AN ELECTRONEGATIVITY MODEL FOR VIBRATIONAL INTENSITIES OF SUBSTITUTED METHANES

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AN ADAPTATION OF ARTHUR FOR MICROCOMPUTERS

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Mixture designs for exploring class diversity and metabolite fingerprinting: An efficient column chromatographic strategy

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)The effects of four solvents, hexane, dichloromethane, ethyl acetate, methanol, and their mixtures on the separation of metabolites in crude extracts of Erythrina speciosa Andrews leaves were investigated using two strategies for open column chromatography. The classical extraction procedure was compared with mobile phases prepared according to a mixture design in order to explore the effects of solvent interactions on metabolite separations. Principal component analysis was used to compare the UV spectra obtained from RP-HPLC-DAD and to estimate the number of independent factors contained in the chromatographic data of the extracts. The results showed that, in addition to solvent polarity, solvent mixtures play an important role in metabolite separation. When pure solvents are used, larger groups of similar spectra are observed in the factor analysis score graphs indicating the same or a limited number of metabolite classes. In contrast solvent mixtures produced score graphs with a larger number of clusters indicating greater metabolic diversity. Besides resulting in more peaks than the pure solvents the chromatographic data of the design mixtures resulted in larger numbers of significant principal components confirming the greater chemical diversity of their extracts. Thus, if the objective of an analysis is to obtain metabolites of the same class, one should use pure solvents. On the other hand, binary and ternary solvent mixtures are recommended for more efficient investigations of class diversity and richer metabolite fingerprints. (C) 2011 Elsevier B.V. All rights reserved.7022288294Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Principal component and Tucker3 analyses of high performance liquid chromatography with diode-array detection fingerprints of crude extracts of Erythrina speciosa Andrews leaves

Mixtures of ethanol, dichloromethane, hexane and acetone obtained according to a statistical design have been used to extract substances from Erythrina speciosa Andrew leaves for chromatographic fingerprinting. The plant extracts from each mixture were analyzed by HPLC-DAD providing UV-vis spectra for each chromatographic peak. These chromatograms and spectra for the design mixtures were then treated with principal component (PCA). Tucker3 and PARAFAC analyses. PCA indicated the existence of five different chromatographic fingerprints for the leave extracts depending on the solvent mixture composition. Different chromatographic peak areas were strongly correlated with the mixture proportions of acetone, dichloromethane and ethanol. Tucker3 and PARAFAC analyses were very useful for identifying simultaneous correlations between chromatographic peak areas, spectral band absorbances and solvent proportions. The acetone proportion was highly correlated with the area of the 3.69 min retention time peak and the spectral absorbances between 250 and 260 nm, consistent with the presence of natural polyphenols. The dichloromethane mixture proportion was strongly correlated with the 12.19 min chromatographic peak area and a single spectral absorbance at 201 nm. This spectral absorption is characteristic of the electronic structures of terpenes and alkaloids. (c) 2012 Elsevier B.V. All rights reserved.736364

Statistical mixture design - Varimax factor optimization for selective compound extraction from plant material

Varimax-transformed chromatograms of compounds extracted from Erythrina speciosa Andrews leaves by simplex centroid design mixtures of dichloromethane, hexane, ethanol and acetone are reported and compared with principal component results. Six varimax factors were investigated focusing on the three main groups of extracted compounds with retention times of 1.7, 3.1 and 6.6 min. Varimax models provide chromatographic loading profiles that are simpler than their principal component counterparts. Furthermore varimax score models in terms of extraction medium compositions are simpler to interpret. The first varimax model results in an optimum extraction mixture of 71% dichloromethane-29% acetone although substitution of acetone by ethanol results in an almost identical extraction profile. The second varimax score model predicts optimum extraction binary mixtures with hexane proportions ranging from 50 to 100% for complementary proportions of either acetone or ethanol. The third varimax factor provides a response surface that is very similar to the one found for the third PC. Confirmatory experiments were performed to validate the model predictions. (C) 2008 Elsevier B.V. All rights reserved.6131485

Speciation of aqueous chromium(VI) solutions with the aid of Q-mode factor analysis followed by oblique projection

