Aman Ken, Håkansson Pär, Westlund Per-Olof
Department of Chemistry, Biophysical Chemistry, Umeå University, S-901 87 Umeå, Sweden.
Phys Chem Chem Phys. 2005 Apr 7;7(7):1394-401. doi: 10.1039/b417157h.
A new computational method is developed for calculating 2H NMR lineshapes of H2O in microheterogeneous systems, such as lyotropic liquid crystals that exhibit curved lipid/water interfaces. The method presented is based on the stochastic Liouville equation (SLE) in its Langevin form. This means that the Liouville equation of motion is combined with Brownian dynamics simulations to describe the stochastic spin-lattice Liouvillian. The NMR relaxation is caused by translational diffusion of the heavy water molecules, along the curved 2H2O/lipid interface. The model used is a nodal surface approximation of the cubic symmetric gyroid minimal surface. This unit cell is then isotropically expanded or distorted in two dimension. The changes in 2H20 NMR lineshapes have been calculated for the enlarged or the distorted cubic unit cell. The timescale of the residual quadrupole interaction, which determines the NMR lineshape, ranges from the Redfield regime to the slow-motional regime depending on the curvature of the interface. The distortion of the cubic phase illustrates the possibility to explore the intermediate interfaces of a phase transition, by means of 2H2O lineshape analysis.
开发了一种新的计算方法，用于计算微非均相体系中H₂O的²H NMR线形，例如呈现弯曲脂质/水界面的溶致液晶。所提出的方法基于朗之万形式的随机刘维尔方程（SLE）。这意味着运动的刘维尔方程与布朗动力学模拟相结合，以描述随机自旋 - 晶格刘维尔算符。NMR弛豫是由重水分子沿弯曲的²H₂O/脂质界面的平移扩散引起的。所使用的模型是立方对称螺旋最小表面的节点表面近似。然后该晶胞在二维上进行各向同性扩展或变形。已针对扩大或变形的立方晶胞计算了²H₂O NMR线形的变化。决定NMR线形的剩余四极相互作用的时间尺度，根据界面的曲率，范围从雷德菲尔德区域到慢运动区域。立方相的变形说明了通过²H₂O线形分析探索相变中间界面的可能性。
