School of Molecular Sciences , University of Western Australia , 35 Stirling Highway , Crawley , WA 6009 , Australia.
Center for Materials Crystallography and Department of Chemistry , Aarhus University , Langelandsgade 140 , DK-8000 Aarhus C , Denmark.
J Am Chem Soc. 2019 Mar 6;141(9):3965-3976. doi: 10.1021/jacs.8b12927. Epub 2019 Feb 21.
High-resolution synchrotron and neutron single-crystal diffraction data of 18-crown-6/(pentakis)urea measured at 30 K are combined, with the aim of better appreciating the electrostatics associated with intermolecular interactions in condensed matter. With two 18-crown-6 molecules and five different urea molecules in the crystal, this represents the most ambitious combined X-ray/synchrotron and neutron experimental charge density analysis to date on a cocrystal or host-guest system incorporating such a large number of unique molecules. The dipole moments of the five urea guest molecules in the crystal are enhanced considerably compared to values determined for isolated molecules, and 2D maps of the electrostatic potential and electric field show clearly how the urea molecules are oriented with dipole moments aligned along the electric field exerted by their molecular neighbors. Experimental electric fields in the range of 10-19 GV m, obtained for the five different urea environments, corroborate independent measurements of electric fields in the active sites of enzymes and provide an important experimental reference point for recent discussions focused on electric-field-assisted catalysis.
将在 30 K 下测量的 18-冠-6/(五聚)脲的高分辨率同步加速器和中子单晶衍射数据进行组合，目的是更好地了解凝聚态物质中分子间相互作用相关的静电。在晶体中，有两个 18-冠-6 分子和五个不同的脲分子，这是迄今为止在包含如此多独特分子的主客体体系的同晶或包合物上进行的最具野心的 X 射线/同步加速器和中子实验电荷密度分析。与孤立分子相比，晶体中五个脲客体分子的偶极矩大大增强，静电势和电场的二维图清楚地显示了脲分子的取向，其偶极矩沿分子相邻体施加的电场排列。在五个不同的脲环境中获得的范围在 10-19 GV m 的实验电场与酶活性部位的电场的独立测量结果相符，并为最近集中讨论电场辅助催化的研究提供了一个重要的实验参考点。
