 has identical superoxide dismutase activity but displays increased peroxidase activity when compared to wild-type SOD1. These results indicate that the G93A mutant SOD1 association with DNA might induce DNA damage and trigger the apoptotic response by activating p53. This toxic activity of mutant SOD1 in the nucleus may play an important role in the complex mechanisms associated with motor neuron death observed in ALS pathogenesis. (C) 2010 Elsevier B.V. All rights reserved.

Arginine vasopressin controls p27(KiP1) protein expression by PKC activation and irreversibly inhibits the proliferation of K-Ras-dependent mouse Y1 adrenocortical malignant cells

The neurohypophyseal hormone arginine vasopressin (AVP) is a classic mitogen in many cells. In K-Ras-dependent mouse Y1 adrenocortical malignant cells, AVP elicits antagonistic responses such as the activation of the PKC and the ERK1/2 mitogenic pathways to down-regulate cyclin D1 gene expression, which induces senescence-associated beta-galactosidase (SA-beta Gal) and leads to cell cycle arrest. Here, we report that in the metabolic background of Y1 cells, PKC activation either by AVP or by PMA inhibits the PI3K/Akt pathway and stabilises the p27(Kip1) protein even in the presence of the mitogen fibroblast growth factor 2 (FGF2). These results suggest that p27(Kip1) is a critical signalling node in the mechanisms underlying the survival of the Y1 cells. In Y1 cells that transiently express wild-type p27(Kip1), AVP caused a severe reduction in cell survival, as shown by clonogenic assays. However, AVP promoted the survival of Y1 cells transiently expressing mutant p27-S10A or mutant p27-T187A, which cannot be phosphorylated at Ser10 and Thr187, respectively. In addition, PKC activation by PMA mimics the toxic effect caused by AVP in Y1 cells, and inhibition of PKC completely abolishes the effects caused by both PMA and AVP in clonogenic assays. The vulnerability of Y1 cells during PKC activation is a phenotype conditioned upon K-ras oncogene amplification because K-Ras down-regulation with an inducible form of the dominant-negative mutant H-RasN17 has resulted in Y1 cells that are resistant to AVP`s deleterious effects. These data show that the survival destabilisation of K-Ras-dependent Y1 malignant cells by AVP requires large quantities of the p27(Kip1) protein as well as phosphorylation of the p27(Kip1) protein at both Ser10 and Thr187. (C) 2011 Elsevier B.V. All rights reserved.

An investigation of the activation process of high temperature shift catalyst

The aim of this work is to address the activation process of a high temperature shift (HTS) catalyst, composed of Fe2O3/Cr2O3/CuO, by analyzing it before activation (HTS-V) and after activation (HTS-A) using complementary characterization techniques. The textural and morphological characterizations were done by transmission electron rnicroscopy (TEM) and nitrogen physisorption at 77 K; crystallographic structure was confirmed by X-ray diffraction (XRD); electronic structure was analyzed by X-ray absorption spectroscopy (XAS) and the chemical composition of the catalyst`s surface was obtained by X-ray photoelectron spectroscopy (XPS). The investigation pointed out that the HTS-V catalyst presents good textural and morphological properties, which are not deeply affected by the activation process (sample HTS-A). The iron oxide phase in the HTS-V catalyst is hematite whereas in HTS-A catalyst is magnetite with Fe2+/Fe3+ ratio close to the expected value (0.5). For both samples, the Cr ions seem to be incorporated in the iron oxide lattice with higher concentration at particle surface. In the HTS-V catalyst, the Cu ions have oxidation number II and occupy in average distorted octahedral sites; after the activation, the Cu ions are partially reduced, suggesting that the reduction of the Cu species is complex. (C) 2007 Elsevier B.V. All rights reserved.

