LIGAND-BINDING BY BUTADIYNE-LINKED PORPHYRIA DIMERS, TRIMERS AND TETRAMERS

Journal article

The binding of oligopyridyl ligands to butadiyne-linked zinc porphyrin dimers, trimers and tetramers has been investigated in detail using NMR and electronic spectroscopy. Pyridine binds to zinc porphyrin monomers in CH 2Cl 2 solution at 300 K with binding constants of ca. 10 3 mol -1 dm 3, while 4,4′-bipyridyl binds to the cyclic zinc porphyrin dimer with a binding constant of 1 × 10 9 mol -1 dm 3, giving an effective molarity, or chelation factor, of 76 mol dm -3. The analogous linear dimer binds to this ligand 100 times less strongly, but adopts a similar conformation when bound. s-Tri(4-pyridyl)triazine has an affinity of ca. 10 10 mol -1 dm 3 for the cyclic zinc trimer, reflecting reasonably good host-guest complementarity. The affinity of 4,4′-bipyridyl for the trimer is ca. 10 5 mol -1 dm 3, implying two-point binding accompanied by host distortion and strain which reduce the binding constant; the trimer is therefore an elastic host, able to respond to the geometrical demands of rigid guests. The cyclic tetramer is a relatively flexible molecule, but its complexes with both bidentate and tetradentate ligands have more highly defined geometries. The cyclic dimer and trimer have open pre-organised cavities, with no conformational barrier to ligand binding inside the cavity, whereas the cyclic tetramer can adopt many conformations in free solution.

Authors: Anderson, H; Anderson, S; Sanders, J

• Publication status: Published
• Journal: JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 1
• Issue: 18
• Pages: 2231-2245
• Publication date: 1995-09-21
• DOI: 10.1039/p19950002231
• EISSN: 1364-5463
• ISSN: 0300-922X
• Language: English