Steady-state and time-resolved studies have been performed on four compounds of the pterin family (pterin, 6-carboxypterin, 6-formylpterin and folic acid) in aqueous solution, using the single photon counting technique. The fluorescence characteristics (spectra, quantum yields, lifetimes) of these compounds and their dependence on the pH have been investigated. Most pterins can exist in two acid-base forms over the pH range between 3 and 13. Emission spectra and excitation spectra were obtained for both forms of each compound studied. Fluorescence quantum yields (phi(F)) in acidic and basic media were measured. The phi(F) of folic acid (< 0.005 in both media) is very low compared to those of pterin (0.27 in basic media and 0.33 in acidic media), 6-carboxypterin (0.18 in basic media and 0.28 in acidic media) and 6-formylpterin (0.07 in basic media and 0.12 in acidic media). The variation in integrated fluorescence intensity and fluorescence lifetimes (tau(F)) was analysed as a function of pH. Dynamic quenching by OH- was observed and the corresponding bimolecular rate constants for quenching of fluorescence (k(q)) were calculated. The reported values for k(q) (M(-1) s(-1)) are 3.6 x 10(9), 1.9 x 10(9) and 1.1 x 10(10) M(-1) s(-1) for pterin, 6-carboxypterin and 6-formylpterin, respectively.

Novel heterogeneous photocatalysts were developed which are able to transfer electrons from excited Ru(II) donors within the zeolite framework to Co(III) acceptor complexes in the exterior. The materials were prepared and characterized by elemental analysis, electrochemical methods, diffuse reflectance, and raster and transmission electron microscopy. The catalysts consist of zeolite Y-encapsulated Ru(bpy) 3 2+ (bpy ) 2,2′bipyridine) sensitizers in close proximity to TiO 2 nanoparticles on the same support. The photophysical properties of Ru(bpy) 3 2+ within the zeolite supercages were investigated at different loadings of Ru(bpy) 3 2+ and TiO 2 . The photoexcited MLCT state of the zeolite-entrapped Ru(bpy) 3 2+ reacts via electron transfer with Co(dpphen) 3 3+ (dpphen ) 4,7-diphenyl-1,10-phenanthroline) in the exterior of the zeolite particles. The relative quenching of Ru(bpy) 3 2+ by external Co(dpphen) 3 3+ increases as the TiO 2 content within the zeolite is increased, where electron transfer from Ru(bpy) 3 2+ complexes within the interior of the zeolite are able to transfer electrons to Co(dpphen) 3 3+ . This observation indicates that electrons can be transported from the interior of the zeolite to the surface in the presence of an appropriate electron relay, such as TiO 2 nanoparticles.

We have revisited the photochromic spiro-dihydroindolizine/betaine (DHI/B) system applying state-of-the-art density functional theory (DFT) calculations in combination with stationary and time-resolved absorption measurements. DHI/B-systems are becoming increasingly important as potential molecular machines, molecular switches, and photoswitchable electron-acceptors. The knowledge of the exact mechanisms of ring opening and closure, as well as of the geometries of DHI and betaine can provide critical information that will enable the design of better molecular machines and optical switches. The first surprising result concerns the electronic structure of the betaines, which is quite different than commonly assumed. The photochemical ring opening of DHI's to betaines is a conrotatory 1,5 electrocyclic reaction, whereas the thermal ring-closing occurs in the disrotatory mode. According to our results, the electrocyclic back reaction of the betaines to the DHI is NOT rate determining, as previously thought, but instead the kinetics are dictated by the cis-trans-isomerization of the betaine.

