Direct Kinetic Observation of the Chemiexcitation Step in Peroxyoxalate Chemiluminescence

A high-energy intermediate in the peroxyoxalate reaction can be accumulated at room temperature under specific reaction conditions and in the absence of any reducing agent in up to micromolar concentrations. Bimolecular interaction of this intermediate, accumulated in the reaction of oxalyl chloride with hydrogen peroxide, with an activator (highly fluorescent aromatic hydrocarbons with low oxidation potential) added in delay shows unequivocally that this intermediate is responsible for chemiexcitation of the activator. Activation parameters for the unimolccular decomposition of this intermediate (Delta H(double dagger) = 11.2 kcal mol(-1); Delta S(double dagger) = -23.2 cal mol(-1) K(-1)) and for its bimolecular reaction with 9,10-diphenylanthracene (Delta H(double dagger) = 4.2 kcal mol(-1); Delta S(double dagger) = -26.9 cal mol(-1) K(-1)) show that this intermediate is much less stable than typical 1,2-dioxetanes and 1,2-dioxetanones and demonstrate its highly favored interaction with the activator. Therefore, it can be inferred that structural characterization of the high-energy intermediate in the presence of an activator must be highly improbable. The observed linear free-energy correlation between the catalytic rate constants and the oxidation potentials of several activators definitely confirms the occurrence of the chemically initiated electron-exchange luminescence (CIEEL) mechanism in the chemiexcitation step of the peroxyoxalate system.

Gas-Phase Acylium Ion Transfer Reactions Mediated by a Proton Shuttle Mechanism

The mechanism and the energy profile of the gas-phase reaction that mimics esterification under acidic conditions have been investigated at different levels of theory. These reactions are known to proceed with rate constants close to the collision limit in the gas-phase and questions have been raised as to whether the typical addition-elimination mechanism via a tetrahedral intermediate can explain the ease of these processes. Because these reactions are common to many organic and biochemical processes it is important to understand the intrinsic reactivity of these systems. Our calculations at different levels of theory reveal that a stepwise mechanism via a tetrahedral species is characterized by energy barriers that are inconsistent with the experimental results. For the thermoneutral exchange between protonated acetic acid and water and the exothermic reaction of protonated acetic acid and methanol our calculations show that these reactions proceed initially by a proton shuttle between the carbonyl oxygen and the hydroxy oxygen of acetic acid mediated by water, or methanol, followed by displacement at the acylium ion center. These findings suggest that the reactions in the gas-phase should be viewed as an acylium ion transfer reaction. (C) 2010 Wiley Periodicals, Inc. Int J Quantum Chem 111: 1596-1606, 2011

The characterisation of the protective film formed by benzotriazole on the 90/10 copper-nickel alloy surface in H2SO4 media

The nature of the protective film formed by benzotriazole (BTAH) on the surface of the 90/10 CuNi alloy in deaerated 0.5 mol L-1 H2SO4 solution containing Fe(III) ions as oxidant was investigated by weight-loss, calorimetric measurements, and by surface-enhanced Raman spectroscopy (SERS). The SERS measurements show that the protective film is composed by the [Cu(I)BTA](n), polymeric complex and that the BTAH molecules are also adsorbed on the electrode surface. A modification of the BET isotherm for adsorption of gases ill solids is proposed to describe the experimental results obtained from weight-loss experiments that suggest an adsorption in multilayers. Electrochemical studies of copper and nickel in 0.5 mol L-1 H2SO4 in presence and absence of BTAH have also been made as an aid to interpret the results. The calculated adsorption free energy of the cuprous benzotriazolate on the surface of the alloy is in accordance with the value for pure copper. (C) 2007 Elsevier Ltd. All rights reserved.

