Publications

Abstract The standard (p(o) = 0.1 MPa) molar enthalpies of formation in the condensed phase of seven isomers of fluoromethylaniline were derived from the standard molar energies of combustion, in oxygen, to yield CO2(g), N-2(g) and HF center dot 10H(2)O(l), at T = 298.15 K, measured by rotating bomb combustion calorimetry. The standard molar enthalpies of vaporization or sublimation of these compounds, also at T = 298.15 K, were determined using Calvet microcalorimetry, while the enthalpies of fusion of the solid compounds were determined by differential scanning calorimetry. The standard molar enthalpies of formation in the gaseous phase, at T = 298.15 K, were derived from the former two experimental quantities. G3MP2//B3LYP calculations were performed for all possible fluoromethylanilines allowing the estimation of data for the isomers that were not studied experimentally. The Cox scheme was applied with two different approaches for the estimation of the standard molar enthalpies of formation of all the isomers studied, and this led to the conclusion that the literature values for the enthalpies of formation of the meta and para isomers of methylaniline seem to be not reliable. Further G3MP2//B3LYPs calculations on the methylaniline isomers yielded new values for the standard molar enthalpies of formation of the isomers of methylaniline, which have been tested under the Cox scheme, resulting in better estimates.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation in the condensed phase of all the fluoroanilines, with the exception of the 2,3,5-trifluoroaniline compound, were derived from the standard molar energies of combustion in oxygen at T = 298.15 K, measured by rotating bomb combustion calorimetry. Calvet high-temperature vacuum sublimation experiments were performed to measure their enthalpies of vaporization or sublimation. These experiments allowed the determination of the standard molar enthalpies of formation in the gaseous phase and at T = 298.15 K. These values are also compared with estimates based on G3MP2B3 and BP86/6-31+G(d) computations, which have been extended also to the fluoroaniline that was not studied experimentally. The results are in close agreement with a mean deviation of similar to 3 kJ center dot mol(-1). The largest difference between experimental and G3MP2B3 values is found for the pentafluoroaniline (-7.0 kJ center dot mol(-1)). For the three monofluoroanilines, the composite approach has been used also to compute gas-phase acidities, electron and proton affinities, ionization enthalpies and N-H bond dissociation enthalpies. The computed values compare well with available experimental results supporting the new computed data.

Abstract Predicting tissue and environmental distribution of chemicals is of major importance for environmental and life sciences. Most of the molecular descriptors used in computational prediction of chemicals partition behavior consider molecular structure but ignore the nature of the partition system. Consequently, computational models derived up-to-date are restricted to the specific system under study. Here, a free energy-based descriptor (del G(k)) is introduced, which circumvent this problem. Based on Delta G(k), we developed for the first time a single linear classification model to predict the partition behavior of a broad number of structurally diverse drugs and other chemicals (1300) for 38 different partition systems of biological and environmental significance. The model presented training/predicting set accuracies of 91.79/88.92%. Parametrical assumptions were checked. Desirability analysis was used to explore the levels of the predictors that produce the most desirable partition properties. Finally, inversion of the partition direction for each one of the 38 partition systems evidences that our models correctly classified 89.08% of compounds with an uncertainty of only +/- 0.17% independently of the direction of the partition process used to seek the model. Other 10 different classification models (linear, neural networks, and genetic algorithms) were also tested for the same purposes. None of these computational models favorably compare with respect to the linear model indicating that our approach capture the main aspects that govern chemicals partition in different systems. (C) 2007 Wiley Periodicals, Inc.

Abstract The apparent water solubility of pentachlorophenol was measured at pH = 6 and at 25 degrees C in pure water, aqueous solutions of three salts (NaCl, KNO3 and CaCl2 at 0.010, 0.10 and LOM) and in aqueous solutions of three fulvic acids samples extracted from a natural soil (sFA), composted sewage sludge (csFA) and composted livestock's material (IsFA). A solubility enhancement method was developed for the measurement of partition coefficients (K-oc, L/kg organic carbon). Pentachlorophenol associates strongly with the fulvic acid samples and the calculated K., were the following (averages and standard deviations): (sFA) (211 22) x 102, (csFA) (253 126) x 102, (IsFA) (235 10) x 10(2). For comparison purposes the K-oc for pyrene were also calculated for the three FA samples and were the following: (sFA) (119 +/- 10) x 10(2), (csFA) (239 21) x 102, (IsFA) (92 10) x 102. The analysis of variance (one-way ANOVA) of the effect of the type of FA sample on the solubilization of pentachlorophenol and pyrene shows that this factor causes significant differences on the aqueous solubilization of these two organic substances.

Abstract The title compound, C14H22N2OS2, contains a disordered isobutyl group. There are no direction-specific interactions between the molecules of the title compound.

Abstract In the title compound, [Ni(C9H10NO2S2)2], the NiII ion adopts a distorted cis-NiS2O2 square-planar geometry arising from the two S,O-bidentate ligands. The thio-phene rings in each ligand are disordered, with site occupancy ratios of 0.874 (3):0.126 (3) and 0.741 (2):0.259 (2). © International Union of Crystallography 2007.

Abstract In the title compound, C17H13N, the dihedral angles between the pyridine ring and the phenyl rings are 29.68 ( 18) and 26.58 (17)degrees. In the crystal structure, the molecules are linked by a weak C-H center dot center dot center dot pi interaction, leading to [0(1) over bar 1] chains. There are no further significant intermolecular interactions.

Abstract The standard (p(0)=0.1 MPa) molar enthalpies of formation, at T=298.15 K, in the gaseous phase, for three tetradentate Schiff bases involving a N2O2 set, N,N'-bis(salicylaldehydo)cyclohexanediimine (H(2)salch), N,N'-bis(acetylacetone)cyclohexanediimine (H(2)acacch) and N,N'-bis(benzoylacetone)cyclohexanediimine (H(2)bzacch), were determined from their enthalpies of combustion and sublimation, obtained by static bomb calorimetry in oxygen and by the Knudsen effusion technique, respectively. The results are compared with identical parameters for related compounds previously studied, resulting from the condensation of salicylaldehyde or beta-diketone with aliphatic diamines.

Abstract In the title complex, [Ni(C14H21N2OS2)(2)], the Ni-II ion is in a square-planar coordination enviroment. The ligands assume a cis arrangement with respect to each other around the Ni-II ion, which lies on a crystallographic twofold rotation axis running parallel to the c axis. The title complex is isostructural with the copper(II) analogue.