Evaluation of the absolute configurational entropy of tri-O-methyl-β-cyclodextrin, a molecule with many degrees of freedom

Abstract

In this study, we evaluated the temperature dependence of the absolute configurational entropy of tri-O-methyl-β-cyclodextrin (TMCD), a molecule with many degrees of freedom. We calculated the configurational entropy from the configurational heat capacity obtained by subtracting the calculated heat capacity due to lattice vibrations and intramolecular vibrations from the heat capacity measured above the glass-transition temperature. We fitted the configurational heat capacity using both a power law and a logarithmic function based on Landau's critical-point theory. The configurational entropy increases more gradually as the temperature increases. We found that the temperature at which the configurational entropy vanishes (the so-called Kauzmann temperature TK) lies between 280 K and 298 K for TMCD. This is about 50 K lower than the glass-transition temperature of TMCD, which is consistent with the expectations.