Pluth Michael D, Bergman Robert G, Raymond Kenneth N
Department of Chemistry, University of California, Berkeley, California 94720, and Chemistry Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
J Am Chem Soc. 2008 May 21;130(20):6362-6. doi: 10.1021/ja076691h. Epub 2008 Apr 29.
Amine nitrogen inversion, difficult to observe in aqueous solution, is followed in a chiral, supramolecular host molecule with purely rotational T-symmetry that reduces the local symmetry of encapsulated monoprotonated diamines and enables the observation and quantification of Delta G (++) for the combined hydrogen-bond breaking and nitrogen inversion/rotation (NIR) process. Free energies of activation for the combined hydrogen-bond breaking and NIR process inside of the chiral assembly were determined by the NMR coalescence method. Activation parameters for ejection of the protonated amines from the assembly confirm that the NIR process responsible for the coalescence behavior occurs inside of the assembly rather than by a guest ejection/NIR/re-encapsulation mechanism. For one of the diamines, N, N, N', N'-tetramethylethylenediamine, the relative energy barriers for the hydrogen-bond breaking and NIR process were calculated at the G3(MP2)//B3LYP/6-31++G(d,p) level of theory, and these agreed well with the experimental data.
胺氮翻转在水溶液中难以观察到，在手性超分子主体分子中可以追踪到，该主体分子具有纯旋转T对称性，降低了被包封的单质子化二胺的局部对称性，并能够观察和量化氢键断裂与氮翻转/旋转（NIR）联合过程的ΔG（++）。手性组装体内氢键断裂与NIR联合过程的活化自由能通过NMR合并方法测定。从组装体中排出质子化胺的活化参数证实，导致合并行为的NIR过程发生在组装体内，而不是通过客体排出/NIR/重新包封机制。对于其中一种二胺N，N，N'，N'-四甲基乙二胺，在G3（MP2）//B3LYP/6-31++G（d，p）理论水平上计算了氢键断裂和NIR过程的相对能垒，这些结果与实验数据吻合良好。
Zotero 插件