Moura Ramos Joaquim J, Pinto Susana S, Diogo Hermínio P
Centro de Química-Física Molecular, Complexo I, IST, Av. Rovisco Pais, 1049-001, Lisbon, Portugal.
Pharm Res. 2005 Jul;22(7):1142-8. doi: 10.1007/s11095-005-5645-1. Epub 2005 Jul 22.
The aims of the study are to characterize the slow molecular mobility in solid raffinose in the crystalline pentahydrate form, as well as in the anhydrous amorphous form (Tg = 109 degrees C at 5 degrees C/min), and to analyze the differences and the similarities of the molecular motions in both forms.
Thermally stimulated depolarization current (TSDC) is used to isolate the individual modes of motion present in raffinose, in the temperature range between -165 and +60 degrees C. From the experimental output of the TSDC experiments, the kinetic parameters associated with the different relaxational modes of motion were obtained, which allowed a detailed characterization of the distribution of relaxation times of the complex relaxations observed in raffinose. The features of the glass transition relaxation in raffinose were characterized by differential scanning calorimetry (DSC).
A complex mobility was found in the crystalline form of raffinose. From the analysis of the TSDC data, we conclude that these molecular motions are local and noncooperative. A sub-Tg relaxation, or secondary process, was also detected and analyzed by TSDC in the amorphous phase. It has low activation energy and low degree of cooperativity. The glass transition was studied by DSC. The fragility index (Angell's scale) of raffinose obtained from DSC data is m = 148.
TSDC proved to be an adequate technique to study the molecular mobility in the crystalline pentahydrate form of raffinose. In the amorphous form, on the other hand, the secondary relaxation was analyzed by TSDC, but the study of the glass transition relaxation was not possible by this experimental technique as a consequence of conductivity problems. The DSC study of the glass transition indicates that raffinose is an extremely fragile glass former.
本研究的目的是表征结晶五水合物形式以及无水无定形形式（在5℃/分钟时玻璃化转变温度Tg = 109℃）的固体棉子糖中的缓慢分子迁移率，并分析两种形式中分子运动的差异和相似性。
使用热刺激去极化电流（TSDC）来分离棉子糖中存在的各个运动模式，温度范围为-165至+60℃。从TSDC实验的实验输出中，获得了与不同弛豫运动模式相关的动力学参数，这使得能够详细表征棉子糖中观察到的复杂弛豫的弛豫时间分布。通过差示扫描量热法（DSC）表征棉子糖中玻璃化转变弛豫的特征。
在棉子糖的结晶形式中发现了复杂的迁移率。通过对TSDC数据的分析，我们得出结论，这些分子运动是局部的且非协同的。TSDC还在非晶相中检测并分析了亚玻璃化转变弛豫或二级过程。它具有低活化能和低协同度。通过DSC研究了玻璃化转变。从DSC数据获得的棉子糖的脆性指数（安吉尔标度）为m = 148。
TSDC被证明是研究结晶五水合物形式棉子糖中分子迁移率的合适技术。另一方面，在无定形形式中，通过TSDC分析了二级弛豫，但由于导电性问题，无法通过该实验技术研究玻璃化转变弛豫。玻璃化转变的DSC研究表明棉子糖是一种极其脆弱的玻璃形成体。