A considerably arduous test of a novel class of composite materials consisting of [Ru(bpy)3]2+ and TiO2 codoped zeolites Y is presented here. The [Ru(bpy)3]2+ and TiO2 codoped zeolites Y served as photocatalysts in the oxidation of the model compounds 2,4-dimethylaniline (2,4-xylidine) by H2O2 in an acidic aqueous medium. Zeolite-embedded TiO2 (nano)particles play an important role in the degradation mechanism. The first step in this complex mechanism is the photoelectron transfer from photoexcited [Ru(bpy)3]2+*, located inside the supercage of zeolite Y, to a neighboring TiO2 nanoparticle. During this electron transfer process, electron injection into the conduction band of TiO2 is achieved. The second decisive step is the reaction of this electron with H2O2, which was previously chemisorbed at the surface-region of the TiO2 nanoparticles. In this reaction, a TiO2 bound hydroxyl radical (TiO2-HO.) is created. This highly reactive intermediate initiates then the oxidation of 2,4-xylidine, which enters the zeolites framework in its protonated form (Hxyl+). The formation of 2,4-dimethylphenol as first detectable reaction product indicated that this oxidation proceeds via an electron transfer mechanism. Furthermore, [Ru(bpy)3]3+, which was created in the initiating photoelectron transfer reaction between [Ru(bpy)3]2+* and TiO2, also takes place in the oxidation of Hxyl+. [Ru(bpy)3]2+ is recycled in that reaction, which also belongs to the group of electron transfer reactions. In addition to the primary steps of this particular Advanced Oxidation Process (AOP), the dependence of the efficiency of the 2,4-xylidine degradation as a function of the [Ru(bpy)3]2+ and TiO2 loadings of the zeolite Y framework is also reported here. The quenching of [Ru(bpy)3]2+* by H2O2 as well as the photocatalytic activity of the [Ru(bpy)3]2+ and TiO2 codoped zeolite Y catalysts both follow a distinct percolation behavior in dependence of their TiO2 content.

A simple and sensitive spectrophotometric method has been developed for the determination of phosphate in mg per liter (parts per million) concentration range in sugarcane juice, water, fertilizer and detergent samples. The amount of phosphate is determined by molybdenum blue phosphorus method in conjugation with UV-visible spectrophotometer. This method is based on the formation of phosphomolybdate complex with the added molybdate followed by the reduction of the complex with hydrazine hydrate in aqueous sulphuric acid medium. The system obeys Lambert-Beer's law at 840 nm in the concentration range 0.1-11 ppm. The colour intensity of the reduced phosphomolybdate solution is found to be proportional to the amount of phosphate present in sugarcane juice, water, fertilizer and detergent samples. The reaction conditions as well as the various experimental parameters affecting the development and stability of the coloured complex were carefully investigated and optimized for the quantitative determination of phosphate present in various samples. The optimized concentrations of various reagents used are 0.20N sulphuric acid, 0.02M hydrazine hydrate and 0.20% ammonium molybdate. The effect of time on the formation of phosphomolybdenum blue complex and addition of the order of the reagents was also studied.

The unique stability and self-assembling properties of porin MspA, a channel protein isolated from Mycobacterium smegmatis, were established using three very different host systems:(1) A very simple and straightforward nanostructuring process was achieved by depositing buffer droplets containing MspA onto highly ordered pyrolytic graphite (HOPG) from the gas phase, followed by thermal curing and high vacuum treatment. Three lateral nanostructures were obtained depending on the protein mass deposited, the temperature during deposition and the subsequent curing process. We report here a detailed statistical analysis of the MspA pore sizes on HOPG.

A series of ruthenium (II)

A novel type of adsorbent, TiO2 impregnated pomegranate peels (PP@TiO2) was successfully synthesized and its efficacy was investigated based on the removal of As(III) from water. The adsorbent was characterized using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectrometer (EDS), X-ray Diffraction (XRD) analysis, and Fourier Transform Infrared (FTIR) Spectroscopy, to evaluate its morphology, elemental analysis, crystallinity, and functional groups, respectively. Batch experiments were conducted on PP@TiO2 for As(III) adsorption to assess the adsorption isotherm, effect of pH, and adsorption kinetics. Characterization data suggested that TiO2 was successfully impregnated on the biomass substrate. The equilibrium data better fitted to the Langmuir isotherm model having a maximum adsorption capacity of 76.92 mg/g and better distribution coefficients (KD) in the order of ~103 mL/g. The highest percentage of adsorption was found at neutral pH. The adsorption kinetics followed the pseudo-2nd-order model. X-ray Photoelectron Spectroscopy (XPS) of the adsorption product exhibited that arsenic was present as As(III) and partially oxidized to As(V). PP@TiO2 can work effectively in the presence of coexisting anions and could be regenerated and reused. Overall, these findings suggested that the as-prepared PP@TiO2 could provide a better and efficient alternative for the synergistic removal of As(III) from water.