Publications

Abstract The standard (p(o) = 0.1 MPa) molar enthalpies of formation of 2-, 3-, and 4-chloronitrobenzene isomers, in the crystalline state, at T = 298.15 K, were derived from the standard (p(o) = 0.1 MPa) massic energies of combustion, in oxygen, at T = 298.15 K, measured by rotating bomb combustion calorimetry. The standard molar enthalpies of sublimation of the isomers, at T = 298.15 K, were obtained by high temperature Calvet microcalorimetry. [GRAPHICS] From the determined experimental data, the values of the gaseous standard (p(o) = 0.1 MPa) molar enthalpies of formation for the three monochloronitrobenzene isomers were derived. The gas-phase enthalpies of formation were also estimated by the empirical scheme developed by Cox showing that for meta- and para-chloronitrobenzene the estimated values are in close agreement with the experimental ones whereas, in the case of ortho-chloronitrobenzene it is shown that a different enthalpic interaction increment is needed, when the substituents in the adjacent carbon ring atoms are a chlorine atom and a nitro group.

Abstract The present work is part of a research program on the energetics of formation of alkyl substituted benzenediols, aiming the study of the enthalpic effect of the introduction of methyl substituents into benzenediols. In this work we present the results of the thermochemical research on 2-methylresorcinol, 3-methylresorcinol, 4-methylresorcinol, and methylhydroquinone. The standard (p degrees = 0.1 MPa) molar enthalpies of formation, in the crystalline phase, at T = 298.15 K, of the compounds mentioned above were derived from their standard massic energies of combustion, measured by static-bomb combustion calorimetry, while the standard molar enthalpies of sublimation of those compounds were obtained by the temperature dependence of their vapour pressures determined by the Knudsen effusion technique. [GRAPHICS] From those experimental values, the standard molar enthalpies of formation of the studied methylbenzenediols in the gaseous phase, at T = 298.15 K were then derived. The results are interpreted in terms of structural contributions to the energetics of the substituted benzenediols and compared with the same parameters estimated from the Cox Scheme. Moreover, the standard (p degrees = 0.1 MPa) molar enthalpies, entropies, and Gibbs energies of sublimation, at T = 298.15 K, were derived for the four isomers of methylbenzenediols.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation of the liquid 2-bromophenol and crystalline 4-bromophenol, respectively, Delta(f)H(m)degrees(l) = -(133.5 +/- 1.4) kJ . mol(-1) and Delta(f)H(m)degrees(cr) = -(152.4 +/- 1.4) kJ . mol(-1), were derived from the standard molar energies of combustion, in oxygen, to yield CO(2)(g) and HBr center dot 600H(2)O(l), at T = 298.15 K, measured by rotating-bomb combustion calorimetry. The Calvet high temperature vacuum sublimation technique was used to measure the enthalpy of vaporization or sublimation of the compounds, Delta(g)(l)H(m)degrees = (55.5 +/- 1.3) kJ . mol(-1) and Delta(g)(cr)H(m)degrees = (83.1 +/- 1.6) kJ . mol(-1). These two thermodynamic parameters yielded the standard molar enthalpies of formation, in the gaseous phase, at T = 298.15 K, of 2- and 4-bromophenol, respectively, Delta(f)H(m)degrees(g) = -(78.0 +/- 1.9) kJ . mol(-1) and Delta(f)H(m)degrees(g) = -(69.3 +/- 2.1) kJ . mol(-1). The experimental values of the gas-phase enthalpies of formation of each compound were compared with estimates using the empirical scheme developed by Cox and with the calculated values based on high-level density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional at the 6-311++G(d,p) basis set.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpy of formation, of the 2.5-dibromonitrobenzene, in the crystalline phase, at T = 298.15 K, was derived from the standard massic energy of combustion, in oxygen, at T = 298.15 K, measured by rotating bomb combustion calorimetry. The Knudsen mass-loss effusion technique was used to measure the vapour pressures of the crystal as a function of the temperature and applying the Clausius-Clapeyron equation, the standard molar enthalpy of sublimation of the compound, at T = 298.15 K, was calculated. [GRAPHICS] The combination of the values ofthe standard molar enthalpy of formation, in the crystalline phase, and the standard molar enthalpy of sublimation of the dibromonitrobenzene isomer, allowed the calculation of the standard (p degrees = 0.1 MPa) molar enthalpy of formation, in the gaseous phase, at T = 298.15 K. Additionally, this value was estimated by employing two different methodologies. One based on the conventional Cox Scheme and another one, much more accurate, based on the values of the standard molar enthalpies of formation of 2- and 3-bromonitrobenzene already determined experimentally. Once the best approach was found, it was applied in the estimation of the standard molar enthalpies of formation of the other five isomers.

