On the contrary, the addition of glycerolslightly increases To. These results indicate that urea can greatly
inhibit the transition while glycerol can promote it. It manifests
that the transition around 40 ◦C for KC/gelatin mixture during cooling
is most likely to originate from hydrogen bonding between KC
and gelatin. Since KC and gelatin attract each other by electrostatic
interaction as mentioned above, the distance between disordered
chains of these two polymers might be shorten by the electrostatic
attraction to favor hydrogen bonding formation. Since the transition
is well above the conformational ordering temperatures of KC
and gelatin, it could be possible that the local structural arrangement
of the biopolymers or the change in local solvent environment
prior to their conformational transitions enables the formation of
intermolecular hydrogen bonds. Indeed, hydrogen bonding is also
the major molecular force that stabilizes gelatin and KC helices in
the ordered state [20].