The motions of biomolecular machines are usually multistep processes, and are involved in a series of conformational changes. In this paper, a novel triply interlocked [2](3)catenane composed of a tris(crown ether) host eTC and a circular ditopic guest with three dibenzyl ammonium (DBA) sites and three N-methyltriazolium (MTA) sites was reported. Due to the multivalency nature of the catenane, the acid-base triggered motion was performed by a stepwise manner. The coconformations of the four related stable states have been directly identified and quantified which confirmed the multistep process. In order to quantify the dynamics with environmental acidity changes, the values of the three levels of dissociation constant pKa have been determined. The special interlocked topology of the [2](3)catenane also endows the motion of each crown ether ring in the host with unexpected selectivity for the MTA sites. This study provides clues to comprehend the underlying motion mechanism of intricate biological molecular machines, and further design artificial molecular machine with excellent mechanochemistry properties.
The hydrogenation of carbon dioxide into value-added chemicals is of great importance for CO 2 recycling. However, the underlying mechanism of CO 2 hydrogenation remains elusive owing to the lack of experimental evidence for the formation of the C−H bond. Herein, the gas-phase reaction of copper hydride anion Cu 2 H 2 − with CO 2 at variable temperatures (∼300−560 K) was investigated. Metal hydrides are the ideal models to study the nature of C−H bond formation in CO 2 hydrogenation, while the related studies are scarcely reported, particularly for the hydrogenation reactions at temperatures above 300 K. The generation of formate (HCO 2 − ) attached on product CuH 2 CO 2 − was identified by temperature-dependent mass spectrometric experiments and density functional theory calculations. Temperature played crucial roles to fine-tune the product selectivity, from Cu 2 H 2 CO 2 − that dominates the room-temperature reaction into CuH 2 CO 2 − at elevated temperatures. The nature behind the temperature-dependent product selectivity and the mechanism of CO 2 hydrogenation has been interpreted by using theoretical calculations. The combined experimental and computational studies have provided solid evidence for the formation of formate attached in CuH 2 CO 2 − .
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