A novel strapped porphyrin receptor for molecular recognition

A novel strapped porphyrin receptor Zn1, in which two electron-rich bis(p-phenylene)-34-crown ether-10 units are incorporated, has been designed and synthesized from the newly developed intermediate 7 for investigating new chemistry of molecular recognition. H-1 NMR and UV-Vis studies revealed that Zn1 displays relatively weak binding abilities to neutral electron deficient naphthalene-1,8,4,5-tetracarboxydiimide (NDI) derivatives 13 (no simple complexing stoichiometry was observed), 19 (K-a=48(+/-5) M-1) and 30 (K-a=46(+/-5) M-1) in chloroform-d, strong binding ability to pyridine derivative 25, (K-a= 1.5(+/-0.12)X10(-1) M-1) in chloroform, moderately strong binding ability to tetracationic compound 35.4PF(6) (K-a=475(+/-50) M-1) in acetone-d(6), and very strong binding affinity to compound 22 (K-a=6.5(+/-0.7)x10(5) M-1), which consists of one pyridine and two NDI units, in chloroform. Remarkable cooperative effect of the intermolecular metal-ligand coordination and donor-acceptor interactions in complex Zn1.22 was observed by comparing the complexing behaviors between Zn1 and the appropriately designed guests. Complex Zn1.22 possesses an unique three-dimensional tri-site binding feature. For comparison, the complexing affinity of 1 toward compounds 13, 19, and 30 in chloroform-d and 35.4PF(6) in acetone-d(6) has also been investigated and the binding patterns in different complexes were explored. The results demonstrate that strapped porphyrin derivatives are ideal precursors for constructing new generation of three-dimensional multi-site artificial receptors for molecular recognition and host-guest chemistry. (C) 2003 Elsevier Science Ltd. All rights reserved.