Evaluation of partition coefficients of low molecular weight solutes between water and micelles of block copolymer of ethylene oxide based on dialysis kinetics and fluorescence spectroscopy

Application of micelle-forming surfactants in various fields of technology and use of micelles as carriers for drug targeting requires simple evaluation of partitioning coefficients of different solutes between water solution and micellar microphase. A number of methods of partitioning evaluation have been already proposed, but most of them are applicable only for fluorescent dyes or require complicated and expensive equipment, such as NMR spectrometers. In the present work two methods of the molar fraction of solubilized material determination are compared. One of the techniques used is based on the changes in fluorescence spectra during solubilization. The other approach is based on the dialysis slowing down, which occurs if the solute is associated with large particles (e.g. micelles). Graphic method of partition coefficient (P) evaluation is proposed and P values of a widely used anti-tumor drug doxorubicin and highly hydrophobic fluorophore perylene are determined. The comparison shows that the results of both methods give very close coincidence. The solubilization data were used for the calculation of the important parameter - the ratio of micelle volume to aggregation number, which makes sense of packing density of the detergent molecules in the micelle. The comparison of this parameter calculated from the solubilization data with that obtained from light scattering experiments is discussed. It is assumed that the dialysis technique could be used for partitioning evaluation of all substances, which may be detected in solution.