Mössbauer Quadrupole Splittings and Electronic Structure in Heme Proteins and Model Systems: A Density Functional Theory Investigation
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- 作者：Yong Zhang ; Junhong Mao ; Nathalie Godbout ; and Eric Oldfield
- 刊名：Journal of the American Chemical Society
- 出版年：2002
- 出版时间：November 20, 2002
- 年：2002
- 卷：124
- 期：46
- 页码：13921 - 13930
- 全文大小：403K
- 年卷期：v.124,no.46(November 20, 2002)
- ISSN：1520-5126
文摘
We report the results of a series of density functional theory (DFT) calculations aimed at predictingthe 57Fe Mössbauer electric field gradient (EFG) tensors (quadrupole splittings and asymmetry parameters)and their orientations in S = 0, 1/2, 1, 3/2, 2, and 5/2 metalloproteins and/or model systems. Excellent resultswere found by using a Wachter's all electron basis set for iron, 6-311G* for other heavy atoms, and 6-31G*for hydrogen atoms, BPW91 and B3LYP exchange-correlation functionals, and spin-unrestricted methodsfor the paramagnetic systems. For the theory versus experiment correlation, we found R2 = 0.975, slope= 0.99, intercept = -0.08 mm sec-1, rmsd = 0.30 mm sec-1 (N = 23 points) covering a 
EQ range of 5.63mm s-1 when using the BPW91 functional and R2 = 0.978, slope = 1.12, intercept = -0.26 mm sec-1,rmsd = 0.31 mm sec-1 when using the B3LYP functional. EQ values in the following systems weresuccessfully predicted: (1) ferric low-spin (S = 1/2) systems, including one iron porphyrin with the usual(dxy)2(dxzdyz)3 electronic configuration and two iron porphyrins with the more unusual (dxzdyz)4(dxy)1 electronicconfiguration; (2) ferrous NO-heme model compounds (S = 1/2); (3) ferrous intermediate spin (S = 1)tetraphenylporphinato iron(II); (4) a ferric intermediate spin (S = 3/2) iron porphyrin; (5) ferrous high-spin(S = 2) deoxymyoglobin and deoxyhemoglobin; and (6) ferric high spin (S = 5/2) metmyoglobin plus twofive-coordinate and one six-coordinate iron porphyrins. In addition, seven diamagnetic (S = 0, d6 and d8)systems studied previously were reinvestigated using the same functionals and basis set scheme as usedfor the paramagnetic systems. All computed asymmetry parameters were found to be in good agreementwith the available experimental data as were the electric field gradient tensor orientations. In addition, weinvestigated the electronic structures of several systems, including the (dxy)2(dxz,dyz)3 and (dxz,dyz)4(dxy)1[Fe(III)/porphyrinate]+ cations as well as the NO adduct of Fe(II)(octaethylporphinate), where interestinginformation on the spin density distributions can be readily obtained from the computed wave functions.
EQ range of 5.63mm s-1 when using the BPW91 functional and R2 = 0.978, slope = 1.12, intercept = -0.26 mm sec-1,rmsd = 0.31 mm sec-1 when using the B3LYP functional. EQ values in the following systems weresuccessfully predicted: (1) ferric low-spin (S = 1/2) systems, including one iron porphyrin with the usual(dxy)2(dxzdyz)3 electronic configuration and two iron porphyrins with the more unusual (dxzdyz)4(dxy)1 electronicconfiguration; (2) ferrous NO-heme model compounds (S = 1/2); (3) ferrous intermediate spin (S = 1)tetraphenylporphinato iron(II); (4) a ferric intermediate spin (S = 3/2) iron porphyrin; (5) ferrous high-spin(S = 2) deoxymyoglobin and deoxyhemoglobin; and (6) ferric high spin (S = 5/2) metmyoglobin plus twofive-coordinate and one six-coordinate iron porphyrins. In addition, seven diamagnetic (S = 0, d6 and d8)systems studied previously were reinvestigated using the same functionals and basis set scheme as usedfor the paramagnetic systems. All computed asymmetry parameters were found to be in good agreementwith the available experimental data as were the electric field gradient tensor orientations. In addition, weinvestigated the electronic structures of several systems, including the (dxy)2(dxz,dyz)3 and (dxz,dyz)4(dxy)1[Fe(III)/porphyrinate]+ cations as well as the NO adduct of Fe(II)(octaethylporphinate), where interestinginformation on the spin density distributions can be readily obtained from the computed wave functions.