Publications

Abstract A set of parameters consistent with the CHARMM force field has been determined for molecular dynamics simulations of several DOTA- and DOTP-Ln(III) chelates. Bonding and van der Waals parameters were derived from the available experimental data and analogy to similar ones in the existing force field. Net atomic charges were derived from ab initio calculations at the Hartree-Fock level to reproduce molecular electrostatic potentials (ESPs), with an effective core potential (ECP) basis set for the metal ion and the 6-31G* basis set for the ligand atoms. The charges are consistent with the TIP3P water model. Preliminary molecular dynamics simulations of the lanthanide chelates in aqueous solution were performed using the Nose-Hoover thermostat at 300 K. The new parameters correctly predicted the molecular structures and stability of the chelates major and minor isomers. (C) 1999 John Wiley & Sons, Inc. Int J Quant Chem 73: 237-248, 1999.

Abstract Estudou-se a influência da concentração de Cu no processo de fermentação alcoólica, nomeadamente no que respeita a fermentação de mostos. A fermentação alcoólica foi estudada num amplo intervalo de concentrações de Cu (desde níveis naturais até 1.0 mM), em dois meios de fermentação diferentes: mostos brancos (que constituem matrizes altamente complexas, contendo diversos ligandos de Cu) e "yeast nitrogen base" (YNB) com glucose. No meio YNB, a produção de etanol e a taxa de fermentação foram altamente influenciadas pela concentração de Cu, sendo que na presença de 0.50 e 1.0 mM Cu a produção de etanol foi dupla da verificada na ausência de Cu adicionado. No entanto, a cinética de fermentação foi mais lenta. Na produção de etanol a partir dos mostos apenas se verificaram efeitos ligeiros com a variação da concentração de Cu, o que significa que o teor de Cu não é responsável por alterações à fermentação, e por isso, encontra-se abaixo de níveis tóxicos relativamente ao desempenho das leveduras. Dum ponto de vista práctico-biotecnológico, os resultados sugerem o interesse em efectuar trabalho futuro sobre a influência do Cu nos meios usados na indústria de produção de etanol, usando a S. cerevisiae ou outras células. A explicação bioquímica para o fenómeno observado é um tópico de investigação que fica em aberto, sendo possível que exista uma ligação entre o efeito do Cu e a disponibilidade de Fe, uma vez que o Cu é necessário para o transporte de Fe para o interior das leveduras.Estudaram-se por potenciometria as propriedades complexométricas para Pb e Cu de quatro vinhos tintos diferentes, produzidos a partir de apenas uma das seguintes castas cultivadas na Região Demarcada do Douro: Tinta Barroca (TB), Tinta Roriz (TR), Touriga Nacional (TN) e Touriga Francesa (TF). Paralelamente estudou-se as propriedades complexométricas dos polifenóis isolados das graínhas (taninos condensados) e das películas (maioritariamente antocianas) duma mistura de uvas das quatro casta ...

Abstract The standard (p(O) = 0.1 MPa) molar enthalpy of combustion at T = 298.15 K of crystalline benzanthrone was determined as Delta(c)H(m)(O) = -(8114.7 +/- 2.0) kJ.mol(-1) by static-bomb calorimetry, and the standard molar enthalpy of formation of the crystal at T = 298.15 K was derived as Delta(f)H(m)(O)(cr) = -(4.1 +/- 3.0) kJ.mol(-1). Vapour pressure as a function of temperature was measured using the mass-loss Knudsen effusion technique, from which the standard molar enthalpy of sublimation at T = 298.15 K was derived as Delta(cr)(g)H(m)(O)= (126.6 +/- 0.6) kJ.mol(-1). The standard molar enthalpy of sublimation at T = 298.15 K was also measured by the quartz oscillator method, Delta(cr)(g)H(m)(O) (129.7 +/- 2.1) kJ.mol(-1) (C) 1999 Academic Press.

Abstract Four monovarietal red wines, Tinta Roriz, Tints Barroca, Touriga Nacional, and Touriga Francesa, were studied for their complexometric properties toward copper. For the purpose, ion selective electrode potentiometric titrations were carried out, and the data were treated by two methods suitable for heterogeneous ligands: the Scatchard plot, which provided the complexation capacity (CCtotal = maximum number of moles of sites per liter), and the differential equilibrium function (DEF), which provided the conditional stability constants of the sites effectively involved in the metal complexation (K-DEF) at a given titration point. The different wines displayed similar properties: CCtotal ranged from 4.5 x 10(-3) (Tinta Barroca) to 4.9 x 10(-3) M (Touriga Francesa), and log K-DEF values were between 4.2 and 6.5. The range of log(\Cu\(bound)/CCtotal) = log theta embraced in the titration was between -0.2 and -1.9. With regard to the natural levels of copper, from 4.4 x 10(-7) (Tinta Roriz) to 1.3 x 10(-6) M (Touriga Nacional), and ligands (CCtotal) in the wines, it can be expected that copper will be strongly complexed in the studied wines (log K-DEF > 6). Studies carried out, in parallel, for solutions of isolated seed tannins and skin polyphenols (mainly anthocyans) showed that their contribution to the CCtotal of the wines was <40% for tannins and <2% for skin polyphenols. However, skin polyphenols were shown to be much stronger copper ligands (log K-DEF = 6.7, log theta = -1.5) than tannins (log K-DEF = 4.5, log theta = -1.5).

