Cyclodextrin‐Based Catenanes Platformed with meso‐Arylporphyrin

“Padlock” structures comprising cyclodextrin (CD) catenanes were successfully constructed using a strong intermolecular interaction of CD with meso-arylporphyrin in water. A water soluble Grubbs's catalyst was used for interlocking CD onto the porphyrin. The novel catenane compounds were useful to elucidate the highly specific intermolecular interactions of methylated CD to meso-(4-sulfonatophenyl)porphyrins in water.

Abstract

Among mechanically interlocked supramolecular systems with cyclodextrins (CDs), successful examples of CD-based catenanes are limited compared to a number of CD rotaxanes owing to the synthetic difficulties. We herein demonstrate an efficient synthesis of a CD-based catenane using a meso-arylporphyrin (Por) platform. Using Por modified with two olefin-terminated oxyethylene chains at the cis-meso-positions, an interlocked Por-CD catenane was synthesized via olefin metathesis in the presence of per-O-methylated β-CD (TMe-β-CD) in water. The novel Por-CD catenane was obtained in 30 % isolated yield, which was characterized by MALDI-TOF mass and NMR spectroscopies. In the latter part, we demonstrate determination of the binding constants between TMe-β-CD and meso-(4-sulfonatophenyl)porphyrin using Por-CD catenane, 2,6-di-O-methyl-β-CD (DMe-β-CD), and ¹³C-labeled TMe-β-CD (¹³C-TMe-β-CD). The host-guest exchange reaction from the Por-CD catenane/DMe-β-CD to the Por-CD catenane/TMe-β-CD complexes was directly monitored through 1D HMQC spectroscopy. The ratio of these complexes revealed the difference in the binding affinities of DMe-β-CD and TMe-β-CD to Por. The stable 1 : 2 inclusion complex between meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and TMe-β-CD has been well-studied for many years. This study is the first to determine the respective binding constants, K ₁ and K ₂, using the model system, to be 3.0×10⁷ M⁻¹ and 3.4×10⁷ M⁻¹, respectively.

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