Publications

Abstract The standard molar enthalpies of formation of the 3-methyl-N-R-2-quinoxalinecarboxamide-1,4-dioxides (R = H, phenyl, 2-tolyl) in the gas phase were derived using the values for the enthalpies of combustion of the crystalline compounds, measured by static bomb combustion calorimetry, and for the enthalpies of sublimation, measured by Knudsen effusion, at T = 298.15 K. These values have also been used to calibrate a computational procedure that has been employed to estimate the gas-phase enthalpies of formation of the corresponding 3-methyl-N-R-2-quinoxalinecarboxamides and also to compute the first, second, and mean N-O bond dissociation enthalpies in the gas phase. It is found that the size of the substituent almost does not influence the computed N-O bond dissociation enthalpies; the maximum enthalpic difference is similar to 5 kJ center dot mol(-1).

Abstract The gaseous standard molar enthalpies of formation of two 2-R-3-methylquinoxaline-1,4-dioxides (R = benzoyl or tert-butoxycarbonyl), at T = 298.15 K, were derived using the values for the enthalpies of formation of the compounds in the condensed phase, measured by static bomb combustion calorimetry, and for the enthalpies of sublimation, measured by Knudsen effusion, using a quartz crystal oscillator. The three dimensional structure of 2-tert-butoxycarbonyl-3-methylquinoxaline-1,4-dioxide has been obtained by X-ray crystallography showing that the two N-O bond lengths in this compound are identical. The experimentally determined geometry in the crystal is similar to that obtained in the gas-phase after computations performed at the B3LYP/6-311 + G(2d,2p) level of theory. The experimental and computational results reported allow to extend the discussion about the influence of the molecular structure on the dissociation enthalpy of the N-O bonds for quinoxaline 1,4-dioxide derivatives. As found previously, similar N-O bond lengths in quinoxaline-1,4-dioxide compounds are not linked with N-O bonds having the same strength. Copyright (c) 2007 John Wiley & Sons, Ltd.

Abstract Silver thin films were deposited with different preferential orientations and special attention was paid to the bioreactivity of the surfaces. The study was essentially focused on the evaluation of the films by x-ray diffraction (XRD), atomic force microscopy (AFM), high-resolution transmission electron microscopy (HRTEM), electron probe microanalysis (EPMA) and contact angle measurements. The deposited thin films were characterized before and after immersion in S-enriched simulated human plasma in order to estimate the influence of the preferential crystallographic orientation on the in vitro behaviour. Silver thin films with and without ( 111) preferential crystallographic orientation were deposited by r.f. magnetron sputtering to yield nanocrystalline coatings, high compact structures, very hydrophobic surfaces and low roughness. These properties reduce the chemisorption of reactive species onto the film surface. The in vitro tests indicate that silver thin films can be used as coatings for biomaterials applications.

Abstract The latest results of voltammetric research on the ionic transfer process of ionisable drugs across bare and lipid-modified liquid-liquid interfaces are reviewed. In recent years, two voltammetric methods have been extensively applied to this purpose, i.e. the classical four electrode voltammetry at the interface between two immiscible electrolyte solutions, and the "three-phase electrode." Thus, a brief background of the methodologies and some successful examples of their application are highlighted in this work. Particular attention is given to the ionic transfer kinetics and to the electro-chemical characterization of the drug-membrane interactions between the ionized drugs and lipid-modified interfaces. Future trends in this area are also mentioned in connection with high-throughput assessment of ADMET properties of drugs.

Abstract The quenching of the fluorescence of excitation emission matrices (EEM) of two samples of dissolved organic matter (DOM) [fulvic acid from a dam water (FA) and a commercial humic acid (HA)], provoked by the metal ions Cu(II), UO22+, Fe(III) and Hg(II), was studied by principal component analysis (PCA) and multivariate curve resolution with alternating least squares (MCR-ALS). PCA of the individual EEM, sets of EEM and the sequential analysis of EEM allows the determination of the number of components that provoke linearly independent variations in the EEM and to assess the trend and stability of the quenching process. Four and three components were detected in the EEM of FA and HA, respectively. Some of these components show quenching in the presence of the studied metal ions and other are not affected. Also, the occurrence of scattering due to hydrolysis of metal ions is detected in the PCA sequential analysis of EEM as function of the metal ion concentration. Excitation and emission spectra and quenching profiles were extracted from EEM using MCR-ALS with non-negativity constraints. Stability constants between FA and HA with the studied metal ions were estimated by a modified Stern-Volmer equation.