The identities of the species of chromium(VI) that are present in aqueous solution, their spectra and their equilibria, continue to be a subject of discussion in the literature. In this paper, the composition of the Cr(VI) equilibria was estimated from the UV-vis spectra of dilute potassium dichromate solutions, without any prior knowledge of the quantities of pure components, with the aid of Imbrie Q-mode factor analysis (Q-mode FA) followed by Varimax rotation and Imbrie oblique projection. Combining these results with the k-matrix method, it was possible to obtain the spectra of the individual Cr(VI) species. Sets of 3.3 x 10(-4) and 3.3 x 10(-5) mol 1(-1) Cr(VI) solutions were studied. In the pH range from 1 to 12, two factors were identified, which were related to the two species, chromate ion (CrO42-) and bichromate ion (HCrO4-). When the analysis was extended to concentrated acid media, another factor appeared, which was related to chromic acid (H2CrO4). No evidence for the dichromate ion (Cr2O72-) was seen at the Cr(VI) concentrations used. The spectra of the pure components were obtained and pK values for the first and second chromic acid dissociations were estimated as -0.54 and 5.8, respectively. (C) 2000 Elsevier Science B.V. All rights reserved.53245346

Investigation of the pH effect and UV radiation on kinetic degradation of anthocyanin mixtures extracted from Hibiscus acetosella

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)The major anthocyanin pigments extracted from Hibiscus acetosella flower were investigated by UV-Vis spectroscopy and multivariate curve resolution-alternating least squares (MCR-ALS). Pure spectra and kinetic of the species present at different pH values were recovered for anthocyanins transformation and degradation products, found with and without UV radiation exposure. In the absence of UV radiation, up to seven different species were detected and by UV radiation exposure, this number increased to up to nine. The species detected in the absence of radiation were also detected when pigments samples were exposed to UV radiation, where degradation occurred faster and two new species appear. The kinetic profiles obtained at different pH values allowed the proposal of a reaction mechanism and pathway. (C) 2010 Elsevier Ltd. All rights reserved.125310201027Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Institute of Chemical and Environmental Research (IIQAB-CSIC) of Barcelona (Spain)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP [04/09231-6

Exploratory analysis of simultaneous degradation of anthocyanins in the calyces of flowers of the Hibiscus sabdariffa species by PARAFAC model

A three-way resolution method based on PARAFAC model was applied for the UV-Vis spectra to study the simultaneous degradation of anthocyanins extracted from fresh calyces of flowers of the Hibiscus sabdariffa. This methodology was used to resolve a chemical system, for which there was no a priori information about the composition or the pure spectra, a so-called black system. In the pH range from 1 to 13, seven species were identified: flavylium cation, carbinol, quinoidal base, E- and Z-chalcones and E- and Z-ionized chalcones. The concentration changes were determined as functions of pH at different wavelengths. The pK values for the acidity constants as well as tautomeric constant were estimated as 2.70, 3.54 and 0.14, respectively. The spectral profiles recovered by the chemometric methods are in excellent agreement with bands of experimental spectra reported in the literature for the species measured at specific pH values.21121523152

MULTICOMPONENT PRINCIPAL COMPONENT REGRESSION AND PARTIAL LEAST-SQUARES ANALYSES OF OVERLAPPED CHROMATOGRAPHIC PEAKS

Principal component and partial least-squares in latent variable regression methods were applied to the multivariate calibration of overlapping chromatographic peaks for toluene, isooctane and ethanol mixtures. The degree of peak overlap was varied using column temperatures of 105, 120 and 130-degrees-C. Even using the most severely overlapped peaks (130-degrees-C), the analysis errors obtained for validation set samples using both regression techniques were of the same size as those encountered using simple linear regression for individual determination of the three constituents. Truncation of the overlapped peak chromatograms appeared to lower the noise level without a significant loss of statistical information about the constituent concentrations.539112313

A chemometric analysis of ab initio vibrational frequencies and infrared intensities of methyl fluoride

Factorial design and principal component analyses are applied to CH3F infrared frequencies and intensities calculated from ab initio wave functions. In the factorial analysis, the quantitative effects of changing from a 6-31G to a 6-311G basis, of including polarization and diffuse orbitals, and of correcting for electron correlation using the second-order Moller-Plesset procedure are determined for all frequencies and intensities. The most significant main effect observed for the frequencies corresponds to the shift from Hartree-Fock to MP2 calculations, which tends to lower all frequency values by approximately 100 cm(-1). For the intensities, the main effects are larger for the CF stretching and the CH3 asymmetric stretching modes. Interaction effects between two or more of the four factors are found to be of minor importance, except for the interaction between correlation and polarization. The principal component analysis indicates that wave functions with polarization and diffuse orbitals at the second-order Moller-Plesset level provide the best estimates for the harmonic frequencies, but not for the intensities. For the frequencies, the first principal component distinguishes between MP2 and Hartree-Fock calculations, while the second component separates the wave functions with polarization orbitals from those without these orbitals. For the intensities, the separation is similar but less well defined. This analysis also shows that wave function optimization to calculate accurate intensities is more difficult than an optimization for frequencies. (C) 1996 by John Wiley & Sons, Inc.17216717