How two molecules self-assemble and what accelerates their assembly

Cram’s supramolecular capsule Octacid4 can irreversibly and noncovalently self-assemble with small- molecule guests at room temperature, but how they self-assemble and what accelerates their assembly are open questions that hold the key to developing noncovalent irreversible complexes. This article reports 72 distinct Octacid4•guest self-assembly pathways captured in unrestricted, unbiased, millisecond molecular dynamics simulations, revealing that the self-assembly process was initiated by the guest interaction with the cavity portal exterior of Octacid4 to increase the portal collisions that led to the portal expansion for guest ingress, accelerated by engaging populated host and guest conformations for the exterior interaction to increase the portal collision frequency, and completed by the portal contraction caused by the guest docking inside the cavity to impede guest egress. These revelations explain why the presence of a cryptic exterior binding site at the rim of the enzyme active site is a fundamental feature of fast enzymes such as acetylcholinesterase and why small molecules adopt local minimum conformations when binding to proteins. Furthermore, these revelations suggest that noncovalent irreversible complexes with fast assembly rates could be developed—by engaging populated host and guest conformations during the exterior interactions—for materials technology, data storage and processing, molecular sensing and tagging, and drug therapy.