Photophysical Properties of Some Flavones Probes in Homogeneous Media

Photophysical properties of five hydroxyflavones (HF) (some typical models of flavonols), (3 - HF, 6 - HF, 7-HF, 3, 6 - diHF and 3, 7 - diHF) were studied in homogeneous media by means of UV–vis and steady-state and time resolved fluorescence spectroscopies. Their absorption and fluorescence characteristics based on the flavonols structure are presented and discussed. It was found that the fluorescence of the flavonols depends on the nature of the solvent and on their molecular structure, especially on the position and the number of the -OH groups of the substituted phenyl ring. Attention is paid to the number of the -OH groups that influence the excited-state intramolecular proton transfer (ESIPT) process. The fluorescence quantum yield and the lifetime of the flavonols in heterogeneous media have been also determined. The results are discussed with relevance to the flavonols as sensitive fluorescence probe and to their microenvironments in the systems of biological interest and especially in a typical protein environment.     

Coordination polymers and a dinuclear complex constructed from zinc(II) ions and fluorescein: iodine adsorption and optical properties

Abstract

1-D coordination polymers, ¹_∞[Zn(fl)₂]·2EtOH and ¹_∞[Zn(fl)₂]·2MeOH, and a dinuclear complex, [{Zn(fl)₂}₂(dienpip)]·4H₂O·4EtOH (dienpip?= N,N′-bis(2-aminoethyl)piperazine), were obtained using Zn(II) ions and fluorescein anions (fl). Thermal analysis shows stability of the polymers after solvent removal up to more than 400?°C. Crystallization solvent molecules were removed under reduced pressure with the preservation of the polymeric structure, ¹_∞[Zn(fl)₂]. Desolvated crystals were exposed to I₂ vapors and the crystal structure determination by X-ray diffraction confirmed the presence of I₂ molecules in the channels generated in crystals by the metal-organic framework. The iodine content, evaluated by X-ray diffraction, corresponds to the overall formula ¹_∞[Zn(fl)₂]·0.3I₂. The optical properties of the coordination polymers and the dinuclear complex have been investigated.     

A bivariate non-homogeneous birth and death model for predator–prey interactions

We propose a bivariate non-homogeneous birth and death process as a model for predator–prey interactions. Its expectation is periodic, as it is a solution to the classical Lotka–Volterra system. Moreover, the mean age at extinction, as defined in Kendall (1948), is infinite.     

On Assessing the Performance of Randomized Algorithms

In this paper we study randomized algorithms with random input. We adapt to such algorithms the notion of probability of a false positive which is common in epidemiological studies. The probability of a false positive takes into account both the (controlled) error of the randomization and the randomness of the input, which needs to be modeled. We illustrate our idea on two classes of problems: primality testing and fingerprinting in strings transmission. Although in both cases the randomization has low error, in the first one the probability of a false positive is very low, while in the second one it is not. We end the paper with a discussion of randomness illustrated in a textbook example.     

Characterization of a new norfloxacin metabolite monitored during a bioequivalence study by means of mass spectrometry and quantum computation

A bioequivalence study of two formulations containing norfloxacin was used for identification and assay of the metabolite of norfloxacin in human serum samples. The bioequivalence study was based on an analytical method using liquid chromatography with fluorescence detection. The plasmatic profile of metabolite was similar to norfloxacin for both formulations. Three plasma fractions of norfloxacin metabolite from a volunteer were isolated by liquid chromatography and investigated by atmospheric-pressure chemical ionization mass-spectrometry. The structure of norfloxacin metabolite (7-aminoethylenamino-6-fluoro-4-hydroxy quinoline-3-carboxylic acid) was identified taking into account also the mass spectrometry investigations achieved for norfloxacin and ciprofloxacin (used as internal standard for the analytical method). A theoretical procedure based on quantum chemical calculations has been also used to explain the mass fragmentation in molecules of norfloxacin metabolite that differ from the molecule of norfloxacin.     

Spectroscopic analysis of the riboflavin—serum albumins interaction on silver nanoparticles

Metallic nanoparticles (NPs) supported on oxides thin films are commonly used as model catalysts for studies of heterogeneous catalysis. Several 4d and 5d metal NPs (for example, Pd, Pt and Au) grown on alumina, ceria and titania have shown strong metal support interaction (SMSI), for instance the encapsulation of the NPs by the oxide. The SMSI plays an important role in catalysis and is very dependent on the support oxide used. The present work investigates the growth mechanism and atomic structure of Rh NPs supported on epitaxial magnetite Fe₃O₄(111) ultrathin films prepared on Pd(111) using the Molecular Beam Epitaxy (MBE) technique. The iron oxide and the Rh NPs were characterized using X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction and photoelectron diffraction (PED). The combined XPS and PED results indicate that Rh NPs are metallic, cover approximately 20 % of the iron oxide surface and show height distribution ranging 3–5 ML (monolayers) with essentially a bulk fcc structure.     

On the Fluorescence of Luminol in a Silver Nanoparticles Complex

The photophysical properties of luminol in a silver nanoparticles complex have been studied by steady-state and time resolved fluorescence spectroscopy. The effect of the serum albumin on the luminol fluorescence in the silver nanoparticles has been also investigated. It was found that the fluorescence quantum yield value of luminol in a silver nanoparticles complex is ??=?0.00407. The decrease of the average fluorescence lifetime value of the luminol in the silver nanoparticles complex was found to be low, <τ>?=?1.712 ns. The luminol does not bind to the serum albumins in the presence of silver nanoparticles. The formation of a new species of luminol on silver nanoparticles is discussed. The results have influence regarding the use of luminol as an assay for bio-analytical applications.     

Sur des familles de critères d'irrationalité

Sans résumé     

Fluorescence Characteristics of some Flavones Probes in Different Micellar Media

The fluorescence characteristics of five hydroxiflavones (HFs) (some typical models of flavonols), (3 - HF, 6 - HF, 7-HF, 3, 6 - diHF and 3, 7-diHF) in the micellar media of non-ionic surfactant (Triton X-100), anionic surfactant (SDS) and the block copolymer Pluronic F127, have been investigated by means of UV–Vis and steady-state and time resolved fluorescence spectroscopies. Attention is paid to both excited-state intra-molecular proton transfer (ESIPT) as well as ground-state intermolecular proton transfer. The influence of the -OH groups as well as the effect of temperature on the dual fluorescence emission, the Normal and Tautomer emissions, are also investigated. The fluorescence quantum yield of the HFs in mentioned micellar media has been also determined. The results are discussed with relevance to the local environment of HFs as sensitive fluorescence probe in biological membrane systems.