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![Protein Film Infrared Electrochemistry Demonstrated for Study of H2 Oxidation by a [NiFe] Hydrogenase](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F55858.jpg&w=3840&q=50)
Protein Film Infrared Electrochemistry Demonstrated for Study of H2 Oxidation by a [NiFe] Hydrogenase
Published on: December 4, 2017
Ferric Heme Superoxide Reductive Transformations to Ferric Heme (Hydro)Peroxide Species: Spectroscopic
Hyun Kim1, Patrick J Rogler1, Savita K Sharma1
1Chemistry Department, Johns Hopkins University, Baltimore, MD, 21218, USA.
Abstract:
A new end-on low-spin ferric heme peroxide, [(PIm )FeIII -(O22- )]- (PIm -P), and subsequently formed hydroperoxide species, [(PIm )FeIII -(OOH)] (PIm -HP) are generated utilizing the iron-porphyrinate PIm with its tethered axial base imidazolyl group. Measured thermodynamic parameters, the ferric heme superoxide [(PIm )FeIII -(O2⋅- )] (PIm -S) reduction potential (E°') and the PIm -HP pKa value, lead to the finding of the OO-H bond-dissociation free energy (BDFE) of PIm -HP as 69.5 kcal mol-1 using a thermodynamic square scheme and Bordwell relationship. The results are validated by the observed oxidizing ability of PIm -S via hydrogen-atom transfer (HAT) compared to that of the F8 superoxide complex, [(F8 )FeIII -(O2.- )] (S) (F8 =tetrakis(2,6-difluorophenyl)porphyrinate, without an internally appended axial base imidazolyl), as determined from reactivity comparison of superoxide complexes PIm -S and S with the hydroxylamine (O-H) substrates TEMPO-H and ABNO-H.
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