Publications

Abstract Chitosan is a natural polysaccharide which strongly interacts with whey proteins in solution. Certain protein-polyelectrolyte complexes and electrostatically assembled thin films have been shown to be good platforms for the preservation of globular and small proteins in their native state mainly due to the hydrophilic nature of these polyelectrolytes and to the lack of physical space for embedded proteins to relax. As a consequence, the use of natural polyelectrolytes in new nanocomposite materials for medicine, chemical analysis, catalysis, etc. has exploded in the last few years. Nevertheless, in many of these applications proteins are immobilized in more open structures without physical restrictions to undergo conformational changes. In this work, we investigate the nature of these transitions for a model whey protein, beta-LG, on a chitosan-decorated Au surface in a scenario for which protein-surface interactions compete with boosted protein-protein non-coulombic forces. The adsorption kinetics, protein mass uptake (plus associated water), and flexibility of the adsorbed layers have been followed in situ by the quartz crystal microbalance with dissipation monitoring (QCM-D). Further ex situ characterization has been performed by atomic force microscopy (AFM) and non-invasive scanning electron microscopy (SEM). The balance between both types of interactions yielded surfaces heavily loaded with protein and water in which orientational transitions seemed restricted. The kinetics of the process was registered in a wide range of concentrations and successfully fitted to a double exponential equation derived from the RSA theory accounting for the establishment of slow post-adsorption conformational transitions.

Abstract Using a model reaction, we recently investigated the thermochemistry and aromaticity systematics of nitrogen, oxygen and sulfur-containing heterocycles that are isoelectronic to the carbocyclic indane and its unsaturated counterpart indene. In this study all of the benzo-annelated species, e.g. indole, indoline, phthalic anhydride, phthalan and benzothiazole, all corresponding to annelation on a formal double bond of the 5-membered ring of the single ring species. In that study we asked "What is to be done about the so-called iso-species?" such as isobenzofuran, anthranil, benzofurazan and 2,1,3-benzothiadiazole, wherein it is annelation of the formal single bond in the 5-membered ring. A modified model reaction is suggested in the current paper where we admit that it is quantitatively untested.

Abstract The decomposition of 1,2-dioxetanone into a CO2 molecule and into an excited state formaldehyde molecule was studied in condensed phase, using a density functional theory approach. Singlet and triplet ground and excited states were all included in the calculations. The calculations revealed a novel mechanism for the chemiluminescence of this compound. The triplet excitation can be explained by two intersystem crossings (ISCs) with the ground state, while the singlet excitation can be accounted by an ISC with the triplet state. The experimentally verified small excitation yield can then be explained by the presence of an energy barrier present in the potential energy surface of the triplet excited state, which will govern both triplet and singlet excitation. It was also found that the triplet ground state interacts with both the triplet excited and singlet ground states. A MPWB1K/mPWKCIS approach provided results in agreement with the existent literature. (c) 2012 Wiley Periodicals, Inc.

Abstract Roca-Sanjuan et al. commented on our paper Density Functional Theory Study of 1,2-Dioxetanone Decomposition in Condensed Phase, by criticizing the use of a closed-shell approach and the differences encountered regarding other previous studies. However, our suggested reaction mechanism was in line with experimental findings, contrary to other computational studies. Moreover, we have presented data to support our use of a closed-shell approach. (c) 2012 Wiley Periodicals, Inc.

Abstract A method has been developed and optimized in order to detect and quantify the non-protein amino acid beta-N-methylamino-L-alanine(BMAA) in cyanobacteria. The novelty of the method is that we have used methanol instead of acetonitrile as the eluent. The method includes extraction with 0.1 M trichloroacetic acid (free BMAA) or protein hydrolysis with 6 M hydrochloric acid (total BMAA), derivatization with AQC (6-aminoquinolyl-N-hydroxysuccinimidyl carbamate) and reversed-phase high-performance liquid chromatography analysis with fluorescence detection (HPLC/FD). Detection limits ranged from 0.35 to 0.75 pg injected, while quantification limits ranged from 1.10 to 2.55 pg injected for total and free BMAA hydrolysis, respectively. The linear response range was up to 850 pmol in both methods, embracing three orders of magnitude. The method was successfully applied to a lyophilized estuarine species of Nostoc (LEGE 06077). All previous published methods for BMAA quantification, using HPLC/FD, have reported the usage of acetonitrile. This is the first report using methanol as the mobile phase. Although the elution strength differs with both solvents, the final method proved efficient for the quantification of BMAA in this complex sample. The method resulted effective, low-priced, and simple, being suitable for routine monitoring of BMAA in cyanobacteria.

