Publications

Abstract Pseudomonas syringae cells were exposed to 100 mu M copper alone, or to previously equilibrated copper sulfate-ligand solutions. Ligand concentrations were determined experimentally as those that reduced the free copper concentration to 5 mu M (determined with a Cu2+-selective electrode). These values were in agreement with those calculated by computational equilibrium simulation based on published stability constants. Exposure of P. syringae cells to copper sulfate, chloride, or nitrate resulted in similar high mortality, suggesting that copper was responsible for cell death. Acetate, succinate, proline, lysine, cysteine, and EDTA significantly reduced both the amount of copper bound to the cells and cell death, indicating that not only strong chelating agents but also weak and moderate copper ligands can effectively antagonize copper toxicity. However, cysteine and EDTA were considerably more effective than acetate, succinate, proline, and lysine, indicating that copper toxicity in not simply a function of free copper concentration but depends on the nature of the ligand. The results suggested that a significant fraction of copper bound to acetate, succinate, proline, or lysine was displaced to the bacteria or, alternatively, mixed copper-ligand-cell complexes could be formed. On the contrary, none of these phenomena occurred for the copper complexes with cysteine or EDTA.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation for the liquid 2-, 4-, 6-, and 8-methylquinolines: C9H6N(CH3) were derived from the standard molar enthalpies of combustion, in oxygen, at the temperature T = 298.15 K, measured by static-bomb combustion calorimetry. The standard molar enthalpies of vaporization for the same compounds were determined by microcalorimetry. The calorimeter was tested by measuring the enthalpies of vaporization of undecane and hexadecane. [GRPAHICS]

Abstract The simultaneous torsion and mass-loss effusion technique was used to measure the vapour pressure of crystalline bis(benzoylacetonato)beryllium (II) - Be(BZAC)(2) - and tris(benzoylacetonato) aluminium(III) - AI(BZAC)(3) -, as a function of temperature, from 415.7 K to 437.6 K and from 461.9 K to 478.2 K respectively. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation, at the mean temperature of the experimental temperature ranges, were derived for both complexes. The mean values obtained from both techniques are: Be(BZAC)(2), Delta(cr)(g)H(m)(o)(426.6 K)=151.6+/-1.8 kJ mol(-1); AI(BZAC)(3), Delta(cr)(g)H(m)(o)(470.1 K)=186.6+/-2.1 kJ mol(-1). Using the estimated value of Delta(cr)(g)C(p)(o) -50 J K-1 mol(-1), for both beryllium(Il) and aluminium(III) complexes, the standard molar enthalpies of sublimation at 298.15 K, were calculated as 158.0+/-1.8 kJ mol(-1) and 195.2+/-2.1 kJ mol(-1) respectively.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of combustion at the temperature T = 298.15K were measured by static-bomb calorimetry for crystalline 2,2'6,6'-tetraethylazobenzene N,N-dioxide, {2,6-(C2H5)(2)C6H3N(O).}2; 2,4,6-tri(1,1-dimethylethyl)nitrosobenzene, 2,4,6-{CH3C(CH3)(2)}3C6H2NO; and 2,4,6-tri(1,1-dimethylethyl)nitrobenzene, 2,4,6-{CH3C(CH3)(2)}3C6H2NO2. The standard molar enthalpies of sublimation at T = 298.15 K of the tri(1,1-dimethylethyl) compounds were measured by microcalorimetry. [GRAPHICS] The standard molar enthalpy of decomposition of {2,6-(C2H5)(2)C6H3N(O).}2 to form 2,6-(C2H5)(2)C6H3NO(g) at T = 298.15K was measured by microcalorimetry: Delta(dec)H(m) degrees/(kJ . mol(-1)) = (200.6 +/- 5.6). Application of group-additivity schemes applied to nitrosobenzene and nitrobenzene derivatives shows that 2,4,6-tri(1,1-dimethylethyl)nitrosobenzene is unstrained whereas the corresponding nitrocompound shows considerable strain in accord with an X-ray structure analysis demonstrating that steric hindrance prevents dimerization of the nitrosoderivative. (C) 1995 Academic Press Limited.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation for crystalline 2,6-dimethylquinoline, 2,6-(CH3)(2)-C9H5N, and 2,7-dimethylquinoline, 2,7-(CH3)(2)-C9H5N, at the temperature T = 298.15 K, were derived from the standard molar energies of combustion, in oxygen, measured by static-bomb calorimetry. The standard molar enthalpies of sublimation, at T = 298.15 K, were measured by microcalorimetry. [GRAPHICS]

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation for crystalline 2-cyanoquinoline, 2-CN-C9H6N, and 3-cyanoquinoline, 3-CN-C9H6N, were derived from the standard molar enthalpies of combustion, in oxygen, at the temperature T = 298.15 K, measured by static bomb-combustion calorimetry; the Knudsen mass-loss effusion technique was used to measure the vapour pressures of the crystals as functions of temperature, and the standard molar enthalpies of sublimation, at T = 298.15 K, were derived by the Clausius-Clapeyron equation. Direct measurements of the standard molar enthalpies of sublimation, using microcalorimetry, for 2-cyanoquinoline and 3-cyanoquinoline confirmed the values from the Knudsen technique. [GRAPHICS] (c) 1995 Academic Press Limited

Abstract The standard molar enthalpies of formation of quinoxaline, quinazoline and phthalazine at 298.15 K in the gaseous state have been determined from the standard molar enthalpies of combustion of the crystalline solids and the respective enthalpies of sublimation: quinoxaline, 240.3 +/- 3.3 kJ mol(-1); quinazoline, 243.1 +/- 2.7 kJ mol(-1); phthalazine, 329.9 +/- 3.3 kJ mol(-1). Ab initio full geometry optimizations at the 3-21G and 6-31G* levels were also performed for these molecules. MP2/RHF/3-21G/3-21G energies were calculated for all isomers, and used to estimate their isodesmic resonance energies.

Abstract Vapour pressures as functions of temperature of seven crystalline copper(II) beta-diketonates, CuL(2), were measured using either the Knudsen mass-loss effusion technique (Oporto apparatus), the simultaneous torsion and mass-loss effusion technique (Utrecht apparatus), or both. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation, at the mean temperature of the experimental temperature range, Delta(cr)(g) H-m degrees ((T)), were derived, and the standard molar enthalpies of sublimation, at the temperature 298.15 K, were calculated: [GRAPHICS] where HACAC, pentane-2,4-dione; HPIPRM, 2,2-dimethylheptane-3,5-dione; HDIBM, 2,6-dimethylheptane-3,5-dione; HIBPM, 2,2, 6-trimethylheptane-3,5-dione; HDPM, 2,2,6,6-tetramethylheptane-3,5-dione; HBZAC, 1-phenylbutane-1,3-dione; and HTFAC, 1,1,1-trifluoropentane-2,4-dione. The consistency of the vapour-pressure measurements was tested by measuring the vapour pressures of benzoic acid, at various temperatures, by different experimental techniques: Knudsen mass-loss effusion, simultaneous torsion and mass-loss effusion technique, and spinning rotor. From the standard molar enthalpies of formation of the gaseous complexes, the mean molar (Cu-O) bond-dissociation enthalpies were derived.