Publications

Abstract Calorimetric measurements are expected to provide useful data regarding the relative stability of alpha- versus beta-amino acid isomers, which, in turn, may help us to understand why nature chose alpha- instead of beta-amino acids for the formation of the biomolecules that are essential constituents of life on earth. The present study is a combination of the experimental determination of the enthalpy of formation of N-benzyl-beta-alanine, and high-level ab initio calculations of its molecular structure. The experimentally determined standard molar enthalpy of formation of N-benzyl-beta-alanine in gaseous phase at T = 298.15 K is (298.8 +/- 4.8) kJ center dot mol(-1), whereas its G3(MP2)//B3LYP-calculated enthalpy of formation is -303.7 kJ center dot mol(-1). This value is in very good agreement with the experimental one. Although the combustion experiments of N-benzyl-alpha-alanine were unsuccessful, its calculated enthalpy of formation is -310.7 kJ center dot mol(-1); thus, comparison with the corresponding experimental enthalpy of formation of N-benzyl-beta-alanine, -(298.8 +/- 4.8) kJ/mol, is in line with the concept that the more branched amino acid (alpha-alanine) is intrinsically more stable than the linear beta-amino acid, beta-alanine.

Abstract A novel volatile microemulsion formed by the catanionic surfactant hexadecyltrimethylammonium octylsulfonate (TA(16)So(8)), heptane and water has been explored as a template for producing nanoparticles of hydrophobic organic materials. Butylated hydroxytoluene (BHT) was employed as the model hydrophobic substance. First, the oil-in-water microemulsion was formed, containing TA16So8 as the single emulsifier and BHT dispersed in the volatile microphase. Microstructure characterization by self-diffusion NMR revealed that BHT was indeed incorporated into the oil droplets and that the mean diameter of the main droplet population was 30 nm, larger than in the BHT-free microemulsion. Next, a rapid solvent and water removal by freeze drying allowed converting the microemulsion droplets into nanoparticles in the form of a dry, fine powder. This powder was freely dispersible in water to yield a stable suspension of amorphous BHT particles with a mean size of 19 nm and zeta-potential of +37 mV. The solid nanoparticles in the aqueous dispersion were thus smaller than the initial microemulsion droplets. For comparison, a conventional o/w microemulsion composed of CTAB and sec-butanol was also tested as a template for BHT particle formation by the same process, and it was found that it yielded crystalline particles of micrometre size. On the basis of our results, we anticipate the catanionic microemulsion method to be an efficient one for producing size-controlled, water-dispersible nanoparticles of other hydrophobic organic materials.

Abstract This work reports the standard (p degrees = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, Delta(f)H degrees(m)(g), of 2,4-, 2,6-, and 3,5-dibromophenol, at T = 298.15 K, respectively, as (59.6 +/- 2.6) kJ . mol(-1), (49.1 +/- 2.2) kJ . mol(-1) and (39.5 +/- 2.0) kJ . mol(-1). These experimental values were derived from the measurements of the standard molar enthalpies of formation, in the crystalline phase, Delta(f)H degrees(m), (2, 4-dibromophenol, Cr) = -(140.9 +/- 2.1) kJ . mol(-1), Delta(f)H degrees(m) (2, 6-dibromophenol, cr) = -(132.5 +/- 1.6) kJ . mol(-1) and Delta fH degrees(m) (3, 5-dibromophenol, cr) = -(134.5 +/- 1.7) kJ . mol(-1), at the same reference temperature, achieved from the standard molar enthalpies of combustion, in oxygen, to yield CO(2)(g) and HBr.600H(2)O(I), measured by rotating-bomb combustion calorimetry, together with measurements of the standard molar enthalpies of sublimation, at T = 298.15 K, as Delta(g)(cr)H degrees(m) (2, 4-dibromophenol) = (81.3 +/- 1.5) kJ . mol(-1), Delta(g)(cr)H degrees(m) (2, 6-dibromophenol) = (83.4 +/- 1.5) kJ . mol(-1) and Delta(g)(cr)H degrees(m) (3, 5-dibromophenol) (94.3 +/- 1.8) kJ . mol(-1), obtained using the Calvet high temperature vacuum sublimation technique. The standard molar enthalpy of sublimation, at T = 298.15 K, for the 3,5-dibromophenol was also determined from the temperature-vapour pressure dependence, obtained by the Knudsen mass loss effusion method, Delta(g)(cr)H degrees(m) (3.5-dibromophenol) = (95.0 +/- 1.1) kJ . mol(-1). For this isomer it is also reported the standard (p degrees = 0.1 MPa) molar entropy and Gibbs energy of sublimation, at T = 298.15 K. The experimental values of the gas-phase enthalpies of formation of each compound were compared with estimates using the empirical scheme developed by Cox and with the calculated values based on density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional at the 6-311++G(d,p) basis set. These two methodologies were also used to estimate the enthalpies of formation in the gas-phase of the 2,3-, 2,5-, and 3,4-dibromophenol.