Abstract The conformational preferences of cocaine and ecgonine methyl ester were determined through ab initio and density functional theory calculations. They share the same preferred orientation of the acetate group with a hydrogen bond between the amine and carbonyl groups, and s-cis conformation for the methoxyl group. The benzoyloxy group of cocaine defines a specific accessible conformational region. In solution the most stable conformers are stabilized by internal hydrogen bonds in contrast to the lesser stables, which are stabilized by solute/solvent interactions. Overall, these conformational features explain why ecgonine methyl ester is the principal metabolite of cocaine in a human environment.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpy of formation of 4,5-dichloro-2-nitroaniline, in the gaseous phase, at T = 298.15 K, was derived from the combination of the values of the standard molar enthalpy of formation, in the crystalline phase, at T = 298.15 K, and the standard molar enthalpy of sublimation, at the same temperature. The standard molar enthalpy of formation, in the crystalline phase, at T = 298.15 K, was derived as -(99.7 +/- 1.6) kJ.mol(-1) from the standard massic energy of combustion, in oxygen, measured by rotating-bomb combustion calorimetry. The standard molar enthalpy of sublimation was calculated. (109.4 +/- 0.9) kJ.mol(-1) by the application of the Clausius-Clapeyron equation, to the vapour pressures measured at several temperatures by Knudsen effusion technique. The standard molar enthalpies of formation, in the gaseous phase, of the six dichloro-2-nitroaniline isomers and of the four dichloro-4-nitroaniline isomers were estimated by the Cox Scheme and by the Domalski and Hearing group additivity method and compared with the available experimental values. For the Domalski and Hearing group additivity method four new correction terms were derived.

Abstract Two new methods for inorganic pyrophosphate (PPi) quantification are described. They are based on the enzymatic conversion of PPi into ATP by firefly luciferase (Luc. E.C. 1.13.12.7) in the presence of dehydroluciferyl-adenylate (L-AMP) followed by the determination of ATP by one of two different procedures, either UV-monitored (260nm) ion-pair-HPLC (IP-HPLC) (method A) or luciferase-dependent bioluminescence in the presence Of its Substrate, firefly luciferin (D-LH(2)) (method B). These methods were subjected to optimization using experimental design methodologies to obtain optimum values for the selected factors: method A-incubation time (t(inc) = 15 min), inactivation time of the enzyme (t(inac) = 2 min), pH of the reaction mixture (pH 7.50) and the concentrations of L-AMP ([L-AMP] = 40 mu M) and luciferase ([Luc] = 0.1 mu M); method B-concentrations of L-AMP ([L-AMP] = 2 mu M), luciferase ([Luc] = 50nM) and luciferin ([LH(2)] = 30 mu M). Method Alias a linear response over the range of 0.1-20 mu M of PPi, with a limit of detection (LOD) of 0.5 mu M and a limit of quantitation (LOQ) of 1.8 mu M. Precision, expressed as relative standard deviation (R.S.D.), is 7.4% at 1 mu M PPi and 5.9% at 8 mu M PPi. Method B has a linear response over the range of 0.75-6.0 mu M of PPi, with LOD and LOQ of 0.624 and 2.23 mu M, respectively, and a R.S.D. of 5.1% at 2.5 mu M PPi and 4.9% at 5 mu M PPi. Under optimized conditions sensitive and robust methods can be obtained for the analysis of PPi impurities in commercial nucleotides and tripolyphosphate (P(3)).

Abstract There are many of pathogen bacteria species which very different susceptibility profile to different antibacterial drugs. There are many drugs described with very different affinity to a large number of receptors. In this work, we selected Drug-Bacteria Pairs (DBPs) of affinity/non-affinity drugs with similar/dissimilar bacteria and represented it as a large network, which may be used to identify drugs that can act on bacteria. Computational chemistry prediction of the biological activity based on one-target Quantitative Structure-Activity Relationship (ot-QSAR) studies substantially increases the potentialities of this kind of networks avoiding time and resource consuming experiments. Unfortunately almost all ot-QSAR models predict the biological activity of drugs against only one bacterial species. Consequently, multi-tasking learning to predict drug's activity against different species with a single model (mt-QSAR) is a goal of major importance. These mt-QSARs offer a good opportunity to construct drug-drug similarity Complex Networks. Unfortunately, almost QSAR models are unspecific or predict activity against only one receptor. To solve this problem, we developed here a multi-bacteria QSAR classification model. The model correctly classifies 202 out of 241 active compounds (83.8%) and 169 out of 200 non-active cases (84.5%). Overall training predictability was 84.13% (371 out of 441 cases). The validation of the model was carried out by means of external predicting series, classifying the model 197 out of 221 (89.4%) cases. In order to show how the model functions in practice a virtual screening was carried out recognizing the model as active 86.7%, 520 out of 600 cases not used in training or predicting series. Outputs of this QSAR model were used as inputs to construct a network. The observed network has 1242 nodes (DBPs), 772,736 edges or DBPs with similar activity (sDBPs). The network predicted has 1031 nodes, 641,377 sDBPs. After edge-to-edge comparison, we have demonstrated that the predicted network is significantly similar to the observed one and both have distribution closer to exponential than to normal.

Abstract The most important limitation of antifungal QSAR models is that they predict the biological activity of drugs against only one fungal species. This is determined due the fact that most of the up-to-date reported molecular descriptors encode only information about the molecular structure. Consequently, predicting the probability with which a drug is active against different fungal species with a single unifying model is a goal of major importance. Herein, we use the Markov Chain theory to calculate new multi-target spectral moments to fit a QSAR model that predicts the antifungal activity of more than 280 drugs against 90 fungi species. Linear discriminant analysis (LDA) was used to classify drugs into two classes as active or non-active against the different tested fungal species whose data we processed. The model correctly classifies 12434 out of 12566 non-active compounds (98.95%) and 421 out of 468 active compounds (89.96%). Overall training predictability was 98.63%. Validation of the model was carried out by means of external predicting series, the model classifying, thus, 6216 out of 6277 non-active compounds and 215 out of 239 active compounds. Overall training predictability was 98.7%. The present is the first attempt to calculate, within a unifying framework, the probabilities of antifungal action of drugs against many different species based on spectral moment's analysis.