Publications

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.

Abstract This paper reports an experimental and computational study on the energetics of 1,2,3-benzotriazin-4(3H)-one. The standard (p degrees = 0.1 MPa) molar enthalpy of formation of solid 1,2,3-benzotriazin-4(3H)-one, at T = 298.15 K, was derived from its standard massic energy of combustion measured by static bomb combustion calorimetry in oxygen. The Calvet high-temperature vacuum sublimation technique was used to measure the respective standard molar enthalpy of sublimation at T = 298.15 K From these two experimentally determined thermodynamic parameters, we have calculated the standard molar enthalpy of formation of 1,2,3-benzotriazin-4(3H)-one in the gas phase at T = 298.15 K, (200.9 +/- 3.8) kJ . mol(-1). Interrelations between structure and energy for 1,2,3-benzotriazin-4(3H)-one, the tautomer 1,2,3-benzotriazin-4(1H)-one, and the enol tautomer 1,2,3-benzotriazin-4-ol were discussed based on density functional theory (DFT) calculations with the B3LYP hybrid functional and the 6-311++G(d,p) basis set. The gas-phase enthalpy of formation of 1,2,3-benzotriazin-4(3H)-one was estimated from quantum chemical calculations using the G3(MP2)//B3LYP composite method. Nucleus-independent chemical shifts (NICS) were also calculated with the purpose of analyzing the aromaticity of the benzenic and heterocyclic rings of the title molecule and others related tautomerically to it.

Abstract Electroactive polymer films based on [Ni(salen)]-type complexes were fabricated and their electronic properties characterized using in situ UV-visible spectroelectrochemistry. The extent of pi electronic delocalisation and electronic asymmetry were manipulated by introduction of different conjugated imine bridges. Measured electronic spectra were interpreted in terms of polaronic states in the band gap and metal-oxidized ligand charge transfer bands. Density functional theory (DFT) calculations for the monomers showed that the HOMO orbital (which governs oxidation potential) is ligand-dominated, and that substituents with greater electronic delocalisation in the diimine bridge decrease the HOMO-LUMO energy gap. Replacement of methyl by methoxyl substituents in the aldehyde moiety increases the calculated dipole moment. Substitution-driven variations in E(HOMO)-E(LUMO) for the monomers were reflected in the corresponding polymer band gaps, demonstrating that monomer electronic properties can be used predictively in the manipulation of polymer electronic properties. An important strategic aspect is the correlation of OFF predictions with the observed electronic properties of monomeric and polymeric materials; the extent to which such modelling can be used to optimise synthetic effort is discussed.

Abstract Vapor pressures of some azides have been determined by the transpiration method. The molar enthalpies of vaporization Delta(g)(I)H(m) of these compounds were derived from the temperature dependencies of vapor pressures. The measured data sets were successfully checked for internal consistency by comparison with vaporization enthalpies of similarly structured compounds.