Metalloporphyrin dimers bridged by a peptoid helix: Host-guest interaction and chiral recognition

Abstract

Co-facial porphyrins have been designed to construct porphyrin tweezers with versatile molecular recognition capabilities. In this study, we synthesized metalloporphyrin-peptoid conjugates (MPPCs) displaying two metalloporphyrins on a peptoid scaffold with either achiral unfolded (1) or helical (2 and 3) secondary structures. Host-guest complexation of MPPCs was realized with various guests of different lengths and basicities, and the extent of complexation was measured by UV-vis and circular dichroism (CD) spectroscopic titration. Intermolecular and intramolecular chirality induction were observed on achiral and chiral peptoid backbones, respectively. Spectroscopic data indicated that a broad scope of achiral guests can be recognized by chiral 2; in particular, longer and more flexible guests were seen to bind more tightly on 2. In addition, chiral 2 provided a distinct CD couplet with DL-, D-, or L-Lys-OMe, which was a result of the diastereomeric host-guest complex formation. Our results indicated that MPPCs can recognize, contrast, and analyze various achiral, chiral, or racemic molecules. Based on co-facial metalloporphyrins present on peptoid scaffolds, we developed a novel class of porphyrin tweezers, which can be further utilized in asymmetric catalysis, molecular sensing, and drug delivery. © 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).