Publications

Abstract The unimolecular decomposition of 1,2-dioxetanedione, the high-energy intermediate of the chemiluminescence peroxyoxalate reaction, was studied by theoretical means for the first time. Our calculations have provided results in line with the experimental data regarding this compound. 1,2-Dioxetanedione decomposes due to a step-wise biradical mechanism. In the biradical region of the decomposition path, there is a path for singlet chemiexcitation. Interactions between the singlet ground and excited states with triplet states can explain the weak unimolecular chemiluminescence of 1,2-dioxetanedione. Copyright (c) 2013 John Wiley & Sons, Ltd.

Abstract Firefly bioluminescence has attracted much attention from the research community due to its most intriguing multicolor bioluminescence. Computational studies have been fundamental to the clarification of this phenomenon. However, no clear demonstration of the accuracy of the theoretical methods used in this field of research has been provided. In this work, we have used luciferin and dehydroluciferin in water as a model for the calculation of the emission wavelength of oxyluciferin and analogs. This model was used in a density functional theory (DFT) benchmarking in which 24 functionals were tested. A non-negligible case to case dependence was observed. However in general, the better classes of the DFT functionals are generalized gradient approximation (GGA) and meta GGA. The generalized gradient exchange functional TPSSVWN5, the hybrid-meta GGA functional mPWKCIS, and the hybrid GGA functional MPWLYP1M also present good results. For the contrary, the popular hybrid GGA functionals present a worse performance. (c) 2012 Wiley Periodicals, Inc.

Abstract The chemiluminescence of simple 1,2-dioxetanone has already been studied by both multiconfigurational and density functional theory calculations. The former approach revealed a step-wise biradical mechanism for its decomposition, whereas the latter revealed a concerted mechanism. The first approach was not in line with both computational and experimental findings, whereas the second mechanism was. Due to these apparent mechanistic contradictions and some concerns regarding our concerted mechanism, and the use of a closed-shell approach and different methods for geometry and single-point calculations, we have revisited the chemiluminescence of this molecule. Once again the concerted mechanism was found to be prevailing, and a closed-shell approach was able to rationalize the chemiluminescence of 1,2-dioxetanone. It was once again noted that an open-shell and a step-wise biradical mechanism cannot explain the chemilu minescence of this molecule. (C) 2013 Wiley Periodicals, Inc.

Abstract A fluorescent hybrid material (PPH-S-CdSe), which comprises cadmium selenide sulphide nanoparticles assembled onto thiol functionalised porous phosphate heterostructures (PPH-SH), was synthesised in aqueous media. This material presents a high stability towards photo-degradation. The obtained nanocomposite was characterised by various techniques such as Fourier transform infrared spectroscopy, energy dispersive X-ray, transmission electron microscopy (TEM), X-ray diffraction, X-ray photoelectron spectroscopy and fluorescence spectroscopy. This fluorescent material showed a red emission at 576nm combined with other at 473nm, explained as different CdS0.42Se0.58 nanoparticles size, supported by TEM images. It was suitable for latent fingermark analysis in a wide range of surfaces. Because of its sensitivity and low cost, it is an actual alternative to conventional powdering materials. Copyright (C) 2012 John Wiley & Sons, Ltd.

Abstract We have performed high level ab initio quantum chemical calculations for 2- and 3-pyrrolidinone; tetrahydro-2- and -3-furanone; 2-, 3-, and 4-piperidinone; and tetrahydro-2-, -3-, and -4-pyranone. The most stable molecular structures were obtained from DFT calculations using the B3LYP density functional and the 6-31G(d) and 6-311+G(3df,2p) basis sets. The respective enthalpies of formation have been computed by the G3(MP2)//B3LYP composite method and appropriately chosen reactions. The calculated results are in excellent agreement with experimental data reported in the literature.

Abstract The standard (p = 0.1 MPa) molar enthalpy of formation of 6,7-dihydro-4(5H)-benzofuranone was measured, at T = 298.15 K, by static bomb calorimetry and the standard molar enthalpy of vaporization, at T = 298.15 K, was obtained using Calvet microcalorimetry. These values were combined together to derive the standard molar enthalpy of formation of the title compound in gaseous phase, at T = 298.15 K, -(226.0 +/- 2.8) kJ . mol (1). [GRAPHICS] Additionally, density functional theoretical calculations using the B3LYP hybrid exchange-correlation energy functional with extended basis sets and also other higher-level ab initio quantum calculations have been performed.

