title: Gas-phase spectroscopy of ferric heme-NO complexes.
abstract: Weakly bound complexes between ferric heme cations and NO were synthesised in the gas phase from ion-molecule reactions, and their absorption measured based on photodissociation yields. The Soret band, which serves as an important marker band for heme-protein spectroscopy, is maximal at 357±5 nm and significantly blue-shifted compared to ferric heme nitrosyl proteins (maxima between 408 and 422 nm). This is in stark contrast to the Q-band absorption where the protein microenvironment is nearly innocent in perturbing the electronic structure of the porphyrin macrocycle. Photodissociation is primarily through loss of NO. In contrast to the Q-band region, two-photon absorption was seen in the Soret band despite NO loss only requiring ∼1 eV. A model based on intersystem crossing to a long-lived triplet state where a barrier has to be surmounted is suggested. Finally, we summarise the measured absorption maxima of heme and its complexes with amino acids and NO.
authors.affiliation: Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C (Denmark), Fax: (+45) 8612 0740. jeanwyer@phys.au.dk.
authors.forename: Jean A
authors.initials: JA
authors.lastname: Wyer
authors.forename: Anders V
authors.initials: AV
authors.lastname: Jørgensen
authors.forename: Bjarke
authors.initials: B
authors.lastname: Møller Pedersen
authors.forename: Steen
authors.initials: S
authors.lastname: Brøndsted Nielsen
mesh_terms: D000818:Animals; D056831:Coordination Complexes / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry*; D005740:Gases / Q000737:chemistry*; D006418:Heme / Q000737:chemistry*; D006736:Horses; D008786:Metmyoglobin / Q000737:chemistry / Q000378:metabolism; D009569:Nitric Oxide / Q000737:chemistry*; D013053:Spectrophotometry
chemical_list: D056831:Coordination Complexes; D005290:Ferric Compounds; D005740:Gases; D008786:Metmyoglobin; D009569:Nitric Oxide; D006418:Heme
keywords: Soret bands; gas-phase spectroscopy; heme proteins; mass spectrometry; nitric oxide