Excited State Processes in 1-Deazariboflavin Studied by Ultrafast Fluorescence Kinetics

The photochemical reactions of the 1-deaza derivative of riboflavin (RF) have been studied by sub-ps time-resolved fluorescence spectroscopy. A potential effect of the solvent polarity and hydrogen bonding capability on the excited state (ES) dynamics was tested by measuring 1-deaza RF in water and, after acetylation of the sugar moiety, also in acetonitrile. Opposite to former reports, which indicated no fluorescence after laser excitation (Spencer et al. [1977] Biochemistry 16 : 3586–3594), we find a significant fluorescence in either solvent. For both compounds, the fluorescence decays are biexponential with lifetimes in the ps time domain (1.8 and 12.5 ps for 1-deaza RF, and 3 and 87 ps for Ac₄-1-deaza RF). In addition, a third, independent fluorescence decay was observed for both compounds. The remarkably slower second decay process for the measurements of the tetra-acetyl derivative in acetonitrile points to the involvement of hydrogen bonding or changes in the protonation/tautomerization state in the ES. In contrast to the parent compound (RF), no triplet state formation can be detected for 1-deaza RF, making the internal conversion and the fluorescence the only decay processes of the ES.     

Nucleophile- or light-induced synthesis of 3-substituted phthalides from 2-formylarylketones

The surprisingly facile conversion (isomerization) of 2-formyl-arylketones into 3-substituted phthalides, as observed for the marine natural product pestalone and its per-O-methylated derivative, was investigated using a series of simple 2-acylbenzaldehydes as substrates. The transformation generally proceeds smoothly in DMSO, either in a Cannizarro-Tishchenko-type reaction under nucleophile catalysis (NaCN) or under photochemical conditions (DMSO, 350 nm).     

On line shape of electromagnetically induced transparency in a multilevel system

We present a detail analysis of the line shape of electromagnetically induced transparency (EIT) in a Doppler broadened five level atomic system based on density matrix formalism. It has been shown that the velocity averaged EIT line shape in a multilevel system is very sharp. The effect of the ground state decay rates on the EIT peak has also been investigated. The linear and non-linear variations of the EIT line width (FWHM) for different pump and probe power ratios are shown. Considering the D₂ transition of ⁸⁵Rb atom the dependence of EIT width and height on pump power has been experimentally measured. Simulated spectra are compared with the experimentally obtained one. The effect of buffer gas on the EIT peak has also been observed experimentally as well as theoretically.     

Reactivation of vanadium-titanium oxide catalysts foro-xylene oxidation to phthalic anhydride

Reactivation with sulfur containing compounds of vanadium-titanium oxide catalysts for partial oxidation ofo-xylene is studied. The efficiency depends on the kind and quantity of sulfur additives. Most proper reactivation towardso-xylene is reached with sulfur in concentrations of 0.20 wt.%.     

Surface oxidation control of nanosized magnetite and Mössbauer measurements

Selected highly homogeneous powders of Fe₃O₄ with different particle size on the nanometer scale (10?±?2 and 3?±?2 nm) obtained by soft-chemical methods were studied by Mössbauer spectroscopy. The study shows clearly the powerful possibilities of Mössbauer spectroscopy to analyze the surface oxidation of nanostructured powders of magnetite. On the other hand, it is shown that for very small superparamagnetic particles the spectrum of magnetite might be quite similar to that of maghemite, making it difficult to distinguish between both phases.     

Influence of particle-number projection on potential energy surfaces of fissioning nuclei

The structure of high-spin states in the transitional nuclei^191,193Hg is described in the framework of the interacting boson fermion model with one broken pair. The results of model calculation reproduce in detail the structure of yrast states up toJ=49/2⁺ ?, including the first backbending, and the two lowest three-neutron negative parity bands.     

Laboratory analyses of 60Co2+, 65Zn2+ and (55+59)Fe3+ radiocations uptake by Lemna minor

The living Lemna minor vascular plant and two different sorbents obtained by chemical treatment of this plant were tested to study the removal process of 60Co2+, 65Zn2+ and (55+59)Fe3+ from low radioactive wastewaters. The most effective sorbent was the protonated biomass, indicating the decisive contribution of the complexation process in the assembly of the uptake mechanisms. The uptake performance of the biosorbent obtained from the L. minor can be increased with approximately 20% by treatment with 0.1 N HNO3. Concerning the metabolically active mechanism, it can be notice the slow elimination of 65Zn2+ and the continuously increase of (55+59)Fe3+ uptake degree. The Na2CO3 generated in situ in systems participates to a double exchange reaction with the metallic cations during the uptake. 60Co2+, 65Zn2+ and (55+59)Fe3+ radiocations prefer for coordination N-donor ligands at the expense O-donors ones.