Amplification of Electronic Circular Dichroism-A Tool to Follow Self-Assembly of Chiral Molecular Capsules.

Marek P Szymański,Marcin Grajda,Agnieszka Szumna

doi:10.3390/molecules26237100

Abstract

Electronic circular dichroism (ECD) can be used to study various aspects of self-assembly (definition of stoichiometric ratios, chirality amplification during self-assembly, host-guest complexation). In this work, we show that ECD is a valuable tool for monitoring the self-assembly of chiral peptide-based capsules. By analyzing the signs, intensities, and temperature dependences of ECD bands, the effects of the non-specific processes can be separated from the restriction of intramolecular motion (RIM) caused by discrete self-assembly. Analysis of experimental and theoretical ECD spectra show that the differences between assembled and non-assembled species originate from induction of inherently chiral conformation and restriction of conformational freedom that leads to amplification of ECD signals during self-assembly of discrete species.

Highlights

Tool to Follow Self-Assembly ofSelf-assembly of molecules under given conditions is a crucial feature that determines their properties and function
We demonstrate the application of Electronic circular dichroism (ECD) spectroscopy for the monitoring of the self-assembly of chiral peptide-based capsules
Results and Discussion tide-based capsules, which are formed by hydrogen bonds between the peptide strands, We have previously reported the synthesis and self-assembly of various peptide-based forming β-sheet-like binding motifs [11–15]

Summary

Introduction

Tool to Follow Self-Assembly ofSelf-assembly of molecules under given conditions is a crucial feature that determines their properties and function. Any change in physical or spectroscopic property can be used to follow the process of self-assembly. Despite the apparent abundance of methods, in many cases, the unambiguous determination of details of a self-assembly process is not trivial. Electronic circular dichroism (ECD) is not the most common method to study self-assembly, but numerous studies have demonstrated that it can address various problems, ranging from the definition of simple stoichiometric ratios between the partners, giving rise to a supramolecular structure to the derivation of thermodynamic parameters, or to the refinement of a structure for a complex or an aggregate [2–5]. The ECD technique has been found useful for the determination of chirality amplification during self-assembly of supramolecular polymers (according to the “sergeants-and-soldiers” rule) [6,7] and for studying host–guest complexation by induced chirality effects [8]. The information encoded in ECD spectra is typically difficult to be assessed directly because the ECD spectra include the contributions of all conformers populated at the working temperature [9,10], and prediction of the spectrum even for a single conformer typically requires quantum calculation

Methods

Results

Conclusion