Abstract The standard (p degrees = 0.1 MPa) molar enthalpies of formation, in the crystalline state, of the 1- and 2-cyanonaphthalene were derived from the standard molar energies of combustion, in oxygen, at T = 298.15 K, measured by static-bomb combustion calorimetry. Vapor pressure measurements at different temperatures, using the Knudsen mass loss effusion technique, enabled the determination of the enthalpy, entropy, and Gibbs energy of sublimation, at T = 298.15 K, for both isomers. The standard molar enthalpies of sublimation, at T = 298.15 K. for 1- and 2-cyanonaphthalene, were also measured by high-temperature Calvet microcalorimetry. [GRAPHICS] Combining these two experimental values, the gas-phase standard molar enthalpies. at T = 298.15 K, were derived and compared with those estimated by employing two different methodologies: one based on the Cox scheme and the other one based on G3MP2B3 calculations. The calculated values show a good agreement with the experimental values obtained in this work.

Abstract This paper reports a combined experimental and computational thermochemical study of 4-benzyloxyphenol. Static bomb combustion calorimetry and Knudsen mass-loss effusion technique were used to determine the standard (p(o) = 0.1 MPa) molar enthalpy of combustion, Delta H-c(m)o = -(6580.1 +/- 1.8) kJ. mol(-1), and of sublimation, Delta H-g(cr)m(o)= (131.0 +/- 0.9) kJ . mol(-1), respectively, from which the standard (p(o) = 0.1 MPa) molar enthalpy of formation, in the gaseous phase, at T = 298.15 K, Delta H-t(m)o = -(119.5 +/- 2.7) kJ . mol(-1) were derived. For comparison purposes, the gas-phase enthalpy of formation of this compound was estimated by G3(MP2)//B3LYP calculations, using a set of gas-phase working reactions; the results are in excellent agreement with experimental data. G3(MP2)//B3LYP computations were also extended to the calculation of the gas-phase enthalpies of formation of the 2- and 3-benzyloxyphenol isomers. Furthermore, this composite approach was also used to obtain information about the gas-phase acidities, gas-phase basicities, proton and electron affinities, adiabatic ionization enthalpies and, finally, O-H bond dissociation enthalpies.

Abstract The present work reports the values of the standard (p degrees = 0.1 MPa) molar enthalpies of formation in the condensed phase of the three isomers of monoiodophenol derived from the standard molar energies of combustion, in oxygen, to yield CO(2)(g), I(2)(cr)., and H(2)O(1), at T = 298.15 K, measured by rotating-bomb combustion calorimetry, as well as the values of the standard molar enthalpies of sublimation, at T = 298.15 K, determined using high-temperature Calvet microcalorimetry. Combining the former two experimental quantities, the standard molar enthalpies of formation in the gaseous phase were derived, at T = 298.15 K: Delta(f)H(m)degrees (2-iodophenol, g) = -(15.3 +/- 2.0) kJ.mol(-1) Delta(f)H(m)degrees(3-iodophenol, g) = -(7.2 +/- 2.1) kJ.mol(-1), and Delta(f)H(m)degrees(4-iodophenol, g) = -(14.3 +/- 2.3) kJ.mol(-1). The experimental values of the gas-phase enthalpies of formation of each compound were compared with estimates using the empirical scheme developed by Cox and with the calculated values based on high-level density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional at the 6-311G(d,p) basis set.

