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- Solution enthalpies of 1,4-dioxane: study of solvent effects through quantitative structure-property relationshipsPublication . Nunes, Nelson; Reis, Marina; Moreira, Luís; Elvas Leitao, Ruben; Martins, FilomenaSolution 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.
- The separation between solvent polarizability and solvent dipolarity: revisiting the Kamlet-Abraham-Taft model equationPublication . Moreira, L.; Elvas Leitao, Ruben; Martins, FilomenaQuantitative 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.
- Solution enthalpies of hydroxylic compoundsPublication . Moreira, Luís; Reis, Marina; Nunes, Nélson; Elvas Leitao, Ruben; Martins, FilomenaSolution 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.
- Solvent effects on solution enthalpies of adamantyl derivativesPublication . Martins, Filomena; Moreira, Luís; Nunes, Nélson; Elvas Leitao, RubenSolution 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.
- UV-Vis spectroscopic study preferential solvation and intermolecular interactions in methanol/1-propanol/acetonitrile by means of solvatochromic probesPublication . Nunes, Nelson Alberto Frade da Silva; Elvas Leitao, Ruben; Martins, FilomenaSolvatochromic UV-Vis shifts of four indicators (4-nitroaniline, 4-nitroanisole, 4-nitrophenol and N,N-dimethy-1-4-nitro aniline) have been measured at 298.15 K in the ternary mixture methano1/1-propanol/acetonitrile (MeOH/1-PrOH/MeCN) in a total of 22 mole fractions, along with 18 additional mole fractions for each of the corresponding binary mixtures, MeOH/1-PrOH, 1-PrOH/MeCN and MeOH/MeCN. These values, combined with our previous experimental results for 2,6-dipheny1-4-(2,4,6-triphenylpyridinium-1-yl)phenolate (Reichardt's betaine dye) in the same mixtures, permitted the computation of the Kamlet-Taft solvent parameters, alpha, beta, and pi*. The rationalization of the spectroscopic behavior of each probe within each mixture's whole mole fraction range was achieved through the use of the Bosch and Roses preferential solvation model. The applied model allowed the identification of synergistic behaviors in MeCN/alcohol mixtures and thus to infer the existence of solvent complexes in solution. Also, the addition of small amounts of MeCN to the binary mixtures was seen to cause a significant variation in pi*, whereas the addition of alcohol to MeCN mixtures always lead to a sudden change in a and The behavior of these parameters in the ternary mixture was shown to be mainly determined by the contributions of the underlying binary mixtures. (C) 2014 Elsevier B.V. All rights reserved.
- QSAR modeling of antitubercular activity of diverse organic compoundsPublication . Kovalishyn, Vasyl; Aires-de-Sousa, Joao; Ventura, Cristina; Elvas Leitao, Ruben; Martins, FilomenaTuberculosis (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.
- Enthalpies of solution of 1-butyl-3-methylimidazolium tetrafluoroborate in 15 solvents at 298.15 kPublication . Reis, Marina; Elvas Leitao, Ruben; Martins, FilomenaEnthalpies 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).
- Zooming in with QSPR on Friedel-Crafts acylation reactions over modified BEA zeolitesPublication . Aleixo, Odrigo; Elvas Leitao, Ruben; Martins, Filomena; Carvalho, Ana; Brigas, Amadeu Fernandes; Nunes, Ricardo; Fernandes, Auguste; Rocha, Joao; Martins, Angela; Nunes, NelsonThe catalytic behaviour of hierarchical BEA zeolites with Si/Al ratio of 12.5 and 32 was studied in Friedel-Crafts acylation reactions using furan, anisole and pyrrole as substrates and acetic anhydride as acylating agent. Hierarchical BEA samples were submitted to alkaline and alkaline + acid treatments. Kinetic modelling using nonlinear regressions applied to a simplified Langmuir-Hinshelwood equation showed that the Si/Al ratio of the parent materials strongly influenced the catalytic behaviour. Catalytic results were correlated with physicochemical properties using a Quantitative Structure-Property Relationship (QSPR) methodology. This approach provided detailed information about the role of key properties on the catalytic behaviour, and pointed out which properties should be modified through direct synthesis and/or post-synthesis treatments to obtain materials with optimized catalytic performance.
- Using solvatochromic probes to investigate intermolecular interactions in 1,4-dioxane/methanol/acetonitrile solvent mixturesPublication . Nunes, Ricardo; Nunes, Nelson; Elvas Leitao, Ruben; Martins, FilomenaUV–Vis absorption spectra of five solvatochromic probes namely, betaine (30), 4-nitrophenol, 4-nitroanisole, 4-nitroaniline and N,N-dimethyl-4-nitroaniline, were obtained at 298.15 K in the binary systems 1,4-dioxane/methanol (MeOH) and 1,4-dioxane/acetonitrile (MeCN), and in the ternary system 1,4-dioxane/methanol/acetonitrile, in a total of 40 new solvent mixtures. Preferential solvation trends were assessed through the Bosch and Rosès formalism for the binary mixtures, and the extended model approach for the ternary mixture, thus allowing the setting up of a preferential solvation order for all entities present in solution, including solvent “complexes”. Synergistic behaviors were spotted in most binary mixtures involving 1,4-dioxane but not in the ternary system which is dominated by a combination of contributions from the three underlying binary mixtures. Kamlet-Taft parameters π*, α and β were also computed for all 40 systems and their variation with composition was thoroughly examined. The addition of small amounts of 1,4-dioxane to the mixtures was seen to cause a significant variation in π*, whereas on the other extreme, in dioxane rich mixtures, a large effect in α was observed, particularly for the system 1,4-dioxane/methanol.
- Solution enthalpies of hydroxylic compoundsPublication . Reis, Marina; Moreira, Luís; Nunes, Nélson; Elvas Leitao, Ruben; Martins, FilomenaSolution 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.
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