Five- and six-coordinate adducts of nitrosamines with ferric porphyrins: Structural models for the type II interactions of nitrosamines with ferric cytochrome P450

Nan Xu, Lauren E. Goodrich, Nicolai Lehnert, Douglas R. Powell, George B. Richter-Addo

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Abstract

Nitrosamines are well-known for their toxic and carcinogenic properties. The metabolic activation of nitrosamines occurs via interaction with the heme-containing cytochrome P450 enzymes. We report the preparation and structural characterization of a number of nitrosamine adducts of synthetic iron porphyrins. The reactions of the cations [(por)Fe(THF)2]ClO 4 (por = TPP, TTP, OEP) with dialkylnitrosamines (R2NNO; R2 = Me2, Et2, (cyclo-CH2) 4, (cyclo-CH2)5, (PhCH2) 2) in toluene generate the six-coordinate high-spin (S = 5/2) [(por)Fe(ONNR2)2]ClO4 compounds and a five-coordinate intermediate-spin (S = 3/2) [(OEP)Fe(ONNMe2)]ClO 4 derivative in 57-72% yields (TPP = 5,10,15,20- tetraphenylporphyrinato dianion, TTP = 5,10,15,20-tetra-p-tolylporphyrinato dianion, OEP = 2,3,7,8,12,13,17,18-octaethylporphyrinato dianion). The N-O and N-N vibrations of the coordinated nitrosamine groups in [(por)Fe(ONNR 2)2]ClO4 occur in the 1239-1271 cm-1 range. Three of the six-coordinate [(por)Fe(ONNR2) 2]ClO4 compounds and one five-coordinate [(OEP)Fe(ONNMe2)]ClO4 compound have been characterized by single crystal X-ray crystallography. All the nitrosamine ligands in these complexes bind to the ferric centers via a sole η1-O binding mode. No arylnitrosamine adducts were obtained from the reactions of the precursor compounds [(por)Fe(THF)2]ClO4 with three arylnitrosamines (Ph2NNO, Ph(Me)NNO, Ph(Et)NNO). However, prolonged exposure of [(por)Fe(THF)2]ClO4 to these arylnitrosamines resulted in the formation of the known five-coordinate (por)Fe(NO) derivatives. The latter (por)Fe(NO) compounds were obtained more readily by the reactions of the three arylnitrosamines with the four-coordinate (por)FeII precursors.

Original languageEnglish (US)
Pages (from-to)4405-4419
Number of pages15
JournalInorganic chemistry
Volume49
Issue number10
DOIs
StatePublished - May 17 2010

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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