Gating in host-guest chemistry refers to conformational changes that occur in response to some stimulus, resulting in opening
or closing of a physical barrier that controls access to the host. Gating due to conformational changes of protein loops is common in enzyme
catalysts: the binding of a substrate in an enzyme often involves the closing of a protein loop to bind the substrate, a type of gating
. Cram’s pioneering work in host-guest chemistry led to the discovery of one molecule inside another and the concept of container
molecules. Cram’s nanometer-scaled container molecules were found by our group to involve gating to allow passage of guest molecules
into or out of the container host . The gating process in container molecules provides a novel way that binding and release of guest
molecules can be controlled, and this has potential applications in controlled drug delivery.