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Relevant academic research and scientific papers

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. 1H 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 (Ka=48(±5)M-1) and 30 (Ka=46(±5)M-1) in chloroform-d, strong binding ability to pyridine derivative 25, (Ka=1.5(±0.12)×103M-1) in chloroform, moderately strong binding ability to tetracationic compound 35.4PF6 (Ka=475(±50)M-1) in acetone-d6, and very strong binding affinity to compound 22 (Ka=6.5(±0.7)×105M-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 35.4PF6 in acetone-d6 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.

Metalloporphyrin receptors for histidine-containing peptides

Two new ditopic metalloporphyrin receptors constructed by combining metalloporphyrin with crown ethers have been prepared and characterized. 1H NMR and MS spectra confirmed the complexation of receptor with peptide driven by coordination interaction and hydrogen bonding. UV/vis experiments revealed that the receptors exhibited high binding affinity to histidine-containing peptides. These receptors could differentiate short peptides of C-terminal histidine and N-terminal histidine and formed the most stable complexes with tripeptide.

Selective recognition of sodium cyanide and potassium cyanide by diaza-crown ether-capped Zn-porphyrin receptors in polar solvents

Two new ditopic porphyrin receptors Zn1, incorporating a diaza-15-crown-5 unit, and Zn2, incorporating a diaza-18-crown-6 unit, have been prepared and characterized. UV-vis study in polar methanol has revealed that Zn1 is able to selectively recognize sodium cyanide over potassium cyanide (the ratio of their binding constant is ca. 56), whereas Zn2 exhibits a higher binding affinity for potassium cyanide over sodium cyanide (the ratio of their binding constant is ca. 12). In contrast, both receptors display substantially weaker binding affinity for sodium thiocyanate and potassium thiocyanate presumably due to a monotopic binding fashion.

Recognition Through Self-Assembly. A Quadruply-Hydrogen-Bonded, Strapped Porphyrin Cleft That Binds Dipyridyl Molecules and A [2]Rotaxane

Quadruply-hydrogen-bonded porphyrin homodimer Zn1·Zn1 has been designed, assembled, and evaluated as a supramolecular cleft-featured receptor for its ability to bind dipyridyl guests in chloroform-d. Monomer Zn1 consists of a 2-ureidopyrimidin-4(1H)-one unit, which was initially reported by Meijer et al., and a zinc porphyrin unit. The zinc porphyrin is strapped with an additional aliphatic chain for controlling the atropisomerization of porphyrin. The 2-ureidopyrimidin-4(1H)-one unit dimerizes exclusively in chloroform even at the dilute concentration of 10-4 M, while the two "strapped" zinc porphyrin units of the homodimer provide additional binding sites for selective guest recognition. 1H NMR studies indicate that the new homodimer Zn1·Zn1 adopts an S-type conformation due to strong donor-acceptor interaction between the electron-rich porphyrin units and the electron-deficient 2-ureidopyrimidin-4(1H)-one unit. 1H NMR, UV-vis, and vapor pressure osmometry investigations reveal that Zn1·Zn1 could function as a new generation of assembled supramolecular cleft, to be able to not only efficiently bind linear dipyridyl molecules 14-17, resulting in the formation of stable termolecular complexes, with Kaasoc values ranging from 3.8 × 106 to 8.9 × 107 M -1, but also strongly complex a hydrogen-bond-assembled [2]rotaxane, 18, which consists of a rigid fumaramide thread and a pyridine-incorporated tetraamide cyclophane, with Kassoc = 1.2 × 104 M-1. 1H NMR competition experiments reveal that complexation to the dipyriyl guests also promotes the stability of the quadruply-hydrogen-bonded dimeric receptor.