Kinetic and Mechanistic Studies on the Reaction of Nitric Oxide with a Water-Soluble Octa-anionic Iron(III) Porphyrin Complex

The polyanionic water-soluble and non-μ-oxo-dimer-forming iron porphyrin iron(III) 54,104,154,204-tetra-tert-butyl-52,56,152,156-tetrakis[2,2-bis(carboxylato)ethyl]-5,10,15,20-tetraphenylporphyrin, (P8-)FeIII (1), was synthesized as an octasodium salt by applying well-established porphyrin and organ...

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Bibliographic Details
Published in:Inorganic chemistry 2005-10, Vol.44 (22), p.7717-7731
Main Authors: Jee, Joo-Eun, Eigler, Siegfried, Hampel, Frank, Jux, Norbert, Wolak, Maria, Zahl, Achim, Stochel, Grazyna, van Eldik, Rudi
Format: Article
Language:English
Subjects:
Anions - chemistry
Iron - chemistry
Kinetics
Metalloporphyrins - chemistry
Metalloporphyrins - metabolism
Molecular Structure
Nitric Oxide - chemistry
Nitric Oxide - metabolism
Solubility
Water - chemistry
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Summary:The polyanionic water-soluble and non-μ-oxo-dimer-forming iron porphyrin iron(III) 54,104,154,204-tetra-tert-butyl-52,56,152,156-tetrakis[2,2-bis(carboxylato)ethyl]-5,10,15,20-tetraphenylporphyrin, (P8-)FeIII (1), was synthesized as an octasodium salt by applying well-established porphyrin and organic chemistry procedures to bromomethylated precursor porphyrins and characterized by standard techniques such as UV−vis and 1H NMR spectroscopy. A single pK a1 value of 9.26 was determined for the deprotonation of coordinated water in (P8-)FeIII(H2O)2 (1-H 2 O) present in aqueous solution at pH 9, is markedly lower than the corresponding value measured for 1-H 2 O at lower pH (k on = 8.2 × 105 M-1 s-1, 24 °C, pH 7). The observed decrease in the reactivity is contradictory to that expected for the diaqua- and monohydroxo-ligated forms of the iron(III) complex and is accounted for in terms of a mechanistic changeover observed for 1-H 2 O and 1-OH in their reactions with NO. The mechanistic interpretation offered is further substantiated by the results of water-exchange studies performed on the polyanionic porphyrin complex as a function of pH, temperature, and pressure.
ISSN:0020-1669
1520-510X
DOI:10.1021/ic050924t