Publications

Abstract The Knudsen mass-loss effusion technique was used to measure the vapor pressures, between 0.1 Pa and 1 Pa, of the three monomethyl benzenedicarboxylates over the following temperature intervals: monomethyl phthalate, between 335.28 K and 355.28 K; monomethyl isophthalate, between 359.26 K and 379.12 K; monomethyl terephthalate, between 363.16 K and 381.51 K. From the variation of the vapor pressures with temperature, the standard molar enthalpies, entropies, and Gibbs energies of sublimation at T = 298.15 K were calculated. The volatility of the studied compounds is compared with the volatilities of the benzene dicarboxylic acids and of the dimethyl benzenedicarboxylates.

Abstract Coumarins, also known as benzopyrones, are present in remarkable amounts in plants, although their presence has also been detected in microorganisms and animal sources. The structural diversity found in this family of compounds led to the division into different categories, from simple coumarins to many other kinds of policyclic coumarins, such as furocoumarins and pyranocoumarins. Simple coumarins and analogues are a large class of compounds that have attracted their interest for a long time due to their biological activities: they have shown to be useful as antitumoural, anti-HIV agents and as CNS-active compounds. Furthermore, they have been reported to have multiple biological activities (anticoagulant, anti-inflammatory), although all these properties have not been evaluated systematically. In addition, their enzyme inhibition properties, antimicrobial and antioxidant activities are other foremost topics of this field of research. The present work is to survey the information published or abstracted from 1990 till 2003, which is mainly related to the occurrence, synthesis and biological importance of simple coumarins and some analogues, such as biscoumarins and triscoumarins. Data are also highlighted, concerning the development of new synthetic strategies that could help in drug design and in the work on SAR or QSAR.

Abstract Dissociation enthalpies of terminal (N-O) bonds, DH degrees(N-O), in amine N-oxides, nitrile N-oxides, pyridine N-oxides, quinoxaline 1,4-dioxides, furoxans, nitrones, azoxy-derivatives, azo-N,N-dioxides, nitro compounds, nitramines, and alkyl nitrates are calculated from published enthalpy of formation, enthalpy of sublimation, and enthalpy of vaporization data. For each class of organic compounds, the calculated DH degrees(N-O) values are critically evaluated. The derived DH degrees(N-O) values can be used to estimate enthalpies of formation of other molecules in each of these classes of organic compounds. (C) 2005 American Institute of Physics.

Abstract A scheme for the simultaneous determination of temperature and analyte concentration for application in luminescence-based chemical sensors is proposed. This scheme is applied to an optical oxygen sensor, which is based on the quenching of the fluorescence of a ruthenium complex. Temperature measurement is performed using the excitation radiation and an absorption long-pass filter. Preliminary results are presented that show the viability of an oxygen measurement that is independent of temperature and optical power level. The possibility of self-referenced temperature measurements with semiconductor nanoparticles is also investigated. In order to optimize the sensor design, several different optical fiber probe geometries for oxygen sensing are tested and compared, including different methods of coupling radiation into the optical fiber system. Polyvinyl alcohol (PVA) and polyacrylamide membranes are tested as supports for sensor immobilization in fiber-optical pH sensing devices in aqueous solution. Some results are presented that show the feasibility of using fiber-optical pH indicators for remote monitoring.

Abstract The formation thermodynamic properties of crystalline and aqueous inosine have been determined by using a combination of calorimetric techniques. Oxygen bomb calorimetric measurements on crystalline inosine yielded a standard molar enthalpy of combustion of Delta(c)H degrees(m) = -(4802.2 +/- 4.5) kJ center dot mol(-1). From this, a value for the standard molar enthalpy of formation Delta(f)H(m)degrees of -(847.9 +/- 4.7) kJ mol-1 was obtained. The standard molar heat capacity of crystalline inosine has been measured over the temperature interval 11 <= T/K <= 325 by using an adiabatic calorimeter. The heat capacities were fit to a series of polynomials from which smoothed values for the standard thermal properties were calculated for 20 <= T/K <= 320. The standard molar entropy Delta(0)(T)S degrees(m) (inosine, cr) at T = 298.15 K is (288.0 +/- 0.6) J center dot K-1 center dot mol(-1) and the standard molar entropy of formation Delta(f)S degrees(m) is -(1449.6 +/- 0.6) J center dot K-1 center dot mol(-1). The standard Gibbs free energy of formation Delta(f)G degrees(m) (inosine, cr) = -(415.7 +/- 4.7) kJ center dot mol(-1). By using literature values of the standard molar enthalpy of solution and the saturation molality of inosine(cr), the standard molar thermodynamic properties of aqueous inosine at T=298.15 K are found to be Delta(f)H degrees(m)(inosine, aq) = -(819.8 +/- 4.7) kJ center dot mol(-1); Delta(f)G degrees(m) (inosine, aq)= -(409.2 +/- 4.8) kJ center dot mol(-1); and Delta(0)(T)S degrees(m)(inosine, aq) = (360.1 +/- 1.8) J center dot K-1 center dot mol(-1). These results are used to calculate standard thermodynamic properties of various aqueous species involving inosine.

Abstract The standard (p(o) = 0. 1 MPa) molar enthalpies of formation of 2-, 3-, and 4-chloroaniline were derived from the standard molar energies of combustion, in oxygen, at T = 298.15 K, measured by rotating bomb combustion calorimetry. The Calvet high-temperature vacuum sublimation technique was used to measure the enthalpies of vaporization or sublimation of the three isomers. These two thermodynamic parameters yielded the standard molar enthalpies of formation of the three isomers of chloroaniline, in the gaseous phase, at T = 298.15 K, as 53.4 +/- 3.1 kJ(.)mol(-1) for 2-chloroaniline, 53.0 +/- 2.8 kJ(.)mol(-1) for 3-chloroaniline, and 59.7 +/- 2.3 kJ(.)mol(-1) for 4-chloroaniline. These values, which correct previously published data, were used to test the computational methodologies used. Therewith, gas-phase acidities, proton affinities, electron donor capacities, and N-H bond dissociation enthalpies were calculated and found to compare well with available experimental data for these parameters.