Publications

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.

Abstract This paper deals with the study of the V-group, family T-even, E. Coli bacteria phage (named unphage). According to electron microscopic pictures, the geometrical parameters of this phage are 750x560 Angstrom (from head) and 900 Angstrom (from tail). Bacterial viruses genome-ds-DNA-expulsion from the phage capsid is induced by temperature and is not accompanied by heat effects (temperature interval 45-75 degreesC). Thus the temperature induced ejection of genetic material from phages is predominantly entropic. ds-DNA output from the capsid increases the viscosity of the phage suspension at least 100 times. ds-DNA output from the capsid is accompanied by a significant change of partial volume. The disruption of 1 mg of phage produces DeltaV=1.3x10(-9) m(3) which corresponds to a volume increase of 200%. This produces exothermic heat effects in closed calorimetric cells, with free volume above the measured liquid. The contraction of the tail of phage plays an important role in the injection, in the step where phage attaches the outer membrane of the host cell. The main factors of the DNA condensation and packaging in the virus head, and after its ejection through the hole with a diameter close to that of ds-DNA, are caused by the surrounding solution quality, so-called hydration forces between ds-DNA parallel packaged segments and more exactly by the difference of this parameter inside and outside the capsid of the phage.

Abstract The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following substituted benzoic acids: 2-amino-3-methylbenzoic acid at T between 343.16 K and 357.17 K; 2-amino-5-methylbenzoic acid at T between 345.15 K and 361.16 K; 2-amino-6-methylbenzoic acid at T between 339.17 K and 355.15 K; 3-amino-2-methylbenzoic acid at T between 367.16 K and 381.22 K; 3-amino-4-methylbenzoic acid at T between 363.18 K and 377.16 K; and 4-amino-3-methylbenzoic acid at T between 367.17 K and 383.14 K. The standard, P-0 = 10(5) Pa, molar enthalpies, entropies, and Gibbs energies of sublimation at T = 298.15 K were derived from the temperature dependence of the vapour pressure using estimated values for the heat capacity differences between the gas and the crystal phases of the studied compounds. [GRAPHICS] (C) 2001 Academic Press.

Abstract Three N-acyl-N',N'-diethylthioureas, RCONHCSNEt2. R = Pr-1, Bu-1, Bu-1, have been prepared and characterised. The standard (p(o) = 0.1 MPa) molar enthalpies of combustion in oxygen of the three crystalline compounds, at T = 298.15 K. have been measured by rotating bomb-combustion calorimetry. and the standard molar enthalpies of sublimation of the compounds by microcalorimetry. These values were used to derive the standard molar enthalpies of formation of the compounds in their crystalline and gaseous phases, respectively. The derived standard molar enthalpies of formation in the gaseous state are discussed comparatively. Acid constants and some complex stabilities have been measured pH-potentiometrically in dioxane-water mixture. The crystal structure of N,N-diethyl-N'-isovaleroyl-thiourea is presented and shows a delocalization of the pi electrons of the C=S group over the carbon-amine nitrogen bond. CS-NEt2 stabilising the molecule, in accordance with the thermochemical results.

Abstract The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following six compounds: 2-methyl-3-nitrobenzoic acid, between T = 357.16 K and T = 371.16 K; 2-methyl-6-nitrobenzoic acid, between T = 355.16 K and T = 369.16 K; 3-methyl-2-nitrobenzoic acid, between T = 371.16 K and T = 385.14 K; 3-merhyl-4-nitrobenzoic acid, between T = 363.21 K and T = 379.16 K; 4-methyl-3-nitrobenzoic acid, between T = 363.10 K and T = 377.18 K; 5-methyl-2-nitrobenzoic acid, between T = 355.18 K and T = 371.08 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 Delta H-g(cr)m(o), entropies Delta S-g(cr)m(o) and Gibbs energies Delta (g)(cr)G(m)(o) of sublimation at T = 298.15 K, were derived: [GRAPHICS] (C) 2001 Academic Press.

Abstract The catecholamines adrenaline, noradrenaline, dopamine, dopa and isoprenaline were oxidized into their respective aminochromes: adrenochrome, noradrenochrome, dopaminochrome, dopachrome and isoprenochrome. Tandem mass spectrometry (MS/MS) fragmentation patterns were examined for the five aminochromes in order to establish a general structural assignment of these oxidation products by electrospray mass spectrometry. Although protonated aminochromes undergo similar fragmentation patterns with a characteristic consecutive loss of two carbonyl groups, the presence of different substituents in the parent compounds led to significant changes in the CID spectra. This feature is more evident for isoprenochrome and dopachrome, especially for the latter where the MS/MS spectrum is dominated by the loss of formic acid. A general pattern of fragmentation for aminochromes is proposed, which should provide a suitable basis to aid their characterization in studies in vivo or in vitro. Copyright (C) 2001 John Wiley & Sons, Ltd.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation for 2,3-, 2,4-, 2,5-, 3,4- and 3,5-trans-dimethoxycinnamic 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. (C) 2001 Academic Press.

Abstract The thermochemistry of adenosine(cr) was studied by a variety of methods: the standard (pressure p degrees = 0.1 MPa) molar enthalpy of combustion in oxygen at T = 298.15 K was measured by means of combustion calorimetry and was found to be Delta (c)H(m)degrees = -(5139.4 +/- 3.3) kJ . mol(-1); the standard molar heat capacity C(p,m)degrees was determined by means of adiabatic calorimetry for the range 11 less than or equal to (T/K) less than or equal to 328 {C(p,m)degrees = (290.10 +/- 0.58) J . K-1 . mol(-1) at T = 298.15 K}; and the saturation molality in water was measured by means of high-performance liquid chromatography and was found to be m(sat) (1.849 +/- 0.015) . 10(-2) mol . kg(-1) at T = 298.15 K. Derived quantities at T = 298.15 K for adenosine(cr) are the standard molar enthalpy of formation Delta (f)H(m)degrees = -(653.6 +/- 3.6) kJ . mol(-1), the third law standard molar entropy S(m)degrees = (289.57 +/- 0.6) J . K-1 . mol(-1) and the standard molar Gibbs free energy of formation Delta (f)G(m)degrees = -(204.4 +/- 3.6) kJ . mol(-1). The function Phi (m)degrees - Delta TS(m)degrees - Delta (T)(0)H(m)degrees /T for adenosine(cr) was tabulated for 5 less than or equal to (T/K) less than or equal to 320. A thermochemical cycle was used to calculate Delta (f)G(m)degrees = -(194.5 +/- 3.6) kJ . mol(-1), Delta (f)H(m)degrees = -(621.3 +/- 3.6) kJ . mol(-1), and m S(m)degrees = (364.6 +/- 0.7) J . K-1 mol(-1) for adenosine(aq) at T = 298.15 K. These values in turn were used to calculate standard molar formation properties at T = 298.15 K and ionic strength I = 0 for the adenosine 5'-monophosphate (AMP), adenosine 5'-diphosphate (ADP), and adenosine 5'-triphosphate (ATP) series of aqueous species. Standard molar transformed formation properties for the aqueous biochemical reactants adenosine, AMP, ADP, and ATP have also been calculated at T = 298.15 K, PH = 7.0, pMg 3.0, and I = 0.25 mol . kg(-1). (C) 2001 Academic Press.