Enthalpies of solution of 1-butyl-3-methylimidazolium tetrafluoroborate in 15 solvents at 298.15 k

Enthalpies of solution of 1-butyl-3-methylimidazolium tetra fluoroborate, [BMIm]BF4, are reported at 298.15 K in a set of 15 hydrogen bond donor and hydrogen bond acceptor solvents, chosen by their diversity, namely, water, methanol, ethanol, 1,2-ethanediol, 2-choroethanol, 2-methoxyethanol, formamide, propylene carbonate, nitromethane, acetonitrile, dimethyl sulfoxide, acetone, N,N-dimethylformamide, N,N-dimethylacetamide, and aniline. These values are shown to be largely independent of [BMIm]BF4 concentration. The obtained enthalpies of solution vary from very endothermic to quite exothermic, thus showing a very high sensitivity of the enthalpies of solution of [BMIm]BF4 to solvent properties. Solvent effects on the solution process of this IL are analyzed by a quantitative structure-property relationship methodology, using the TAKA equation and a modified equation, which significantly improves the model's predictive ability. The observed differences in the enthalpies of solution are rationalized in terms of the solvent properties found to be relevant, that is, pi* and E-T(N)

Solvent effects on solution enthalpies of adamantyl derivatives

Solution enthalpies of 1-bromoadamantane, 1-adamantanol, and 2-adamantanone in a large set of protic and aprotic solvents are reported at 298.15 K. Solvent effects on the solution processes of these solutes are analyzed in terms of a modified TAKA equation, involving delta(cav) h (s) as the cavity term. The nature and magnitude of the major interactions which influence these processes are assessed and discussed in terms of the solutes' characteristics. New insights on the solution processes under scrutiny are presented

Solution enthalpies of hydroxylic compounds

Solution enthalpies of adamantan-1-ol, 2-methyl- butan-2-ol, and 3-methylbutan-1-ol have been measured at 298.15 K, in a set of 16 protogenic and non-protogenic solvents. The identification and quantification of solvent effects on the solution processes under study were performed using quantitative-structure property relationships. The results are discussed in terms of solute-solvent-solvent interactions and also in terms of the influence of compound's size and position of its hydroxyl group

QSAR modeling of antitubercular activity of diverse organic compounds

Tuberculosis (TB) is a worldwide infectious disease that has shown over time extremely high mortality levels. The urgent need to develop new antitubercular drugs is due to the increasing rate of appearance of multi-drug resistant strains to the commonly used drugs, and the longer durations of therapy and recovery, particularly in immuno-compromised patients. The major goal of the present study is the exploration of data from different families of compounds through the use of a variety of machine learning techniques so that robust QSAR-based models can be developed to further guide in the quest for new potent anti-TB compounds. Eight QSAR models were built using various types of descriptors (from ADRIANA.Code and Dragon software) with two publicly available structurally diverse data sets, including recent data deposited in PubChem. QSAR methodologies used Random Forests and Associative Neural Networks. Predictions for the external evaluation sets obtained accuracies in the range of 0.76-0.88 (for active/inactive classifications) and Q(2)=0.66-0.89 for regressions. Models developed in this study can be used to estimate the anti-TB activity of drug candidates at early stages of drug development (C) 2011 Elsevier B.V. All rights reserved

Solution enthalpies of 1,4-dioxane: study of solvent effects through quantitative structure-property relationships

Solution enthalpies of 1,4-dioxane have been obtained in 15 protic and aprotic solvents at 298.15 K. Breaking the overall process through the use of Solomonov's methodology the cavity term was calculated and interaction enthalpies (Delta H-int) were determined. Main factors involved in the interaction enthalpy have been identified and quantified using a QSPR approach based on the TAKA model equation. The relevant descriptors were found to be pi* and beta, which showed, respectively, exothermic and endothermic contributions. The magnitude of pi* coefficient points toward non-specific solute-solvent interactions playing a major role in the solution process. The positive value of the beta coefficient reflects the endothermic character of the solvents' hydrogen bond acceptor (HBA) basicity contribution, indicating that solvent molecules engaged in hydrogen bonding preferentially interact with each other rather than with 1,4-dioxane. (C) 2013 Elsevier B.V. All rights reserved

Densities and refractive indices for the ternary mixture methanol/propan-1-Ol/acetonitrile

Refractive indices, n(D), and densities, rho, at 298.15 K were measured for the ternary mixture methanol (MeOH)/propan-1-ol (1-PrOH)/acetonitrile (MeCN) for a total of 22 mole fractions, along with 18 mole fractions of each of the corresponding binary mixtures, methanol/propan-1-ol, propan-1-ol/acetonitrile and methanol/acetonitrile. The variation of excess refractive indices and excess molar volumes with composition was modeled by the Redlich-Kister polynomial function in the case of binary mixtures and by the Cibulka equation for the ternary mixture. A thermodynamic approach to excess refractive indices, recently proposed by other authors, was applied for the first time to ternary liquid mixtures. Structural effects were identified and interpreted both in the binary and ternary systems. A complex relationship between excess refractive indices and excess molar volumes was identified, revealing all four possible sign combinations between these two properties. Structuring of the mixtures was also discussed on the basis of partial molar volumes of the binary and ternary mixtures

