Publications

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.

Abstract The phase behavior over the entire concentration range for the system didodecyldimethylammonium bromide (DDAB)-sodium taurodeoxycholate (STDC)-water, at 25 degrees C, has been investigated, with emphasis on the DDAB-rich part. Polarizing microscopy, SAXS, H-2 NMR and H-1 self-diffusion NMR have been used in combination as probing techniques for phase behavior and microstructure. The system forms four major phases, all deriving from the respective binary surfactant systems. The two lamellar phases originating from the binary DDAB-water axis (D-I and D-II, at 3-30 and 83-91 wt.% DDAB, respectively) are only able to incorporate small amounts of STDC. The D-II phase solubilizes a comparatively higher amount of bile salt (up to ca. 6 wt.%), while the D, phase takes up less than 0.25 wt.%. From the STDC-water axis, a solution phase and a "hexagonal-like" liquid crystalline phase are derived, at 0-26 and 37-60 wt.% of STDC, respectively. Heterogeneous regions are also indicated on the basis of NMR and SAXS data. The most striking feature is the large extension of the isotropic solution phase, which originates from the water corner and curves toward the DDAB-rich side of the phase diagram. Even though at the upper limit of the solution phase the amount of water is reduced to 10 wt.%, the measured water and DDAB self-diffusion coefficients exclude the possibility of reverse-type structures.

Abstract Studies on the complexation of copper(II) by phenolic acids, as ligand models of humic substances were done by potentiometry. The acids under study were: 3,4-dihydroxyhydrocinnamic acid or hydrocaffeic acid (1), 3,4-dihydroxyphenyl acetic acid (2) and 3,4-dihydroxybenzoic acid or protocatechuic acid (3). Acidity constants of the ligands and the formation constants of metal-ligand complexes were evaluated by computer programs. The carboxylic group of the phenolic acids has different pK(a1) values, being the dissociation constants intrinsically related with the distance between the function and the aromatic nucleus. The results obtained allow concluding that acidity constants of the catechol moiety of the compounds are similar with pK(a2) and pK(a3) values between 9.47-9.41 and 11.55-11.70. The complexation properties of the three ligands towards copper(II) ion are quite similar, being the species found not different either in nature or stability. Although the model ligands have some structural differences no significant differences were found in their complexation properties towards copper(II). So, it can be postulated that complexation process is intrinsically related with the presence of a catechol group.

Abstract The viability of inertization of galvanic wastes through their incorporation in clay-based materials, such as common formulations for tiles and bricks, is here studied by determining the leaching kinetics in different media. Metals immobilization is assured by firing at reasonably high temperatures, since intimately contact and/or reaction between residue and clay particles is promoted but also due to formation of insoluble metal oxides that rest unreactive towards clay grains. For most metals, leaching rate follows a zero-order kinetic law, with values between 0.001 to 0.1 mg/(g day cm(2)). Leaching velocity tends to increase with rising atomic numbers: Zn &LT; Cu &LT; Ni &LT; Cr. These values depend exponentially on the relative sludge content.