Publications

Abstract Dilute solutions of catanionic vesicles formed by the mixed single-chained (sodium dodecylsulphate, SDS) and double-chained (didodecyldimethylammonium bromide, DDAB) surfactants have been investigated by differential scanning calorimetry. It is for the first time reported a gel-to-liquid crystal phase transition temperature, T-m, in this type of mixed vesicles. The SDS-rich vesicles (at X-SDS = 0.71) show a concentration-dependent T-m in the range 9-16 degreesC. Addition of salt is seen to have an effect on T-m similar to that observed with increasing surfactant concentration, both inducing a decrease in T-m. These results differ from those obtained for neat DDAB vesicles. The observed effects in the two types of vesicles are rationalised in terms of headgroup electrostatic interactions which may have influence on the chain packing and phase transition temperature.

Abstract The phase behavior and aggregate structure of the didodecyldimethylammonium bromide (DDAB)-sodium taurodeoxycholate-water mixed surfactant system have been investigated in the dilute (above 95 wt% water) cationic-rich area, at 25 degreesC. A combination of techniques has been used, including polarizing and video-enhanced light microscopy, cryogenic transmission electron microscopy and water self-diffusion NMR. Between the dilute lamellar phase (approximate to4-30 wt% DDAB) and the very narrow isotropic solution (below 0.5 wt% DDAB), the lamellar dispersions formed by DDAB contain different types of vesicle structures (vesicles, microtubules and multilamellar structures). On addition of bile salt to the DDAB dispersions, strong electrostatic headgroup interactions and geometric packing effects (owing to the unusual molecular structure of the anionic surfactant) are present. The vesicle aggregates, however, are able to incorporate an amount of bile salt up to roughly 20 mol%. Further addition induces a macroscopic phase separation, with the formation of a strong white dispersion. The light and electron micrographs show that the vesicles are spherical and integral, undergoing an increase in size when the bile salt concentration is varied between 0 and 10 mol%. At higher bile salt concentration, smaller vesicles, tubular structures and submicron-sized dispersion droplets are observed. Water self-diffusion NMR measurements give further information regarding vesicle size and polydispersity.

Abstract The standard (pdegrees = 0.1 MPa) molar enthalpies of formation Delta(f)H(m)degrees, at the temperature 298.15 K, for crystalline 2,3,4-, 2,4,5-, 2,4,6- and 3,4,5-trichloroaniline were derived from the molar enthalpies of combustion Delta(c)H(m)degrees in oxygen using rotating bomb combustion calorimetry. The reaction products were CO2(g), NI(g), and HCl . 600H(2)O(l). The standard molar enthalpies of sublimation Delta(cr)(g)H(m)degrees at T = 298.15 K were measured by Calvet microcalorimetry. The results are as follows: [GRAPHICS] The derived standard molar enthalpies of formation of the gaseous compounds were compared with values estimated by assuming the enthalpy increment for substitution of chlorine in aniline to be the same as for substitution into benzene.

Abstract A cellulase from Trichoderma reesei was immobilized on Eudragit L-100, a reversibly soluble polymer depending on the pH of the medium. The solubility of the modified cellulase was studied at different pH values. By changing the pH, the adsorption equilibrium of the derivatized proteins is switched towards the liquid phase, thus making recycling possible. This method allows for improved stability, without major loss of specific activity. The adsorption of cellulase on Eudragit lowers the enthalpy of denaturation, but affects only slightly the denaturation temperature. The use of carbodiimide was ineffective on linking the enzymes covalently to the polymer, since the immobilization process was found to be only mediated by non-covalent forces.

Abstract The coordination chemistry involved in the assisted transfer of Rh-III by interfacial coordination with 2,5,8-trithia[9],(2,9)1, 10-phenanthrolinophane (L) has been studied at the water/1,2-dichloroethane interface by cyclic voltammetry. The dependence of the half-wave transfer potential on the ligand and metal concentrations suggests the [Rh(L)Cl-2](+) formulation for the complex cation involved in the assisted transfer, In contrast, from the reaction of L in refluxing MeCN/water solution the [Rh(L)Cl][BF4](2).2MeCN compound has been isolated and structurally characterised. In the [Rh(L)Cl](2+) complex cation L acts as an N2S3 donor encapsulating the metal centre within a cavity having a square-based pyramidal geometry. A chloride ligand completes the distorted octahedral coordination sphere around the Rh-III ion.

Abstract Xanthine oxidase (XO) is a highly versatile flavoprotein enzyme, ubiquitous among species (from bacteria to human) and within the various tissues of. mammals. The enzyme catalyses the oxidative hydroxylation of purine substrates at the molybdenum centre (the reductive half-reaction) and subsequent reduction Of O-2 at the flavin centre with generation of reactive oxygen species (ROS), either superoxide anion radical or hydrogen peroxide (the oxidative half-reaction). Many diseases, or at least symptoms of diseases, arise from a deficiency or excess of a specific metabolite in the body. For an example of an excess of a particular metabolite that produces a disease state is the excess of uric acid which can led to gout. Inhibition of XO decreases the uric acid levels, and results in an antihyperuricemic effect. Allopurinol, first synthesised as a potential anticancer agent, is nowadays a clinically useful xanthine oxidase inhibitor used in the treatment of gout. There is overwhelming acceptance that xanthine oxidase serum levels are significantly increased in various pathological states like hepatitis, inflammation, ischemia-reperfusion, carcinogenesis and aging and that ROS generated in the enzymatic process are involved in oxidative damage. Thus, it may be possible that the inhibition of this enzymatic pathway would be beneficial. In this review the State of the Art will be presented, which includes a summary of the progress made over the past years in the knowledge of the structure and mechanism of the enzyme, associated pathological states, and in the efforts made towards the development of new xanthine oxidase inhibitors.

Abstract The standard (p(o) = 0,1 MPa) molar enthalpies of combustion in oxygen, at T = 298.15 K, were measured by rotative bomb calorimetry for crystalline N,N-diethyl-N'-furoylthiourea, (2-C4H3O)CONHCSN(C2H5)(2), HFET, and N,N-diisobutyl-N'-furoylthiourea, (2-C4H3O)CONHCSN(iso-C4H9)(2), HFIB. The standard molar enthalpies of sublimation of both HFET and HFIB were measured by high-temperature Calvet microcalorimetry. These values were used to derive the standard molar enthalpies of formation of the compounds, in their crystalline and gaseous phases. [GRAPHICS] (C) 2002 Published by Elsevier Science Ltd.

Abstract Complexation properties of an anthropogenic fulvic acid (FA) extracted from a composted sewage sludge (csFA) for Cu(II), Pb(II) and Cd(II) were studied at pH=6 and at a concentration of 25 mg L-1. For the case of Cu(II), a particular analysis of the complexation phenomena was done at pH values of 3, 4, 5 and 6 and at aqueous FA concentrations of 25, 50 and 100 mg L-1 by synchronous excitation molecular fluorescence spectroscopy (SyF). Potentiometric titrimetry with Cu(II). Pb(II), Cd(II) and H+ ion-selective electrodes and acid-base conductimetric titrations were used to obtain experimental information about the acid properties and complexation phenomena. A comparison of the results obtained for csFA with a natural soil FA (sFA) was made. Differences have been detected in the structural composition of the two samples and in the structure of the binding sites. In the csFA, binding site structures containing nitrogen probably play an important role in the complexation, besides oxygen containing structures. Complexation by sFA is mainly due to carboxylic and phenolic structures. Nevertheless, this work shows that csFA have macroscopic complexation properties (magnitude of the conditional stability constant and binding sites concentration) somewhat similar to the natural sFA samples.