Characteristics of hydrogen bond formation between sugar and polymer in freeze‐dried mixtures under different rehumidification conditions and its impact on the glass transition temperature

Water Sorption Glass Transition Protein-Stabilizing Behavior of an Amorphous Sucrose Matrix Combined With Various Materials

“…Hence, the values of T g for the dried and rehumidified sucroseadditive mixtures were determined by differential scanning calorimetry (DSC) using a Perkin-Elmer DSC Pyris (Norwalk, CT) in the same manner as was used in our previous study. 24 Two to 5 mg samples were transferred into 20 mL aluminum pans under a nitrogen atmosphere and hermetically sealed. The samples were scanned at a rate of 108C/min from a prescribed temperature (at least 508C lower than the T g ) to 1808C, using an empty aluminum pan as a reference.…”

“…This suggests that the amount of hydration water for sucrose and additive in the mixture are lower than those for sucrose alone and additive alone. 13,24,27,28 This can be explained as follows. A larger sized molecule is likely to form a less dense matrix, 28,29 which would contain some dead spaces and thus a larger number of free side-chain polar groups, such as hydroxyl groups in polysaccharides, which play a major participant in the sorption of water.…”

“…Hence, the amounts of hydration water replaced by the sucrose-additive hydrogen bonds were estimated for mixtures containing polysaccharides, CDs, and PVPs, using the same procedures as was used in our previous studies. 24,27,28 Namely, the water contents of the mixtures, w (g-water/g-dry matter) were converted to the amount of water involved in a sample containing 1 g of sucrose, W (g-water/g-sucrose) and were plotted against the amount of additive added to 1 g of sucrose (Fig. 2).…”

“…The plots for W were approximated by one or two lines; The number of approximated lines indicates the hydration states and the slopes of the lines are considered to be proportional to the amount of hydration water for the additive component. 24,28 The water contents of an additive embedded in amorphous sucrose, w 0 add (g/gdry additive) were calculated, using the following equation (1).…”

“…On the other hand, hydrogen bonds between sucrose and large-sized additives are considered to be approximately equal in strength, or only slightly stronger than sucrosesucrose hydrogen bonds, as indicated by quite the slight increase in T g in the low additive content region at RH 0-23%. Whereas marked increases in T g in the additive content range (<25%) at RH 33% were observed in our previous study 13,24 and explained as follows: 13,24 hydration water for an amorphous sugar matrix serves to weaken the mean strength of interactions holding the matrix together. When the strength of the mean interaction for the matrix is decreased below that for sucrose-additive interactions, sucrose-additive interactions become more relevant and can contribute to holding the matrix in the solid phase and the consequent increase in T g .…”