Hanna Grajek

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.

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.

Excitation energy transport and trapping in concentrated solid solutions of flavomononucleotide

Excitation energy transport and trapping is studied for monomer-fluorescent dimer system of flavomononucleotide (FMN) in polyvinyl alcohol films (PVA). It is shown that the theory neglecting reverse energy transfer (RET) from dimers to monomers does not allow for the explanation of concentration quenching and concentration depolarization results presented herein. Much better agreement has been obtained using generalized energy transport theory in which fluorescent dimers are treated as imperfect traps for excitation energy. Such parameters like the dimer quantum yield and its emission anisotropy are estimated.

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 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.

The effect of temperature on FMN absorption spectra in rigid poly(vinyl alcohol) matrices.

Electronic absorption spectra of flavomononucleotide (FMN) in poly(vinyl alcohol) films (PVA) were measured over the concentrations ranging from 6.9 x 10(-4) to 6.8 x 10(-1) M and temperatures from 263 to 338 K. The FMN absorption spectra measurements performed at room temperature have shown two ranges of different changes as a function of dye concentration. For concentrations c<10(-1) M (range I) the spectra exhibited regular changes showing an isosbestic point, which evidences the equilibrium between monomers and dimers. However, for range II (c>1.05 x 10(-1) M) the FMN absorption spectra occurred to be almost independent of concentration and they nearly overlapped with the dimer spectrum (within the error limit). Temperature measurements have shown that the FMN absorption spectra in PVA are stable over a wide temperature range. The mean distances between FMN molecules in PVA films are calculated. For maximal concentrations (from the range II), they are below 13.1 A, whereas the mean dimensions of FMN monomers and dimers are 15.8 and 21.1 A, respectively, which indicates that the orientation of dimers and monomers in the PVA film cannot be random at high concentrations. Molecules are partly ordered, adopting approximately parallel orientation, which is in agreement with the calculations of dimer structure by molecular modelling method (MMM).

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.

Excitation Energy Transport in a Concentrated System of Flavomononucleotide in Polyvinyl Alcohol Films

Excitation energy transport mechanism of flavomononucleotide polyvinyl alcohol films is studied. Excitation wavelength and temperature dependences of fluorescence spectra and quantum yields for different concentrations of the dye are investigated. 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 the forward and in the reverse direction. It was found that, contrary to liquid solutions, the dimerization constant of flavomononucleotide in polyvinyl alcohol films does not depend on temperature and that the irregularities observed can be explained by the temperature-dependent changes in the quantum yield of the monomer–dimer system and the effect of inhomogeneous orientation broadening of energy levels.

The influence of fluorescence concentration quenching on the emission anisotropy of flavins in glycerine-water solutions.

Abstract— The measurements of the emission anisotropy r/r0 of flavomononucleotide (FMN) within a range of concentrations of 10–5–10‐1mol/L in glycerine‐water solutions of different viscosities‐0.056 Pa/s (system I) and 0.256 Pa/s (system II) have been carried out.

Secondary emission influenced fluorescence decay of a homogeneous fluorophore solution

An analytical expression is found allowing the calculation of the secondary emission influenced fluorescence decay of a homogeneous fluorophore solution. Before starting the calculation one has to know the shape of the primary fluorescence decay of the fluorophore and the value of the parameter κ denoting the ratio of the secondary to primary steady-state fluorescence intensities. The method elaborated by Budó and Ketskeméty is recommended for evaluation of the parameter κ. The main importance of the obtained expression is that it can be used to recover parameters characterizing the fluorescence decay in the absence of secondary emission. The cases of monoexponential, biexponential and multiexponential primary fluorescence decays are discussed in detail.