SPECTROSCOPIC STUDY OF MOLECULAR ASSOCIATIONS BETWEEN RIBOFLAVIN AND SOME (DIHYDRO) BETA-CARBOLINE DERIVATIVES

The spectrophotometric and thermodynamic properties of molecular complexes of riboflavin (RFN) with some dihydro beta-carboline derivatives have been investigated by using electronic absorption and fluorescence spectroscopic methods in aqueous solution. The molecular associations have been examined by means of electronic absorption spectra, since in each, a new charge transfer-like band has been located, and also by observing the variation of the fluorescence emission of RFN on the solutions. The formation constants for the molecular complexes were determined from absorption data, using the Forster-Hammick-Wardley method. The quenching phenomenon observed in RFN fluorescence is related to the concentration of the dihydro beta-carboline derivatives, allowing the calculation of the quenching constants for RFN-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 dihydro beta-carboline molecule on the stability of the complexes formed was also investigated.