TIME-COURSE DIFFUSION of HYDROGEN PEROXIDE USING MODERN TECHNOLOGIES

The concern with the hydrogen penetration towards the pulp can be observed on the literature by the great number of papers published on this topic; Those measurements often uses chemical agents to quantify the concentration of the bleaching agent that cross the enamel and dentin. The objective of this work was the quantification of oxygen free radicals by fluorescence that are located in the interface between enamel and dentin. It was used to accomplish our objectives a Ruthenium probe (FOXY R - Ocean Optics(R)) a 405nm LED, a bovine tooth and a portable diagnostic system (Science and support LAB - LAT - IFSC/USP). The fluorescence of the probe is suppressed in presence of oxygen free radicals in function of time. The obtained results clearly shows that the hydrogen peroxide when not catalyzed should be kept in contact with the tooth for longer periods of time.

Respiratory pressures and expiratory peak flow rate of patients undergoing coronary artery bypass graft surgery

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Effect of a leukotriene inhibitor (MK886) on nitric oxide and hydrogen peroxide production by macrophages of acutely and chronically stressed mice

We evaluated the effect of a leukotriene inhibitor (MK886) on nitric oxide (NO) and hydrogen peroxide (H2O2) production by peritoneal macrophages of mice subjected to acute and chronic stress. Acute stress was induced by keeping mice immobilized in a tube for 2 h. Chronic stress was induced over a 7-day period by the same method, but with increasing duration of immobilization. The effects of MK886 were investigated in-vitro after incubation with peritoneal macrophages, and in-vivo by submitting mice to stress and treating them daily with MK886. Supernatants of macrophage cultures were collected for NO determination and adherent cells were used for H2O2 determination. Macrophages from mice submitted to acute or chronic stress showed no alterations in H2O2 production. However, macrophages of acutely and chronically stressed mice showed inhibition of NO after incubation with MK886 in-vitro. Administration of MK886 to chronically stressed mice increased generation of H2O2 and inhibited production of NO. Our data suggest an important role of leukotrienes in NO synthesis, which is important in controlling replication of several infectious agents, mainly in stressed and immunosuppressed animals.

Dynamics of glyphosate-induced conformational changes of Mycobacterium tuberculosis 5-enolpyruvylshikimate-3-phosphate synthase (EC 2.5.1.19) determined by hydrogen-deuterium exchange and electrospray mass spectrometry

The enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) catalyzes the reaction between shikimate 3-phosphate and phosphoenolpyruvate to form 5-enolpyruvylshikimate 3-phosphate, an intermediate in the shikimate pathway, which leads to the biosynthesis of aromatic amino acids. EPSPS exists in an open conformation in the absence of substrates and/or inhibitors and in a closed conformation when bound to the substrate and/or inhibitor. In the present report, the H/D exchange properties of EPSPS from Mycobacterium tuberculosis (Mt) were investigated for both enzyme conformations using ESI mass spectrometry and circular dichroism (CD). When the conformational changes identified by H/D exchanges were mapped on the 3-D structure, it was observed that the apoenzyme underwent extensive conformational changes due to glyphosate complexation, characterized by an increase in the content of alpha-helices from 40% to 57%, while the beta-sheet content decreased from 30% to 23%. These results indicate that the enzyme underwent a series of rearrangements of its secondary structure that were accompanied by a large decrease in solvent access to many different regions of the protein. This was attributed to the compaction of 71% of alpha-helices and 57% of beta-sheets as a consequence of glyphosate binding to the enzyme. Apparently, MtEPSPS undergoes a series of inhibitor-induced conformational changes, which seem to have caused synergistic effects in preventing solvent access to the core of molecule, especially in the cleft region. This may be part of the mechanism of inhibition of the enzyme, which is required to prevent the hydration of the substrate binding site and also to induce the cleft closure to avoid entrance of the substrates.

