Plasticization, antiplasticization, and molecular packing in amorphous carbohydrate-glycerol matrices.
Plasticization, antiplasticization, and molecular packing in amorphous carbohydrate-glycerol matrices.
复制标题
无定形碳水化合物-甘油基质中的增塑、反增塑和分子堆积。
作者：
M. Roussenova;M. Murith;A. Alam;J. Ubbink
正电子湮没寿命谱（帕尔斯）结合热力学测量和分子量测量，系统地探讨了无定形麦芽糊精-甘油基质的分子堆积。在T = 25 °C下，在0和0.54之间的水活度范围内平衡麦芽糊精-甘油基质，以分析水和甘油两者对基质的平均分子孔尺寸和比容的影响。在玻璃态下，甘油导致平均分子孔尺寸的系统性减小。相反，水以复杂的方式与碳水化合物基质相互作用。热力学聚类理论表明，在很低的水含量的水分子分散良好，并与碳水化合物链密切相关。在这种情况下，水作为抗增塑剂，从而减少了分子孔的大小。相反，在较高的水含量下，当仍处于玻璃态时，水通过增加碳水化合物基质的平均孔体积而充当增塑剂。这种增塑主导的机制可能是由于水与碳水化合物链上的羟基残基形成氢键的能力及其流动性之间的相互作用，这与基质的整体流动性显著脱钩。我们的研究结果是至关重要的甘油对这些碳水化合物基质的生物稳定性能的影响的理解，因为它提供了第一个洞察如何分子包装可以在这样的矩阵中的动态。
The molecular packing of amorphous maltodextrin-glycerol matrices is systematically explored by combining positron annihilation lifetime spectroscopy (PALS) with thermodynamic measurements and dilatometry. Maltodextrin-glycerol matrices are equilibrated at a range of water activities between 0 and 0.54 at T = 25 °C to analyze the effect of both water and glycerol on the average molecular hole size and the specific volume of the matrices. In the glassy state, glycerol results in a systematic reduction of the average molecular hole size. In contrast, water interacts with the carbohydrate matrix in a complex way. Thermodynamic clustering theory shows that, at very low water contents the water molecules are well dispersed and are closely associated with the carbohydrate chains. In this regime water acts as an antiplasticizer, whereby it reduces the size of the molecular holes. Conversely, at higher water contents, while still in the glassy state, water acts as a plasticizer by increasing the average hole volume of the carbohydrate matrices. This plasticization-dominated mechanism is likely to be due to the interplay between the ability of water to form hydrogen bonds with the hydroxyl residues on the carbohydrate chains and its mobility, which is significantly decoupled from the bulk mobility of the matrix. Our findings are of key importance for the understanding of the effect of glycerol on the biostabilization performance of these carbohydrate matrices, as it provides a first insight on how molecular packing can relate to the dynamics in such matrices.