INVESTIGATION OF THE HARDENING REACTION OF GELATIN WITH C-13 LABELED FORMALDEHYDE BY SOLUTION AND SOLID-STATE C-13-NMR SPECTROSCOPY

Model reactions of the hardening of gelatin with C-13 labeled formaldehyde were monitored by C-13 NMR spectroscopy in solution and in the solid state. In solution primary attack of formaldehyde first forms methylols of lysine residues and later of arginine residues, which react to a lysine-arginine crosslink. During the drying process of hardened gelatin, in addition to the lysine-arginine crosslink an arginine-arginine crosslink is formed. The rate of crosslink formation is strongly influenced by humidity.