Publications

Abstract The assisted transfer of silver ion, Ag+, by complexation of Ag+ with the tetrakis(4-chlorophenyl)borate (TPBCl-) anion was studied at the interface between two immiscible electrolyte solutions (ITIES). The elucidation of the interfacial mechanisms employed the cyclic voltammetry technique applied to macro and micro liquid/liquid interfaces. This procedure allowed to identify Ag+ as the species which is transferred at the liquid/liquid interface and also the formation of an 1:2 metal:ligand complex when TPBCl- is in excess. The value for the formal transfer potential of silver(I) from aqueous to 1,2-dichloroethane was evaluated and the association constant for the [Ag(TPBCl)(2)](-) complex was determined.

Abstract The standard (pdegrees = 0.1 Mpa) molar enthalpy of formation for liquid sulpholane was derived from the standard molar enthalpy of combustion, in oxygen at T = 298.15 K, measured by rotating bomb combustion calorimetry. The standard molar enthalpy of vaporization, at T = 298.15 K, was measured by Calvet microcalorimetry. The results are: Delta(f)H(m)degrees(l) = -(425.7 +/- 1.7)kJmol(-1;) Delta(1)(g) H(m)degrees = 69.1 +/- 1.4 kJ mol(-1); and Delta(f)H(m)degrees (g) = -(356.6 +/- 2.2)kJmol(-1). Additionally, high-level density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional have been performed for sulpholane in order to obtain its geometry, enthalpy of formation in the gaseous phase and strain energy.

Abstract Interfacial tension was used to study the electrochemical properties of the interface between LiCl in water and tetraalkylammonium tetraphenylborate in 1,2-dichloroethane. The interfacial tension decrease with decreasing of the size of the cation of the organic supporting electrolyte on the order TBA(+) < THA(+) < THpA(+) < TOA(+). The decrease of interfacial tension is also observed at the electrocapillary maximum the potential of which (potential of zero charge) shift towards more positive values in the order TBA(+) > THA(+) > THpA(+) > TOA(+). This fact maybe an evidence that there is an increase of adsorption when the alkyl chain length of the organic cation is reduced.

Abstract Dehydroluciferyl-coenzyme A (L-CoA) was chemically synthesized and characterized by MS, UV-vis spectrometry and RP-HPLC. The identity of the chemically synthesized compound with the one that was produced by firefly luciferase was confirmed. Moreover, the reversibility of the enzymatic conversion of dehydroluciferin reversible arrow dehydroluciferyl-adenylate reversible arrow L-CoA was also confirmed. The chemical synthesis of L-CoA, described here, may help the clarification of the activator effect of CoA on luciferase bioluminescent assays, in which the enzyme catalyzed formation of L-CoA and the consequent destruction of L-AMP is one of the possible explanations for that effect.

Abstract The antiproliferative and cytotoxic properties of polyphenolic acid derivatives, structurally related with the natural models caffeic and gallic acids. have been tested in human cervix adenocarcinoma cells (HeLa). Simultaneous structural information was obtained for these Compounds through theoretical ab initio methods. This study was conducted for the following esters: methyl caffeate (MC, 1), propyl caffeate (PC, 2), octyl caffeate (OC, 3), methyl gallate (MG, 4), propyl gallate (PG, 5) and octyl gallate (OG, 6). A significant growth-inhibition effect was assessed for some of these compounds, clearly dependent on their structural characteristics. Marked structure-activity relationships (SARs)-namely the number of hydroxyl ring substituents-were found to rule the biological effect of such systems.

Abstract The analysis of opiates is of vital interest in drug abuse monitoring and research. This review presents a general overview of the electrochemical methods used for detection and quantification of opiates in a variety of matrices. Emphasis has been placed on the voltammetric methods used for study and determination of morphine, codeine, and heroin. Specific issues that need to be solved and better explained as well as future trends in the use of electrochemical methods in the examination of opiates are also discussed.

Abstract A complete conformational analysis of beta-nitrostyrene and beta-methyl-beta-nitrostyrene derivatives was carried out by Raman spectroscopy coupled to ab initio MO calculations. Apart from the optimised geometrical parameters of the most stable conformers of the molecules under study, the corresponding harmonic vibrational frequencies were calculated, as well as potential-energy profiles for several internal rotations within the molecules. At the light of these results, a complete assignment of the Raman spectra of the solid samples was performed. The conformational behaviour of this kind of systems was found to be mainly determined by the stabilising effect of pi-electron delocalisation.

Abstract A conformational analysis of 3-(3,4,5-trihydroxyphenyl)-2-propenoic acid (3,4,5-trihydroxycinnamic acid, THPPE), a trihydroxylated cinnamic acid analogous to caffeic acid (a natural compound often present in diet), was carried out by Raman spectroscopy coupled to Ab initio MO calculations. Apart from the optimised geometrical parameters for the most stable conformers of this compound, and for one of its dimeric species, the corresponding harmonic vibrational frequencies, as well as potential-energy profiles for rotation around several bonds within the molecule, were obtained. Twenty one distinct conformers were found for THPPE, the lowest energy ones-THPPE 1 and THPPE 2-displaying a completely planar geometry. The conformational preferences of this system were thus found to be mainly ruled by the stabilising effect of pi-electron delocalisation. At the light of these results, a complete assignment of the corresponding solid state Raman spectra was performed.

Abstract The oxidative behavior of heroin in aqueous solution is reported. In order to identify its oxidation peaks, several metabolites, 6-monoacetylmorphine, 3-monoacetylmorphine and norheroin, were synthesized and their electrochemical behavior studied using differential pulse voltammetry. The anodic waves observed for heroin correspond to the oxidation of the tertiary amine group and its follow-up product (secondary amine), and to the oxidation of the phenolic group obtained from hydrolysis, at alkaline pHs, of the 3-acetyl group. The results enabled a new oxidative mechanism for heroin to be proposed in which a secondary amine, norheroin, and an aldehyde are obtained. The voltammetric behavior of 6-monoacetylmorphine and morphine was found to be similar demonstrating that the presence of an acetyl substituent on the 6-hydroxy group does not have a relevant influence on the peak potential of the wave resulting from oxidation of the 3-phenolic group.

Abstract The oxidation of codeine on glassy carbon electrodes has been studied in detail using differential pulse voltammetry. The results obtained using a glassy carbon electrode clearly show a much more complex oxidation mechanism than that previously reported when platinum and gold electrodes were used. To clarify the codeine oxidative profile, several metabolites and analogues of this alkaloid, codeine N-oxide, norcodeme, dihydrocodeine, acetylcodeine and 6-chlorodesoxycodeine, were synthesized and studied. It was deduced that the anodic waves observed in codeine oxidation are related to the presence of methoxy, hydroxy and tertiary amine groups. Due to the similarity of potentials at which these oxidative processes take place, at some pHs an overlap of peaks occurs and only one anodic wave is observed.