Abstract The cycloaddition between glyoxylate imines possessing two chiral auxiliaries, N-(R)- or N-(S)-1-phenylethyl and 8-phenylmenthyl or 8-phenylneomenthyl, and cyclopentadiene is described. Computational calculations using density functional theory with the Becke, three-parameter, LeeYangParr functional and the 6-31G(d) basis set were performed to better understand the highly diastereoselective mechanism and the exo-selectivity observed experimentally for these ionic aza-DielsAlder reactions. Copyright (c) 2011 John Wiley & Sons, Ltd.

Abstract The use of additives for the electrodeposition from deep eutectic solvents is still an unexplored area however of the upmost importance to understand the role of additives in metal electrodeposition in new media such as DES. In this study we describe the effect of three additives with complexing properties and their effect on the voltammetric profile of tin and the deposit morphology. It is shown that EDTA and HEDTA do not alter the voltammetric profile of tin. In contrast the addition of Idranal VII has a pronounced effect the voltammetric behavior of tin and in the tin deposit morphology.

Abstract A fluorescence derivatization method for the quantification of the anthelmintic drug niclosamide in organized media (methyl-beta-cyclodextrin) is described. The derivatization reaction is based on a 3 h reduction reaction of the nitro group in niclosamide to an amino group by hydrogenation catalyzed by Pd/C in methanol:ethyl acetate (1:3). The aminoniclosamide exhibits a maximum of fluorescence at 431 nm (excitation at 280 nm) that is markedly enhanced when methyl-beta-cyclodextrin is present. The methodology was assessed by the analysis of pure and dosage forms. The method showed a linear range between 0 and 2200 mu g L-1 with a limit of detection of 45.7 nIe and a precision (relative standard deviation) of 4.1% in niclosamide. The effect of various interferents, such as niclosamide, fructose and 2-cyano-6-metoxybenzothiazole, in several tolerance ratios, was investigated respected to aminoniclosamide.

Abstract The present work reports an experimental study on the energetics of 2,1,3-benzothiadiazole and a computational study on its structure, energetics and aromaticity. In the experimental part the standard (p(o) = 0.1 MPa) massic energy of combustion, at T = 298.15 K, was measured by rotating bomb combustion calorimetry, in oxygen, and allowed the calculation of the respective standard molar enthalpy of formation, in the crystalline phase, at T = 298.15 K. The standard molar enthalpy of sublimation, at T = 298.15 K, was measured by high-temperature Calvet microcalorimetry. From the combination of data obtained by both techniques we were able to calculate the respective standard molar enthalpy of formation, in the gas phase, at T = 298.15 K: (276.6 +/- 2.5) kJ . mol (1). This thermochemical parameter was compared with estimates obtained from high level ab initio quantum chemical calculations using the G3(MP2)//B3LYP composite method and various appropriately chosen reactions. The molecular structure of 2,1,3-benzothiadiazole was obtained from DFT calculations with the B3LYP density functional and various basis sets: 6-31G(d), 6-311(d, p), 6-311+G(3df, 2p), aug-ccpVTZ and aug-ccpVQZ and its aromaticity and that of some related molecules were evaluated by analysis of nucleus independent chemical shifts (NICS) values.

Abstract Firefly luciferase exhibits a multicolor bioluminescence, which is caused by the modulation of the emission of oxyluciferin by intermolecular interactions. One of the objectives of the present paper was analyze the possible effect of the charge density of the emitter in the color tuning. Theoretical calculations on oxyluciferin, and its respective moieties, demonstrated that no correlation between charge density and light emission can be found once solvent effects are considered. Further computational calculations demonstrate that intermolecular interactions modulate the emission by affecting the geometry of oxyluciferin, which controls the energy gap between the excited and ground state. Direct intermolecular interactions and polarity also affect the color of emission of oxyluciferin, by the same mechanism. Also, the effect of charge density modulation of Keto-(-1). A novel emitter, 5-hydroxyoxyluciferin, was considered and demonstrated to be more red-shifted that oxyluciferin.