Sgarlata Carmelo, Mugridge Jeffrey S, Pluth Michael D, Zito Valeria, Arena Giuseppe, Raymond Kenneth N
Department of Chemistry, University of California, Berkeley and Chemical Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, 94720-1460, USA.
Istituto di Biostrutture e Bioimmagini, CNR, UOS Catania, Via P. Gaifami 18, 95125, Catania, Italy.
Chemistry. 2017 Nov 27;23(66):16813-16818. doi: 10.1002/chem.201703202. Epub 2017 Nov 8.
The supramolecular assembly [Ga L ] acts as a nanoscale flask to mediate the reactivity of encapsulated reactive guests and also functions as a catalyst to carry out enzyme-like chemical transformations. The guest binding to the interior cavity and exterior of this host is difficult to untangle because multiple equilibria occur in solution, and only when refining simultaneously data obtained from different techniques, such as NMR, UV/Vis, and calorimetry, can the accurate solution thermodynamics of these host-guest systems be determined. This study reports the driving forces for the inclusion and stepwise exterior guest binding of different aliphatic quaternary ammonium guests to the [Ga L ] assembly. Encapsulation into the host cavity was found to be an entropy-driven process, whereas exterior ion association is driven either by enthalpically favorable attractive forces or by the entropy gain due to desolvation, depending on guest size and character. The analysis of the energetics of reaction may help predicting and understanding the intimate role and contribution of the transition state in those rate-accelerated reactions involving this supramolecular assembly as an enzyme-like molecular flask.
超分子组装体[Ga L]充当纳米级烧瓶，介导被封装的活性客体的反应性，还作为催化剂进行类似酶的化学转化。由于溶液中会出现多个平衡，因此很难理清客体与该主体内部腔室和外部的结合情况，只有同时精炼从不同技术（如核磁共振、紫外可见光谱和量热法）获得的数据，才能确定这些主客体系统准确的溶液热力学。本研究报告了不同脂肪族季铵盐客体包合进入[Ga L]组装体以及逐步与外部客体结合的驱动力。发现包封进入主体腔室是一个熵驱动的过程，而外部离子缔合则取决于客体的大小和性质，要么由焓有利的吸引力驱动，要么由去溶剂化导致的熵增加驱动。对反应能量学的分析可能有助于预测和理解过渡态在那些涉及这种超分子组装体作为类似酶的分子烧瓶的速率加速反应中的密切作用和贡献。
