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  • Title: Influence of water and trehalose on α- and β-relaxation of freeze-dried lysozyme formulations.
    Author: Vallaster B, Engelsing F, Grohganz H.
    Journal: Eur J Pharm Biopharm; 2024 Jan; 194():1-8. PubMed ID: 38029940.
    Abstract:
    Molecular mobility in form of alpha and beta relaxations is considered crucial for characterization of amorphous lyophilizates and reflected in the transition temperatures Tgα and Tgβ. Based on an overview of applied methods to study beta relaxations, Dynamic Mechanical analysis was used to measure Tgα and Tgβ in amorphous freeze-dried samples. Lysozyme and trehalose as well as their mixtures in varying ratios were investigated. Three different residual moisture levels, ranging from roughly 0.5-7 % (w/w), were prepared via equilibration of the freeze-dried samples. Known plasticising effects of water on Tgα were confirmed, also via differential scanning calorimetry. In addition and contrary to expectations, an influence of water on the Tgβ also was observed. On the other hand, an increasing amount of trehalose lowered Tgα but increased Tgβ showing that Tgα and Tgβ are not paired. The findings were interpreted with regard to their underlying molecular mechanisms and a correlation with the known influences of water and trehalose on stability. The results provide encouraging hints for future stability studies of freeze-dried protein formulations, which are urgently needed, not least for reasons of sustainability.
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