The Effect of Aliphatic Alcohols on the Thermal Stability of Tropocollagen Under Acidic Conditions

Monohydric and dihydric alcohols have been added to aqueous solutions of rat tail tendon collagen at pH 3.0 and their effects on the thermal denaturation temperature, T m , of the protein have been studied. At concentrations less than 2 M all the monohydric alcohols gave linear curves of T m vs alcohol concentration with negative slopes. The extent of lowering of T m increased with increasing C n for the n‐alcohols from C 1 , to C 4 . An alcohol with its carbon chain branched at the α‐carbon atom lowered T m less than its straight‐chain isomer but branching at the β‐carbon atom produced little effect. At high alcohol concentrations positive deviations from linearity were observed in the T m vs c curves indicating a competitive stabilizing effect. Of the dihydric alcohols, ethylene glycol and propane‐1:3‐diol each increased T m at all concentrations whereas propane‐J: 2‐diol decreased T m except at very high concentration ( < 10 M). The addition of ethanol (20% v/v) had only a small effect on the relations between both T m and pH and T m and concentration of added salts at pH 3.0. It is concluded from these data that addition of alcohols has only small effects on the contribution to the stability of tropocollagen from electrostatic interactions but major effects on the contributions from hydrogen‐ and hydrophobic‐bonding. The net effect appears to depend primarily on the hydrophobic‐hydrophilic balance and steric factors in the alcohol molecule.