Parameterization of hydrophobic properties of aqueous polymeric biphasic systems and water-organic solvent systems

Abstract

Partition coefficients for a homologous series of dinitrophenylated amino acids with aliphatic side-chains have been determined in two aqueous polymeric Ficoll-dextran 70 and dextran 500-polyethylene glycol 6000 biphasic systems and in the systems formed by n-octanol and the aqueous phases of the above systems. The results afford an estimation of the free energy of transfer of a CH 2 group from one to the other phase of the systems examined. This parameter (Δ g tr CH 2 ) was taken as a measure of the hydrophobic character of an aqueous phase with respect to n-octanol. It was shown that when the partition of a set of homologues in two biphasic systems is correlated according to the known equation ln K i = a ln K o + b, where K i and K o are the partition coefficients for a given solute in the ith system and in the system chosen for reference, respectively, the parameter a is related to the Δ g tr 1 CH 2 and Δ g tr 0 CH 2 by a = Δ g tr 1 CH 2 /Δ g tr 0 CH 2 . This equation was used to determine the hydrophobic character of various organic solvents and that of the aqueous polymeric phases of the aqueous biphasic systems studied, and was found to be valid for comparison of the partition values determined in an aqueous polymeric biphasic system and in the water- n-octanol system. This seems to extend the possibilities of structure-activity relationships studies as the Ficoll-dextran aqueous biphasic system provides as promising a means for their study in biological chemistry as the water- n-octanol system in drug research.