A. N. Sobchuk

Dipole moments of 4'-aminoflavonol fluorescent probes in different solvents.

Electrooptical absorption measurements (EOAM) were used to measure the dipole moments of the normal form of 4′-(dimethylamino)-3-hydroxyflavone (FME), and 4′ N-(15-azacrown-5)-3-hydroxyflavone (FCR) in 1,4-dioxane, toluene, and cyclohexane. With these probes excited-state intramolecular proton transfer (ESIPT) takes place. For comparison, the dipole moments of 4′-(dimethylamino)-3-metoxyflavone (FME3ME), for which ESIPT is lacking, were measured, too. For all three probes the ground (μg) and excited Franck-Condon state (μeFC) electrical dipole moments are parallel to each other and also parallel to the transition dipole moment. The electrical dipole moments of FCR, FME, and FME3ME in their ground state have values within the range (12.0–17.7) × 10−30 C m. Upon optical excitation, the dipole moments increase by (41.9–52.9) ×10−30 C m. The value of the change of the dipole moment vector Δaμ with excitation to the Franck-Condon state and the value of the vector μeFC for FCR and FME are practically independent on the solvent polarity. From this point of view and due to large values of the dipole moments FCR and FME are very promising probes for the investigation of the distribution of the local polarity in biological systems using site-selective excitation of the different sites. Our steady-state fluorescence studies on FME and FCR have demonstrated a high spectral sensitivity of the normal form to such solvent characteristics as polarity.

Subnanosecond spectrofluorimetry of new indolocarbazole derivatives in solutions and protein complexes and their dipole moments

The spectral and temporal characteristics of new 6,12-dimethoxyindolo[3,2-b]carbazole, 5,11-dimethyl-6,12-dimethoxyindolo[3,2-b]carbazole, and 5,11-dihexyl-6,12-di(hexyloxy)indolo[3,2-b]carbazole fluorescence probes in organic solvents and protein complexes are studied. The dipole moments of indolocarbazoles in 1,4-dioxane were measured by electrooptical absorption method. The measured dipole moments have values within the range of (3.1–3.6) × 10−30 C m in the equilibrium ground state and increase to (4.8–5.6) × 10−30 C m after excitation. The excited state lifetime of indolocarbazole derivatives increases with increasing polarity and viscosity of the environment. The binding of indolocarbazoles with trypsinogen and human serum albumin increases the fluorescence intensity, changes the intensity ratio of fluorescence bands, and increases the average excited state lifetime of indolocarbazoles. The analysis of the instantaneous fluorescence spectra and fluorescence decay parameters at different wavelengths revealed the existence of several types of probe binding sites in proteins. It is found that the fluorescence characteristics of indolocarbazole derivatives depend on the conformation rearrangements of trypsinogen due to its thermal denaturation.

Ultrafast time-resolved fluorescence spectroscopy of novel ketocyanine dyes

Using ultrafast time-resolved fluorescence spectroscopy, the fluorescent characteristics of two ketocyanine dyes—2,5-di[(E)-1-(4-diethylaminophenyl)methylidene]-1-cyclopentanone (CPET) and 2,5-di⨑ub;(E)-1-[4-(4,7,10,13-tetraoxa-1-azacyclopentadecyl)phenyl] ???methylidene⫂ub;-1-cyclopentanone (CPCR)—are studied in organic solvents and in membranes of human erythrocyte ghosts. The position of the fluorescence spectrum of each probe depends strongly on the polarity of the environment due to a considerable change in the dipole moment of the probe after its excitation. An inhomogeneous broadening of the electronic spectra of both dyes is observed, which manifests itself in the bathochromic shift of the fluorescence spectrum upon displacement of the excitation frequency toward the red edge of the absorption spectrum, as well as in the dependence of the shape of the excitation spectrum on the frequency of recording. The lifetime of the excited state of the probes increases with increasing polarity or viscosity of the environment. Analysis of the instantaneous emission spectrum of CPET and of its fluorescence decay time distribution in human erythrocyte ghosts shows that there are two types of binding sites of the probe to the lipid membrane.

Spectral and photochemical characteristics of the photosensitizers chlorin e6 and photolon in the presence of melanin

The effect of DOPA melanin on the spectral and kinetic properties of the photosensitizers chlorin e6 and Photolon in buffer solutions with different pH (8.5, 7.0, and 6.0) is studied. The data obtained indicate that no complex formation between molecules of DOPA melanin and either photosensitizer in the ground or excited states occurs (at least, at melanin concentrations ≤0.1 mg/ml). The presence of melanin in the samples has no effect on the spectral-luminescent or kinetic characteristics of either chlorin e6 or Photolon. At a small concentration of DOPA melanin (≤0.02 mg/ml), the quantum yield of generation of singlet oxygen by the photosensitizers does not change; however, the generation efficiency of singlet oxygen decreases due to the shielding action of melanin.

System for the optical diagnosis of tumors, and using it to identify pituitary adenoma

This paper discusses the autofluorescence kinetics of healthy and tumorous tissues of the pituitary, as well as their diffuse scattering spectra in the wavelength ranges, respectively, of 380–600 and 350–1000 nm. Measurements were made by means of apparatus consisting of two units, a time-correlated photon-counting system, and a unit for exciting and recording the spectra of diffusely scattered light. It is found that a significant difference is observed in the mean autofluorescence time of tumorous and healthy tissues in the 380–600-nm spectral range. It is established that the intensity of diffusely reflected light is significantly lower in samples of healthy tissues than in samples of pituitary adenoma in the wavelength range 650–1000 nm. The sensitivity and specificity of the identification of the pituitary tissues after the data were processed by means of discriminant analysis were 100%.