AGGREGATION OF POLYUNSATURATED FATTY-ACIDS IN THE PRESENCE OF CYCLODEXTRINS

The aggregation behaviour of the polyunsaturated fatty acids (PUFA) linoleic acid and arachidonic acid was studied in the presence of cyclodextrins (CDs). The influence of CD concentration on CMC of PUFA suggests that two CD molecules bind sequentially to one molecule of PUFA. Two equilibrium constants, K-1 representing the interaction of the first CD molecule, and K-2, the interaction of the second, were determined by non-linear regression of the PUFA CMC versus CD concentration data to an expression deduced from the reaction scheme in the equilibrium. The effect of pH and the structure of the CD on the equilibrium constants was studied. It is postulated that the first CD molecule interacts with the carboxyl group of PUFA through hydrogen bonding when the fatty acid is protonated, while the second CD molecule binds to the hydrocarbon chain of the PUFA through hydrophobic interaction. The formation of hydrogen bonds was principally affected by the inner diameter of the CD, while the hydrophobic interactions were very strongly affected by the polarity of the CD group coating the inner channel. The relevance of the results for the development of enzyme assays involving fatty acids is discussed.