Metalloporphyrin Dimers Bridged by a Peptoid Helix: Host-Guest Interaction and Chiral Recognition

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.