Publications

Abstract The standard (pdegrees = 0.1 MPa) molar enthalpies of formation for 2-, 3-, and 4-methoxyphenol and 2,3-, 2,6-, and 3,5-dimethoxyphenol in the gaseous phase were derived from the standard molar enthalpies of combustion, in oxygen, at 298.15 K, measured by static bomb combustion calorimetry, and the standard molar enthalpies of evaporation at 298.15 K, measured by Calvet microcalorimetry: 2-methoxyphenol, -(246.1 +/- 1.9) kJ mol(-1); 3-methoxyphenol, -(240.4 +/- 2.1) kJ mol(-1); 4-methoxyphenol, -(229.7 +/- 1.8) kJ mol(-1); 2,3-dimethoxyphenol, -(386.0 +/- 2.2) kJ mol(-1); 2,6-dimethoxyphenol, -(381.7 +/- 1.9) kJ mol(-1); 3,5-dimethoxyphenol, -(399.4 +/- 3.0) kJ mol(-1). Density functional theory calculations for all the methoxy- and dimethoxyphenols and respective phenoxyl radicals and phenoxide anions were performed using extended basis sets, which allowed the estimation of the gas-phase enthalpies of formation for all compounds. The good agreement of the calculated and experimental gas-phase enthalpies of formation for the closed-shell systems gives confidence to the estimates concerning the isomers which were not experimentally studied and to the estimates concerning the radicals and the anions. Substituent effects on the homolytic and heterolytic O-H bond dissociation energies have been analyzed, the results being in good agreement with available experimental data. Detailed analysis of these effects suggests that electronic exchange phenomena between the substituents dominate the effect the substituents have on these systems.

Abstract The development of an reverse-phase HPLC-Photodiode Array (HPLC-DAD) to separate, identify and evaluate biological and synthetic catecholamines and their respective aminochromes, was discussed. The aminochromes characterization in HPLC chromatograms was done using collected fractions and tandem mass spectrometry applying a general pattern fragmentation. Spiking serum or whole blood with adrenochrome, followed by perchloric acid addition, sample centrifugation and neutralization allowed adrenochrome recoveries of approximately 100%. It was observed that the comparative analysis of the MS spectra of adrenochrome detected in rat blood and of the adrenochrome standard solution, both on MS and MS/MS modes were very similar.

Abstract The transfer of a phenolsulfonephthalein dye (bromophenol blue, BPB) across the water/1,2-dichloroethane (DCE) interface was studied by means of cyclic voltammetry, two-phase extraction techniques and in situ spectrophotometry. For the first time it was observed the transfer of two differently charged species originated from deprotonation of H2BPB. The values of the acidity constants were obtained (pK(ai)(w) = 3.1 +/- 0.2 and pK(a2)(w) = pK(a1)(w) 4.3 +/- 0.2) and an ionic partition diagram of BPB between water and DCE was constructed. The diagram is the basis for the proposed dye transfer mechanism which was validated using voltabsorptometric measurements. Physicochemical parameters were also obtained and relations between lipophilicity and structure accessed.

Abstract The metabolism of 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) has recently been implicated in the mechanisms underlying ecstasy-induced neurotoxicity and hepatotoxicity. However, its potential role in ecstasy-induced kidney toxicity has yet to be investigated. Thus, primary cultures of rat and human renal proximal tubular cells (PTCs) were used to investigate the cytotoxicity induced by MDMA and its metabolites methylenedioxyamphetamine (MDA), alpha-methyldopamine (alpha-MeDA), and the glutathione (GSH) conjugates 5-(glutathion-S-yl)-alpha-MeDA and 2,5-bis(glutathion-S-yl)-alpha-MeDA. Cell viability was evaluated using the mitochondrial MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay. MDMA and MDA were not found to be toxic to either rat or human PTCs at any concentration tested (100-800 muM). In contrast, 800 muM a-MeDA caused 60% and 40% cell death in rat and human PTCs, respectively. Conjugation of alpha-MeDA with GSH resulted in the formation of even more potent nephrotoxicants. Thus, exposure of rat and human PTC monolayers to 400 muM 5-(glutathion-S-yl)-alpha-MeDA caused approximately 80% and 70% cell death, respectively. 5-(Glutathion-S-yl)-alpha-MeDA (400 muM) was more toxic than 2,5-bis(glutathion-S-yl)-alpha-MeDA to rat renal PTCs but equally potent in human renal PTCs. Pre-incubation of rat PTCs with either acivicin, an inhibitor of gamma-glutamyl transpeptidase (gamma-GT), or bestatin, an inhibitor of aminopeptidase M, resulted in increased toxicity of 5-(glutathion-S-yl)-alpha-MeDA but had no effect on 2,5-bis(glutathion-S-yl)-alpha-MeDA-mediated cytotoxicity. The present data provide evidence that metabolism is required for the expression of MDMA-induced renal toxicity in vitro. In addition, metabolism of 5-(glutathion-S-yl)-alpha-MeDA by gamma-GT and aminopeptidase M to the corresponding cysteinS-yl-glycine and/or cystein-S-yl conjugates is likely to be associated with detoxication of this compound. Thus, it appears that toxicity induced by thioether metabolites of ecstasy at the apical membrane of renal proximal tubular cells is the result of extracellular events, presumably redox cycling.