Time Evolution of the Activation Energy in a Batch Chemical Oscillator

The batch-operated bromate/phosphate/acetone/dual catalyst system was studied at four temperatures between 5 and 35 degrees C. The dynamics was simultaneously followed by potential measurements with platinum and bromide selective electrodes, and spectroscopically at two different wavelengths. By simultaneously recording these four time series it was possible to characterize the dynamics of the sequential oscillations that evolve in time. The existence of three sequential oscillatory patterns at each temperature allowed estimating the activation energies in each case. Along with the activation energy of the induction period, it was possible to trace the time evolution of the overall activation energy at four different stages as the reaction proceeds. The study was carried out for two different sets of initial concentrations and it was observed that the overall activation energy increases as reactants turn into products. This finding was propounded as a result of the decrease in the driving force, or the system`s affinity, of the catalytic oxidative bromination of acetone with acidic bromate, as the closed system evolves toward the thermodynamic equilibrium.

Activation Energies of the Electrooxidation of Formic Acid on Pt(100)

The electrooxidation of small organic molecules on platinum surfaces usually involves different structure-dependent steps that include adsorption and desorption of various species and multiple reaction pathways. Because temperature plays a decisive role on each individual step, understanding its global influence on the reaction mechanism is often a difficult task, especially when the system is studied under far from equilibrium conditions in the presence of kinetic instabilities. Aiming at contributing to unravel this problem, herein, we report an experimental study of the role played by temperature on the electrooxidation of formic acid on a Pt(100) electrode. The system was investigated under both close and far from equilibrium conditions, and apparent activation energies were estimated using different strategies. Overall, comparable activation energies were estimated under oscillatory and quasi-stationary conditions, at high potentials. At low potentials, the poisoning process associated with the formic acid dehydration step presented a negligible dependence with temperature and, therefore, zero activation energy. On the basis of our experimental findings, we suggest that formic acid dehydration is the main, but maybe not the unique, step that differentiates the temperature dependence of the oscillatory electrooxidation of formic acid on Pt(100) with that on polycrystalline platinum.

On the activation and physical degradation of boron-doped diamond surfaces brought on by cathodic pretreatments

The electrochemical activation and physical degradation of boron-doped diamond (BDD) electrodes with different boron doping levels after repeated cathodic pretreatments are reported. Galvanostatic cathodic pretreatment passing up to -14000 C cm(-2) in steps of -600 C cm(-2) using -1 A cm(-2) caused significant physical degradation of the BDD surface, with film detachment in some areas. Because of this degradation, a great increase in the electrochemically active area was observed in Tafel plots for the hydrogen evolution reaction (HER) in acid media. The minimum cathodic pretreatment needed for the electrochemical activation of the BDD electrodes without producing any observable physical degradation on the BDD surfaces was determined using electrochemical impedance spectroscopy (EIS) measurements and cyclic voltammetry: -9 C cm(-2), passed at -1 A cm(-2). This optimized cathodic pretreatment can be safely used when electrochemical experiments are carried out on BDD electrodes with doping levels in the range between 800 and 8000 ppm.

Thermal stability of extracellular hemoglobin of Glossoscolex paulistus: Determination of activation parameters by optical spectroscopic and differential scanning calorimetric studies

Glossoscolex paulistus hemoglobin (HbGp) was studied by dynamic light scattering (DLS), optical absorption spectroscopy (UV-VIS) and differential scanning calorimetry (DSC). At pH 7.0, cyanomet-HbGp is very stable, no oligomeric dissociation is observed, while denaturation occurs at 56 degrees C, 4 degrees C higher as compared to oxy-HbGp. The oligomeric dissociation of HbGp occurs simultaneously with some protein aggregation. Kinetic studies for oxy-HbGp using UV-VIS and DES allowed to obtain activation energy (E(a)) values of 278-262 kJ/mol (DES) and 333 kJ/mol (UV-VIS). Complimentary DSC studies indicate that the denaturation is irreversible, giving endotherms strongly dependent upon the heating scan rates, suggesting a kinetically controlled process. Dependence on protein concentration suggests that the two components in the endotherms are due to oligomeric dissociation effect upon denaturation. Activation energies are in the range 200-560 kJ/mol. The mid-point transition temperatures were in the range 50-65 degrees C. Cyanomet-HbGp shows higher mid-point temperatures as well as activation energies, consistent with its higher stability. DSC data are reported for the first time for an extracellular hemoglobin. (C) 2010 Elsevier B.V. All rights reserved.