The role of aliphatic alcohols on the stability of collagen and tropocollagen.

The role of aliphatic alcohols on the temperatures of the helix-coil (Trr) and of the melting transformation (Tr) for collagen in water solutions was investigated. Alcohols used were CH,OH, C2H50H, and C3H70H and the role of chloroethanol was also investigated. The results indicate that on increasing alcohol concentration both Tr and Trr are initially depressed (i.e. the random coil form is favored with respect to both the helical and the crystalline form) the order for increasing alcohol effectiveness being C&H,ClOH > C3H70H > CzH50H > CH30H. In the case of the melting transition a subsequent reincrease of Tr with further increase of alcohol content was observed, and in this region the order for increasing effectiveness for depressing the melting temperature was CHpOH > C2H60H > CzHTOH. Measurements of the equilibrium degree of swelling for cross-linked collagen membranes indicates that the over-all degree of swelling decreases with increasing alcohol concentration. However, measurements of the selective absorption of the alcohols by the membrane reveal a behavior which can be correlated to the melting behavior; i.e. the absorption goes through a maximum on increasing alcohol content and the order for increasing absorption is CaH,OH > C~HSOH > CH30H below the maximum and CHpOH > GH50H > C3H70H above the maximum. The depressing effect on Z’r and Trr observed in diluted alcohol solutions is attributed to a solvation of the side chain apolar groups which become exposed during the transitions.