Complex numbers-partial least-squares applied to the treatment of electrochemical impedance spectroscopy data.

This work investigated the application of partial least-squares regression of complex numbers on multivariate data obtained by electrochemical impedance spectroscopy (EIS). The use of complex numbers-PLS was evaluated in the individual determination of two well-known redox probes: ferrocyanide and hydroquinone. The predictive ability of complex numbers-PLS was evaluated for EIS spectra obtained at different applied potentials and perturbation amplitudes, and was also compared to that obtained with PLS applied to EIS data presented as real numbers - only the real or imaginary part of the complex impedance, or the absolute impedance or the phase angle. It is shown that complex numbers-PLS is more efficient (better prediction models) when more complex electrochemical systems (hydroquinone) are probed. Excellent predictions were obtained for the determination of hydroquinone and catechol in the direct analysis of spiked tap water samples with EIS and complex numbers-PLS.

Assessment of semiempirical enthalpy of formation in solution as an effective energy function to discriminate native-like structures in protein decoy sets.

In this work, we tested the PM6, PM6-DH+, PM6-D3, and PM7 enthalpies of formation in aqueous solution as scoring functions across 33 decoy sets to discriminate native structures or good models in a decoy set. In each set these semiempirical quantum chemistry methods were compared according to enthalpic and geometric criteria. Enthalpically, we compared the methods according to how much lower was the enthalpy of each native, when compared with the mean enthalpy of its set. Geometrically, we compared the methods according to the fraction of native contacts (Q), which is a measure of geometric closeness between an arbitrary structure and the native. For each set and method, the Q of the best decoy was compared with the Q0 , which is the Q of the decoy closest to the native in the set. It was shown that the PM7 method is able to assign larger energy differences between the native structure and the decoys in a set, arguably because of a better description of dispersion interactions, however PM6-DH+ was slightly better than the rest at selecting geometrically good models in the absence of a native structure in the set. © 2016 Wiley Periodicals, Inc.

Determination and evaluation of the mineral composition of Obi (Cola acuminate).

The obi (Cola acuminate) is a native fruit from Africa, which has been mainly used in the production of soft drinks and also in rituals of African religions. In this paper, the mineral composition of obi collected in seven different cities from Bahia State, Brazil was determined and evaluated using multivariate analysis. The samples were digested using nitric acid and hydrogen peroxide and were analyzed using inductively coupled plasma optical emission spectrometry. The accuracy of the method was confirmed by analysis of a certified reference material of apple leaves, furnished by National Institute of Standard and Technology. The study involved 46 samples, being 18 of the red specie and 28 for the white specie. The results expressed as milligrams of element per 100 g(-1) of sample demonstrated that the concentration ranges varied of 21.28-548.77 for potassium, 15.73-129.85 for phosphorous, 27.95-286.92 for calcium, 7.67-134.45 for magnesium, 0.05-1.41 for manganese, 0.21-0.94 for iron, 0.11-0.39 for copper, 0.27-1.35 for zinc, and 0.025-0.517 for strontium. The principal component analysis and hierarchical cluster analysis evidenced that the mineral composition of the red specie is different of the white specie. The red obi has mineral content higher than white obi.