FLUOROMETRIC STUDIES OF THE FORMATION OF RIBOFLAVIN-BETA-CYCLODEXTRININCLUSION COMPLEX - DETERMINATION OF THE STABILITY CONSTANT BY USE OFA NONLINEAR LEAST-SQUARES MODEL

The non-linear least-squares model for calculation of the stability co nstant (K-st) of a drug-cyclodextrin complex has been used in fluorime try studies. Complexation of riboflavin with beta-cyclodextrin (beta-C yD) was monitored fluorimetrically by measuring changes in the fluores cence intensity of the vitamin in the presence of various amounts of b eta-CyD. Formation of an inclusion complex was confirmed in the solid state by differential scanning calorimetry (DSC) and in aqueous soluti on by proton nuclear magnetic resonance spectroscopy (H-1 NMR). The ex perimental K-st value (2112 M(-1)) derived from the fluorimetry studie s appeared to fit well to a 1:1 drug-to-cyclodextrin molar ratio accor ding to the non-linear mathematical model. The model is particularly s uitable for fluorescent compounds of which fluorescence intensity is i nfluenced by the presence of cyclodextrins.