Surface properties of unsaturated non-oxidized and oxidized free fatty acids spread as monomolecular films at an argon/water interface

The interfacial properties of monomolecular films of stearic acid (SA) olei c acid (OA), linoleic acid (LA), ricinoleic acid (RA), 13(S)-hydroperoxyoct adeca-9Z, 11E-dienoic acid (13-HPODE) and 13(S)-hydroxyoctadeca-9Z, 11E-die noic acid (13-HODE) were studied by recording the changes occurring in resp onse to monomolecular film compression in their surface pressure and surfac e potential at the argon/water interface. The oxidized free fatty acids are more expanded than the parent non-oxidized free fatty acids, reflecting a higher hydrophilic-lipophilic balance. The lift-off values of the molecular area of 13-HODE, 13-HPODE and RA were 68, 74 and 106 Angstrom(2) molecule( -1), respectively, as compared to 47 and 40 Angstrom(2) molecule(-1) in the case of LA and OA, respectively. Variations in the molecular orientation o f free fatty acids can result in large changes in the dipole moment which a re not accompanied by appreciable changes in the surface pressure. In the c ase of the oxidized free fatty acids, the spontaneous desorption into the a queous phase was found to increase at increasing surface pressures. The des orption rates of OA and LA increased dramatically in the presence of P-cycl odextrin (P-CD); whereas the presence of P-CD only slightly increased the d esorption rates of the oxidized free fatty acids. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.