HYDRATION AND MICELLIZATION PROCESSES OF N-OCTYL BETA-D-GLUCOPYRANOSIDE IN AQUEOUS-SOLUTION - A THERMODYNAMIC AND FLUOROMETRIC STUDY IN THEABSENCE AND PRESENCE OF SALTS

A thermodynamic and fluorimetric study of a nonionic surfactant widely used in the biochemical field, n-octyl beta-D-glucopyranoside (OBG), has been carried out in aqueous solution at 25 degrees C, in the absen ce and presence of salts containing divalent cations. For that purpose , three highly accurate experimental techniques have been used: densit y, speed of sound and steady-state fluorescence. A method for the simu ltaneous measurement of the speed of sound and the density has been se t up. With this method, quantities such as the apparent molar volume V -phi and the apparent molar isoentropic compressibility K-s,K-phi of t he OBG, in the binary system (OBG/water) as well as in the ternary sys tem (OBG/salt/water), have been determined. The corresponding hydratio n numbers nh of the monomers, either isolated or in the micellar form, have also been evaluated. The speed of sound data permit also to obta in the critical micellar concentration, cmc, of OBG aggregates, which, together with the fluorescence results, provides the aggregation numb er N of the micelles. Furthermore, the fluorescence data afford intere sting information regarding the micropolarity of the micellar environm ent. With all this information, an exhaustive analysis of the hydratio n and micellization processes of OBG and of the effect of salts contai ning divalent cations, in particular Ca2+, on these processes has been carried out, with special emphasis on the solute-solvent and solute-s olute interactions.