Abstract We have performed a study of the structure and energetics of some chlorohydroxypyridines based on experimental calorimetry techniques and high level ab initio computational calculations. The standard (p degrees = 0.1 MPa) molar enthalpies of formation of 2-chloro-3-hydroxypyridine (2-Cl-3-OHPy), 2-chloro-6-hydroxypyridine (2-Cl-6-OHPy) and 3-chloro-5-hydroxypyridine (3-Cl-5-OHPy) in the crystalline phase, at T = 298.15 K, were derived from the respective standard massic energies of combustion measured by rotating-bomb combustion calorimetry, in oxygen, at T = 298.15 K. The standard molar enthalpies of sublimation, at T = 298.15 K, were measured by Calvet microcalorimetry. From these experimentally determined enthalpic parameters we have derived the standard molar enthalpies of formation of the three compounds in the gaseous phase, at T = 298.15 K: 2-Cl-3-OHPy, -(76.8 +/- 2.0) kJ . mol(-1); 2-Cl-6-OHPy, -(105.0 +/- 1.7) kJ . mol(-1), 3-Cl-5-OHPy -(61.2 +/- 2.4) kJ . mol(-1). These values were compared with estimates obtained from very accurate computational calculations using the G3(MP2)//B3LYP composite method and appropriately chosen reactions. These calculations have also been extended to the remaining chloro hydroxypyridine isomers that were not studied experimentally. Based on B3LYP/6-31G* optimized geometries and calculated G3(MP2)//B3LYP absolute enthalpies some structure-energy correlations were discussed.

Abstract The measurement of serum C-reactive protein (CRP) levels has been given particular interest as a marker of inflammation associated with cardiovascular diseases. CRP belongs to the pentraxin family of proteins and the routine clinical analysis of CRP in blood samples is used as an important factor in primary prevention programmes together with causative and predisposing factors. This review focuses on the most representative methodologies and strategies for CRP detection and quantification that have been recently proposed, as well as reviewing those that are currently being developed for the specific, sensitive, inexpensive and high-throughput blood analysis of this protein.

Abstract Adsorption of uranyl ions onto kaolinite, montmorillonite, humic acid and composite clay material (both clays and humic acid) was studied by measuring the system response to clay suspensions (pre-equilibrated with or without uranyl) and to perturbations of the solution chemistry. Adsorption behavior of selected materials under the frame of batch experiments was tested at high uranyl concentrations (6-1170 mu g/mL; 2.5 x 10(-2) to 4.9 mu M), whereas that under flow through continuous stirred reactor experiments was tested at low concentrations (1.00 x 10(-4) to 1.18 x 10(-4) M). Both experiments were developed at pH 4.5 and ionic strength 02 mM. The adsorption experiments follow a Langmuir isotherm model with a good correlation coefficient (R-2 > 0.97). The calculated amount of adsorbed and desorbed uranyl was carried out by numeric integration of the experimental data, whereas the desorption rates were determined from the breakthrough curve experiments. Kaolinite with highly disordered structure adsorbed less uranyl (3.86 x 10(-6) mol/g) than well-ordered kaolinite (1.76 x 10(-5) mol/g). Higher amount of uranyl was adsorbed by montmorillonite (3.60 x 10(-5) mol/g) and only half of adsorbed amount was desorbed (1.85 x 10(-5) mol/g). The molecular interactions between kaolinite, montmorillonite, humic acid, composite material and saturated uranyl ion solutions were studied by molecular fluorescence, infrared and X-ray photoelectron spectroscopy. The Stem-Volmer constant obtained for montmorillonite (2.6 x 10(3) M-1) is higher than for kaolinite (0.3 x 10(3) M-1). Molecular vibrations of Si-O stretching and Al-OH bending related to hydroxylated groups ( SiOH or AlOH) of kaolinite and montmorillonite show structural changes when uranyl ions are adsorbed. X-ray photoelectron spectroscopy shows that the U 4f(7/2) core level signals occur at 380.5 eV in either kaolinite or montmorillonite that resulted from the interaction of aluminol surface sites with the (UO2)(3)(OH)(5)(+).

Abstract This is the first report of a study employing a computational approach to study the binding of (D/L)-luciferyl-adenlyates and dehydroluciferyl-adenylate to firefly luciferase. A semi-empirical/molecular mechanics methodology was used to study the interaction between these ligands and active site molecules. All adenylates are complexed with the enzyme, mostly due to electrostatic interactions with cationic residues. Dehydroluciferyl-adenylate is expected to be a competitive inhibitor of luciferyl-adenylate, as their binding mechanism and affinity to luciferase are very similar. Both luciferyl-adenylates adopt the L-orientation in the active site of luciferase.