Absolute configuration and host-guest binding of chiral porphyrin-cages by a combined chiroptical and theoretical approach

Jiangkun Ouyang,Paula C P Teeuwen,Marc Geerts,Jean-Valère Naubron,Johannes A A W Elemans,Nicolas Vanthuyne,Sara Chentouf,Roeland J M Nolte,Pieter J Gilissen,Danni Wang,Jeanne Crassous,Paul Tinnemans,Floris P J T Rutjes,Anne Swartjes

doi:10.1038/s41467-020-18596-1

Abstract

Porphyrin cage-compounds are used as biomimetic models and substrate-selective catalysts in supramolecular chemistry. In this work we present the resolution of planar-chiral porphyrin cages and the determination of their absolute configuration by vibrational circular dichroism in combination with density functional theory calculations. The chiral porphyrin-cages form complexes with achiral and chiral viologen-guests and upon binding one of the axial enantiomorphs of the guest is bound selectively, as is indicated by induced-electronic-dichroism-spectra in combination with calculations. This host-guest binding also leads to unusual enhanced vibrational circular dichroism, which is the result of a combination of phenomena, such as rigidification of the host and guest structures, charge transfer, and coupling of specific vibration modes of the host and guest. The results offer insights in how the porphyrin cage-compounds may be used to construct a future molecular Turing machine that can write chiral information onto polymer chains.

Highlights

Porphyrin cage-compounds are used as biomimetic models and substrate-selective catalysts in supramolecular chemistry
We present induced circular dichroism (ICD) experiments showing that the chiral porphyrin cage molecules display enantioselectivity in the binding of both achiral and chiral N,Nsubstituted 4,4′-bipyridinium guest molecules and that on binding one of the interconverting axial enantiomorphs of the guest is preferred
The experimental IR and vibrational circular dichroism (VCD) spectra of (−)−1 and (+)−1 were recorded in the region from 1825 to 1025 cm−1 ((−) stands for the first eluted fraction showing a negative sign in the Circular dichroism (CD) spectrum at 254 nm and (+) for the second eluted fraction showing a positive sign in the CD spectrum at 254 nm)

Summary

Introduction

Porphyrin cage-compounds are used as biomimetic models and substrate-selective catalysts in supramolecular chemistry. In this work we present the resolution of planar-chiral porphyrin cages and the determination of their absolute configuration by vibrational circular dichroism in combination with density functional theory calculations. We report the efficient and straightforward resolution of two planar chiral porphyrin-cages (1 and 2, see Fig. 1a) by chiral HPLC and the determination of their absolute configurations by vibrational[3] and electronic circular dichroism[17] in combination with DFT and TD-DFT calculations. These absolute configurations have been checked by X-ray diffraction, which confirmed the assignments made by the combined spectroscopic-theoretical analysis. Chiral cage compounds 1 and 2 provided with a catalytically active metal (e.g. manganese) and light-switchable chiral functions on their cavity walls, are conceived to be used for that purpose[19,20,21]

Methods

Results

Conclusion