title: The diagnostic vibrational signature of pentacoordination in heme carbonyls.
abstract: Heme-carbonyl complexes are widely exploited for the insight they provide into the structural basis of function in heme-based proteins, by revealing the nature of their bonded and nonbonded interactions with the protein. This report presents two novel results which clearly establish a FeCO vibrational signature for crystallographically verified pentacoordination. First, anisotropy in the NRVS density of states for ν(Fe-C) and δ(FeCO) in oriented single crystals of [Fe(OEP)(CO)] clearly reveals that the Fe-C stretch occurs at higher frequency than the FeCO bend and considerably higher than any previously reported heme carbonyl. Second, DFT calculations on a series of heme carbonyls reveal that the frequency crossover occurs near the weak trans O atom donor, furan. As ν(Fe-C) occurs at lower frequencies than δ(FeCO) in all heme protein carbonyls reported to date, the results reported herein suggest that they are all hexacoordinate.
authors.affiliation: Department of Chemistry and Biochemistry, North Dakota State University , Fargo, North Dakota 58105, United States.
authors.forename: Douglas P
authors.initials: DP
authors.lastname: Linder
authors.forename: Nathan J
authors.initials: NJ
authors.lastname: Silvernail
authors.forename: Alexander
authors.initials: A
authors.lastname: Barabanschikov
authors.forename: Jiyong
authors.initials: J
authors.lastname: Zhao
authors.forename: E Ercan
authors.initials: EE
authors.lastname: Alp
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Sturhahn
authors.forename: J Timothy
authors.initials: JT
authors.lastname: Sage
authors.forename: W Robert
authors.initials: WR
authors.lastname: Scheidt
authors.forename: Kenton R
authors.initials: KR
authors.lastname: Rodgers
mesh_terms: D016880:Anisotropy; D002248:Carbon Monoxide / Q000737:chemistry; D002254:Carbonates / Q000737:chemistry; D018360:Crystallography, X-Ray; D005290:Ferric Compounds / Q000737:chemistry; D006420:Hemeproteins / Q000737:chemistry*; D007501:Iron / Q000737:chemistry; D008024:Ligands; D050050:Protein Carbonylation; D013237:Stereoisomerism
chemical_list: D002254:Carbonates; D005290:Ferric Compounds; D006420:Hemeproteins; D008024:Ligands; D002248:Carbon Monoxide; D007501:Iron; C486982:siderite