Abstract The factors that affect trihalomethane (THM) (chloroform, bromodichloromethane, chlorodibromomethane and bromoform) formation from the chlorination of aqueous solutions of hydrophobic fulvic acids (FA) were investigated in a prototype laboratorial simulation using factorial analysis. This strategy involved a fractional factorial design (16 plus 5 center experiments) of five factors (fulvic acids concentration, chlorine dose, temperature, pH and bromide concentration) and a Box Behnken design (12 plus 3 center experiments) for the detailed analysis of three factors (FA concentration, chlorine dose and temperature). The concentration of THM was determined by headspace analysis by GC-ECD. The most significant factors that affect the four THM productions were the following: chloroform-FA concentration and temperature; bromodichloromethane-FA concentration and chlorine dose; chlorodibromomethane-chlorine dose; and, bromofonn-chlorine dose and bromide concentration. Moreover, linear models were obtained for the four THM concentrations in the disinfection solution as function of the FA concentration, chlorine dose and temperature, and it was observed that the complexity of the models (number of significant factors and interactions) increased with increasing bromine atoms in the THM. Also, this study shows that reducing the FA concentration the relative amount of bromated THM increases.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation of 2-chloro-4-nitrophenol, 4-chloro-2-nitrophenol, and 4-chloro-3-nitrophenol in the solid phase, Delta H-f degrees(m)(cr), at T = 298.15 K, were derived from the standard molar enthalpies of combustion measured by rotating-bomb combustion calorimetry, in oxygen. Enthalpies of fusion of the solid compounds were measured by differential scanning calorimetry. The standard molar enthalpies of sublimation, at T = 298.15 K, were measured by Calvet microcalorimetry. Summing the obtained Delta H-f degrees(m) (cr) and Delta H-g(cr)degrees(m) values, it was possible to derive the values of the standard molar enthalpies of formation in the gaseous phase, at T = 298.15 K: Delta H-f degrees(m)(4-chloro-3-nitrophenol, g) = -(108.8 +/- 3.7) kJ.mol(-1). Density functional theory calculations were also performed for all possible chloronitrophenol isomers using the B3LYP functional and the 6-31G** basis set. These calculations allowed the estimation of the standard molar enthalpies of formation in the gaseous phase for all isomers including those not studied experimentally. Identical DFT calculations were also carried out for the respective phenoxyl radicals and phenoxide anions which allowed the estimation of the O-H homolytic bond dissociation energies and gas-phase acidities.

Abstract The standard (p degrees = 0.1 MPa) molar energies of combustion in oxygen, at T = 298.15 K, of four 1,3-benzodioxole derivatives (5-oxoethyl-1,3-benzodioxole, 5-cyano-1,3-benzodioxole, 5-nitro-1,3-benzodioxole, and 5-methyl-1,3-benzodioxole) were measured by static bomb calorimetry. The standard molar enthalpies of vaporization or of sublimation, at T = 298.15 K, were measured by Calvet microcalorimetry. Combining these results, the standard molar enthalpies of formation of the compounds in the gas phase, at T = 298.15 K, have been calculated: 5-oxoethyl-1,3-benzodioxole (-319.3 +/- 2.8) kJ.mol(-1); 5-cyano-1,3-benzodioxole (-23.2 +/- 2.2) kJ.mol(-1); 5-nitro-1,3-benzodioxole (-176.0 +/- 3.2) kJ.mol(-1) and 5-methyl-1,3-benzodioxole (-184.7 +/- 3.5) kJ.mol(-1). The most stable geometries of all the compounds were obtained using the density functional theory with the B3LYP functional and two basis sets: 6-31G** and 6-311G**. The nonplanarity of the molecules was analyzed in terms of the anomeric effect, which is believed to arise from the interaction between a nonbonded oxygen p(pi) orbital and the empty orbital sigma*(CO) involving the other oxygen atom. Calculations were performed to obtain estimates of the enthalpies of formation of all the substituted benzodioxoles using appropriate isodesmic reactions. There is good agreement between theoretical and experimental results. This agreement allows us to estimate the enthalpies of formation of some 1,3-benzodioxole derivatives whose experimental study was impossible.

Abstract The CCAAT/enhancer-binding protein beta (C/EBPbeta) transcription factor has been associated with several cancer models. In this study, the expression of C/EBPbeta was analysed in a series of 90 gastric carcinomas (GCs). We also assessed the effect of C/EBPbeta on COX-2 expression. In normal gastric mucosa, C/EBPbeta expression was restricted to cells in the proliferative zone. In intestinal metaplasia, dysplasia, and GC of the intestinal and atypical subtypes, C/EBPbeta was over-expressed (p < 0.0001, for the association with histological type). C/EBPbeta and, Ki67, a marker of cell proliferation, were also co-expressed in primary GC. We also observed an overlap between C/EBPbeta and COX-2 expression in GC. Using GC cell lines we show that CIEBPbeta can regulate the expression of endogenous COX-2 and transactivate the promoter of the COX-2 gene, depending on its methylation status. These results suggest that C/EBPbeta may be a marker of neoplastic transformation and also play an active role in gastric tumourigenesis by regulating COX-2 expression. Copyright (c) 2006 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Abstract The standard molar enthalpies of combustion, sublimation, and formation of three nitrogen-containing heterocycles, namely, 2-benzimidazolinone, 2-benzoxazolinone and 3-indazolinone were determined calorimetrically. The standard (p degrees similar to 0.1 MPa) molar enthalpies of formation in the gas phase were derived from the standard molar enthalpies of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry and from the standard molar enthalpies of sublimation at T 298.15 K, measured by Calvet microcalorimetry. Moller-Plesset calculations at the MP2 level and density functional calculations with the B3LYP functional and extended basis sets were also performed to determine the energetically preferred tautomeric form of the molecules. The results were qualitatively independent of the calculational level, where in general the DFT calculations were in better agreement with experiment than those from MP2. The gas and solid phase enthalpic differences between imines and amides, wherein -CH = N- is contrasted with -CONH-, have been studied and roughly constant values have been found.