Abstract The structural elucidation of 24 xanthones with different substitution patterns was performed by spectroscopic methods, namely 2D NMR techniques, such as correlation spectroscopy (COSY), nuclear Overhauser effect (NOE), heteronuclear correlation (HETCOR) and a 1D NMR technique, selective insensitive nuclei enhanced by polarization transfer (INEPT). (C) 1997 John Wiley & Sons, Ltd.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation of eight copper(II) fluorinated beta-diketonates at the temperature 298.15 K were determined by high-precision solution and reaction calorimetry. The standard molar enthalpies of sublimation of the same copper(II) complexes at the temperature 298.15 K were determined by effusion methods. From the enthalpies of formation of the complexes in the gaseous state, the average molar dissociation enthalpies [D-m] (Cu-O) were derived and compared with identical parameters obtained for non-fluorinated copper(II) beta-diketonates. [GRAPHICS] The following abbreviations are used in the table: HTFBA, 4,4,4-trifluoro-1-phenylbutane-1,3-dione; HTFFBD, 4,4,4-trifluoro-1-(2-furanyl)-butane-1,3-dione; HTFNBD, 4,4,4-trifluoro-1-(2-naphthyl)-butane-1,3-dione; HTFHD, 1,1,1-trifluorohexane-2,4-dione; HTFMHD, 1,l,1-trifluoro5-methylhexane-2,4-dione; HTFDHD, 1,1,1-trifluoro-5,5-dimethylhexane 2,4-dione; HTFMHPD, 1,1,1-trifluoro-5-methylheptane-2,4-dione; HHPFDOD, 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyloctane-4,6-dione. (C) 1998 Academic Press.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation Delta(f)H(m)degrees(cr) at T = 298.15 K were determined using static-bomb calorimetry for crystalline 4-methylpyridine N-oxide (4MePyNO), 3-cyanopyridine N-oxide (3CNPyNO), 4-cyanopyridine N-oxide (4CNPyNO), 3-hydroxypyridine N-oxide (3OHPyNO), 2-pyridinecarboxylic acid N-oxide (2CO(2)HpyNO), 4-pyridinecarboxylic acid N-oxide (4CO(2)HPyNO), 3-methyl-4-nitropyridine N-oxide (3Me4NO(2)PyNO), 2-pyridinecarboxylic acid (2CO(2)HPy), and 4-pyridinecarboxylic acid (4CO(2)HPy). The standard molar enthalpies of sublimation Delta(c)(rg) H(m)degrees at T = 298.15 K were measured by microcalorimetry, or by a mass-loss effusion technique, and from the enthalpies of formation of the gaseous compounds the dissociation enthalpies D(m)degrees of the (N+-O-) dative covalent bonds were derived. [GRAPHICS] Comparison has been made with D(m)degrees(N-O) values in pyridine N-oxide derivatives. (C) 1998 Academic Press.

Abstract The even chain length cerium(III) carboxylates from the octanoate to the octadecanoate have been synthesised by metathesis. Thermogravimetry shows the presence of coordinated water for the short chain homologues, whereas the longer chain ones only contain adsorbed water. X-Ray diffraction and IR spectral measurements show that the solid phase has a lamellar, bilayer structure with planes of the cerium(III) ions coordinated to the carboxylate groups. The phase behaviour of the carboxylates has been studied by DSC and polarized-light microscopy. One or more mesophases are observed over the temperature range 70-120 degrees C and melting occurs between 130 and 150 degrees C. The textures observed on the polarizing microscope clearly show the anisotropic nature of the mesophases. Although the overall enthalpy and entropy of melting of these compounds increase with increasing chain length, the values are considerably lower than expected for complete fusion of the alkyl chains. Competition between melting of the chains and changes in the metal-carboxylate coordination region is the major factor responsible for the differences observed in the phase behaviour between the short and long chain derivatives.

Abstract Catanionic mixtures are aqueous mixtures of oppositely charged surfactants which display novel phase behavior and interfacial properties in comparison with those of the individual surfactants. One phase behavior property is the ability of these systems;to spontaneously form stable vesicles at high dilution. The phase behavior of the mixture sodium dodecyl sulfate (SDS) - didodecyldimethylammonium bromide (DDAB) in water has been studied in detail, and two regions of isotropic vesicular phases (anionic-rich and cationic-rich) were identified. Cryo-transmission electron microscopy allowed direct visualization of relatively small and polydisperse unilamellar vesicles on the SDS-rich side. Monitoring of the microstructure evolution from mixed micelles to vesicles as the surfactant mixing ratio is varied toward equimolarity was also obtained. Further information was provided by water self-diffusion measurements by pulsed field gradient spin-echo NMR. Water molecules can be in fast or slow exchange between the inside and outside of the vesicle with respect to the experimental time scale, depending on membrane permeability and vesicle size. For the SDS-rich vesicles, a slow-diffusing component of very low molar fraction observed for the echo decays was traced down to very large vesicles in solution, Light microscopy confirmed the presence of vesicles of several microns in diameter. Thus, polydispersity seems to be an inherent feature of the system.