Temperature-scanning infrared spectroscopic analysis of sugar glasses using principal component analysis

Sugars, such as sucrose and trehalose, can protect biological materials during drying. Protective properties of sugars have been attributed to their ability to form hydrogen bonds and facilitate glass formation during dehydration. The aim of this study was to identify intermolecular interactions in amorphous sugar matrices that are involved in glass formation and determine thermophysical properties. Therefore, we studied sugar glasses composed of sucrose, trehalose, and sucrose/albumin mixtures using temperature-scanning infrared spectroscopy (FTIR) empowered by principal component analysis (PCA). Spectral pre-processing procedures included selection of spectral regions, baseline correction, and vector-normalization. PCA revealed that the glass transition coincides with notable changes in the high wavenumber region of the spectra, i.e., in the OH-stretching region. This indicates that particularly hydrogen bonding interactions change during the glass transition. The shape of the broad OH-stretching band depicts strong and weak hydrogen bonding interactions, at respectively low and high νOH wavenumber positions. The glass transition is associated with a change in the thermal expansion coefficient of hydrogen bonding interactions, i.e., the length of intermolecular hydrogen bonds, which increases during the glass transition. Besides deriving the glass transition temperature, Tg, PCA on temperature-dependent spectra revealed differences in hydrogen-bonding networks amongst sucrose and trehalose glasses. Also, protein addition alters the hydrogen-bonding network of a sugar glass, which coincides with an increase in Tg and molecular packing. Taken together, FTIR combined with PCA is a promising tool to study molecular physical characteristics of sugar glasses used for dry preservation of biomolecules and cells.