Solution-phase structural characterization of supramolecular assemblies by molecular diffraction.
Solution-phase structural characterization of supramolecular assemblies by molecular diffraction.
复制标题
通过分子衍射对超分子组装体进行溶液相结构表征。
DOI：
10.1021/ja0659065
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发表时间：
2007
影响因子：
15
通讯作者：
D. Tiede
中科院分区：
文献类型：
--
作者：
J. L. O’Donnell;X. Zuo;A. Goshe;L. Sarkisov;R. Snurr;J. Hupp;D. Tiede
基于铼配位化学的四个分子方阵的结构在溶液中得到了表征，采用对分布函数（PDF）分析，测量了大于1 A的空间分辨率的广角x射线散射。在本报告中，我们特别关注了吡嗪和联吡啶边缘正方形在溶液中测量的结构与使用x射线晶体学和基于几何优化和经典力场的分子动力学模拟的模型确定的这些分子在固态中的结构的比较。这些组合的广角散射主要由涉及一个或多个铼原子的对相关控制，在PDF图中，边缘和对角线Re-Re相互作用都很突出。吡嗪方在溶液中具有相对刚性的结构，其PDF峰的位置和线宽与晶体结构数据的计算结果非常接近。对于联吡啶边的正方形，沿着分子边测量的实验PDF峰与静态模型计算的PDF峰的位置和线宽相匹配。相反，在分子方的对角线距离上测量到的PDF峰明显偏离从静态晶体学和能量最小化模型计算得到的峰。相反，实验数据表明对角线距离的构型展宽。在这方面，分子动力学模拟指出了蝴蝶型运动调节Re-Re对角线距离的重要性。事实上，通过假设蝴蝶形状的双峰分布在Re-Re-Re-Re - re扭转角上相差约25度，实验数据可以很好地拟合。此外，测量结果还提供了溶剂排序的证据，通过超分子组装检测到溶剂缔合和排斥区域。
Structures of four molecular squares based on rhenium coordination chemistry have been characterized in the solution phase using pair distribution function (PDF) analyses of wide-angle X-ray scattering measured to better than 1 A spatial resolution. In this report we have focused, in particular, on a comparison of structures for pyrazine- and bipyridine-edged squares measured in solution with structures determined for these molecules in the solid state using X-ray crystallography and models derived from geometry optimization and molecular dynamics simulations using a classical force field. The wide-angle scattering for these assemblies is dominated by pair correlations involving one or more rhenium atoms, with both edge and diagonal Re-Re interactions appearing prominently in PDF plots. The pyrazine square is characterized by a relatively rigid structure in solution, with PDF peak positions and linewidths corresponding closely to those calculated from crystal structure data. For the bipyridine-edged square, the experimental PDF peaks measured along the molecular sides match the positions and linewidths of the PDF peaks calculated from static models. In contrast, PDF peaks measured across the diagonal distances of the molecular square deviate significantly from those calculated from the static crystallographic and energy minimized models. The experimental data are instead indicative of configurational broadening of the diagonal distances. In this respect, molecular dynamics simulations point to the importance of butterfly type motions that modulate the Re-Re diagonal distance. Indeed, the experimental data are reasonably well fit by assuming a bimodal distribution of butterfly conformers differing by approximately 25 degrees in the Re-Re-Re-Re torsion angle. Additionally, the measurements provide evidence for solvent ordering by the supramolecular assemblies detected as regions of solvent association and exclusion.