Thiothionyl bromide (S=SBr2): The elusive isomer of dibromodisulfane (BrSSBr)

CCSD(T) with a series of correlation consistent basis up to quadruple-zeta is used to investigate the structures, vibrational spectra, relative stability, heats of formation, and barrier to isomerization of S=SBr2 and BrSSBr. It represents the most accurate and detailed characterization of these molecules to date. We show that the frequency mode at 302 cm(-1), detected in various studies and assigned to impurities by some authors, and to the anti-symmetric SBr stretch in BrSSBr by others, thus in fact corresponds to the anti-symmetric SBr stretch in the elusive S=SBr2 species; it thus corroborates and complements an earlier partial IR spectra study attributable to S=SBr2. Including corrections for relativistic and core-valence correlation effects, we also predict 26.33 (12.74) kcal/mol for Delta H-f (298.15 K) of S=SBr2 (BrSSBr). For the S=SBr2 -> BrSSBr reaction, our best estimates for the Gibbs free energy and the enthalpy of the reaction at 298.15 K are -13.71 and -13.44 kcal/mol, respectively. For a value of Delta G(#) equal to 23.52 kcal/mol, we estimate a TST rate constant, at 298.15 K, of 3.57 x 10(-5) s(-1). (c) 2007 Elsevier B.V. All rights reserved.

Ab Initio Analysis of Monomers and Dimers of Trialkylphosphine Oxides: Structural and Thermodynamic Stability

Structural and thermodynamic stabilities of monomers and dimers of trialkylphosphine oxides (TRPO) were Studied using quantum chemistry calculations. Density functional theory calculations were carried Out and the structures Of four TRPO have been determined: TMPO (methyl; R = CH(3)), TEPO (ethyl; R = CH(3)CH(2)), TBPO (n-butyl; R = CH(3)(CH(2))(3)), and TOPO (n-octyl; R = CH(3)(CH(2))(7)). TRPO homodimers were investigated considering two isomeric possibilities for each dimer. Relative binding energies and the enthalpic and entropic contributions to the Gibbs free energy were Calculated for all dimers. The formation of dimers from the individual monomeric TRPO species as a function of temperature was also analyzed. (C) 2008 Wiley Periodicals, Inc. Int J Quantum Chem 109: 250-258, 2009

On the interaction of bovine serum albumin with ionic surfactants: Temperature induced EPR changes of a maleimide nitroxide reflect local protein dynamics and probe solvent accessibility

The interaction of bovine serum albumin (BSA) with the ionic surfactants sodium dodecylsulfate (SDS, anionic), cetyltrimethylammonium chloride (CTAC, cationic) and N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS, zwitterionic) was studied by electron paramagnetic resonance (EPR) spectroscopy of spin label covalently bound to the single free thiol group of the protein. EPR spectra simulation allows to monitor the protein dynamics at the labeling site and to estimate the changes in standard Gibbs free energy, enthalpy and entropy for transferring the nitroxide side chain from the more motionally restricted to the less restricted component. Whereas SDS and CTAC showed similar increases in the dynamics of the protein backbone for all measured concentrations. HPS presented a smaller effect at concentrations above 1.5 mM. At 10 mM of surfactants and 0.15 mM BSA, the standard Gibbs free energy change was consistent with protein backbone conformations more expanded and exposed to the solvent as compared to the native protein, but with a less pronounced effect for HPS. In the presence of the surfactants, the enthalpy change, related to the energy required to dissociate the nitroxide side chain from the protein, was greater, suggesting a lower water activity. The nitroxide side chain also detected a higher viscosity environment in the vicinity of the paramagnetic probe induced by the addition of the surfactants. The results suggest that the surfactant-BSA interaction, at higher surfactant concentration, is affected by the affinities of the surfactant to its own micelles and micelle-like aggregates. Complementary DLS data suggests that the temperature induced changes monitored by the nitroxide probe reflects local changes in the vicinity of the single thiol group of Cys-34 BSA residue. (C) 2011 Elsevier B.V. All rights reserved.

