SPECTROSCOPIC STUDY OF MOLECULAR ASSOCIATIONS BETWEEN FMN AND BETA-CARBOLINES

The spectrophotometric and thermodynamic properties of molecular complexes of flavin mononucleotide (FMN) (riboflavin 5'-phosphate) with some beta-carboline derivatives have been investigated in aqueous solution. The molecular associations have been examined by means of electronic absorption spectra, since in each a new charge-transfer band has been located, and also the variation of the fluorescence emission of FMN on the solutions has been observed. The formation constants for the molecular complexes were determined from absorption data using the Foster-Hammick-Wardley method. The quenching phenomenon observed in FMN fluorescence is related to the concentration of the beta-carboline derivatives, allowing the calculation of the quenching constants for FMN-beta-carboline complexes. Thermodynamic parameters have been determined from the values of association constants for the molecular complexes at various temperatures. The influence of substituents in the beta-carboline molecule on the stability of the complexes formed was also investigated.