Solvation in aqueous binary mixtures: consequences of the hydrophobic character of the ionic liquids and the solvatochromic probes

Information on the solvation in mixtures of water, W, and the ionic liquids, ILs, 1-allyl-3-R-imidazolium chlorides; R = methyl, 1-butyl, and 1-hexyl, has been obtained from the responses of the following solvatochromic probes: 2,6-dibromo-4-[(E)-2-(1-R-pyridinium-4-yl)ethenyl] phenolate, R = methyl, MePMBr2; 1-octyl, OcPMBr(2), and the corresponding quinolinium derivative, MeQMBr(2). A model developed for solvation in binary mixtures of W and molecular solvents has been extended to the present mixtures. Our objective is to assess the relevance to solvation of hydrogen-bonding and the hydrophobic character of the IL and the solvatochromic probe. Plots of the medium empirical polarity, E-T(probe) versus its composition revealed non-ideal behavior, attributed to preferential solvation by the IL and, more efficiently, by the IL-W hydrogen-bonded complex. The deviation from linearity increases as a function of increasing number of carbon atoms in the alkyl group of the IL, and is larger than that observed for solvation by W plus molecular solvents (1-propanol and 2-(1-butoxy)ethanol) that are more hydrophobic than the ILs investigated. This enhanced deviation is attributed to the more organized structure of the ILs proper, which persists in their aqueous solutions. MeQMBr(2) is more susceptible to solvent lipophilicity than OcPMBr(2), although the former probe is less lipophilic. This enhanced susceptibility agrees with the important effect of annelation on the contributions of the quinonoid and zwitterionic limiting structures to the ground and excited states of the probe, hence on its response to both medium composition and lipophilicity of the IL.

Aging reduces complexity of heart rate variability assessed by conditional entropy and symbolic analysis

Increasing age is associated with a reduction in overall heart rate variability as well as changes in complexity of physiologic dynamics. The aim of this study was to verify if the alterations in autonomic modulation of heart rate caused by the aging process could be detected by Shannon entropy (SE), conditional entropy (CE) and symbolic analysis (SA). Complexity analysis was carried out in 44 healthy subjects divided into two groups: old (n = 23, 63 +/- A 3 years) and young group (n = 21, 23 +/- A 2). It was analyzed SE, CE [complexity index (CI) and normalized CI (NCI)] and SA (0V, 1V, 2LV and 2ULV patterns) during short heart period series (200 cardiac beats) derived from ECG recordings during 15 min of rest in a supine position. The sequences characterized by three heart periods with no significant variations (0V), and that with two significant unlike variations (2ULV) reflect changes in sympathetic and vagal modulation, respectively. The unpaired t test (or Mann-Whitney rank sum test when appropriate) was used in the statistical analysis. In the aging process, the distributions of patterns (SE) remain similar to young subjects. However, the regularity is significantly different; the patterns are more repetitive in the old group (a decrease of CI and NCI). The amounts of pattern types are different: 0V is increased and 2LV and 2ULV are reduced in the old group. These differences indicate marked change of autonomic regulation. The CE and SA are feasible techniques to detect alteration in autonomic control of heart rate in the old group.

Do estilo em ciência e em história das ciências

Ao considerar o conhecimento científico como uma forma de pensamento simbólico, entende-se com isso não simples sistemas de signos, mas conteúdos de pensamento (expressos por conceitos) ligados entre si e que fazem sentido, que são, no espaço das representações mentais, os substitutos do "dado objetivo" que se supõe subjazer à experiência que fazemos do "mundo" pelos sentidos e, nesse nível indissociavelmente, pelo entendimento. Esse pensamento simbólico adquire densidade e consistência pela "tecelagem" realizada graças ao trabalho dos pensamentos individuais que se comunicam, social e culturalmente, inscritos no tempo da história. Da tensão dinâmica entre o sujeito do conhecimento, que busca a inteligibilidade (pela operação de sua razão), e a objetividade dos conteúdos que ele se propõe (inicialmente dados, depois modificados ou produzidos), resulta o movimento do pensamento científico e a transformação dos conhecimentos. Esse trabalho do pensamento simbólico é marcado por um estilo próprio a cada um, mas que em parte pode ser comum em contextos, escolas ou tradições. Em ciência e em história das ciências, o estilo intervém em dois níveis: o da abordagem "objetal" da produção das obras pelos cientistas e o da abordagem "reflexiva" da história epistemológica e da filosofia, que se interrogam sobre a significação tanto dos próprios conteúdos de conhecimento quanto do pensamento racional, simbólico, cuja função é manifestá-los.