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Nitrous-Acid-Mediated Synthesis of Iron–Nitrosyl–Porphyrin: pH-Dependent Release of Nitric Oxide

Authors

  • Jagannath Bhuyan,

    1. Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur-208016, U.P. (India)
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  • Prof. Sabyasachi Sarkar

    Corresponding author
    1. Department of Chemistry, Bengal Engineering and Science University, Shibpur, Howrah-711103 (West Bengal)
    • Department of Chemistry, Bengal Engineering and Science University, Shibpur, Howrah-711103 (West Bengal)

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Abstract

Two iron–nitrosyl–porphyrins, nitrosyl[meso-tetrakis(3,4,5-trimethoxyphenylporphyrin]iron(II) acetic acid solvate (3) and nitrosyl[meso-tetrakis(4-methoxyphenylporphyrin]iron(II) CH2Cl2 solvate (4), were synthesized in quantitative yield by using a modified procedure with nitrous acid, followed by oxygen-atom abstraction by triphenylphosphine under an argon atmosphere. These nitrosyl porphyrins are in the {FeNO}7 class. Under an argon atmosphere, these compounds are relatively stable over a broad range of pH values (4–8) but, under aerobic conditions, they release nitric oxide faster at high pH values than that at low pH values. The generated nitric-oxide-free iron(III)–porphyrin can be re-nitrosylated by using nitrous acid and triphenylphosphine. The rapid release of NO from these FeII complexes at high pH values seems to be similar to that in nitrophorin, a nitric-oxide-transport protein, which formally possesses FeIII. However, because the release of NO occurs from ferrous–nitrosyl–porphyrin under aerobic conditions, these compounds are more closely related to nitrobindin, a recently discovered heme protein.

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