Reactions of iron porphyrins with methyl radicals

Journal Article · Wed May 20 04:00:00 EDT 1981 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00400a036· OSTI ID:6255298

Brault, D; Neta, P

The reactions of methyl radicals with ferric, ferrous, and iron-free-deuteroporphyrin have been investigated in neutral and alkaline water-2-propanol mixtures. Steady-state radiolysis of methyl chloride saturated solutions of ferric deuteroporphyrin, or chemical reduction of ferric deuteroporphyrin solutions containing methyl iodide, led to a new species which is spectrophotometrically characterized. The yield (G approx. = 3) and the redox titration (2 reducing equivalents) strongly suggest the structure DPFe/sup III/CH/sub 3/. This product is found to be stable under anaerobic conditions but is oxidized to the initial ferric form in the presence of air. Pulse radiolysis experiments show that methyl radicals react with both ferric and ferrous deuteroporphyrin with reaction rate constants of 2.3 x 10/sup 9/ and 3.9 x 10/sup 9/ M/sup -1/ s/sup -1/, respectively. The reaction with iron-free deuteroporphyrin is much slower, demonstrating that methyl radicals react with iron porphyrin at the iron center. The transient species resulting from the scavenging of a methyl radical by ferric porphyrin DPFe/sup IV/CH/sub 3/ undergoes a further slow reaction leading to ferrous deuteroporphyrin (t/sub 1/2/ approx. = 200 ..mu..s). Electron (or methyl) transfer between DPFe/sup IV/CHTnumber and ferrous deuteroporphyrin leading to DPFe/sup III/CH/sub 3/ and ferric deuteroporphyrin is shown to occur with a second-order rate constant k = 4 x 10/sup 8/ M/sup -1/ s/sup -1/. The reactions of ..cap alpha..-hydroxyisopropyl radicals with ferric, ferrous, and iron-free deuteroporphyrin and with methyl iodide were also studied. The reactions of methyl radicals are discussed in relation to the hypothesis of radical-mediated toxicity of halogenated compounds.

• Research Organization: Univ. of Notre Dame, IN
• OSTI ID: 6255298
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 103:10; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
400600* -- Radiation Chemistry
ALKYL RADICALS
AQUEOUS SOLUTIONS
CARBOXYLIC ACIDS
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTIONS
CHEMISTRY
CHLORINATED ALIPHATIC HYDROCARBONS
DATA
DECOMPOSITION
DEUTERIUM
DISPERSIONS
ELECTROMAGNETIC RADIATION
EXPERIMENTAL DATA
GAMMA RADIATION
HALOGENATED ALIPHATIC HYDROCARBONS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROGEN ISOTOPES
INFORMATION
IONIZING RADIATIONS
IRON COMPOUNDS
ISOTOPES
KINETICS
LABELLED COMPOUNDS
LIGHT NUCLEI
METHYL CHLORIDE
METHYL RADICALS
MIXTURES
NUCLEI
NUMERICAL DATA
ODD-ODD NUCLEI
ORGANIC ACIDS
ORGANIC CHLORINE COMPOUNDS
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PORPHYRINS
RADIATION CHEMISTRY
RADIATION EFFECTS
RADIATIONS
RADICALS
RADIOLYSIS
REACTION KINETICS
SOLUTIONS
STABLE ISOTOPES
TRANSITION ELEMENT COMPOUNDS