Wolnica K, Dulski M, Kaminska E, Tarnacka M, Wrzalik R, Śmiszek-Lindert W E, Kaminski K, Paluch M
Silesian Center for Education and Interdisciplinary Research, 75 Pulku Piechoty 1a, 41-500, Chorzow, Poland.
A. Chelkowski Institute of Physics, University of Silesia, 75 Pulku Piechoty 1, 41-500, Chorzow, Poland.
Sci Rep. 2018 Mar 28;8(1):5312. doi: 10.1038/s41598-018-23117-8.
Intra- and intermolecular studies on the molten L-sorbose have been carried out at variable temperature conditions to determine the crosover temperature (T ). In addition, isothermal time-dependent FTIR and Raman measurements were performed to probe the pace of mutarotation and activation energy of this reaction in the studied saccharide, which varied from 53-62 kJ/mol up to 177-192 kJ/mol below and above T , respectively. To explain the change in activation barrier for the mutarotation a complementary analysis using difference FTIR spectra collected around T = 365 K in the hydroxyl region has been done. It was found that the alteration of kinetic parameters and molecular dynamics around T are strictly related to the variation in the strength of H-bonds which above T are significantly weaken, increasing the freedom of rotation of functional groups and movement of individual molecules. That phenomenon most likely affects the proton transfer, underlying molecular mechanism of mutarotation, which may lead to the significant increase in activation barrier. The new insight into a molecular aspect of the mutarotation around T has created an opportunity to better understanding the relationship between physics of condensed matter and the potential role of H-bonds dynamics on the progress of the chemical reaction in highly viscous systems.
在可变温度条件下对熔融L-山梨糖进行了分子内和分子间研究，以确定交叉温度（T ）。此外，还进行了等温时间相关的傅里叶变换红外光谱（FTIR）和拉曼测量，以探究所研究糖类中变旋反应的速率以及该反应的活化能，在T 以下和以上时，活化能分别在53 - 62 kJ/mol至177 - 192 kJ/mol范围内变化。为了解释变旋反应活化能垒的变化，已使用在365 K附近羟基区域收集的差示FTIR光谱进行了补充分析。结果发现，T 附近动力学参数和分子动力学的变化与氢键强度的变化密切相关，在T 以上氢键显著减弱，增加了官能团的旋转自由度和单个分子的移动。这种现象很可能影响质子转移，而质子转移是变旋反应的潜在分子机制，这可能导致活化能垒显著增加。对T 附近变旋反应分子层面的新认识为更好地理解凝聚态物质物理学与氢键动力学在高粘性系统化学反应进程中的潜在作用之间的关系创造了机会。
