An Experimental and Density Functional Theoretical Investigation of Iron-57 Mössbauer Quadrupole Splittings in Organometallic and Heme-Model Compounds: Applications to Carbonmonoxy-Heme Protein S
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- 作者：Robert H. Havlin ; Nathalie Godbout ; Renzo Salzmann ; Mark Wojdelski ; William Arnold ; Charles E. Schulz ; and Eric Oldfield
- 刊名：Journal of the American Chemical Society
- 出版年：1998
- 出版时间：April 8, 1998
- 年：1998
- 卷：120
- 期：13
- 页码：3144 - 3151
- 全文大小：162K
- 年卷期：v.120,no.13(April 8, 1998)
- ISSN：1520-5126
文摘
We have investigated the 57Fe Mössbauerquadrupole splittings in the following compounds byusing density functional theory, and in some cases via experiment:Fe(CO)3(cyclo-butadiene),Fe(CO)5, Fe(CO)3(1,4-butadiene), CpFe(CO)2Me,Fe(CO)3(propenal), CpFe(CO)2Cl,(CO)(pyridine)(DMGBPh2)2Fe(II)(DMG = dimethylglyoximato),(CO)(pyridine)(DMGBBN)2Fe(II) (BBN =9-borabicyclo[3.3.1]nonane), (CO)(1-methylimidazole)(5,10,15,20-tetraphenylporphinato)Fe(II),(CO)(pyridine)(5,10,15,20-tetraphenyl-porphinato)Fe(II),(nitrosobenzene)(pyridine)(5,10,15,20-tetraphenylporphinato)Fe(II),(pyridine)2(5,10,15,20-tetraphenylporphinato)Fe(II),(1-methylimidazole)2(5,10,15,20-tetramesitylporphinato)Fe(II),and (trimethylphosphine)2(2,3,7,8,12,13,17,18-octaethylporphinato)Fe(II).The electric field gradients at iron were evaluatedbyusing a locally dense basis approach: a Wachters' all electronrepresentation for iron, a 6-311++G2d basisforall atoms directly bonded to iron, and either a 6-31G* basis for allother atoms or, in the case of themetalloporphyrins, a 6-31G*/3-21G* or 4-31G* basis, with the smallerbasis being used on the peripheralatoms. Using a value of 0.16 × 10-28m2 for the quadrupole moment of57Fem, we find good agreementbetween theoretical and experimental quadrupole splittings: a slopeof 1.04, an R2 value of 0.975, andaroot-mean-square error of 0.18 mm s-1, forthe 14 compounds examined. We have also investigatedtheeffects of the CO ligand tilt and bend on the 57Fequadrupole splittings in several heme models. Thetheoreticalresults provide no support for the very large (40
deg.gif">) Fe-C-O bondangles suggested by several diffractionstudies on Physeter catodon carbonmonoxymyoglobin(P21 crystals). In contrast, theexperimental results for(CO)(1-MeIm)(5,10,15,20-tetraphenylporphinato)Fe(II),which contains a linear and untilted Fe-CO, are invery close accord with the experimental values for CO-myoglobin: 0.35mm s-1 for the model systemversus0.363-0.373 mm s-1 for MbCO, withVzz oriented perpendicular to theporphyrin plane, as found experimentally.Calculations on metalloporphyrins at the more distorted X-raygeometries yield quadrupole splittings around2 mm s-1, inconsistent withexperiment.
deg.gif">) Fe-C-O bondangles suggested by several diffractionstudies on Physeter catodon carbonmonoxymyoglobin(P21 crystals). In contrast, theexperimental results for(CO)(1-MeIm)(5,10,15,20-tetraphenylporphinato)Fe(II),which contains a linear and untilted Fe-CO, are invery close accord with the experimental values for CO-myoglobin: 0.35mm s-1 for the model systemversus0.363-0.373 mm s-1 for MbCO, withVzz oriented perpendicular to theporphyrin plane, as found experimentally.Calculations on metalloporphyrins at the more distorted X-raygeometries yield quadrupole splittings around2 mm s-1, inconsistent withexperiment.