Weng Lindong, Elliott Gloria D
Department of Mechanical Engineering and Engineering Sciences, University of North Carolina at Charlotte, Charlotte, North Carolina 28223, United States.
J Phys Chem B. 2015 Jun 4;119(22):6820-7. doi: 10.1021/acs.jpcb.5b01675. Epub 2015 May 20.
Approximately a decade ago it was observed that adding a small amount (5 wt %) of glycerol to trehalose could substantially improve the stability of enzymes stored in these glasses even though the final glass transition temperature (Tg) was reduced by ∼20 K. This finding inspired great interest in the fast dynamics of dehydrated trehalose/glycerol mixtures, leading to the observation that suppression of fast dynamics was optimal in the presence of ∼5 wt % of glycerol. It was also recognized that the fast dynamics should, in theory, be related to the fragility of these glass formers, but experimental confirmation of this hypothesis has been lacking for trehalose/glycerol mixtures or any other mixtures of this nature. In the present study a dynamic mechanical analyzer (DMA) was used to determine both the Tg and the kinetic fragility index (m) of trehalose/glycerol mixtures within the mass fraction range of 80-100 wt % of trehalose. It was found that the fragility index correlated with the mass fraction of trehalose in a nonmonotonic manner, with a local minimum between 87.5 and 95 wt % of trehalose, whereas the composition dependence of Tg was found to follow a Gordon-Taylor-like relationship, with no local minimum. The composition of 5-12.5 wt % glycerol in trehalose thus yielded a matrix that maximized the strong glass-forming contribution of glycerol, while minimizing its Tg lowering effect. This quantitative evidence supports speculation about the fragility characteristics of these mixtures that has been ongoing for the past decade. The DMA-based Tg and fragility determination method developed in this study represents a new approach for identifying optimal compositions for preservation of biologics.
大约十年前，人们观察到，即使最终玻璃化转变温度（Tg）降低了约20 K，向海藻糖中添加少量（5 wt%）甘油也能显著提高储存在这些玻璃态中的酶的稳定性。这一发现引发了人们对脱水海藻糖/甘油混合物快速动力学的极大兴趣，进而观察到，在存在约5 wt%甘油的情况下，快速动力学的抑制效果最佳。人们还认识到，从理论上讲，快速动力学应该与这些玻璃形成剂的脆性有关，但对于海藻糖/甘油混合物或任何其他此类性质的混合物，这一假设一直缺乏实验证实。在本研究中，使用动态力学分析仪（DMA）来测定海藻糖质量分数范围为80 - 100 wt%的海藻糖/甘油混合物的Tg和动力学脆性指数（m）。结果发现，脆性指数与海藻糖的质量分数呈非单调关系，在海藻糖质量分数为87.5%至95 wt%之间存在局部最小值，而Tg的组成依赖性则遵循类似Gordon - Taylor的关系，没有局部最小值。因此，海藻糖中5 - 12.5 wt%的甘油组成产生了一种基质，既能使甘油的强玻璃形成贡献最大化，又能使其Tg降低效应最小化。这一量化证据支持了过去十年来对这些混合物脆性特征的推测。本研究中开发的基于DMA的Tg和脆性测定方法代表了一种确定用于生物制品保存的最佳组成的新方法。
