Heme models I. solution behavior of a water soluble iron porphyrin

✍ Scribed by John D. Stong; Charles R. Hartzell

• Book ID: 104106089
• Publisher: Elsevier Science
• Year: 1976
• Weight: 771 KB
• Volume: 5
• Category: Article
• ISSN: 0006-3061
• DOI: 10.1016/s0006-3061(00)82020-7

✦ Synopsis

A well-behaved water soluble iron-porphyrin system, meso-tetra-(4-carboxyphenyl) porphinato iron (III) was synthesized. Its solution behavior is described using visable and electron paramagnetic resonance (EPR) spectroscopy_ The complex exists in solution as three distinct forms of bridged dimes, 0x0, hydroxo and aquo, with the following pK's: 0x0 f Hf == hydroxo, pK = 9.58; hydroxo + H* * aquo, pK = 6.72. In the presence of excess imidazole the second pK is found to be 7.05. Detailed analysis of the interaction of the hydroso-bridged form with imidazole is presented. It is found that one dimer unit simultaneously binds two imidazole molecules, with an over-all equilibrium constant log Keq = -1.22. EPR spectra are presented for the various forms of iron-porphyrin discussed_ 'The vertical lines above and below Fe in the structures shown here, and used elsewhere in this paper represent the plane of the porphyrin ring so that a clearer designation of the axial ligands to the iron atom may result_ Nothing is implied in these structures concerning bond types and angles.