Volume 219, Issue 6 - 6

Laser induced fluorescence spectroscopy has emerged as the most powerful analytical tool to image reactive processes in a variety of systems. The purpose of the article is to review state-of-the-art example applications from a variety of research fields, which make use of LIF imaging for the visualisation of chemical reactions. Examples range from gas phase diagnostics of reacting flows to biomedical applications. There is a growing trend in the spectroscopy community to “work across disciplines” and one aim of this article is to highlight common principles behind seemingly unconnected research applications and to provide an incentive for spectroscopists to find novel application areas for their techniques and to point them to relevant literature.

Quantitative correlation of the solubility phenomena and understanding of the dissolution mechanism are complex due to interplay of different types of intermolecular forces in the solubilization processes. Attempts have been made to understand the solubilization process by determining the Δ G 0 int terms for neutral benzoic acid and substituted benzoic acids using the solubility values of neutral acids reported from our laboratory and the scaled particle theory. Similarly, Δ G 0 int terms for the anions are also calculated. Δ G 0 int values for neutral (HA) and charged ions (A − ) are opposite. Different aspects of solubility and dissociation processes for the substituted acids and the effects of substitution have been explained with success. The limitations of the method have also been emphasized.

The Λ 0 values and association constants of some salts of medicinal interest in aqueous solution have been determined. The division of Λ 0 of salts into single ion values λ 0 + and λ 0 − have been made using λ 0 Na+ and λ 0 Cl− values from the literature. The Λ 0 , λ 0 + and λ 0 − values have been found to be fairly high in aqueous solution and comparatively lesser than those in acetonitrile. Most of the drugs have been found to be dissociated as ions though association of some of the salts has been observed. The calculations of r ± of ions in water show considerable decrease in the radii values of ions in water from which inference regarding the extent of hydrophobic interactions can be made.

Correlations between the catalytic performance and the electrochemical properties in heterogeneous catalysis were observed, using perovskite-like oxides La 2−x Sr x MO 4 ( x = 0.0, 0.5, 1.0, M = Cu, Ni) as the model catalysts and CO oxidation as the probe reaction. For a reaction that contains reducing agent in the feed gas, the activity depends mainly on the area of redox peak in the CV curves, while has no much relation to the symmetry of the redox potentials. The irreversible cycle in the first CV curves of LaSrCuO 4 suggested that the first step of the reaction is adsorption, corresponding to M n+ (Cu 2+ ) to M (n+1)+ (Cu 3+ ).

The interaction of pentoxifylline (PTX), a methylxanthine derivative drug, with cysteine on the hanging mercury drop electrode studied by square-wave voltammetry, cyclic voltammetry and UV-Vis spectroscopy at phosphate buffer (pH 7.4) in the presence and absence of UV irradiation. The addition of PTX to cysteine solution results in the decrease of peak currents of mercurous cysteine thiolate and the shift of its voltammetric reversible peak towards positive potentials. Electrochemical data indicated a 1:1 molecular complex formation of PTX with cysteine by means of electrostatic interaction and intermolecular forces. For the long UV irradiation times (25–85 min), voltammogram of the cysteine solution gave the reduction peaks of sulphonyl radical (−0.056 V), disulfidic anion (−0.684 V) and free cystine (−0.800 V) due to probably the formation of thiyl radical. With adding of PTX to the UV irradiated cysteine solution, a new peak at −0.292 V was observed. The peak at −0.292 V was also obtained for the cysteine and PTX mixture under UV irradiation, but the peaks of sulphonyl radical and disulphidic anion were no seen. As a result, this irreversible peak at −0.292 V may be assigned to the reduction of an electroactive species which is formed from PTX–cysteine complex under UV irradiation. PTX prevents the formation of thiyl radical and its further oxidation.

A generalization of the Arrhenius equation to include some non-Arrhenius equations for a description of a wide class of ionic conductors is proposed. The generalization is through a fractalization of the temperature term in the original Arrhenius equation. The result agrees well with some experimental data and the physical significances are deduced.

The PDPT is most commonly used to describe the adsorption on microporous active carbons at 77.3 K. The micropore distribution functions were calculated assuming a slit-like model for the micropores and applied to the adsorption of argon on four active carbons.

The reaction of NO 2 with CF 2 CFBr has been studied at 322.6, 333.1 and 343.4 K, using a conventional static system. The initial pressure of CF 2 CFBr was varied between 26.9 and 75.5 torr and that of NO 2 between 9.6 and 41.9 torr. Two experiments were made in presence of CF 4 used as inert gas at the pressure of 238.8 and 334.6 torr, respectively. Five products were observed: CF 2 (NO 2 )C(O)F, CF 2 (NO 2 )CFBr(NO 2 ), BrNO, Br 2 and NO. The distribution of the products CF 2 (NO 2 )C(O)F and CF 2 (NO 2 )CFBr(NO 2 ) was independent of the initial pressure of the reactants and the total pressure, but the relation CF 2 (NO 2 )C(O)F/CF 2 (NO 2 )CFBr(NO 2 ) increased with the temperature. The reaction is homogeneous and independent of the total pressure. The following mechanism was postulated to explain the experimental results: 1 CF 2 CFBr + NO 2 → CF 2 (NO 2 )C • FBr 2 CF 2 (NO 2 )C • FBr + NO 2 + M → CF 2 (NO 2 )CFBrNO 2 + M 3 CF 2 (NO 2 )C • FBr + NO 2 → CF 2 (NO 2 )C(O)F + BrNO 4 2BrNO ↔ Br 2 + 2NO k 1 = (1.51 ± 0.45) × 10 6 exp(−(10.88 ± 1) kcal mol −1 / RT ) dm 3 mol −1 s −1 .

The equilibrium distribution constants of electroneutral bromophenol blue and bromocresol green between the 1,2-dichloroethane and aqueous phases were determined from extraction measurements. By using known thermodynamic parameters and applying general relations, the dissociation constants of these two organic dyes in 1,2-dichloroethane saturated with water were calculated.