Cinnamoyl pyrones in proton-donating media: electronic structure and spectral properties of protolytic forms.

Spectral properties of cinnamoyl pyrone (CP) and its derivatives were studied in water-alcohol and water solutions within a wide pH/H(0) range. It was found that the most of CP may exist in neutral, anionic and cationic forms, except for alkylamino substituted CP, which can also form dications. The constants characterizing equilibria between all the protolytic forms were obtained. CP anions appears as a result of 4-hydroxy group dissociation. It was found that the acidity of CP decreases upon the excitation, that excepts the photodissociation or intramolecular proton transfer in the excited state. The formation of cations and dications occurs by means of protonation of alkylamino group or/and exocyclic carbonyl group. The theoretical analysis of electronic structure has shown that long-wavelength electronic transitions of neutral and anionic CP forms are of interfragmental charge-transfer (ICT) character. However, in the case of anions, ICT is hindered due to their nonplanar geometrical structure. The band maxima positions in experimental absorption spectra of neutral CP and in absorption and emission spectra of cations correlate linearly with theoretical estimations of charge transfer in CP molecules. The absence of the fluorescence, characteristic for the most of neutral CP, is due to the intersystem crossing, that is proved by the appearance of the phosphorescence of non-fluorescent CP at low temperatures.

[Effect of temperature on the modification of spectral properties of tryptophan aqueous solutions induced by water previously treated with laser radiation].

It was shown that preliminary exposure of a solvent (water) to low-intensity laser radiation reduces the tryptophan fluorescence intensity, and this fluorescence quenching effect is retained throughout the temperature range explored (from 8 up to 50 degrees C). The effects found are interpreted as resulting from changes in solvent properties induced by the action of electromagnetic radiation on interaction of water molecules with solute.

Fluorescence behavior of chromones containing several protolytic centers 3-Thiazolylchromones: Emission band assignment and pH dependent effects.

Fluorescence properties of 3-thiazolylchromones (TC) were studied in the wide H(0)/pH range -10 to 12. It was found that the number of the excited TC protolytic forms exceeds their quantity in the ground state. The formation of the new emitting species was explained as the result of the dramatic changes in the acid-base characteristics of three protolytic centers of TC molecules under the electronic excitation. The quantum chemical evaluation of the relative thermodynamic stability of all the possible excited TC acid-base forms aiming to find out, which of them should be the most energetically favorable, was made. The assignment of the experimentally observed emission bands to the above mentioned acid-base forms of 3-thiazolylchromones was carried out. The pH/H(0) ranges, where all of the detected protolytic forms could be observed, were determined. The dissociation and protonation constants of 3-thiazolylchromones in the ground and excited states were estimated. The most probable mechanism of the excited TC cation-tautomer formation was discussed.

Spectral and acid-base features of 3,7-dihydroxy-2,8-diphenyl-4H,6H-pyrano[3,2-g]chromene-4,6-dione (diflavonol)--a potential probe for monitoring the properties of liquid phases.

Diflavonol is a molecule that can exist in neutral or anionic form and in several tautomeric forms in ground and excited states. Absorption and emission spectroscopy combined with theoretical calculations have shown that only one tautomer of neutral diflavonol exists in the ground state, but two exist in the excited state. In the latter case, one is the tautomer originating from the ground state tautomer, which exists in strongly protic solvents, the other is the phototautomer occurring in weakly protic or aprotic solvents as a result of the intramolecular transfer of one proton. The OH groups present in diflavonol and involved in weak intramolecular hydrogen bonds exhibit a proton-donating ability reflected by the experimental values of acidity constants or theoretical enthalpies and free energies of proton detachment. The electronically excited molecule is a relatively strong acid when it loses one proton. With increasing basicity of the medium, monoanionic and dianionic forms occur which exhibit spectral characteristics and an emission ability different from those of neutral diflavonol. These interesting features of diflavonol open up possibilities for the analytical use of the compound and its application as a spectral probe sensitive to the properties of liquid phases.

[Method of identification of natural vegetable oils]. / Sposob identifikatsii natural'nykh rastitel'nykh masel.

The natural compounds which are present in vegetable oils were investigated by absorption and three-dimensional fluorescence spectroscopy. It was found that some of these components could be used as internal markers for identification and quantitative analysis of vegetable oils. The presence of specific fluorophores permits to develop an individual fluorescent "finger-print" criteria for all the studied oils, which can be used for detection of product falsification.

[Structural and functional changes in various cells following radiation exposure]. / Strukturno-funktsional'nye izmeneniia v kletkakh razlichnykh tipov posle radiatsionnogo vozdeistviia.

Structural and functional changes in thymocytes, splenocytes and hepatocytes, taking place under gamma-irradiation of cellular suspensions were investigated. It was found that splenocytes begin to lose their functional activity and structural features at a dose of 2 Gy. Increasing the irradiation dose leads to the acceleration of these processes. Thymocytes lose rapidly their functional activity at 2 Gy, but they maintain their structure and membrane parameters even after irradiation with a dose of 10 Gy. In comparison with other cell types, hepatocytes exhibit the greatest stability under the influence of gamma-radiation.

[Radiation-induced changes in the structure of erythrocyte membrane proteins]. / Radiatsionno-indutsiruemye izmeneniia struktury belkov éritrotsitarnykh membran.

Structural changes in proteins of erythrocyte membranes induced by gamma-radiation at doses of 10-10(3) Gy were studied using the method of tryptophan fluorescence quenching by acrylamide. It was found that the exposure to ionizing radiation leads to a decrease in intramolecular dynamics of membrane proteins.

[Study of thymocytes resistance to ionising irradiation in vitro]. / Izuchenie ustoichivosti timotsitov k ioniziruiushchemu izlucheniiu v usloviiakh in vitro.

The influence of ionising irradiation with doses of 0.5, 1, 2 Gy upon the suspension of mice thymocytes was studied. The state of the system of lipid peroxidation-antioxidation activity and structural and functional state of cell membrane was studied. It was found that, 15 minutes' after irradiation POL processes are within the norm. But the content of vitamins A and E decreases (the former after 0.5 Gy, the latter after 1 Gy). Changes in structural and functional state of thymocyte membranes can be observed by using fluorescent probes. Particularly, it turned out that after irradiation accessibility of incorporated proteins increases, the polarity of lipids increases and the lipophility of membrane lipids decreases. These changes can lead to short-time increase in specific functional activity of cells, but they can cause rapid death of cells as well.