[en] A spectrofluorometric method for the determination of bentazone residues has been developed. The method is performed in N,N-dimethyl-formamide as solvent. The results were compared with those obtained by incorporation of the compound in α-cyclodextrin and liquid chromatography with spectrophotometric detection at 340 nm. The fluorescence intensity is linearly related to bentazone concentration with a detection limit of 3.3 ng ml^-1 and a relative standard deviation of 1% at the 0.55 μg ml^-1 level. The method was applied to herbicide added (0.2 μg ml^-1) to beans with recoveries of 100.8% compared with 96% by the liquid chromatographic method. (author). 23 refs.; 4 figs.; 2 tabs

[en] Published in summary form only

[en] Technological advances over recent years resulted in increasing use of array detectors such as CCD cameras for spectroscopic measurements. This article discusses means to apply imaging detectors to fluorescence analysis with nanosecond time resolution. Two approaches are presented, both use frequency domain measurements with modulated excitation source . Use of an imaging single photon detector is most appropriate for fast time resolved spectroscopy, while an intensified CCD based system is best suited to fluorescence microscopy. (author). 10 refs.; 3 figs

[en] Fluorescence studies of transthyretin (TTR) were conducted to detect structural changes associated with the environment of its two tryptophans, induced by binding of thyroxine (T₄). Non-radiative tryptophans relaxation rate has an activation energy of 6.4 kcal/mol for TTR, which is decreased to 4.4 kcal/mol for TTR-T₄ complex. The maximum fluorescence wavelength was red-shifted as the excitation wave-length was increased. T₄ changed the magnitude of this shift. T₄ binding per se changed the emission maximum reflecting different environments of the tryptophans. Double-quenching experiments also showed that T₄ produces changes in the tryptophans environments. These findings were interpreted as the result of structural alterations in the protein matrix induced by T₄ which contribute in part to explain the negative cooperativity associated with the occupancy of the second binding site. (author). 19 refs.; 3 figs.; 1 tab

No abstract available

[en] The fluorimetric instrumentation and analysis method for uranium determination in geological, biological and water samples are explained. Methods and techniques used for uranium analysis are briefly summarized. Factors influencing the analysis, such as, (interference, quenching effect, impurities, acids, fusion agents) and how-to-overcome them are reported. The digestion procedures and the utilizing of the following methods (extraction, internal standard, extrapolation) for the determination of uranium in different kinds of samples by fluorimetry are investigated. In addition to that, the way of operating instrument, preparing the calibration graphs and finally the evaluation of the results are explained. (author). 12 refs., 12 figs., 7 tabs

[en] Citrinin (CIT) is a nephrotoxic mycotoxin produced by several Aspergillus, Penicillium and Monascus species. CIT is unavoidable contaminant of different foods and drinks due to its wide occurrence and high thermal stability. For this reason, development of new, more sensitive analytical methods and decontamination strategies has high importance. In our study, the complex formation of CIT with native and chemically modified cyclodextrins was investigated using fluorescence spectroscopy. Furthermore, thermodynamic and molecular modeling studies were also performed for the deeper understanding of these host-guest interactions. Our results show that among the tested compounds methylated β-cyclodextrins form the most stable complexes with CIT and these derivatives cause the highest fluorescence enhancement of CIT as well. These observations recommend that some of the chemically modified derivatives show more favourable properties than the native cyclodextrin, and suggesting more promising analytical applicability and higher affinity as potential toxin binders.

[en] The photophysical properties of pyronin B (PyB) and pyronin Y (PyY) in reverse micelles formed with water/sodium bis (2-ethyl-1-hexyl) sulfosuccinate (AOT)/n-heptane were investigated by UV–vis absorption, steady-state and time-resolved fluorescence spectroscopy techniques. This study was carried out a wide range of reverse micelle sizes, with hydrodynamic radii ranging from 1.85 to 9.38 nm. Significant photophysical parameters as band shifts, fluorescence quantum yields and fluorescence lifetimes were determined to understand how photophysical and spectroscopic features of the dye compounds were affected by the variation of reverse micelle sizes. In this regard, control of reverse micelle size by changing W₀, the molar ratio of water to surfactant, allowed tuning the photophysical properties of the dyes in organic solvent via reverse micelle. Non-fluorescent H-aggregates of pyronin dyes were observed for the smaller reverse micelles whereas an increase in the reverse micelle size induced an increment in the amount of dye monomers instead of dye aggregates. Thus, the fluorescence intensities of the dyes were improved by increasing W₀ due to the predomination of the fluorescent dye monomers. As a result, the fluorescence quantum yields also increased. The fluorescence lifetimes of the dyes in the reverse micelles were determined by the time-resolved fluorescence decay studies. Evaluation of the fluorescence lifetimes calculated for pyronin dyes in the reverse micelles showed that the size of reverse micelle affected the fluorescence lifetimes of pyronin dyes. -- Highlights: • The photophysical properties of pyronin dyes were examined by spectroscopic techniques. • Optical properties of the dyes were tuned by changing of W₀ values. • The fluorescence lifetime and quantum yield values of the dyes in reverse micelles were discussed

[en] Highlights: • Clioquinol inhibits the fibril formation of hen egg-white lysozyme. • The binding between clioquinol and hen egg-white lysozyme prevents the exposure of hydrophobic regions. • Clioquinol retards the conversion of α-helix to β-sheet of hen egg-white lysozyme. Here, we reported the role of clioquinol in amyloid aggregation of hen egg white lysozyme (HEWL) under stressful conditions by several biophysical methods including thioflavin-T (ThT) fluorescence, Congo red (CR), circular dichroism (CD) and transmission electron microscopy. Our work showed that CQ inhibited the fibril formation of HEWL and the inhibitory effects depended on the concentrations of CQ. Furthermore, fluorescence spectra were used to study the conformation changes of HEWL caused by CQ. These data revealed that the interactions of CQ with HEWL changed the tertiary structure and inhibited the hydrophobic exposure of HEWL.

[en] Published in summary form only