Design, synthesis and biologival evaluation of novel isoniazid derivatives with potente antitubercular activity

The disturbing emergence of multidrug-resistant strains of Mycobacterium tuberculosis (Mtb) has been driving the scientific community to urgently search for new and efficient antitubercular drugs. Despite the various drugs currently under evaluation, isoniazid is still the key and most effective component in all multi-therapeutic regimens recommended by the WHO. This paper describes the QSAR-oriented design, synthesis and in vitro antitubercular activity of several potent isoniazid derivatives (isonicotinoyl hydrazones and isonicotinoyl hydrazides) against H37Rv and two resistant Mtb strains. QSAR studies entailed RFs and ASNNs classification models, as well as MLR models. Strict validation procedures were used to guarantee the models' robustness and predictive ability. Lipophilicity was shown not to be relevant to explain the activity of these derivatives, whereas shorter N-N distances and lengthy substituents lead to more active compounds. Compounds I, 2, 4, 5 and 6, showed measured activities against H37Rv higher than INH (i.e., MIC <= 0.28 mu M), while compound 9 exhibited a six fold decrease in MIC against the katG (S315T) mutated strain, by comparison with INH (Le., 6.9 vs. 43.8 mu M). All compounds were ineffective against H37Rv(INH) (Delta katG), a strain with a full deletion of the katG gene, thus corroborating the importance of KatG in the activation of INH-based compounds. The most potent compounds were also shown not to be cytotoxic up to a concentration 500 times higher than MIC. (C) 2014 Elsevier Masson SAS. All rights reserved

Fighting collinearity in QSPR equations for solution kinetics with the Monte Carlo method and total weighting

A Monte Carlo method is used in addition to functional and individual weighting to overcome multicollinearity problems in multiple linear regression equations applied as quantitative-structure-property-relationships, allowing the estimation of correct coefficient confidence intervals. The method was applied to rate constants for the Menschutkin reaction between Et3N and EtI in mono- and di-alcohols, at 25.00 ºC. Results show that the use of our methodology produces a significant improvement upon confidence interval estimates regardless of the level of collinearity present. Addition of weighting shows additional advantages, increasing the overall consistency of the regression process.info:eu-repo/semantics/publishedVersio

Revisiting the reactions of t-BuX (X = Br, I) with monoalcohols: a mechanistic analysis through numerical integration and nonlinear regression methods

The reactions of two tertiary butyl halides, i.e., t-BuBr and t-BuI, with monoalcohols (methanol, i-propanol, and t-butanol) have been studied at several temperatures during extended periods of time to acquire kinetic data for both the solvolytic step and the subsequent reactions. Reaction progress was followed by conductimetry, and calibration curves were obtained for all systems under study to derive concentration versus time curves for the significant intermediate species, the formed acid, HX. The GMS comprehensive mechanism, previously proposed by Gonçalves, Martins, and Simões for these reactions, was successfully tested using numerical integration associated with nonlinear regression, confirming the predicted distinct behaviors for methanol (and for that matter also for primary alcohols), secondary, and tertiary alcohols. Results show that accurate rate constants could be obtained in all cases and that the step that follows solvolysis can affect significantly the solvolytic rate constant and therefore any consequent reliable mechanistic analysis.info:eu-repo/semantics/acceptedVersio

The separation between solvent polarizability and solvent dipolarity: revisiting the Kamlet-Abraham-Taft model equation

Quantitative structure-property relationships were established using multiple linear regressions to cor-relate log k values for the heterolysis reaction of 3-bromo-3-ethylpentane using three well-known model equations, the Kamlet-Abraham-Taft (KAT), the Catalan (Cat) and the Laurence (Lau) equations. The a pri-ori exclusion of the hydrogen bond acceptor (HBA) basicity descriptor for all tested models led to similar responses, thus emptying the argument of an alleged use of a non-balanced set of solvents. Concurrently, a new method was devised to split the original Kamlet-Taft p* descriptor into two independent contri-butions which separately quantify the solvent's polarizability (DI) and dipolarity (Dip). A modified version of the KAT equation (mKAT) including both DI and Dip, together with the exclusion of the HBA basicity descriptor was applied to five selected solvent-dependent physicochemical processes. Results showed that the mKAT model provided significant improvements over the original KAT model. Additionally, it was shown that the introduction of DI in the truncated KAT equation could lead to misleading or, at best, inconclusive interpretations of solvent effects. Finally, the performance of mKAT model was compared with Catalan's and Laurence's model equations in terms of statistical results, relevance of descriptors and gas-phase predictions. In general, these three model equations show very similar outcomes although the mKAT model exhibits an overall better performance.info:eu-repo/semantics/publishedVersio