Monitoring the positioning of short polycationic peptides in model lipid bilayers by combining hydrogen/deuterium exchange and electrospray ionization mass spectrometry

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Hydrogen/deuterium exchange mass spectrometry for characterizing phosphoenolpyruvate-induced structural transitions in Mycobacterium tuberculosis 5-enolpyruvylshikimate-3-phosphate synthase (EC 2.5.1.1)

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of antioxidant agents on bond strength of composite to bleached enamel with 38% hydrogen peroxide

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influence of chemical activation of a 35% hydrogen peroxide bleaching gel on its penetration and efficacy-In vitro study

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Positronium impact excitation of hydrogen molecule to B-1 Sigma(+)(u) and b(3)Sigma(+)(u) states

Calculation for the electronic excitation of the ground state of H-2 to B (1) Sigma(u)(+) and b(3) Sigma(u)(+) states by positronium- (Ps) atom impact has been carried out using the first Born approximation considering discrete Ps excitations up to n = 6 and Ps ionization in the final state. To include the effect of electron exchange, we propose an alternative approximation scheme in the light of the Rudge approach, which takes into account the composite nature of the Ps-atom projectile.

Low-energy muon-transfer reaction from hydrogen isotopes to helium isotopes

Direct muon transfer in low-energy collisions of the muonic hydrogen H-mu and helium (He++) is considered in a three-body quantum-mechanical framework of coordinate-space integro-differential Faddeev-Hahn-type equations within two- and six-state close coupling approximations. The final-state Coulomb interaction is treated without any approximation employing appropriate Coulomb waves in the final state. This procedure of treating Coulomb interaction leads to much improved results for low-energy transfer rates. The present results agree reasonably well with previous semiclassical calculations. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Positronium-hydrogen atom elastic scattering at medium energies

We study the elastic scattering of positronium atoms by hydrogen atoms at medium energies using partial-wave Born-Oppenheimer (BO) exchange amplitudes and report accurate BO cross sections in the energy range 0 to 60 eV. The present BO results agree with a 22-state R-matrix and a five-state coupled-channel model potential calculation, but disagree strongly with a conventional close-coupling calculation as well as its input BO amplitudes at medium energies.

Positronium scattering by a hydrogen molecule including exchange

We perform a three-positronium (Ps) state [Ps(ls,2s,2p)] coupled-channel calculation of Ps-H-2 scattering including the effect of electron exchange. At medium energies, higher excitations and ionization of Ps are treated within the framework of the first Born approximation. In both cases exchange is included using a recently proposed nonlocal model exchange potential which is free of non-orthogonality problems common in the usual antisymmetrization scheme. The present total cross sections at low and medium energies are in encouraging agreement with experiment.

Positronium-hydrogen-atom scattering in a five-state model

The scattering of orthopositronium (Ps) by hydrogen atoms has been investigated in a five-state coupled-channel model allowing for Ps(1s)H(2s,2p) and Ps(2s,2p)H(1s) excitations using a recently proposed electron-exchange model potential. The higher (n greater than or equal to 3) excitations and ionization of the Ps atom are calculated using the first Born approximation. Calculations are reported of scattering lengths, phase shifts. elastic, Ps and H excitation, and total cross sections. Remarkable correlations are observed between the S-wave Ps-H binding energy and the singlet scattering length, effective range, and resonance energy obtained in various model calculations. These correlations suggest that if a Ps-H dynamical model yields the correct result for one of these four observables, it is expected to lead to the correct result for the other three. The present model, which is constructed so as to reproduce the Ps-H resonance at 4.01 eV, automatically yields a Ps-H bound state at - 1.05 eV that compares well with the accurate value of - 1.067 eV. The model leads to a singlet scattering length of 3.72a(0) and effective range of 1.67a(0), whereas the correlations suggest the precise values of 3.50a(0) and 1.65a(0) for these observables, respectively. [S1050-2947(99)07703-3].

Convergent variational calculation of positronium-hydrogen-atom scattering lengths

We present a convergent variational basis-set calculational scheme for elastic scattering of the positronium atom by the hydrogen atom in S wave. Highly correlated trial functions with appropriate symmetry are needed to achieve convergence. We report convergent results for scattering lengths in atomic units for both singlet (= 3.49 +/-0.20) and triplet (= 2.46 +/-0.10) states.

Effect of electron exchange in positronium-hydrogen scattering

The elastic and inelastic scattering of ortho-positronium (Ps) by the hydrogen atom have been investigated using a three-Ps-state close-coupling approximation. The higher (n greater than or equal to 3) excitations and ionization of the Ps atom are treated within the framework of the Born approximation. In both cases the effect of electron exchange has been included by a parameter-free nonlocal model potential derived from an antisymmetrization of the wavefunction followed by the removal of nonorthogonality. Calculations are reported of scattering lengths,phase shifts, and of elastic, Ps excitation, and total cross sections. The trend of present target elastic total cross section agrees qualitatively with available experimental results on Ps-impact scattering.