Partition coefficients of ?-phenylalkanols between water and sodium deoxycholate micelles

Abstract

The partition coefficient of ω-phenylalkanols [C6H5(CH2)mpOH, m p =3–6] between water and micelles of sodium deoxycholate (NaDC) has been determined by a differential spectroscopic method at 25°C. The linear dependence of thestandard free energy change of transfer calculated from the partition coefficient on the alkyl chain length of the alkanols (m p ≥4) yields the standard free energy change per methylene group [δGo(CH2)]. δGo(CH2) value for the present system, −3.21 kJ-mol −1 is larger in magnitude than that for sodium dodecylsulfate (SDS)-ω-phenylalkanol system, −2.40 kJ-mol −1 . The result indicates that the alkyl chain of ω-phenylalkanols has higher affinity to NaDC micelles than to SDS micelles although the molecular structure of NaDC is more rigid and bulkier than that of SDS and the aggregation number of micelles of the former is much smaller than that of micelles of the latter. On the basis of the linear relation between the effect of added ω-phenylalkanols on the critical micelle concentration of NaDC (−dCcmc/dCa) and the partition coefficient, it is found that the degree of ionization of NaDC micelles is not influenced by solubilization of ω-phenylalkanols into the micelles.