Cobalt porphyrin-mediated oxygen transport in a polymer membrane. Effect of the cobalt porphyrin structure on the oxygen-binding reaction, oxygen-diffusion constants, and oxygen-transport efficiency

New derivatives of (meso-α,α,α,α-tetrakis(O-pivalamidophenyl)por phinato) cobalt (CoPs) were characterized by oxygen-binding equilibrium and rate constants of the cobalt centered in the porphyrins. They depended on the structure of the porphyrin; for example, the rate constants of oxygen binding and dissociation (k_on and k_off) for α³β-CoP₄P (Chart 1) were 3 and 20 times as large as those for α⁴-CoB₄P, respectively. Oxygen transport through the polymer membranes containing CoPs as the fixed oxygen carriers was facilitated and was affected by the oxygen-binding character or the structure of CoPs. The logarithmically linear correlation of the oxygen-dissociation rate constant of CoPs (k_off = (3-66) × 10³ S^-1) with the diffusion constant of oxygen via CoPs fixed in the membranes (D_cc = (3-140) × 10^-9 cm² S^-1) was given for those six CoP derivatives.