Abstract Thermodynamic properties of 3- and 4-phenoxyphenol have been determined by using a combination of calorimetric and effusion techniques as well as by high-level ab initio molecular orbital calculations. The standard (p degrees = 0.1 MPa) molar enthalpies of formation in the condensed and gas states, Delta(f)H(m)degrees(cr or 1) and Delta(f)H(m)degrees(g), at T = 298.15 K, of 3- and 4-phenoxyphenol were derived from their energies of combustion in oxygen, measured by a static bomb calorimeter, and from the enthalpies of vaporization or sublimation derived respectively by Calvet microcalorimetry for the 3-phenoxyphenol and, by Knudsen effusion technique for the 4-phenoxyphenol. The theoretically estimated gas-phase enthalpies of formation were calculated from high-level ab initio molecular orbital calculations at the G3(MP2)//B3LYP level of theory. Furthermore, this composite approach was also used to obtain information about the gas-phase acidities, gas-phase basicities, proton and electron affinities, adiabatic ionization enthalpies, and, finally, O-H bond dissociation enthalpies. The good agreement between the G3MP2B3-derived values and the experimental gas-phase enthalpies of formation for the 3- and 4-phenoxyphenol gives confidence to the estimate concerning the 2-phenoxyphenol isomer, which was not experimentally studied, and to the estimates concerning the radical and the anion. Additionally, the experimental values of gas-phase enthalpies of formation were also compared with estimates based on the empirical scheme developed by Cox.

Abstract The description of the reassembling and testing of a twin heat conduction, high-precision, drop microcalorimeter for the measurement of heat capacities of small samples are presented. The apparatus, originally developed and used at the Thermochemistry Laboratory, Lund, Sweden, has now been reassembled and modernized, with changes being made as regarding temperature sensors, electronics and data acquisition system. The apparatus was thereafter thoroughly tested, using benzoic acid and hexafluorobenzene as test substances. The accuracy of the C(p,m)(c) (298.15 K) data obtained with this apparatus is comparable to that achieved by high-precision adiabatic calorimetry. Here we also present the results of heat capacity measurements on of some polyphenyls (1,2,3-triphenylbenzene, 1,3,5-triphenylbenzene, p-terphenyl, m-terphenyl, o-terphenyl, p-quaterphenyl) at T = 298.15 K, measured with the renewed high precision heat capacity drop calorimeter system. The high resolution and accuracy of the obtained heat capacity data enabled differentiation among the ortho-, meta-, and para-phenyl isomers.

Abstract Porous phosphate heterostructures (PPH), functionalized with different ratios of aminopropyl and mercaptopropyl groups, labelled as N(x=5,25,50)-PPH and S(x=5,25,50)-PPH, respectively, were tested as adsorbents for Ni(II) and Hg(II) found in industrial sewage from electroplating processes and button battery recycling. X-ray diffraction was used to study the structures. The specific surface area of the pristine material (PPH) was 620 m(2) g(-1), whereas the specific surface areas of the modified mercaptopropyl (S(5)-PPH) and aminopropyl (N(5)-PPH) were 472 and 223 m(2) g(-1), respectively. The adsorption data were fitted to a Langmuir isotherm model. The S(5)-PPH material was saturated by 120 mmol Hg(II) per 100 g of material, whereas for Ni(II) adsorption, N(25)-PPH material displayed the highest adsorption with a saturation value of 43.5 mmol per 100 g. These results suggest that functionalized PPH materials may be promising toxic metal scavengers and that they may provide an alternative environmental technology.

Abstract We herein report the reversible formation of a planar lamellar phase as an intermediate structure in a vesicle-micelle transition induced by temperature, for a salt-free catanionic surfactant-water system. Turbidity, small-angle neutron scattering, dynamic light scattering and microscopy data altogether demonstrate that the vesicles formed by hexadecyltrimethylammonium octylsulfonate (TA(16)So(8)) in water fuse at high temperature into planar lamellae before transforming into elongated micelles. On cooling the micelles first nucleate into lamellae, and only then vesicles appear through lamellae fission. This behavior is both intriguing and counter-intuitive, since a monotonous dependence of the spontaneous curvature of the surfactant film on temperature should be expected.