Hydrogen Bonding Interactions and Enthalpy Relaxation in Sugar/Protein Glasses

In this study, hydrogen bonding interactions and enthalpy relaxation phenomena of sugar and sugar/protein glasses have been studied using Fourier transform infrared spectroscopy and differential scanning calorimetry. The sugar OH band in Fourier transform infrared spectra was used to derive the glass transition temperature, T_g, and the wavenumber-temperature coefficient (WTC) of the OH band. A study on mixtures of sucrose and albumin revealed that the glass transition temperature and strength of hydrogen bonds increased with increasing percentages of albumin. WTC_g and T_g derived from sucrose/albumin glasses showed a negative linear correlation. The Lu-Weiss equation was used to fit T_g data of sucrose/albumin mixtures. An inflection point was observed at a 1:1 mass ratio, which coincided with an inflection of the OH-stretching band denoting a change in hydrogen bonding interactions. Enthalpy relaxation, which is seen as an endothermic event superimposed on the glass transition in differential scanning calorimetry thermograms, increases with increasing storage temperature. Activation energies of enthalpy relaxation of sucrose and sucrose/albumin glasses were determined to be 332 and 236 kJ mol^-1, respectively. Addition of albumin to sucrose increases the T_g, average strength of hydrogen bonding, heterogeneity, and the enthalpy relaxation time, making the glass more stable during storage at room temperature.