A revision (C35r) to the CHARMM ether force field is shown to reproduce experimentally observed conformational populations of dimethoxyethane. Molecular dynamics simulations of 9, 18, 27, and 36-mers of polyethylene oxide (PEO) and 27-mers of polyethylene glycol (PEG) in water based on C35r yield a persistence length lambda = 3.7 A, in quantitative agreement with experimentally obtained values of 3.7 A for PEO and 3.8 A for PEG; agreement with experimental values for hydrodynamic radii of comparably sized PEG is also excellent. The exponent upsilon relating the radius of gyration and molecular weight (R(g) proportional, variantM(w)(upsilon)) of PEO from the simulations equals 0.515 +/- 0.023, consistent with experimental observations that low molecular weight PEG behaves as an ideal chain. The shape anisotropy of hydrated PEO is 2.59:1.44:1.00. The dimension of the middle length for each of the polymers nearly equals the hydrodynamic radius R(h)obtained from diffusion measurements in solution. This explains the correspondence of R(h) and R(p), the pore radius of membrane channels: a polymer such as PEG diffuses with its long axis parallel to the membrane channel, and passes through the channel without substantial distortion.

译文

对CHARMM醚力场的修订 (C35r) 显示为重现实验观察到的二甲氧基乙烷构象种群。基于C35r的水中9、18、27和36聚环氧乙烷 (PEO) 和27聚乙二醇 (PEG) 的分子动力学模拟产生的持续长度 λ = 3.7 a,与实验获得的PEO的3.7 A和PEG的3.8 A的数值定量一致; 与相当大小的PEG的流体动力半径的实验值的一致性也很好。来自模拟的PEO的旋转半径和分子量 (R(g) 比例,变量m (w)(upsilon)) 相关的指数upsilon等于0.515/- 0.023,与低分子量PEG表现为理想链的实验观察结果一致。水合PEO的形状各向异性为2.59:1.44:1.00。每种聚合物的中间长度尺寸几乎等于从溶液中的扩散测量获得的流体动力半径R(h)。这解释了R(h) 和R(p) 的对应关系,即膜通道的孔半径: 诸如PEG之类的聚合物以其长轴平行于膜通道的方式扩散,并通过该通道而不会产生实质性变形。

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