Publications

Abstract A chemiluminescent flow system for bromate detection, based on the reaction of bromate with sulphite in acid medium and using the steroid hydrocortisone as sensitiser, was studied. A factorial analysis strategy for the study of the effect on the system response of the experimental factors, flow rates of two pumps (Q(1) - acid sulphite plus hydrocortisone aqueous solution; Q(2) carrier, water), sample injection volume (V-L), reactor volume (V-R), sulphite concentration (C-S), hydrocortisone concentration (C-H) and acid concentration (C-A), was used. Screening analysis of the system performance was made using Plackett Burman designs. The system optimisation procedure was achieved by three levels three factors full factorial designs. V-L and C-H are the most significant factors - a quadratic C-H term was also observed to be significant. The optimised system responded linearly (logarithm of the detector signal as function of the logarithm of the bromate concentration) in the concentration range between 3.6 x 10(-7) and 5.0 x 10(-4) M with a limit of detection of about 8.0 x 10(-8) M (about 10 microg/l). An analysis of some interfering ions was made and it was suggested that bromide and chloride begin to quench chemiluminescence when they are in a 10-fold excess relatively to bromate concentration.

Abstract Firefly oxyluciferin (2-(6'-hydroxybenzothiazolyl)-4-hydroxythiazole) was chemically synthesized and characterized by means of C-13 and H-1 NMR, UV-vis spectrometry and RP-HPLC using different pH elution conditions. One of the chromatographic peaks observed in luciferase-catalyzed reaction mixtures was identified Lis corresponding to oxyluciferin.

Abstract The standard (p(o) = 0.1 MPa) enthalpies of formation of 2,6-di-tert-butyl-4-methylphenol and 3,5-di-tert-butylphenol in the gaseous phase, -315.5 +/- 4.4 kJ mol(-1) and -312.7 +/- 4.6 kJ mol(-1), respectively, were derived from the standard enthalpies of combustion, in oxygen, at 298.15 K, measured by static bomb combustion calorimetry, and from the standard enthalpies of sublimation, at 298.15 K, measured by Calvet microcalorimetry. The O-H bond dissociation enthalpies in those compounds were determined in benzene by photoacoustic calorimetry, leading to the standard enthalpies of formation of the gaseous phenoxy radicals: -189 +/- 8 kJ mol(-1) and -154 +/- 6 kJ mol(-1), respectively. These results were used to calculate enthalpies of substituent redistribution reactions, which are proposed as a method to estimate new data for substituted phenols.

Abstract The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following crystalline dicarboxylic acids: succinic acid, between T = 360.11 K and T = 375.14 K; methylsuccinic acid, between T = 343.12 K and T = 360.11 K; 2,2-dimethylsuccinic acid, between T = 350.11 K, and T = 365.11 K; 2-methylglutaric acid, between T = 338.38 K and T = 347.63 K; and 2,2-dimethylglutaric acid between T = 342.18 K and T = 352.66 K. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation were derived by the Clausius-Clapeyron equation and the molar entropies of sublimation at equilibrium pressures were calculated. Using estimated values for the heat capacity differences between the gas and the crystal phases of the studied compounds, the standard, p(o) = 10(5) Pa, molar enthalpies, entropies and Gibbs energies of sublimation at T = 298.15 K, were derived: (C) 2001 Academic Press

Abstract The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of two crystalline ruthenium complexes: tris(1,1,1-trifluoro-2,4-pentanedionate)ruthenium(III) {Ru(tfacac)(3)}, between T = 350.20 K and T = 369.17 K and tris(1,1,1,5,5,5-hexafluoro-2,4-pentanedionate)ruthenium(III) {Ru(hfacac)(3)} between T = 299.15 K and T = 313.14 K. From the temperature dependence of the vapour pressure of the crystalline compounds, the standard molar enthalpies of sublimation were derived by the Clausius-Clapeyron equation and the molar entropies of sublimation at equilibrium pressures were calculated. By using an estimated value for the heat capacity differences between the gas and the crystal phases the standard, p(o) = 10(5) Pa, molar enthalpies, entropies, and Gibbs energies of sublimation at T = 298.15 K, were derived: [GRAPHICS] (C) 2001 Academic Press.

Abstract The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following crystalline compounds: 1,2-diphenylethane (bibenzyl), between T = 289.16 K and T = 303.20 K, and of 3-phenylpropiolic acid between T = 329.15 K and T = 343.15 K. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation at the mean temperature of the experimental range were derived by the Clausius-Clapeyron equation. From these results the standard, p degrees = 10(5) Pa, molar enthalpies, entropies, and Gibbs energies of sublimation at T = 298.15 K, were calculated: [GRAPHICS] (C) 2001 Academic Press.

Abstract The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following compounds: 3-phenylpropionic acid, between T = 305.17 K and T = 315.17 K, 3-(2-methoxyphenyl)propionic acid, between T = 331.16 K and T = 347.16 K; 3-(4-methoxyphenyl)propionic acid, between T = 341.19 K and T = 357.15 K; 3-(3,4-dimethoxyphenyl)propionic acid, between T = 352.18 K and T = 366.16 K. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation Delta (g)(cr)H(m)degrees were derived by the Clausius-Clapeyron equation and the molar entropies of sublimation at equilibrium pressures were calculated. On the basis of estimated values for the heat capacity differences between the gas and the crystal phases of the studied compounds the standard, p degrees = 10(5) Pa, molar enthalpies, entropies and Gibbs energies of sublimation at T = 298.15 K, were derived: [GRAPHICS] (C) 2001 Academic Press.

Abstract The Knudsen mass-loss effusion technique was used to measure the vapor pressures as a function of temperatures of the following crystalline carboxylic acids: 2-phenylacetic acid, between 305.17 K and 321.16 K; 2-phenylbutyric acid, between 309.16 K and 323.16 K, and 5-phenylvaleric acid, between 315.15 K and 327.18 K. From the temperature dependence of the vapor pressure of the crystalline samples, the standard molar enthalpies of sublimation at the mean temperature of the experimental range were derived by using the Clausius-Clapeyron equation. From these results the standard molar enthalpies, entropies, and Gibbs functions of sublimation at T = 298.15 K were calculated. A correlation between the enthalpies of sublimation and the temperature of sublimation at a reference pressure (p = 10(5) Pa) for some carboxylic acids and other organic compounds is presented.

Abstract The phase transitions occurring in aqueous solutions of macromolecules and their complex structures (like order-disorder transitions in proteins or nucleic acids solutions) are usually accompanied by small changes in their specific partial volumes. If the quantity of these substances in the closed calorimetric vessels is relatively large (few mg) and if the phase transition is accompanied by a high change of specific partial volume (like in solution of bacteriophages), it is possible to detect some imaginary heat effects in the DSC calorimeters which have closed (sealed) vessels with free volume above the liquid.