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 capacity of the CH(2) group in aqueous solution is independent of the type of compound used for its determination, is positive at low temperature, and is linearly decreasing in magnitude with an increase in temperature. 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 that the partial heat capacity of CONH group in aqueous solution depends on the type of model compound used for its determination. These differences correlate with the difference in the water accessible surface area of atoms in the CONH group in different model compounds.
Makhatadze
G I
GI
Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA. qegim@ttacs.ttu.edu
Lopez
M M
MM
Privalov
P L
PL