Chaperone-like chiral cages for catalyzing enantio-selective supramolecular polymerization

Yu Wang,Pixian Peng,Matthew M Sartin,Pei Zhang,Zhongqun Tian,Xujing Lin,Xiaoyu Cao,Hongxun Fang,Yibin Sun,Peichen Shi

doi:10.1039/c9sc02412c

Abstract

Cage catalysis has emerged as an important approach for mimicking enzymatic reactions by increasing the reaction rate and/or product selectivity of various types of covalent reactions. Here, we extend the catalytic application of cage compounds to the field of non-covalent molecular assembly. Acid-stable chiral imine cages are found to catalyze the supramolecular polymerization of porphyrins with an accelerated assembling rate and increased product enantioselectivity. Because the imine cages have a stronger interaction with porphyrin monomers and a weaker interaction with porphyrin assemblies, they can fully automatically detach from the assembled products without being consumed during the catalytic process. We reveal the kinetics of the auto-detachment of cages and the chirality growth of the assemblies using spectroscopic characterization studies. We find that the passivation groups attached to the cages are important for maintaining the structural stability of the cages during catalyzed assembly, and that the steric geometries of the cages can profoundly affect the efficiency of chiral regulation. This strategy demonstrates a new type of catalytic application of cage compounds in the field of molecular assembly, and paves the way to controlling supramolecular polymerization through a catalytic pathway.

Highlights

Circular dichroism (CD) and UV-vis spectroscopy were used to show the catalytic behavior of CAAA-1 for regulating the enantioselective supramolecular polymerization of TPPS
A er 48 hours, the formation of chiral TPPS H-assemblies was indicated by the strong excitoncoupled CD peaks at 400 nm and 453 nm and the corresponding UV-vis absorption peak at 419 nm (Fig. 2A and B)
Chiral imine cages regulate the chirality of TPPS assemblies and serve as spectroscopic probes to allow monitoring of the assembly and self-detachment kinetics

Summary

Introduction

Either inside[36,37,38] or outside[39] the cage cavities All these strategies are designed to realize the essential feature of cage catalysis: cages co-assemble with the reactants, and automatically release the resulting products a er facilitating the reactions. This could lead to the automatic release of products from the cages a er the enantioselective polymerization of TPPS (Fig. 1D). Comparison experiments with several cages and small molecules, we demonstrate that the passivation groups attached to the cages are important for maintaining the structural integrity of the cages during catalyzed assembly, and that their steric geometry can profoundly impact the chiral transfer between cages and assemblies

Molecular structures and schematic procedures of catalyzed assembly

Spectroscopic characterization of chiral supramolecular polymerization

Recovery of the cage catalyst

Acid stability of the truxene–CHDA imine cage

Structural sensitivity to chiral transfer

Conclusion