Regina Drabent

Fluorescence properties of plant anthocyanin pigments. I. Fluorescence of anthocyanins in Brassica oleracea L. extracts

Abstract The fluorescence of anthocyanin pigments in water extracts of Brassica oleracea L. (red cabbage) has been studied. The fluorescence spectra and fluorescence excitation spectra of pigments in starting extracts and in chromatographic fractions have been measured. It has been stated that the group of fluorescent anthocyanins (or other fluorescent species as well) exists in water extracts of red cabbage. Attempts to separate the fluorescence spectra, characteristic of these compounds, have been undertaken by choosing proper parameters for measurements of fluorescence spectra and fluorescence excitation spectra and deconvolution of registered fluorescence spectra. Three fluorescent species, ZI, ZII and ZIII, are distinguished. Their fluorescence spectra are centred at 363, 434 and 519 nm, respectively. It is suggested that fluorescence investigations, apart from the standard methods of visible absorption spectroscopy, may extend the possibilities of analysis and registration of the changes of anthocyanins in these extracts.

Absorption of the flavin dimers

Abstract The electronic absorption spectra of the flavomononucleotide (FMN) in aqueous solution and in glycerine-water solution with change of the dye concentration have been measured. The FMN dimer absorption spectrum, monomer absorption spectrum, dimerization constant K and molar fraction of the monomer were calculated. It was found that FMN dimerization constants in aqueous solution were Ka = 118.0 l/mol and in glycerine Kg = 20.5 l/mol. In the region of the monomer absorption band two dimer absorption bands appear, in accordance with the Kasha molecular exciton theory.

Spectroscopic investigation of the equilibria of the ionic forms of sinapic acid

The equilibria of the ionic forms of sinapic acid (SA) in Britton-Robinson buffer at pH 1.9–11.5 and 297 K were studied using spectrophotometry and spectrofluorimetry. Three ionic forms of SA were found. Equilibrium constants and pK values were calculated. The absorption and fluorescence spectra for all the ionic forms of SA were determined.

The structure of the flavomononucleotide dimer

Abstract Structural parameters of the flavomononucleotide (FMN) dimer in water and glycerin-water solution have been established on the basis of spectroscopic studies and the Kasha theory. A parallel-plane dimer model is proposed, in which the monomer units are arranged face to face. For the FMN dimer in water, the distance between the planes of monomer units is equal to R = 3.5 ± 0.3 A , and the angle α1 ( ∢ ( M I M I ′ )) between the moments of transition S1 → S0 (absorption band I) and the angle αII ( ∢ ( M II M II ′) ) between the moments of transition S2 → S0 (band II) of monomer units are equal to α1 = 71 ± 4° and αII = 0 ± 4°, respectively. From the mentioned orientation of absorption transition moments of FMN monomer units in the dimer, a conclusion may be drawn that the angel, φ, between the transition moments S1 → S0 and S2 → S0 is equal to 36 ± 4°. This orientation is consistent with the results of Johansson obtained for FMN molecules in lamellar liquid crystals. Similar R, αI and αII values were obtained for the FMN dimer in the water-glycerin solution.

Spectroscopic manifestations of flavomononucleotide dimers in polyvinyl alcohol films.

Absorption and fluorescence spectra of flavomononucleotide (FMN) in polyvinyl alcohol films (PVA) over a very wide concentration range are investigated. The dimerization constant as well as the pure monomer and dimer spectra are calculated and the structural parameters of FMN dimer are established. Excitation wavelength and temperature dependencies of FMN/PVA fluorescence spectra for different FMN concentrations were carried out. These measurements together with those of absorption reveal that dimers are imperfect traps for excitation energy and that the energy transfer can occur both in forward and in reverse direction. Moreover, it was shown that the observed temperature changes in fluorescence spectra may be qualitatively explained by the effect of inhomogeneous broadening of FMN energy levels and by the presence of fluorescent dimers.

The photocycle of bacteriorhodopsin immobilized in poly(vinyl alcohol) film

The kinetics of photoelectric and optical signals were measured on samples containing oriented purple membranes immobilized in a poly(vinyl alcohol) film and on purple membranes introduced into a PVA—H2O mixture. The bacteriorhodopsin photocycle in the PVA—H2O mixture was complete. The only observed changes were the slowing down of the optical and electrical signals in relation to the M412‐O640 and O640‐bRa11‐trans steps. In the PVA film the O640 intermediate disappeared and a negative photoelectric signal appeared.

Anisotropy of poly(vinyl alcohol) films in the u.v. and i.r. regions of the spectrum

Abstract Absorption properties of anisotropic poly(vinyl alcohol) (PVA) films in u.v., Vis, and i.r. spectral regions were investigated. The orientation of the transition moments with respect to the long axis of the chain was determined together with the arrangement of PVA chain. Anisotropic PVA matrices should be considered in terms of binary solvents since together with crystallites, there are regions of amorphous structure.

Fluorescence Studies on Association of Human Translation Initiation Factor eIF4E with mRNA cap-Analogues

Binding of a long series of mono- and dinucleotide analogues of the 7-methylguanosine containing 5′-mRNA-cap to human protein translation initiation factor eIF4E has been investigated by means of fluorescence. A new methodological approach in gathering and analysis of the fluorescence data provided us with very accurate values of the association equilibrium constant K and normalized, maximal quenching of the protein fluorescence ΔFmax, during titration of eIF4E by various cap-analogues. The results confirm participation of at least two conserved tryptophan residues of eIF4E in interaction with 7-methylguanine, as has been described recently for murine eIF4E, complexed with 7-methyl-GDP in crystal (Marcotrigiano et al., 1997, Cell 89, 951), and for yeast eIF4E, complexed with the same ligand in solution (Matsuo et al., 1997, Nature Struct. Biol. 4, 717). On the other hand binding by eIF4E of unmethylated guanine nucleotides and N2,N2,7-trimethylguanine containing nucleotides differ substantially from the way of binding of the regular mRNA-cap. Influence of the structural features of the cap-analogues, especially the type of the second nucleoside in the dinucleotide caps, on their association with eIF4E and biological activities in in vitro protein translation systems has been discussed in light of the known structures of the eIF4E -7- methyl-GDP complexes in crystal and solution.

The flavin dimers I. The application of absorption in anti-stokes excitation region to investigate the flavin dimer formation

Abstract The dimer formation process of the flavin in aqueous solution has been studied. The difference absorption spectra with the change of concentration in Stokes and anti-Stokes excitation region of the flavomononucleotide and riboflavin were measured. The highest temperature in which the dimers still appear is discussed. It is suggested that this temperature Td can be treated as one of the empirical parameters which describe the dimer formation process of the dyes in solutions. The aqueous solution of flavins with the concentration c⩽5·10−5 M at room temperature can be treated as a flavin monomers solution. For higher concentrations the flavin monomers and dimers exist in a solution at room temperature.

INVESTIGATIONS ON THE FLUORESCENCE CONCENTRATION QUENCHING OF FLAVOMONONUCLEOTIDE IN GLYCERINE‐WATER SOLUTIONS

We measured concentration changes of the fluorescence quantum yield η/ηo of flavomononucleotide (FMN) in glycerine‐water solutions of various viscosities. The results obtained show that FMN dimers are traps for the exciting light energy as well as the energy transferred non‐radiatively. Very good agreement between the experimental and theoretical η/ηo results was obtained. It has been shown that in the investigated solutions non‐radiative energy transfer from monomers to dimers takes place, preceded by the migration of energy. It has been stated that no monomer quenching occurs in these solutions. The contribution of the individual fluorescence concentration quenching mechanisms has been determined.