分子动力学模拟水分对小分子糖玻璃态转变温度及扩散性质的影响

Effect of Moisture Content on Glass Transition Temperature and Diffusion Properties of Low-molecular-weight Sugars by Molecular Dynamics Simulation

为了预测水分对蔗糖、海藻糖等小分子糖玻璃态温度和扩散系数的影响,在恒温恒压（NPT）系综和COMPASS力场条件下,利用分子动力学模拟方法,通过模拟小分子糖体系在180~460 K温度范围内的比体积,与对应的温度作图,获得不同水分含量下小分子糖的玻璃态转变温度;在298 K下,模拟得到在不同水分含量下糖体系中水分子的均方位移（MSD）,分析了水分对小分子糖扩散性质的影响;同时研究了温度为298 K,水分含量为5.0%时,小分子糖体系中氧原子与水中氧原子之间的径向分布函数。研究结果表明：在相同水分含量下,海藻糖的玻璃态转变温度大于蔗糖,海藻糖与水分子形成氢键的能力要大于蔗糖;随着水分含量的增加,两种糖模型的Tg都呈现显著下降趋势,水分子更容易在糖模型中扩散,与糖分子发生相互作用的概率增大。

In this study, the effect of different moisture contents on glass transition temperature （Tg） and diffusion properties of low-molecular-weight sugars （such as sucrose and trehalose） were evaluated, using the COMPASS force field and isothermal-isobaric （NPT） ensemble. Molecular dynamics simulation was used to obtain the glass transition temperatures of sugars by simulating a plot of the specific volume of low-molecular-weight sugar in a temperature range of 180 K to 460 K versus the corresponding temperature. At 298 K, the mean square displacement （MSD） of water molecules in the sugar systems with varying moisture content was simulated, and the effect of moisture content on the diffusion properties was analyzed. In addition, when the temperature was 298K and the moisture content was 5%, the radial distribution function （RDF） of oxygen atoms in water and in the low-molecular-weight sugar system was studied. The results indicated that the value of Tg and the ability to form hydrogen bonds with water molecules were higher for trehalose than for sucrose at the same moisture content. With increasing moisture content, the value of Tg in the two sugar models showed a significant downward trend, water molecules more easily diffused into the sugar systems, and the chance to interact with sugar molecules increased.