The features of fluorescence emission in a dye-doped dense multiple scattered medium under pulsed laser pumping are considered in terms of confined excitation in small zones associated with laser speckles occurring in a pumped medium. The results of numerical modeling of the fluorescence emission kinetics are compared to the experimental data obtained using the rhodamine 6G-doped layers of the densely packed TiO2 (anatase) particles pumped at 532 nm by 10 ns laser pulses. The intensity of pump radiation during the action of laser pulses was varied from 1·105 W/cm2 to 5·107 W/cm2. In the recovery of the ratios of stimulated to a spontaneous emission, the spectra of the stimulated component were fitted using the spectral function derived by R. Dicke. In the framework of the considered concept, saturation of the ratio of the stimulated to a spontaneous emission and linear growth of an integrated fluorescence output with a practically unchangeable half-width of the emission spectra at high pump intensities are interpreted.
We have studied the interaction between polycyclic aromatic hydrocarbons (pyrene and anthracene) with human serum albumin (HSA) and human blood plasma. We have shown that the increase in the fluorescence intensity and the decrease in the polarity index of pyrene on going from an aqueous solution to a pH 7.4 buffer solution of HSA suggests that polycyclic aromatic hydrocarbons are localized in the hydrophobic microphase of the proteins. The increase in the fluorescence intensity for anthracene and pyrene, and also the decrease in the polarity index of pyrene on going from HSA to blood plasma is connected with the fact that polycyclic aromatic hydrocarbons can bind both to plasma proteins and to plasma lipids. When sodium dodecyl sulfate (SDS) is added to the blood plasma in a concentration greater than the critical micelle concentration, we observe an increase in the fluorescence intensity and the polarity index of pyrene. We hypothesize that this is connected with localization of pyrene near the interface between the hydrophobic and hydrophilic phases of the protein-SDS system. We have established that SDS leads to a change in the structure of blood plasma proteins and promotes escape of polycyclic aromatic hydrocarbons from the protein globules.Key words: human blood plasma, human serum albumin, polycyclic aromatic hydrocarbons, sodium dodecyl sulfate, fluorescence.Introduction. Luminescent probes are widely used in studying structural changes in proteins, lipoproteins, and also in studying the properties of biological membranes [1,2]. The properties of nonpolar microregions in microheterogeneous media have been studied using luminescent probes: polycyclic aromatic hydrocarbons, which due to hydrophobic interactions tend to escape from the polar aqueous medium or macrophase of the solution into the nonpolar microphase, i.e., into the interior volume of the surfactant micelles, which is followed from the changes in the vibrational structure of the fluorescence spectra of the probes [3]. The use of the fluorescence of pyrene, which belongs to the class of polycyclic aromatic hydrocarbons, is well known [4-6] for determination of changes in the physicochemical properties of biological systems and model lipid membranes. Analysis of the changes in the vibrational structure of the fluorescence spectra of pyrene [3-5] also makes it possible to obtain information about the polarity of the microenvironment of the luminescent probe when its position changes in different microheterogeneous media. In [6], using data from analysis of the vibronic structure of the monomer luminescence spectrum of pyrene in a model membrane of phosphatidylcholine liposomes, it was hypothesized that the pyrene molecules can not only move laterally along the surface of the membrane, but also can undergo transmembrane motion. Thus the use of a method based on analysis of changes in the vibronic structure of the fluorescence spectra of pyrene molecules is promising for studying processes connected with a change in where polycyclic aromatic hydroca...
The influence of the human serum albumin (HSA) denaturation by a surface-active substance (sodium dodecyl sulfate (SDS)) on the phosphorescence of a luminescent probe (eosin) has been investigated. The dependences of the eosin-phosphorescence intensity on the SDS concentration were determined at different pH levels of an HSA solution. It has been shown that at SDS concentrations lower than the critical concentration necessary for micelle formation, the hydrophobic interactions of eosin with the protein influence the deactivation of the eosin triplet states.Keywords: protein, phosphorescence at room temperature, human serum albumin, surface-active substance, sodium dodecyl sulfate, micelle, protein denaturation, luminescent probe. Introduction.Structural changes in proteins can be determined by different methods, such as the methods of x-ray structural analysis [1], nuclear magnetic resonance [2], laser-correlation spectroscopy of dynamic light scattering [3], luminescence [4], etc. Fluorescence methods allow one to determine the polarity of the chromophore microsurrounding and the rate of rotational diffusion of a protein and its conformational mobility [5]. In [6,7], the structural dynamics of proteins was determined by the phosphorescence of their chromophoric groups (tryptophanyl) at room temperature. However, the number of chromophoric groups possessing phosphorescence is limited, which generates a need for the development of methods that would allow one to investigate the structural changes in proteins with the use of luminescent probes related to them. For example, in [8], in investigating the phosphorescence decay kinetics of isothiocyanate derivatives of eosin and erythrosin, related to proteins, the accessibility of the active centers of metalloenzymes was detected and the possibility of investigating the diffusion collisions of proteins in solutions was demonstrated. In [9], the influence of the molecular dynamics of proteins on the photoinduced electron transfer in the eosin-myoglobin complex has been revealed. Thus, the method of investigating the structure of proteins and the dynamics of its change by the phosphorescence of luminescent probes related to them holds much promise.In the present work, a method is proposed for control of the structural transformation of a protein by the changes in its absorption and fluorescence spectra and the changes in the intensity and lifetime of phosphorescence of a luminescent probe related to it. We investigated the deactivation of the triplet states of a luminescent probe caused by changes in the structure of a protein under the action of a surface-active substance present in concentrations critical for the micelle formation. The importance of investigating the action of a surface-active substance on the structure of a protein is explained by the fact that many biological and pharmaceutical systems contain proteins and surface-active substances [10]. Such investigations allows one, on the one hand, to obtain data on the changes in the structure of protein compoun...
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