Autoxidation of fatty acid monolayers adsorbed on silica gel: I. Nature of adsorption sites.

An unsaturated fatty acid monolayer deposited on a silica gel surface has been chosen as a model for studying non-enzymatic autoxidation of membrane lipids. Studies to determine the suitability of this system as a model for biomembranes were conducted to define the nature of the monolayers, particularly with respect to the factors determining the concentration of the fatty acid molecule on unit area of the surface. The results from adsorption isotherm, high temperature dehydroxylation, and infrared spectra studies show that adsorption of a monomolecular layer of fatty acids occurs and that the number of molecules absorbed corresponds to the number of isolated, non-hydrogen-bonded silanol groups. It is presumed the binding is by hydrogen bonding of the carboxyl groups to silanol groups. The packing density of the fatty acid molecules is 1.25 molecule/100 A2 which is similar to the density of the isolated silanol sites on the surface.