On the interaction of bovine serum albumin with ionic surfactants: Temperature induced EPR changes of a maleimide nitroxide reflect local protein dynamics and probe solvent accessibility

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Dispersões sólidas de sinvastatina: preparação, caracterização, no estado sólido utilizando técnicas emergentes e estudo de estabilidade

This thesis aimed to assess the increase in solubility of simvastatin (SINV) with solid dispersions using techniques such as kneading (MA), co-solvent evaporation (ES), melting carrier (FC) and spray dryer (SD). Soluplus (SOL), PEG 6000 (PEG), PVP K-30 (PVP) e sodium lauryl sulphate (LSS) were used as carriers. The solid dispersions containing PEG [PEG-2(SD)], Soluplus [SOL-2(MA)] and sodium lauryl sulphate [LSS-2(ES)] were presented with a greater increase in solubility (5.02, 5.60 and 5.43 times respectively); analyses by ANOVA between the three groups did not present significant difference (p<0.05). In the phase solubility study, the calculation of the Gibbs free energy (ΔG) revealed that the spontaneity of solubilisation of SINV occurred in the order SOL>PEG >PVP 75%>LSS, always 80%. The phase diagrams of PEG and LSS presented solubilization stoichiometry of type 1:1 (type AL). The diagrams with PVP and SOL tend to 1:2 stoichiometry (type AL + AP). The stability coefficients (Ks) of the phase diagrams revealed that the most stable reactions occurred with LSS and PVP. The solid dispersions were characterized by Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), particle size distribution (PSD), near-infrared spectroscopy imaging (NIR-CI) and X-ray diffraction of the powder using the Topas software (PDRX-TOPAS). The solid dispersion PEG-2(SD) presented the greatest homogeneity and the lowest degree of crystallinity (18.2%). The accelerated stability study revealed that the solid dispersions are less stable than SINV, with PEG-2(SD) being the least stable, confirmed by FTIR and DSC. The analyses by PDRX-TOPAS revealed the amorphous character of the dispersions and the mechanism of increasing solubility

Desenvolvimento de um destilador solar para tratamento de águas de produção de petróleo com vistas a sua utilização na agricultura e geração de vapor

The production of petroleum is frequently accomplished with great volumes of water, that it is carried of the underground with the oil. It is a challenge of the present century the development of technologies that allow the use of waste water for purposes that consume great amounts of water and don't demand as rigid as the one of the drinking water requirements. The solar distillation has been configuring as an alternative of clean technology for desalination of brine and saline. Besides causing the minimum possible damage to the environment, it takes advantage of an abundant and free energy source: the solar energy. That study aims to develop a Solar Distillator for treatment of the produced water of the oil wells, to obtain an efluent to use in agriculture and vapor generation. The methodology for collection, conservation and analysis of the physical-chemical parameters obeyed the norms in APHA (1995). The sampling was of the composed type. Experiments were accomplished in the solar distillation pilot and simulation in thermostatic bathing. The operation was in batch system and for periods of 4, 6 and 12 h. The developed Distillator is of the type simple effect of two waters. It was still tested two inclination angles for covering; 20º and 45º. The Distillator presented minimum of 2,85 L/m2d revenues and maximum of 7,14 L/m2d. The removals of salts were great than 98%. The removal of TOC in the simulation was great than 90%. In agreement with the data of energy and mass balance, it was verified that the developed solar Distillator presented compatible revenues with those found in literature for similar types. It can be inferred that the obtained distilled water assists to the requirements CONAMA in almost all the points and could be used for irrigation of cultures such as cotton and mamona. As the distilled water has characteristics of fresh water it can be used in the generation of vapor

Síntese e caracterização de tensoativos e estudo de equilíbrio de fase dos sistemas CnH2n+2/H2O/CnH2n+1COONa/But-OH

