Um software para análise multivariada foi desenvolvido com o objetivo de oferecer uma ferramenta computacional livre com interface gráfica amigável para pesquisadores, professores e estudantes com interesse em quimiometria. O Chemoface possui módulos capazes de resolver problemas relacionados com planejamento experimental, reconhecimento de padrões, classificação e calibração multivariada. É possível obter uma variedade de gráficos e tabelas para explorar os resultados. Neste trabalho, as principais funcionalidades do Chemoface são exploradas usando estudos de caso reportados na literatura, tais como otimização de adsorção de corante índigo em quitosana usando planejamento fatorial completo, análise exploratória de amostras de própolis caracterizadas por ESI-MS (espectrometria de massas com ionização electrospray) usando PCA (análise de componentes principais) e HCA (análise hierárquica de agrupamentos), modelagem MIA-QSAR (análise multivariada de imagem aplicada à relações quantitativas estrutura-atividade) para predição de parâmetro cinético relacionado à atividade de peptídeos contra dengue usando PLS (método de quadrados mínimos parciais), e classificação de amostras de vinho de diferentes variedades usando PLS-DA (PLS para análise discriminante). Todos os exemplos são ilustrados com gráficos e tabelas obtidos no Chemoface. A software for multivariate analysis was developed in order to provide a free computational tool with user-friendly graphical interface for researchers, professors and students with interest in chemometrics. Chemoface comprises modules that can solve problems related to experimental design, pattern recognition, classification and multivariate calibration. It allows obtaining a variety of high quality graphics and tables to explore results. In this work, the main features of Chemoface are explored using case studies reported in the literature, such as optimization of adsorption of indigo dye on chitosan using full factorial design, exploratory analysis of propolis samples characterized by ESI-MS (electrospray ionization-mass spectrometry) using PCA (principal component analysis) and HCA (hierarchical cluster analysis), MIA-QSAR (multivariate image analysis applied to quantitative structure activity relationship) modeling for the prediction of kinetic parameter related to activities of peptides against dengue using PLS (partial least squares), and classification of wine samples from different varieties using PLS-DA (PLS discriminant analysis). All examples are illustrated with graphs and tables obtained by means of Chemoface.

The present study shows that a hydrogen bond between the OH group and the fluorine atom is not involved in the (1h)J(FH) spin-spin coupling transmission either for 4-bromo-2-fluorophenol or 2-fluorophenol. In fact, according to a quantum theory of atoms in molecules analysis, no bond critical point is found between O-H and F moieties. The nature of the transmission mechanism of the Fermi contact term of the (1h)J(FH) spin-spin coupling is studied by analyzing canonical molecular orbitals (see J. Phys. Chem. A 2010, 114, 1044), and it is observed that virtual orbitals play only a quite minor role in its transmission. This is typical of a Fermi contact term transmitted mainly through exchange interactions owing to the overlap of proximate electronic clouds; therefore, it is suggested to identify them as (nTS)J(FH) coupling where n stands for the number of formal bonds separating the coupling nuclei. In the cases studied in this work is n = 4. Results presented in this work could provide an interesting rationalization for different experimental signs known in the current literature for proximate J(FH) couplings.

The anomeric effect has been assigned as being due to hyperconjugation, electrostatic/steric interactions or exchange effects; thus, there is no general consensus about its actual origin. The classical hyperconjugation model, usually investigated using natural bond orbital (NBO) analysis, has been arbitrarily refuted because it would not explain some cases of the preferred equatorial anomer over the axial one in polar solution. In this study, hyperconjugation was shown to be dependent on the medium and NBO analysis explains quite well the estimated amounts of axial and equatorial 2-substituted tetrahydropyrans (substituents = F, OH, NH2 and CN) both in the gas phase and aqueous solution. Overall, there is no reason to abandon the hyperconjugation model as it plays a dominating role of the anomeric effect in some systems, while NBO analysis reproduces the energetic profiles on the basis of both hyperconjugative and Lewis-type contributions.

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A QSAR method based on MIA (multivariate image analysis) descriptors is applied to a series of 2-amino-6-arylsulfonylbenzonitriles and their thio and sulfinyl congeners, compounds with anti-HIV-1 activity. Two models were built in order to appraise the modelling capability when different drawing programs are used to create the set of molecules. Both models showed good predictive ability, with cross-validated Q2 of 0.712 and 0.624, and Q2 for an external validation set of 0.823 and 0.747. An ADME evaluation, by calculating the topological polar surface area (TPSA) and parameters derived from the rule of five, was also performed to proposed compounds in order to suggest absorption profiles for potential new drugs.

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The conformational equilibria of trans-1-methoxy-2-chloro-(1), trans-1-methoxy-2-bromo-(2) and trans-1-methoxy-2-iodocyclohexane (3), and their corresponding alcohols (4-6), were studied through a combined method of NMR, theoretical calculations and solvation theory. They can be described in terms of the axial-axial and equatorial-equatorial conformations, taking into account the main rotamers of each of these conformations. From the NMR experiments at 183 K in CD 2 Cl 2 -CS 2 , it was possible to observe proton H 2 in the ax-ax and eq-eq conformers separately for 1 and 2, but not for 3, which gave directly their populations and conformer energies. In the alcohols the proportion of the ax-ax conformer was too low to be detected by NMR under these conditions. Those HH couplings together with the values at room temperature, in a variety of solvents allowed the determination of the solvent dependence of the conformer energies and hence the vapor state energy difference. The DE (E ax -E eq ) values in the vapor state for 1, 2 and 3 are À0.05, 0.20 and 0.55 kcal mol À1 , respectively, increasing to 1.10, 1.22 and 1.41 kcal mol À1 in CD 3 CN solution (1 kcal = 4.184 kJ). For 4-6 the eq-eq conformation is always much more stable in both non-polar and polar solvents, with energy differences ranging from 1.78, 1.94 and 1.86 kcal mol À1 (in CCl 4 ) to 1.27, 1.49 and 1.54 kcal mol À1 (in DMSO), respectively. Comparison of the hydroxy and methoxy compounds gives the intramolecular hydrogen bonding energy for the alcohols as 1.40, 1.36 and 1.00 kcal mol À1 (in CCl 4 ) for 4, 5 and 6, respectively.

This paper emphasizes that fluorine atoms in organic molecules need special geometric requirements to experience intramolecular hydrogen bonds (H-bonds). Calculations at the B3LYP/aug-cc-pVDZ theoretical level and using the quantum theory of atoms in molecules applied over a series of monocyclic compounds, which have similar CLC(F)-C(OH)LC fragments, predict that the F … HO intramolecular H-bond does not exist when forming five-membered rings. Indeed, it is shown that the geometric restrictions imposed by the rigid rings are the main reasons in preventing fluorine participating in such a F … HO intramolecular H-bond.