UC Riverside

Self-assembled cages are produced via self-assembly using metal ligand subcomponents that form a variety of polyhedral species that are capable of mimicking enzymatic catalysis and substrate recognition. A spacious Fe4L6 tetrahedral cage acts as a catalytic inhibitor in base-mediated reactions. By introducing 5 % of this Fe4L6 cage complex the conjugate addition between ethyl cyanoacetate and β-nitrostyrene, catalyzed by proton sponge, is significantly reduced from 83 % to less than 1 % under identical conditions. The catalytic inhibition mechanism is unique and unusual: the octacationic Fe4L6 cage enhances the acidity of exogenous water in acetonitrile by favorably binding the conjugate acid of the basic catalyst which ultimately moderates its basicity. This inhibition only occurs with the Fe4L6 host possessing a spacious cavity. Smaller tetrahedra or Fe2L3 helicates exhibit minimal inhibition.

The same spacious M4L6 tetrahedral cage catalyzes the oxidative dimerization of alkanethiols via favorable coencapsulation of two molecules of thiol and a redox active metallic cofactor. The host supplies its own metallic cofactor from partial disassembly of the cage structure, depositing Fe(II) into solution. Remarkably, the host enables size-selective oxidation and can discriminate between alkanethiols of identical reactivity based solely on their sizes via selective molecular recognition.A series of Zn4L4 self-assembled cages with functional groups appended to their exterior were synthesized. The unfunctionalized analogues possess freely rotating aryl groups in the ligand, while the introduction of inert functional groups acts as a "doorstop," preventing rotation and slowing down guest exchange rates. The cages have identical charges and cavities, and the anion exchange process is regulated by multiple factors, including anion size, anion leaving group, and the electronic and steric nature of the pendant groups. The external groups regulate associative and dissociative exchange mechanisms which contribute to anion selectivity and exchange rates. Slight changes to the cage’s molecular architecture can vary binding affinities for similar anions like PF6- and SbF6- by up to 400-fold in identically sized cavities. Lastly, this work concludes with a brief discussion on larger functionalized ligands that can form spacious M4L4 cages. These cages can internally orient functional groups, potentially serving as biomimetic catalysts.