Cross linking of collagen in the presence of oxidizing lipid.

Gelatin films containing unsaturated lipid have been exposed to ultraviolet and visible irradiation. No sign of paramagnetism could be detected in the films, although the gelatin was undergoing cross-linking reactions. The addition of nitroxyl-forming radical scavengers decreased the rate of cross-linking as did addition of ascorbic acid to the reacting mixture. Nitroxyls could not be detected in the gels, however. The conclusion is drawn that the main reaction in the cross-linking reaction of collagen is a condensation of amino groups and extrinsic or intrinsic carbonyl groups. The extrinsic aldehydes are formed in the autoxidation of unsaturated lipid.