Effect of structure of polymer ligands on oxygen-bindingproperties of cobaltporphyrin complexes
Synthesis and characteristics of 4-vinylimdazole,1-methyl-4-vinylimdazole, and their copolymers with octyl methacrylate, and the oxygen-binding properties of cobaltporphyrin (CoP) complexes with vinylimdazole copolymers were studied. The molecular mass and vinylimidazole content of poly(octyl methacrylate-co-4-vinylimidazole) (PO4Im) and poly(octyl methacrylate-co-1-methyl-4-vinylimidazole) (POM4Im) were determined by GPC and elemental analysis, respectively. PO4Im or POM4Im and CoP in dichloromethane solution were mixed to complex the imidazolyl residue of copolymers with the fifth coordination site of CoP to get CoP complexes. CoP complex displayed a reversible change in the UV-visible absorption spectrum from the deoxy form to the oxygen-binding one with an isosbestic point, in response to the partial oxygen pressure of the atmosphere. The oxygen-binding equilibrium curves of CoP complexes obeyed Langmuir isotherm, to give the oxygen-binding affinity p_ 50 .The oxygen-binding affinity of PO4Im-CoP complex was larger than that of POM4Im-CoP complex. It was assumed that hydrogen bond formed in PO4Im improved the oxygen-binding affinity of the CoP complex. The binding and dissociation rate constants of oxygen to and from CoP complexes were large, which indicates a very rapid oxygen-binding.