Department of Chemistry, Indian Institute of Technology , Guwahati, Assam, India -781039.
J Phys Chem B. 2014 Jan 30;118(4):1052-63. doi: 10.1021/jp407782x. Epub 2014 Jan 21.
We have carried out molecular dynamics simulation to investigate the role of trehalose molecules on the change in the structural and dynamical properties of aqueous N-methylacetamide (NMA) solution. In this study, we considered six different trehalose concentrations ranging from 0 to 66%. Results are discussed in the framework of hydrophobic interactions between different methyl groups of NMA, structure of the solutions, and hydrogen bonding interactions between different solution species. We observe that the propensity of hydrophobic association through the methyl groups of NMA is essentially insensitive to trehalose concentration except for higher trehalose concentration where the hydrophobic interactions between the hydrophobic methyl groups are getting reduced. Also observed are (i) trehalose induced slight collapse of the second hydration shell of water, (ii) presence of excess water molecules near NMA, and (iii) exclusion of trehalose from NMA. Our NMA-water radial distribution function analyses followed by average number of hydrogen bonds per NMA calculations reveal that, in the hydration of NMA molecules, its carbonyl group oxygen (over amide hydrogen) is predominantly involved. As trehalose is added, we observe, in accordance with the water replacement hypothesis, the replacement of water-NMA hydrogen bonds by NMA-trehalose hydrogen bonds, keeping the average number of hydrogen bonds formed by a single NMA with different solution species essentially unchanged. Our hydrogen bond calculations further reveal that addition of trehalose replaces water-NMA hydrogen bonds by water-trehalose hydrogen bonds. And as a result, we find that the average number of hydrogen bonds formed by a water molecule remain unchanged. We also find that addition of trehalose decreases the translational motion of all the solution species sharply.
我们进行了分子动力学模拟，以研究海藻糖分子在改变含水 N-甲基乙酰胺（NMA）溶液的结构和动力学性质中的作用。在这项研究中，我们考虑了六种不同的海藻糖浓度，范围从 0 到 66%。结果是在 NMA 不同甲基之间的疏水相互作用、溶液结构以及不同溶液物种之间的氢键相互作用的框架内讨论的。我们观察到，NMA 中不同甲基之间的疏水性缔合的趋势基本上对海藻糖浓度不敏感，除了较高的海藻糖浓度外，其中疏水甲基之间的疏水相互作用减少。还观察到（i）海藻糖引起水的第二水合壳的轻微塌陷，（ii）NMA 附近存在过量的水分子，以及（iii）海藻糖从 NMA 中排除。我们对 NMA-水的径向分布函数分析以及每个 NMA 的平均氢键数的计算表明，在 NMA 分子的水合作用中，其羰基氧（超过酰胺氢）主要参与。随着海藻糖的加入，我们观察到，根据水置换假说，水-NMA 氢键被 NMA-海藻糖氢键取代，保持单个 NMA 与不同溶液物种形成的氢键的平均数量基本不变。我们的氢键计算进一步表明，海藻糖的加入通过水-海藻糖氢键取代水-NMA 氢键。结果，我们发现水分子形成的氢键的平均数量保持不变。我们还发现，海藻糖的加入使所有溶液物种的平动运动急剧下降。
