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.
Highlights
In photosynthetic light-harvesting complexes, the distance between numerous pigments and their arrangement are precisely controlled by a helical protein matrix
By the complexation of an achiral porphyrin tweezer with a chiral guest, the chirality of the guest can be transferred to the host; subsequently, the interporphyrin arrangement prefers a certain chiral twist depending on the asymmetric configuration of the guest
Metal incorporation on protocol the porphyrin ring was performed with zincwere acetate or copper acetate in resin-bound peptoid employing the method (Scheme 1) reported previously [14,15]
Summary
In photosynthetic light-harvesting complexes, the distance between numerous pigments and their arrangement are precisely controlled by a helical protein matrix. This spatial regulation is directly related to the highly efficient natural photosynthetic process [1,2]. Various efforts have been made to improve the function of these multiporphyrin systems, including the construction of co-facial porphyrins on molecular scaffolds such as neucleotides [10], anthrancenics [10,11], peptide [12,13], and other peptidomimetics [14,15,16]. Co-facial porphyrins have been actively used in the design of porphyrin tweezers.
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