Quaternary 2:2 Complexes as Kinetic Intermediates: Unveiling an Overlooked Pathway in Cucurbit[8]uril-Mediated Assembly
Image credit: CCS摘要
Molecular assembly is typically viewed as a stepwise process from lower- to higher-order structures. Here, we uncovered an alternative kinetic pathway in the cucurbit[8]uril (CB[8])-mediated assembly, where a transient quaternary (2:2) complex formed before the thermodynamically favored ternary (2:1) product. Stopped-flow spectroscopy and structural analysis confirmed the 2:2 intermediate, which formed 36-fold faster than the direct 1:1 → 2:1 pathway at 298 K. The system thus accumulated in the 2:2 state before relaxing to the 2:1 product. These findings revise the conventional binary-to-ternary model and highlight the mechanistic relevance of higher-order intermediates. It also refines our understanding of apparent cooperativity within a complex assembly network. Recognizing such kinetic complexity opens new avenues for dynamic control in the design of high-performance functional and structural materials.
