HEAT-CAPACITIES OF PROTEIN FUNCTIONAL-GROUPS

Using a precise technique of scanning calorimetry the heat capacities of a series of carboxylic acids and their sodium salts, alcohols, and N-substituted amides have been measured from 5 to 100 degrees C. From these data, the partial molar heat capacities of -CH2-, -CONH-, -COOH, and -COONa groups have been determined. It is shown that the heat cap acity of the -CH2- group in aqueous solution is independent of the typ e of compound used for its determination, is positive at low temperatu re, and is linearly decreasing in magnitude with an increase in temper ature. In contrast, the heat capacities of -COOH and -COONa groups in aqueous solution are negative at room temperature and their magnitude non-linearly decreases with an increase in temperature. It appears tha t the partial heat capacity of -CONH- group in aqueous solution depend s on the type of model compound used for its determination. These diff erences correlate with the difference in the water accessible surface area of atoms in the -CONH- group in different model compounds. (C) 19 97 Elsevier Science B.V.