Investigation of the Hardening Reaction of Gelatin with 13C Labeled Formaldehyde by Solution and Solid State 13C NMR Spectroscopy

M odel reactions o f the hardening o f gelatin with 13C labeled form aldehyde were m onitored by 13C N M R spectroscopy in solution and in the solid state. In solution prim ary attack o f form aldehyde first forms methylols o f lysine residues and later o f arginine residues, which react to a lysine-arginine crosslink. D uring the drying process o f hardened gelatin, in addition to the lysine-arginine crosslink an arginine-arginine crosslink is form ed. The rate o f crosslink form ation is strongly influenced by humidity.