DFT calculations of 57Fe Mössbauer isomer shifts and quadrupole splittings for iron complexes in polar dielectric media: Applications to methane monooxygenase and ribonucleotide reductase
✍ Scribed by Wen-Ge Han; Tiqing Liu; Timothy Lovell; Louis Noodleman
- Publisher
- John Wiley and Sons
- Year
- 2006
- Tongue
- English
- Weight
- 695 KB
- Volume
- 27
- Category
- Article
- ISSN
- 0192-8651
No coin nor oath required. For personal study only.
✦ Synopsis
Abstract
To predict the isomer shifts of Fe complexes in different oxidation and spin states more accurately, we have performed linear regression between the measured isomer shifts (δ~exp~) and DFT (PW91 potential with all‐electron triple‐ζ plus polarization basis sets) calculated electron densities at Fe nuclei [ρ(0)] for the Fe^2+,2.5+^ and Fe^2.5+,3+,3.5+,4+^ complexes separately. The geometries and electronic structures of all complexes in the training sets are optimized within the conductor like screening (COSMO) solvation model. Based on the linear correlation equation δ~exp~ = α[ρ(0) − 11884.0] + C, the best fitting for 17 Fe^2+,2.5+^ complexes (totally 31 Fe sites) yields α = −0.405 ± 0.042 and C = 0.735 ± 0.047 mm s^−1^. The correlation coefficient is r = −0.876 with a standard deviation of SD = 0.075 mm s^−1^. In contrast, the linear fitting for 19 Fe^2.5+,3+,3.5+,4+^ complexes (totally 30 Fe sites) yields α = −0.393 ± 0.030 and C = 0.435 ± 0.014 mm s^−1^, with the correlation coefficient r = −0.929 and a standard deviation SD = 0.077 mm s^−1^. We provide a physical rationale for separating the Fe^2+,2.5+^ fit from the Fe^2.5+,3+,3.5+,4+^ fit, which also is clearly justified on a statistical empirical basis. Quadrupole splittings have also been calculated for these systems. The correlation between the calculated (Δ__E__~Q(cal)~) and experimental (Δ__E__~Q(exp)~) quadrupole splittings based on |Δ__E__~Q(exp)~| = A |Δ__E__~Q(cal)~| + B yields slope A, which is almost the ideal value 1.0 (A = 1.002 ± 0.030) and intercept B almost zero (B = 0.033 ± 0.068 mm s^−1^). Further calculations on the reduced diferrous and oxidized diferric active sites of class‐I ribonucleotide reductase (RNR) and the hydroxylase component of methane monooxygenase (MMOH), and on a mixed‐valent [(tpb)Fe^3+^(μ‐O)(μ‐CH~3~CO~2~)Fe^4+^(Me~3~[9]aneN~3~)]^2+^ (S = 3/2) complex and its corresponding diferric state have been performed. Calculated results are in very good agreement with the experimental data. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 1292–1306, 2006