Phthalocyanines picket fence’ porphyrins

Iron(ii) porphyrins, like iron(n) phthalocyanin, interact reversibly with Oj in aqueous solution but subsequently dimerize and are oxidized to iron(ra). Sterically hindered o/ /A >-analylamide derivatives of iron(ii) porphyrins, the picket fence porphyrins, prevent dimerization and hence oxidation and serve as models for the high-afl nity J -state of Hb(ii). Using as the proximal base 2-methylimidazoIe, which has a steric interaction with the porphyrin ring and holds the iron in its unliganded position below the ring, a low-affinity T-form of the complex can be produced. In the crystalline state, picket fence porphyrins show co-operativity very similar to that shown by haemoglobin in mechanistic and quantitative detail. ... 

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