Anomalous Behavior of Linear Hydrocarbon Chains in Water-DMSO Binary Mixture at Low DMSO Concentration
Anomalous Behavior of Linear Hydrocarbon Chains in Water-DMSO Binary Mixture at Low DMSO Concentration
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DOI：
10.1021/jp110549h
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发表时间：
2011-06-16
影响因子：
3.3
通讯作者：
Bagchi, Biman
中科院分区：
文献类型：
--
作者：
Ghosh, Rikhia;Banerjee, Saikat;Bagchi, Biman
我们发现，当DMSO的摩尔分数为0.05（x（DMSO）= 0.05）时，中间长度（n = 30-40）的线性烃链在水溶液中呈现最稳定的折叠构象。在纯水中，相同的链在折叠和延伸的卷曲构象之间表现出间歇性振荡。即使当本体中DMSO的摩尔分数为0.05时，在链长为30（n = 30）的烃周围的第一水合层中DMSO的浓度也高达17%。在烃链周围形成这样的疏水环境可以被视为塌陷构象获得额外稳定性的原因。我们发现第二个异常行为出现在x（DMSO）= 0.15附近，由于DMSO在水中的甲基基团的链状聚集，降低了水合层中DMSO分子的相对浓度。随着DMSO浓度的逐渐增加，它逐渐达到伸展的卷曲结构作为稳定构象。虽然Flory-Huggins理论（对于二元混合物溶剂）未能预测x（DMSO）= 0.05时的异常，但它似乎捕捉到了0.15时异常的本质。
We find that at a mole fraction 0.05 of DMSO (x(DMSO) = 0.05) in aqueous solution, a linear hydrocarbon chain of intermediate length (n = 30-40) adopts the most stable collapsed conformation. In pure water, the same chain exhibits an intermittent oscillation between the collapsed and the extended coiled conformations. Even when the mole fraction of DMSO in the bulk is 0.05, the concentration of the same in the first hydration layer around the hydrocarbon of chain length 30 (n = 30) is as large as 17%. Formation of such hydrophobic environment around the hydrocarbon chain may be viewed as the reason for the collapsed conformation gaining additional stability. We find a second anomalous behavior to emerge near x(DMSO) = 0.15, due to a chain-like aggregation of the methyl groups of DMSO in water that lowers the relative concentration of the DMSO molecules in the hydration layer. We further find that as the concentration of DMSO is gradually increased, it progressively attains the extended coiled structure as the stable conformation. Although Flory-Huggins theory (for binary mixture solvent) fails to predict the anomaly at x(DMSO) = 0.05, it seems to capture the essence of the anomaly at 0.15.