Publications

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.

Abstract Pancreatic ribonuclease A may be cleaved to produce two fragments: the S-peptide (residues 1-20) and the S-protein (residues 21-124), The S-peptide, or a truncated version designated as the S15 peptide (residues 1-15), combines with the S-protein to produce catalytically active complexes. The conformation of these peptides and many of their analogues is predominantly random coil at room temperature; however, they populate a significant fraction of helical form at low temperature under certain solution conditions. Moreover, they adopt a helical conformation when bound to the S-protein. A hybrid sequence, disulfide-stabilized peptide (ApaS-25), designed to stabilize the helical structure of the S-peptide in solution, also combines with the S-protein to yield a catalytically active complex. We have performed high-precision titration microcalorimetric measurements to determine the free energy, enthalpy, entropy, and heat capacity changes for the binding of ApaS-25 to S-protein within the temperature range 5-25 degreesC. The thermodynamic parameters for both the complex formation reactions and the helix-to-coil transition also were calculated, using a structure-based approach, by calculating changes in accessible surface area and using published empirical parameters. A simple thermodynamic model is presented in an attempt to account for the differences between the binding of ApaS-25 and the S-peptide, From this model, the thermodynamic parameters of the helix-to-coil transition of S15 can be calculated. (C) 2001 Wiley-Liss, Inc.

Abstract The standard (p(0) = 0.1 MPa) molar enthalpies of formation of crystalline bis(N-benzoyl-N',N'-diethylureato)copper(II), Cu(BETU)(2), and bis(N-benzoyl-N',N'-diisobutylureato)copper(II), Cu(BIBU)(2), were measured, at T = 298.15 K, by solution-reaction isoperibol calorimetry, respectively, as -(833.7 +/- 9.7) and -(1050.6 +/- 12.1) U mol(-1). The standard molar enthalpy of sublimation, at T = 298.15 K, of Cu(BETU)(2) Was determined by a Knudsen effusion technique as (180 +/- 37) kJ mol(-1). These values were used to derive the standard molar enthalpy of formation of Cu(BETU)(2) in gaseous phase, and to evaluate the mean metal-ligand dissociation enthalpy of the complex relative to that of the ligand with hydrogen.