Publications

Abstract Templated microspheres based on the sol-gel process usually present low density, high surface area, excellent loading capacity, biocompatibility, and high thermal and mechanical stability, which make them ideal for a vast number of applications, from sensors to separation processes. The preparation of these templated microspheres, obtained by some sol-gel route, is here the subject of a review. The purposes and ways of insertion of templates inside a sol-gel matrix are diversified. Most commonly, templates are intended to produce some sort of controlled microstructure, either by simply reverting the volume occupied by the template to pore volume of identical dimensions or by directing the self-organization within the sol-gel network during the synthesis. Mesoporous spherical gels or glasses and composites have extensively been produced in this manner, using surfactants and polymeric materials as preferential templates. It is also common to find the utilization of templates related to the very process of achieving the microspheric format of the gels, which in many instances is designed to produce hollow spheres. Bulky templates in the micrometer range, such as whole cells, other microspheres or gas bubbles, are usually applied for the purpose. Molecularly imprinted microspherical gels have also been reported in the recent years. In this case, an usually small molecule of interest is added as template to the solgel mixture. It is expected that, upon removal from the final gel, the template will leave a cavity with the size and shape of the template, as well as some functionally complimentary chemical microenvironment.

Abstract The role of the electrode material on the interfacial double layer structure of a series of ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate ([C4MIM][PF6]), 1-butyl-3-methylimidazolium bis(trifluoromethyl-sulfonyl) imide ([C4MIM][Tf2N]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([C4MIM][BF4]) was investigated on gold (Au) and platinum (Pt) electrodes. The aim of this work is to contribute with experimental data to complement theoretical models that are currently under discussion in order to describe the structure of the double layer formed at the interface electrode/ionic liquid. There is still a controversy about the general shape that differential capacitance curves should present and researchers still continue making efforts to correlate the nature of the electrode/ionic liquid with the shape of the curves. Differential capacitance curves at the Au and Pt interface shows that the values of capacity follow the same order C [C4MIM][PF6] < C [C4MIM][Tf2N] < C [C4MIM][BF4]. However, the values of C are considerably lower for Pt when compared with Au for all three liquids studied. The alkyl chain length effect on the differential capacity curves was also studied at the Pt/[CnMIM][Tf2N] interface (where n = 2, 4 and 6). The results follow an expected trend except for the liquid [C6MIM][Tf2N] that shows a value of capacity near to that obtained for [C2MIM][Tf2N]. Since ionic liquids have great applicability in energy storage devices and capacitors it is of great importance to evaluate the dependence of differential capacitance as function of temperature. The results indicate that the capacity increases with increasing temperature for all systems studied in this work.

Abstract 2-Ethylhexyl 4-methoxycinnamate (EHMC) is a very commonly used UVB filter that is known to isomerize from the (E) to the (Z) isomer in the presence of light. In this study, we have performed high level quantum chemical calculations using density functional theory (DFT) with the B3LYP density functional and extended basis sets to study the gas-phase molecular structure of EHMC and its energetic stability. Calculations were also performed for related smaller molecules cinnamic acid and 4-methoxycinnamic acid. Charge delocalization has been analyzed using natural charges and Wiberg bond indexes within the natural bond orbital analysis and using nucleus independent chemical shifts. Density functional theory calculations reveal that the (E) isomer of EHMC is more stable than the (Z) by about 20kJmol(-1) in both the gas and aqueous phases. The enthalpy of formation in the gas phase of (E)-EHMC was derived from an isodesmic bond separation reaction. Long-range corrected DFT calculations in implicit water were made in order to understand the excited state properties of the (E) and (Z) isomers of EHMC. Copyright (c) 2013 John Wiley & Sons, Ltd.

Abstract Six dioxetanone molecules, ranging in complexity from simple dioxetanone to firefly dioxetanone, were studied by performing M06/6-311G(d,p) calculations. The quantum theory of atoms in molecules and the electron localization function was applied to analyze the peroxide and carbon-carbon bonds of the dioxetanone ring. Both approaches demonstrated that the peroxide bond is not covalent, but charge-shifted. This means that for this bond the covalent "electron sharing" is relatively unimportant, and it is the stabilizing resonance energy that causes the bonding. For the contrary, the carbon-carbon bond is covalent. These discoveries indicate that no biradical species should be formed in the dioxetanone decomposition, and that the most probable rate-determining step should be the carbon-carbon cleavage.

Abstract The main objective of this study was to simulate for the first time a complex sol-gel system aimed at preparing the (S)-naproxen-imprinted xerogel with an explicit representation of all the ionic species at pH 9. For this purpose, a series of molecular dynamics (MD) simulations of different mixtures, including species never studied before using the OPLS-AA force field, were prepared. A new parametrization for these species was developed and found to be acceptable. Three different systems were simulated, representing two types of pregelification models: the first one represented the initial mixture after complete hydrolysis and condensation to cyclic trimers (model A); the second one corresponded to the same mixture after the evaporation process (model B); and the last one was a simpler initial mixture without an explicit representation of all of the imprinting-mixture constituents (model C). The comparison of systems A and C mainly served the purpose of evaluating whether an explicit representation of all of the components (model A) was needed or if a less computationally demanding system in which the alkaline forms of the silicate species were ignored (model C) would be sufficient. The results confirmed our hypothesis that an explicit representation of all of the imprinting-mixture constituents is essential to study the molecular imprinting process because a poor representation of the ionic species present in the mixture may lead to erroneous conclusions or lost information. In general, the radial distribution function (RDF) analysis and interaction energies demonstrated a high affinity of the template molecule, 2-(6-methoxynaphthalen-2-yl)propanoate (NAP(-), the conjugate base of (S)-naproxen), for the gel backbone, especially targeting the units containing the dihydroimidazolium moiety used as a functional group. Model B, representing a nearly gelled sol where the density of silicates and solvent polarity were much higher relative to the other models, allowed for much faster simulations. That gave us the chance to observe the templating effect through a comparative analysis and observation of the trajectories from simulations with the template- versus non-template-containing mixtures. Overall, a strong coherence between the imprinting-relevant interactions, aggregation, or the silicate network texturing effects taken out of the simulations and the experimentally high imprinting performance and porosity features of the corresponding gels was achieved.