Publications

Abstract The thermochemistry of alpha-D-xylose(cr) was studied by means of oxygen bomb calorimetry and a Physical Property Measurement System (PPMS) in zero magnetic field. The sample of alpha-D-xylose(cr) used in this study was one well-characterized by HPLC, Karl Fischer analysis, NMR, and by carbon dioxide analysis. The standard molar enthalpy of combustion was found to be Delta H-c(m)o = -(2342.2 +/- 0.8) kJ.mol(-1) at T = 298.15 K and at the standard pressure p degrees = 0.1 MPa. The standard molar heat capacity for alpha-D-xylose(cr) was measured with the PPMS over the temperature range 1.9001 <= T/K <= 303.66. At T = 298.15 K, C-p,m(o) = (178.1 +/- 1.8) J.K-1.mol(-1). The values of C-p,m(o) were fit as a function of T by using theoretical and empirical models for appropriate temperature ranges. The results of these fits were used to calculate values of C-p,m(o), the entropy increment Delta S-T(0)m(o), Delta H-T(0)m(o), and Phi(o)(m) = (Delta S-T(0)m(o) - Delta H-T(0)m(o)/T) from T = 0.5 K to T = 300 K. Derived quantities for alpha-D-xylose(cr) are the standard molar enthalpy of formation Delta H-f(m)o = -(1054.5 +/- 1.1) kJ.mol(-1), the third law standard molar entropy S-m(o) = (175.3 +/- 1.9) J.K-1.mol(-1), and the standard molar Gibbs energy of formation Delta(f)G(m)(o) = -(750.5 +/- 1.0) kJ.mol(-1). A comparison of values of Delta H-c(m)o and S-m(o) for the five-carbon aldoses demonstrated a striking similarity in the values of these respective properties for alpha-D-xylose(cr), D-ribose(cr), and D-arabinose(cr). Thermochemical network calculations were performed that led to values of the standard formation properties at T = 298.15 K for a variety of biochemical substances: D-xylose(aq), D-xylose(aq), D-xylose(2) (aq), D-lyxose(cr and aq), D-lyxose (aq), D-xylulose(aq), xylitol(aq), 1,4-beta-D-xylobiose(am and aq), and 1,4-beta-D-xylotriose(am and aq).

Abstract Recommended vapor pressure data for ferrocene (CAS Registry Number: 102-54-5) in the temperature range from 242 K to 447 K were developed by the simultaneous correlation of critically assessed vapor pressures, heat capacities of the crystalline phase and the ideal gas, and calorimetrically determined enthalpies of sublimation. All of the properties needed for the correlation were newly determined in this work. The value for the enthalpy of sublimation, Delta(g)(cr) H-m(298.15 K) = (74.38 +/- 0.38) kJ.mol(-1), is recommended. Comparisons with literature values are shown for all measured and derived properties.

Abstract Has been noticed a decline in students' interest in learning science. It is necessary, therefore, an implementation of teaching strategies that enable students to understand the usefulness of learning science and relevance of scientific knowledge. Given the unquestionable importance of pedagogical integration of technology, the design of digital learning resources can be relevant to motivate and encourage the involvement of young people in the construction of learning. It is this philosophy that fits PROFILES European project, and its predecessor PARSEL. This paper will present the basic principles of these projects, also referring to the potential of inquiry in the teaching and learning of science. In close connection with the inquiry and educational technology this paper also presents two examples of digital educational resources, developed by us, to enhance the learning of science, more effective and meaningful for students.

Abstract In this work an analysis of the effect of ortho, meta and para isomerization and the number of phenyl rings on the heat capacity and phase behavior of oligophenyls, n(Ph), from 3 up to 5 is presented. The phase behavior from 298.15 K to the melting temperature was analysed by differential scanning calorimetry (DSC) and the temperature, enthalpies and entropies of fusion along the oligophenyls series were determined. With the exception of terphenyl isomers, the meta oligophenyls series show lower melting temperatures and higher entropies of fusion. Heat capacities, at T = 298.15 K, were determined for the ortho and meta quaterphenyl and p-quinquephenyl oligomers by means of high precision drop calorimetry. The heat capacities of the ortho and meta isomers are systematically lower than those of the corresponding para isomers. It was found that the subtle isomerization effect on the heat capacity is partially related to the ring rotation restrictions in their supramolecular structure and increases with the increase of the number of phenyl rings.

