Biomedical subjects

S K Gularian

Publications and source records attributed to S K Gularian.

4 recordsLinked to original sources

PubMed1997

The spatial structure of lipids in human leukocytes: studies by nonradiative energy transfer.

The spatial structure of lipids in living human lymphocytes and granulocytes has been studied using the energy transfer between lipophilic fluorescent probes. One of the probes, an energy donor (DMC), was localized in the lipid interior, whereas another donor (K-68) and an energy acceptor (DSP-12) were near the lipid/water interface. The energy transfer in lymphocytes was the same as in artificial lipid membranes (liposomes). Obviously, in lymphocytes as in liposomes, both donors are localized near the lipid surface (the distance from the donors to the lipid surface is less than Forster's radius R0, i.e., 3.4-5 nm). On the contrary, in granulocytes, the energy transfer from K-68 was 2.2 times more efficient than from the lipid-immersed DMC. It was suggested that a fraction of DMC molecules was immersed into some lipid particles, and the distance from the molecules to the surface of the particles was greater than R0. The positions of the DMC fluorescence spectrum maxima in lymphocytes and in liposomes were the same, but in granulocytes the spectrum was blue-shifted (as in the case of lipoproteins). After subcellular fractionation the DMC fluorescence intensity correlated only with phospholipid concentration in different fractions but not with protein or nucleic acid concentrations. It was suggested that lipid organelles are the main source of the DMC fluorescence. The studies of cell-lipoprotein model mixtures support the suggestion that lipids in lymphocytes are mainly present as lamellar structures (membranes); the presence of lipoprotein-like particles of rather small radius can not be excluded either. On the other hand, in addition to membrane lipids, granulocytes have lipid-containing particles similar to large serum very low density lipoproteins.

Chalcone↗

PubMedDate not supplied

[Fluorescent probe 4-dimethylaminochalcone: mechanism of fluorescence quenching in nonpolar media].

The reasons for the high sensitivity of the fluorescent probe 4-dimethylaminochalcone (DMC) to nonpolar environment were explored. It was shown that, at room temperature, the fluorescence quantum yield in nonpolar media at 20 degrees C is lower than 0.01 (0.001 in methylcyclohexane). However, as temperature was lowered to -196 degrees C, the yield in methylcyclohexane increased more than 200 times. At the same time, the oscillator strength of absorption transition increased, and the absorption spectrum was shifted to red. These results, together with quantum chemistry calculations suggest that, for fluorescence quenching to occur, some barrier in the DMC molecule, probably the barrier of rotation about C-C bonds, should be overcome. In other words, the quenching is associated with the transition of DMC molecules from a flat conformation (energy minimum) to other, nonflat conformations through rotations about C-C bonds. The phosphorescence of DMC at low temperatures was detected. This suggests that fluorescence quenching is caused by radiationless transitions from the excited singlet level to the ground and triplet levels, and rotation about bonds facilitates these transitions.

Chalcone↗

PubMedDate not supplied

[Low-density lipoproteins with different capacity for aggregation].

Preparations of low-density lipoproteins from healthy donor blood contain lipoprotein particles with different capacity for aggregation: upon stirring, some particles form aggregates significantly more quick than others. After stirring, lipoprotein particles are separated by ultracentrifugation into two fractions: a fraction of large aggregates and a fraction of small particles without intermediate forms. It is known that lipoprotein aggregates can accelerate intracellular accumulation of lipids. Therefore, it is supposed that particles of high aggregation ability are more atherogenic.

Centrifugation, Density Gradient↗

PubMedDate not supplied

[The lipophilic fluorescent probe 4-dimethylaminochalcone: factors responsible for the fluorescence yield].

Factors responsible for fluorescence quenching of the lipophylic fluorescent probe 4-dimethylaminochalcone in nonpolar and polar media were studied. The femtosecond dynamics of 4-dimethylaminochalcone excited state was measured using the absorption method of "excitation probing". In nonpolar hexane where the fluorescence quantum yield is very low (0.001), all excited 4-dimethylaminochalcone molecules go to the triplet state with a rate constant of 2.10(11) s(-1). At the same time, the radiation rate constant is 1000 times lower; therefore, such a fast transition to triplet is the major cause of the very small fluorescence yield. In polar acetone, the fluorescence yield is 220 times higher than in hexane. In acetone, no transitions to triplet state were detected. At the same time, a radiationless conversion to the ground state took place with a rate constant of 10(9) s(-1), which decreased the fluorescence yield to 0.22. The activation energy of the quenching processes is polarity dependent and decreases from 6 in nonpolar to 3 kcal/mol in polar media. The yield of 4-dimethylaminochalcone fluorescence varies hundreds times in media of different polarity but is a linear function of the Lippert's polarity parameter f(epsilon,n) where epsilon is the dielectric constant at low frequencies. It is supposed that polar media stabilize the "flat" conformation of the 4-dimethylaminochalcone molecule prior to its excitation, and this conformation is optimal for fluorescence. In this case, stabilization is determined only by medium polarity.

Chalcone↗