Publications

Abstract Direct and continuous measurement of dissolved CO2 (dCO(2)) is crucial for intensive aquaculture, especially in shallow raceway systems (SRS). In this work the performance of a portable dissolved CO2 probe analyzer was tested for the effects of different aqueous solutions, pure oxygen injection and agitation. Laboratory results showed significant (p < 0.05) solution effects on probe performance for low (10-20 mg L-1) and high (30-50 mg L-1) dCO(2) concentrations. Globally performance was better in deionized water, followed by marine fish farm water and artificial seawater. Accuracy and response time were the parameters most affected by the type of solution tested. Linearity was always observed (R-2 = 0.995-0.999). The probe was sensitive to 1 mg L-1 dCO(2) increments for concentrations <6 mg L-1 in artificial seawater. Pure oxygen injection did not affect probe readouts, and agitation was needed for better accuracy and response time. In real marine SRS with tanks in series dCO(2) dynamics was revealed using the probe coupled to a developed flow cell. A prototype SRS was built and used to study dCO(2) dynamics without endangering cultivated fish. Generally, results obtained indicate that the probe tested although precise, is better suited for discrete, single-point dCO(2) monitoring, being a limited resource for the special needs of shallow raceway systems. As SRS represent a paradigm change in aquaculture, new water quality monitoring strategies and instrumentation are needed, especially for dCO(2). Fiber optic sensors can be a solution for continuous, multipoint monitoring, thus contributing to the understanding of water quality dynamics in hyperintensive aquaculture systems.

Abstract Firefly luciferase catalyzes a light-emitting reaction in which an excited-state product is formed. Both experimental and theoretical methodologies are used to study this system, and the reactions catalyzed by luciferase are relatively well characterized. However, the mechanism by which an excited-state product is formed is still unknown. This Minireview deals with the current understanding of firefly bioluminescence and chemiluminescence. Thermal decomposition of simple 1,2-dioxetanes is also discussed, due to their role in formation of the excited-state bioluminophore.

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.