INTERACTION OF IONIC MICELLES WITH THE HYDROPHOBIC FLUORESCENT-PROBE 1-ANILINO-8-NAPHTHALENESULFONATE

The critical micelle concentration (cmc) of sodium dodecyl sulfate (NaDDS) and sodium decyl sulfate (NaDS) was measured at various NaCl concentrations by observing the increase in fluorescent intensity of 1-anilino-8-naphthalenesulfonate (ANS ammonium salt). It was found that these data agreed with the literature data on cmc, as measured by other methods. The thermodynamic parameters of the interaction between the probe ANS and the alkyl sulfates micelles NaDDS and NaDS were measured. These data showed that all these processes gave negative enthalpy values. Further, in all systems, the addition of salt (NaCl) increases the association constant between the probe ANS and the micelle (NaDDS or NaDS). Data for NaDDS and NaDS showed that the interaction with the probe ANS is hydrophobic since the free energy of binding is more negative in the case of NaDDS than in the NaDS system. © 1979 American Chemical Society.