Department of Chemistry, The University of Western Ontario, London, Ontario, Canada N6A 5B7.
J Phys Chem B. 2011 Sep 8;115(35):10447-55. doi: 10.1021/jp204559y. Epub 2011 Aug 12.
Charged-induced conformational changes of sodiated poly(ethylene glycol) (PEG-(Na(+))(n)) in a vacuum and water droplets were studied using molecular simulations. In a vacuum, compact and partially unwound conformations were identified by analyzing occupation probabilities on reaction surfaces defined by the accessible surface area of the macroion, the distance between the centers of mass of the PEG molecule and of the cations and radius of gyration of the macromolecule. The critical charge of the macromolecule for which there is coexistence of various conformations was estimated using the Rayleigh criterion for the breakdown of highly charged droplets and compared with that observed in the simulations. The simulation findings agreed well with the Rayleigh prediction. The properties of sodiated PEG macromolecules in the presence of solvent and ions were also investigated. It was found that the macroion becomes saturated with charge. The highly charged state leads to an extended conformation that is partially expelled by the droplet. However, a portion of the chain is still in contact with the solvent. Drying-out of the solvent leaves the macroion in a stretched necklace-like conformation. The mechanism of release of sodiated PEG from an aqueous droplet was shown to be distinctly different from that of a protonated polyhistidine in a water nanodroplet, demonstrating sensitivity of the disintegration mechanism of the nanodroplet to the degree of hydrophilicity of the macroion.
采用分子模拟方法研究了在真空和液滴中钠离子诱导的聚乙二醇（PEG-（Na(+））（n））的构象变化。在真空中，通过分析可及表面积、PEG 分子和阳离子质心之间的距离以及大分子的回转半径定义的反应表面上的占据概率，确定了紧密和部分展开的构象。使用高度荷电液滴破裂的瑞利判据估计了大分子的临界电荷，该电荷存在各种构象共存，并将其与模拟中观察到的进行了比较。模拟结果与瑞利预测吻合良好。还研究了溶剂和离子存在下的聚乙二醇大分子的性质。结果发现，大分子带电荷达到饱和。高度荷电状态导致大分子伸展，部分被液滴排斥。然而，部分链仍与溶剂接触。溶剂干燥后，大分子呈伸展的项链状构象。从水液滴中释放出的聚乙二醇的机制明显不同于质子化聚组氨酸在水纳米液滴中的释放机制，表明纳米液滴的崩解机制对大分子亲水性的敏感程度。
