Time filter

Source Type

Lugo, Spain

Torres M.D.,Escola Tecnica Superior de Enxenaria | Moreira R.,Escola Tecnica Superior de Enxenaria | Chenlo F.,Escola Tecnica Superior de Enxenaria | Vazquez M.J.,Facultade de Ciencias
Carbohydrate Polymers

Water adsorption isotherms of carboxymethyl cellulose (CMC), guar gum (GG), locust bean gum (LBG), tragacanth gum (TG) and xanthan gum (XG) were determined at different temperatures (20, 35, 50, and 65 °C) using a gravimetric method. Several saturated salt solutions were selected to obtain different water activities in the range from 0.09 to 0.91. Water adsorption isotherms of tested hydrocolloids were classified like type II isotherms. In all cases, equilibrium moisture content decreased with increasing temperature at each water activity value. Three-parameter Guggenheim-Anderson-de Boer (GAB) model was employed to fit the experimental data in the water activity range and statistical analysis indicated that this model gave satisfactory results. CMC and GG were the most and the least hygroscopic gums, respectively. Sorption heats decreased with increasing moisture content. Monolayer moisture content evaluated with GAB model was consistent with equilibrium conditions of maximum stability calculated from thermodynamic analysis of net integral entropy. Values of equilibrium relative humidity at 20 °C are proposed to storage adequately the tested gums. © 2012 Elsevier Ltd. All rights reserved. Source

Paradelo R.,Facultade de Farmacia | Moldes A.B.,Facultade de Ciencias | Prieto B.,Facultade de Farmacia | Sandu R.-G.,Facultade de Farmacia | Barral M.T.,Facultade de Farmacia
Compost Science and Utilization

A combination of physical, chemical, spectroscopic and biochemical parameters, along with different plant assays, was used to assess the maturity and stability of nine finished composts obtained from several raw materials (biodegradable fraction of municipal solid waste, green waste, sewage sludge, manure, and grape marc), and by different procedures (aerobic and anaerobic processing, industrial-scale and laboratory scale). Measures of total, alkali-soluble and water-soluble organic matter, N forms, colour, absorbance, respiration, dehydrogenase activity, and phytotoxicity were performed. The selection of a single parameter for stability and maturity evaluation for all the composts was not possible. A significant positive correlation (P<0.01) was found between microbial respiration and dehydrogenase activity. Also, significant correlations were found between dehydrogenase activity and water-soluble C (P<0.05) and water-soluble N (P<0.05), which are presumably the main forms of energy used by microorganisms. Nevertheless, common maturity/stability indicators, such as the C/N ratio in the solid and the aqueous phase, were not related either to microbial activity or phytotoxicity. In fact, the results of the plant growth tests were not correlated • to any other parameter. A principal component analysis was performed to differentiate those parameters giving the maximum information about the status of each compost. A combination of a measure of humification and a measure of microbial activity or water-soluble organic carbon could be used to explain the differences in the stability of the composts, whereas for maturity evaluation plant tests are necessary. Source

Fong-Padron C.,University of Santiago de Compostela | Cabaleiro-Lago E.M.,Facultade de Ciencias | Rodriguez-Otero J.,University of Santiago de Compostela
Chemical Physics Letters

A computational study has been performed in order to characterize the interactions in ternary systems formed by an ion pair of ionic liquids (ILs): C1mim+BF4-,C1mim+NO3- and [C 1mim+][CF3COO-], and one water molecule. Using CCSD(T) values extrapolated to basis set limit as reference, the performance of six different functionals has been assessed giving the following order (from better to worse performance): M06-HF ∼ M05-2X > M06-2X > B97D > PBE0 > B3LYP. The best functionals perform similarly to MP2/aug-cc-pVTZ, with mean absolute deviations around 0.7 kcal/mol, whereas PBE0 and B3LYP deviate by more than 2.0 kcal/mol. © 2014 Elsevier B.V. All rights reserved. Source

Rilo E.,Facultade de Ciencias | Vila J.,Facultade de Ciencias | Garcia-Garabal S.,Facultade de Ciencias | Varela L.M.,Grupo de Nanomateriales y Materia Blanda | Cabeza O.,Facultade de Ciencias
Journal of Physical Chemistry B

We present experimental measurements of specific electrical (or ionic) conductivity of seven binary systems of 1-ethyl-3-methyl imidazolium alkyl sulfate (EMIM-CnS) with water or ethanol. Electrical conductivity was measured at 298.15 K in all ranges of concentrations and selected mixtures also at 288.15, 308.15, and 318.15 K. The alkyl chains of the anions used are ethyl (EMIM-ES), butyl (EMIM-BS), hexyl (EMIM-HS), and, only for mixtures with ethanol, octyl (EMIM-OS). Let us note that the four ionic liquids (ILs) measured are miscible in water and ethanol at those temperatures and atmospheric pressure in all ranges of concentrations, but EMIM-OS jellifies for a given range of concentration with water. We compare the measured data in terms of the alkyl chain length and solvent nature. Data are compared with previously scarce results for these same systems and also for other aqueous and ethanol mixtures with ILs. In addition, we verify that our data fit the universal theoretical expression with no fitting parameters given by the pseudolattice-based Bahe-Varela model, except for IL concentrated mixtures. To fit well all ranges of concentrations, we add to the original equation two phenomenological terms with one fitting parameter each. Finally, we calculate the molar conductivity and fit it successfully with an expression derived from Onsager theory. © 2013 American Chemical Society. Source

Campo-Cacharron A.,Facultade de Ciencias | Cabaleiro-Lago E.M.,Facultade de Ciencias | Rodriguez-Otero J.,University of Santiago de Compostela
Journal of Computational Chemistry

Complexes formed by substituted buckybowls derived from corannulene and sumanene with sodium cation or chloride anion have been computationally studied by using a variety of methods. Best results have been obtained with the SCS-MP2 method extrapolated to basis set limit, which reproduces the highest-level values obtained with the MP2.X method. All bowls form stable complexes with chloride anion, with stabilities ranging from -6 kcal/mol in the methylated corannulene derivative to -45 kcal/mol in the CN-substituted sumanene. The opposite trend is observed in sodium complexes, going from deeply attractive complexes with the methylated derivatives (-36 kcal/mol with sumanene derivative) to slightly repulsive ones in the CN-substituted bowls (2 kcal/mol in the corannulene derivative). Anion complexes are stabilized by large electrostatic interactions combined with smaller though significant dispersion and induction contributions. Conversely, cation complexes are stabilized by large induction contributions capable of holding together the bowl and the cation even in cases where the electrostatic interaction is repulsive. The effect of substitution is mainly reflected on changes in the molecular electrostatic potential of the bowl and, thus, in the electrostatic contribution to the interaction. Therefore, the variations in the stability of the complexes on substitution could be roughly predicted just considering the changes in the electrostatic interaction. However, other contributions also register changes mainly as a consequence of displacements on the position of the ion at the minimum, so the accurate prediction of the stability of this kind of complexes requires going further than the electrostatic approach. © 2014 Wiley Periodicals, Inc. Source

Discover hidden collaborations