Wolnica K, Dulski M, Kaminska E, Cecotka A, Tarnacka M, Wrzalik R, Kaminski K, Paluch M
Silesian Center for Education and Interdisciplinary Research, 75 Pulku Piechoty 1a, 41-500 Chorzow, Poland.
Phys Chem Chem Phys. 2017 Aug 9;19(31):20949-20958. doi: 10.1039/c7cp02046e.
Comprehensive FTIR studies on the progress of mutarotation in d-fructose mixed with maltitol have been carried out over a wide range of temperatures, both above and below the glass transition temperature T. In addition to the analysis of single bands, we have developed a completely new approach considering the full spectral range to follow the overall progress of the reaction. We have found that at the calorimetric T, there is a clear change in the temperature dependence of constant rates. The activation barrier for mutarotation changes from around 59 kJ mol (the supercooled state) to around 249 kJ mol (the glassy state). This dramatic variation in the activation barrier is consistent with the change in the mechanism of this specific chemical conversion, as theoretically considered by Wlodarczyk et al. [Phys. Chem. Chem. Phys., 2014, 16, 4694-4698]. Alternatively, it can also be connected to the change in the viscosity of the sample. Additionally, we investigated the relationship between constant rates (k) of mutarotation, structural relaxation times (τ), and dc conductivity (σ) above and below the glass transition temperature. It was found that there was a linear correlation between all these quantities; they scale with various exponents changing at T. Our results also indicate that a single activation barrier might not be sufficient to describe the mutarotation process.
我们在高于和低于玻璃化转变温度(T)的很宽温度范围内，对与麦芽糖醇混合的(d -)果糖变旋过程进行了全面的傅里叶变换红外光谱（FTIR）研究。除了对单个谱带进行分析外，我们还开发了一种全新的方法，考虑整个光谱范围来跟踪反应的整体进程。我们发现，在量热(T)时，恒定速率的温度依赖性有明显变化。变旋的活化能垒从约(59 kJ/mol)（过冷状态）变为约(249 kJ/mol)（玻璃态）。这种活化能垒的显著变化与这种特定化学转化机制的变化一致，正如Wlodarczyk等人[《物理化学化学物理》，2014，16，4694 - 4698]从理论上所考虑的那样。或者，它也可以与样品粘度的变化联系起来。此外，我们研究了玻璃化转变温度上下变旋的恒定速率（(k)）、结构弛豫时间（(\tau)）和直流电导率（(\sigma)）之间的关系。结果发现，所有这些量之间存在线性相关性；它们以在(T)处变化的各种指数进行缩放。我们的结果还表明，单一的活化能垒可能不足以描述变旋过程。
