Pressure studies on the metallation of porphyrin-carrying copolymers

Four kinds of water-soluble porphyrin-carrying copolymers (PCs) were prepared by the coupling of copolymers containing 4-chloromethylstyrene residues with porphyrins which carry a 4-pyridine moiety. The complex formation of porphyrin group in the PC with a zinc(II) ion was examined at various pressures (0.1-150 MPa). At atmospheric pressure, the second-order rate constants for the metallation reaction of porphyrin carrying copolymers were much smaller than that of free porphyrin (meso-tetrakis(1-methylpyridinium-4-yl)porphin p-toluenesulfonate, TMPyP) due to the electrostatic repulsion of zinc(II) ion by the cationic copolymers. The volumes of activation obtained for the polymer systems were more negative than that for free TMPyP system, showing that a larger enhancement of hydration along the activation process occurred in the polymer systems. This is probably due to an increase in hydrophilicity of the porphyrin moiety from the initial state to the activated complex, which might result in the extension of copolymer chains.