Abstract The metabolism of apomorphine is quite complex due to interactions with proteins and other tissue components that affect its pharmacokinetic profile. The electrochemical oxidation mechanism of apomorphine and of some synthesised apomorphine derivatives was studied. It was found to be related to the reaction of o-diphenol and tertiary amine groups and strongly dependent on pH.

Abstract A square wave voltammetric (SWV) method and a flow injection analysis system with electrochemical detection (FIA-EC) using a glassy carbon electrode were evaluated for the determination of codeine in pharmaceutical preparations. The interference of several compounds, such as acetaminophen, guaiacol, parabens, ephedrine, acetylsalicylic acid and caffeine, that usually appear associated with codeine pharmaceutical preparations was studied. It was verified that these electroanalytical methods could not be used with acetaminophen present in the formulations and that with guaiacol, parabens or ephedrine present the use of the FIA-EC ystem was impracticable. A detection limit of 5 mumol L-1 and a linear calibration range from 40 to 140 mumol L-1 was obtained with the SWV method. For the flow injection analysis procedure a linear calibration range was obtained from 7 to 50 mumol L-1 with a detection limit of 3 mumol L-1 and the FIA-EC system allowed a sampling rate of 115 samples per hour. The results obtained by the two methods, SWV and FIA-EC, were compared with those obtained using reference methods and demonstrated good agreement, with relative deviations lower than 4%.

Abstract A detailed study of the oxidative behaviour of apomorphine in aqueous media is reported. Resorting to the synthesis of apomorphine derivatives it was possible to identify all the anodic oxidation peaks of apomorphine, which are related to the oxidation of the catechol and tertiary amine groups. These findings were revealed to be important since they could lead to a better understanding of the biological interactions of apomorphine and gain insight into its metabolic pathways. During the voltammetric studies, it was also found that apomorphine forms a complex with borate through the catechol group leading to an increase of its oxidation potential. This property could be very useful with regard to the stabilization of apomorphine solutions since it could drastically reduce its autoxidation.

Abstract The native DNA duplex may be viewed as a cooperatively-ordered H bonded structure, including well localized Watson-Crick base pairs and H-bounded networks of hydration parts of the DNA-solvent interface in the grooves of the helix. In this paper, we present the effect of different metal ions (Li+, Mg2+ and Cu2+) on the denaturational heat capacity increment (DeltaC(p)) for calf thymus DNA. Since the contribution from the ordered hydration water fraction disruption energy to the total enthalpy and heat capacity increment values of double helix melting is significant, it must be possible to detect the effect of metal ions on the structural ordering/disordering of the H-bounded network in the hydration shell of the DNA duplex. Experimental results suggest that Li+, which is preferentially adsorbed in the minor groove of B-DNA and should contribute significantly to the stabilization of B-form, has a pronounced influence on the value of DeltaC(p). For the system Mg2+-DNA, the values of DeltaC(p) are also significant, which can be explained by the formation of inner hydration sphere complexes and immobilization of structural water by the grooves of the duplex, stabilizing the helix. The effect of Cu2+ ions is much more pronounced. The satellite peaks of calf thymus DNA become lower as the concentration of Cu2+ increases and for concentrations of Cu2+ higher than 0.010M, they disappear and DeltaC(p) = 0. This is indicative of the known preference of Cu2+ for purins and GC rich sites of DNA, binding to the N7 of guanine. As a result, disruption of the base stacking and hydrogen bounded water networks in the grooves of the double helix takes place.

Abstract The standard (p(o) = 0.1 MPa) molar enthalpies of formation for 2-, 3-, and 4-transmethoxycinnamic acids in the gaseous phase were derived from the standard molar enthalpies of combustion in oxygen of the crystalline compounds determined by static bomb combustion calorimetry at T = 298.15 K and from the literature values for the respective enthalpies of sublimation.