VOLUMETRIC PROPERTIES OF PROTEINS AND THEIR ANALOGS IN DILUTED WATER SOLUTIONS .2. PARTIAL ADIABATIC COMPRESSIBILITIES OF AMINO-ACIDS AT 15-70-DEGREES-C

Apparent adiabatic compressibilities of 21 amino acids have been measured by means of a high-precision ultrasonic technique in diluted aqueous solutions, about 0.3 wt % over the temperature range 15-70-degrees-C. At these low concentrations the values obtained can be considered to approximate limiting partial compressibilities. Addivity of molar compressibility with respect to atomic composition of molecules was analyzed by using a simple additive scheme. Partial compressibilities of atomic groups have been determined as functions of temperature and interpreted in terms of hydration and intramolecular interactions between different parts of a molecule. It has been shown that atomic groups can be divided into four main classes-charged, nonpolar, polar "single", and polar "clustered" (brought together)-which substantially differ from each other in their influence on volume and compressibility of water and on their temperature derivatives.