The growing utilization of surfactants in several different areas of industry has led to an increase on the studies involving solutions containing this type of molecules. Due to its amphiphilic nature, its molecule presents one polar part and one nonpolar end, which easily interacts with other molecules, being able to modify the media properties. When the concentration in which its monomers are saturated, the airliquid system interface is reached, causing a decrease in interfacial tension. The surfactants from pure fatty acids containing C8, C12 and C16 carbonic chains were synthesized in an alcoholic media using sodium hydroxide. They were characterized via thermal analysis (DTA and DTG) and via infrared spectroscopy, with the intention of observing their purity. Physical and chemical properties such as superficial tension, critical micelle concentration (c.m.c), surfactant excess on surface and Gibbs free energy of micellization were determined in order to understand the behaviour of these molecules with an aqueous media. Pseudo-ternary phase diagrams were obtained aiming to limit the Windsor equilibria conditions so it could be possible to understand how the surfactants carbonic chain size contributes to the microemulsion region. Solutions with known concentrations were prepared to study how the surfactants can influence the dynamic light scattering spectroscopy (DLS) and how the diffusion coefficient is influenced when the media concentration is altered. The results showed the variation on the chain size of the studied surfactant lipophilic part allows the conception of surfactants with similar interfacial properties, but dependent on the size of the lipophilic part of the surfactant. This variation causes the surfactant to have less tendency of microemulsionate oil in water. Another observed result is that the n-alcanes molecule size promoted a decrease on the microemulsion region on the obtained phase diagrams

Efeito Kerr magneto-óptico; Ressonância ferromagnética; Acoplamento bilinear; Acoplamento biquadrático

In this work, we investigated the magnetic properties of a monocrystalline Fe thin film and of Fe(80 Å)/Cr(t)/Fe(80 Å) tri-layers, with the nonmagnetic metallic Cr spacer layer thickness varying between 9 Å < t < 40 Å. The samples were deposited by the DC Sputtering on Magnesium Oxide (MgO) substrates, with (100) crystal orientation. For this investigation, experimental magneto-optical Kerr effect (MOKE) magnetometry and ferromagnetic resonance (FMR) techniques were employeed. In this case, these techniques allowed us to study the static and dynamical magnetization properties of our tri-layers. The experimental results were interpreted based on the phenomenological model that takes into account the relevant energy terms to the magnetic free energy to describe the system behavior. In the case of the monocrystalline Fe film, we performed an analytical discussion on the magnetization curves and developed a numerical simulation based on the Stoner-Wohlfarth model, that enables the numerical adjustment of the experimental magnetization curves and obtainment of the anisotropy field values. On the other hand, for the tri-layers, we analyzed the existence of bilinear and biquadratic couplings between the magnetizations of adjacent ferromagnetic layers from measurements of magnetization curves. With the FMR fields and line width angular dependencies, information on the anisotropy in three layers was obtained and the effects of different magnetic relaxation mechanisms were evidenced. It was also possible to observe the dependence of the epitaxy of the multilayers with growth and sputtering parameters. Additionally it was developed the technique of AC magnetic susceptibility in order to obtain further information during the investigation of magnetic thin films

Temperature-dependent vortex matter in a superconducting mesoscopic circular sector

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

Vortex state in a mesoscopic flat disk with rough surface

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Vortices in a mesoscopic superconducting circular sector

In the present paper we develop an algorithm to solve the time dependent Ginzburg-Landau equations, by using the link variables technique, for circular geometries. In addition, we evaluate the Helmholtz and Gibbs free energy, the magnetization, and the number of vortices. This algorithm is applied to a circular sector. We evaluate the superconduting-normal magnetic field transition, the magnetization, and the superconducting density. Our results point out that, as we reduce the superconducting area, the nucleation field increases. Nevertheless, as the angular width of the circular sector goes to small values the asymptotic behavior is independent of the sample area. We also show that the value of the first nucleation field is approximately the same independently of the form of the circular sector. Furthermore, we study the nucleation of giant and multivortex states for the different shapes of the present geometry.

Properties of hydrogenated amorphous carbon films deposited by PECVD and modified by SF6 plasma

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)