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Theory of gated hemicarcerands and Diels-Alder reactions of tetrazines


The concept of gating was introduced into host-guest chemistry by our group in the 1990s, as a result of computational studies on Cram's hemicarcerands. Since that time, a variety of gated host systems have been developed by our group and others. The gated hemicarcerands presented in this dissertation are examples of hosts with controllable gates that function upon external stimuli, which we refer to as redox reaction gated hemicarcerands and photochemically gated hemicarcerands. In both cases, a chemically modifiable moiety was installed on the host molecule so that it undergoes chemical change in response to external stimuli. In particular, we took advantage of disulfide-dithiol interchange (redox reaction control) and anthracene dimerization (photochemical control) to achieve gating in these hemicarcerands. Molecular mechanics computations were employed to understand the experimental observations during the complexation and decomplexation processes.

The second part of this dissertation focuses on understanding Diels-Alder reactivities of a wide range of organic molecules with the tools of computational chemistry. Among these extensively studied molecules, tetrazine is the most outstanding one, in the sense that its cycloaddition reactions with strained alkenes are extremely rapid, with second order rate constants up to 2000 M-1s-1. Such reactions take place at a decent rate even at micromolar concentration, suggesting their application in live cell imaging. The emerging use of tetrazines as labeling reagents has added an extra dimension to bioorthogonal cycloadditions. Our computational studies have provided a thorough understanding of the cycloaddition reactivities and a guideline for developing new reagents.

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