MERCURY(II) REACTIONS WITH WATER-SOLUBLE PORPHYRINS

Below pH 1 at 25-degrees-C, equilibrium constants were measured for the reaction of Hg2+ with the free base of tetrakis(N-methyl-2-pyridiniumyl)porphyrin, the monocation of tetrakis(N-methyl-4-quinoliniumyl)porphyrin, and the diacid of tetrakis(N-methyl-4-pyridiniumyl)porphyrin, all of which produce complexes of the composition Hg2-P2+ which have the presumed structure [Hg-P-Hg]2+. Near neutral pHs, the free bases of the pyridiniumylporphyrins form 1:1 adducts with mercury(II), formulated as (HO)2Hg-P2- or O-Hg-P2-, and the corresponding equilibrium constants are reported. Kinetic studies of the reaction of M(II) (M = Zn, Cu) with several of the Hg2-Ps gave evidence for [M-P-Hg] intermediates, which either react with Hg2+ to re-form Hg2-P2+ or decompose to the final M(II)-P adduct. The catalysis of M(II)-P formation by added Hg(II) ions is traced to the extremely rapid formation of mercury-porphyrin intermediates.