A Fourier-transform infrared spectroscopy study of sugar glasses Original Research Article

Fourier-transform infrared spectroscopy (FTIR) was used to study the hydrogen-bonding interactions that take place in vitrified carbohydrates of different chain lengths. The band position of the OH stretching band (νOH) and the shift in band position as a function of temperature were determined from the FTIR spectra as indicators for the length and strength of intermolecular hydrogen bonds, respectively. Differential scanning calorimetry (DSC) was used to corroborate the FTIR studies and to measure the change in heat capacity (ΔCp) that is associated with the glass transition. We found that with increasing Tg, the band position of νOH increases, the wavenumber–temperature coefficient of νOH in the glassy state, WTCg, increases, whereas ΔCp decreases. The positive correlation that was found between νOH and the glass transition temperature, Tg, indicates that the length of the hydrogen bonds increases with increasing Tg. The increase in WTCg with increasing Tg indicates that the average strength of hydrogen bonding decreases with increasing Tg. This implies that oligo- and polysaccharides (high Tg) have a greater degree of freedom to rearrange hydrogen bonds during temperature changes than monosaccharides (low Tg). Interestingly, WTCg and ΔCp showed a negative linear correlation, indicating that the change in heat capacity during the glass transition is associated with the strength of the hydrogen-bonding network in the glassy state. Furthermore, we report that introduction of poly-l-lysine in glassy sugar matrices decreases the average length of hydrogen bonds, irrespective of the size of the carbohydrate. Palmitoyl–oleoyl-phosphatidylcholine (POPC) vesicles were found to only interact with small sugars and not with dextran.