Abstract Condensed phase standard (p degrees = 0.1 MPa) molar enthalpies of formation for 2-coumaranone and 3-coumaranone were derived from the standard molar enthalpies of combustion, in oxygen, at T = 298.15 K, measured by mini-bomb combustion calorimetry. Standard molar enthalpies of sublimation of both isomers were determined by Calvet microcalorimetry. These results were combined to derive the standard molar enthalpies of formation of the compounds, in gas phase, at T = 298.15 K. Additionally, accurate quantum chemical calculations have been performed using DFT methods and high level composite ab initio calculations. Theoretical estimates of the enthalpies of formation of the compounds are in good agreement with the experimental values thus supporting the predictions of the same parameters for isobenzofuranone, an isomer which has not been experimentally studied. The relative stability of these isomers has been evaluated by experimental and computational results. The importance of some stabilizing electronic intramolecular interactions has been studied and quantitatively evaluated through Natural Bonding Orbital (NBO) analysis of the wave functions and the nucleus independent chemical shift (NICS) of the studied systems have been calculated in order to study and establish the effect of electronic delocalization upon the relative stability of the isomers.

Abstract A new water-soluble porphyrin, 5,10,15,20-tetrakis(4-piperidyl)porphyrin (T(4-Pip)P), has been synthesized. T(4-Pip)P is related to the extensively studied water-soluble porphyrin 5,10,15,20-tetrakis(4-pyridyl)porphyrin (T(4-Py)P) but has substituents with different electronic and hydrogen-bonding properties and is soluble over a much larger pH range due to the higher pK(a) of its conjugate acid T(4-H-Pip)P4+. Investigations of the ionic self-assembly reactions of T(4-H-Pip)P4+ with anionic water-soluble porphyrins reveal that it forms nanoscale materials.

Abstract Thermotropic liquid crystal formation by salt-free catanionic surfactants (alkyltrimethylammonium alkylsulfonates, herein designated as TA(m)So(n)) has been investigated as a function of chain length mismatch (asymmetry). Previous studies on these compounds have revealed an unusual and rich asymmetry-dependent lyotropic phase behavior. Herein, phase transition temperatures and transition enthalpies/entropies were determined by differential scanning calorimetry, while mesophases were assigned by polarized light microscopy. Three series of compounds were investigated, namely: the TA(16)So(n) series, where n = 6-10; the TA(m)So(8) series, where m = 12-16; and a constant m + n series, TA(m)So(n) where m + n = 22. Typically, several solid phases and two smectic mesophases are found prior to isotropization to the liquid phase. As asymmetry decreases, two somewhat counterintuitive tendencies emerge: a general decrease in enthalpy/entropy for solid-solid and solid-first mesophase transitions, and an increase in solid-first mesophase transition temperatures. Yet, solid phases are seen to be more stable for the most asymmetric compounds, while the second mesophase is more stable for the least asymmetric ones, in what appears to be a more complex behavior than expected. The results are globally interpreted in terms of subtle differences in chain interdigitation and packing, and odd-even chain effects.

Abstract Herbicides are important for the control of weed growth but increasing use causes environmental problems and undesirable side effects in crops. Phenoxy acid herbicides with auxin-like activity have been used against grass and broad leaf weeds in many crops, such as rice, winter wheat and soybean. Carcinogenicity in humans and embryotoxicity in animals have been described as the main hazards of phenoxy acid herbicides. Thermal denaturation of double stranded DNA has been used as a measure of the effect of harmful chemical substances on the structure and stability of the DNA molecule. Hence, the interaction between several phenoxy acid herbicides (phenoxyacetic acid, 4- chlorophenoxyacetic acid, MCPA, mecoprop, 2,4-D and dichlorprop) and Calf thymus DNA was assessed by UV-Vis absorption spectroscopy. UV spectra and melting curves have been recorded for solutions at constant DNA concentration and using different concentrations of each of the herbicides under study. The transition temperature values and the thermodynamic parameters of DNA thermal denaturation have been determined. The studies performed so far help to understand herbicide-DNA interactions gathering suitable information for the (re)design of new molecules with lower potential risk to humans.

Abstract Thermodynamic properties of ortho, meta and para methoxybenzamides were determined using the Knudsen effusion method and calorimetric experiments as well as computational approaches. The vapour pressure of the crystalline phase of the three isomers was measured and values of the standard (po = 0.1 MPa) molar enthalpy, Gibbs energy and entropy of sublimation, at T = 298.15 K, were derived. Static bomb combustion calorimetry was used to measure the standard molar enthalpies of combustion from which the standard molar enthalpies of formation in the crystalline state, at T = 298.15 K, were derived. Together with the standard molar enthalpies of sublimation, these results yielded the standard molar enthalpies of formation in gaseous phase of the three isomers. The standard Gibbs energies of formation in crystalline and gaseous phases were also derived and used to differentiate the thermodynamic stability of the three isomers. Moreover, differential scanning calorimetry analysis enabled determination of the temperature and molar enthalpies of fusion of the studied compounds. Gas-phase enthalpies of formation of the three compounds were estimated computationally at the G3 and G4 levels of theory and compared with the experimental results.