180
M. Gruden et al.
12. Yang T-C, Maeser NK, Laryukhin M, Lee H-I, Dean DR, Seefeldt LC, Hoffman BM (2005)
The interstitial atom of the nitrogenase FeMo-cofactor: ENDOR and ESEEM evidence that it
is not a nitrogen. J Am Chem Soc 127:12804–12805. https://doi.org/10.1021/ja0552489
13. Lancaster KM et al (2011) X-Ray emission spectroscopy evidences a central carbon in the
nitrogenase iron-molybdenum cofactor. Science 334:974–977. https://doi.org/10.1126/science.
1206445
14. Bjornsson R et al (2014) Identification of a spin-coupled Mo(III) in the nitrogenase iron—
molybdenum cofactor. Chem Sci 5:3096–3103. https://doi.org/10.1039/c4sc00337c
15. Sippel D et al (2018) A bound reaction intermediate sheds light on the mechanism of nitrogenase. Science 359:1484–1489. https://doi.org/10.1126/science.aar2765
16. Cao L, Ryde U (2018) Influence of the protein and DFT method on the broken-symmetry and
spin states in nitrogenase. Int J Quantum Chem 118:e25627. https://doi.org/10.1002/qua.25627
17. Cao L, Caldararu O, Ryde U (2017) Protonation states of homocitrate and nearby residues
in nitrogenase studied by computational methods and quantum refinement. J Phys Chem B
121:8242–8262. https://doi.org/10.1021/acs.jpcb.7b02714
18. Siegbahn PEM (2018) A major structural change of the homocitrate ligand of probable importance for the nitrogenase mechanism. Inorg Chem 57:1090–1095. https://doi.org/10.1021/acs.
inorgchem.7b02493
19. Siegbahn PEM (2016) Model calculations suggest that the central carbon in the femo-cofactor
of nitrogenase becomes protonated in the process of nitrogen fixation. J Am Chem Soc
138:10485–10495. https://doi.org/10.1021/jacs.6b03846
20. Siegbahn PEM (2018) Is there computational support for an unprotonated carbon in the E4
state of nitrogenase? J Comput Chem 39:743–747. https://doi.org/10.1002/jcc.25145
21. Dau H, Iuzzolino L, Dittmer J (2001) The tetra-manganese complex of photosystem II during
its redox cycle—X-ray absorption results and mechanistic implications. BBA-Bioenergetics
1503:24–39. https://doi.org/10.1016/s0005-2728(00)00230-9
22. Krewald V et al (2015) Metal oxidation states in biological water splitting. Chem Sci
6:1676–1695
23. Rohde JU et al (2003) Crystallographic and spectroscopic characterization of a nonheme
Fe(IV)-O complex. Science 299:1037–1039. https://doi.org/10.1126/science.299.5609.1037
24. Fukuzumi S, Morimoto Y, Kotani H, Naumov P, Lee Y-M, Nam W (2010) Crystal structure of
a metal ion-bound oxoiron(IV) complex and implications for biological electron transfer. Nat
Chem 2:756–759. https://doi.org/10.1038/nchem.731
25. McDonald AR, Que Jr L (2013) High-valent nonheme iron-oxo complexes: synthesis, structure,
and spectroscopy. Coord Chem Rev 257:414–428. https://doi.org/10.1016/j.ccr.2012.08.002
26. Swart M (2013) A change in oxidation state of iron: scandium is not innocent. Chem Commun
49:6650–6652. https://doi.org/10.1039/C3CC42200C
27. Swart M (2008) Accurate spin-state energies for iron complexes. J Chem Theory Comp
4:2057–2066
28. Perdew JP, Burke K, Ernzerhof M (1996) Generalized gradient approximations made simple.
Phys Rev Lett 77:3865–3868
29. Grimme S (2006) Semiempirical GGA-type density functional constructed with a long-range
dispersion correction. J Comput Chem 27:1787–1799
30. Swart M, Solà M, Bickelhaupt FM (2009) A new all-round DFT functional based on spin states
and S N 2 barriers. J Chem Phys 131:094103
31. Han W-G, Liu T, Lovell T, Noodleman L (2006) DFT calculations of 57 Fe Mössbaurer isomer
shifts and quadrupole splittings for iron complexes in polar dielectric media: applications to
methane monooxygenase and ribonucleotide reductase. J Comput Chem 27:1292–1306
32. Güell M, Solà M, Swart M (2010) Spin-state splittings of iron(II) complexes with trispyrazolyl
ligands. Polyhedron 29:84–93. https://doi.org/10.1016/j.poly.2009.06.006
33. MacBeth CE et al (2004) Utilization of hydrogen bonds to stabilize M-O(H) units: synthesis
and properties of monomeric iron and manganese complexes with terminal oxo and hydroxo
ligands. J Am Chem Soc 126:2556–2567. https://doi.org/10.1021/ja0305151
M. Gruden et al.
12. Yang T-C, Maeser NK, Laryukhin M, Lee H-I, Dean DR, Seefeldt LC, Hoffman BM (2005)
The interstitial atom of the nitrogenase FeMo-cofactor: ENDOR and ESEEM evidence that it
is not a nitrogen. J Am Chem Soc 127:12804–12805. https://doi.org/10.1021/ja0552489
13. Lancaster KM et al (2011) X-Ray emission spectroscopy evidences a central carbon in the
nitrogenase iron-molybdenum cofactor. Science 334:974–977. https://doi.org/10.1126/science.
1206445
14. Bjornsson R et al (2014) Identification of a spin-coupled Mo(III) in the nitrogenase iron—
molybdenum cofactor. Chem Sci 5:3096–3103. https://doi.org/10.1039/c4sc00337c
15. Sippel D et al (2018) A bound reaction intermediate sheds light on the mechanism of nitrogenase. Science 359:1484–1489. https://doi.org/10.1126/science.aar2765
16. Cao L, Ryde U (2018) Influence of the protein and DFT method on the broken-symmetry and
spin states in nitrogenase. Int J Quantum Chem 118:e25627. https://doi.org/10.1002/qua.25627
17. Cao L, Caldararu O, Ryde U (2017) Protonation states of homocitrate and nearby residues
in nitrogenase studied by computational methods and quantum refinement. J Phys Chem B
121:8242–8262. https://doi.org/10.1021/acs.jpcb.7b02714
18. Siegbahn PEM (2018) A major structural change of the homocitrate ligand of probable importance for the nitrogenase mechanism. Inorg Chem 57:1090–1095. https://doi.org/10.1021/acs.
inorgchem.7b02493
19. Siegbahn PEM (2016) Model calculations suggest that the central carbon in the femo-cofactor
of nitrogenase becomes protonated in the process of nitrogen fixation. J Am Chem Soc
138:10485–10495. https://doi.org/10.1021/jacs.6b03846
20. Siegbahn PEM (2018) Is there computational support for an unprotonated carbon in the E4
state of nitrogenase? J Comput Chem 39:743–747. https://doi.org/10.1002/jcc.25145
21. Dau H, Iuzzolino L, Dittmer J (2001) The tetra-manganese complex of photosystem II during
its redox cycle—X-ray absorption results and mechanistic implications. BBA-Bioenergetics
1503:24–39. https://doi.org/10.1016/s0005-2728(00)00230-9
22. Krewald V et al (2015) Metal oxidation states in biological water splitting. Chem Sci
6:1676–1695
23. Rohde JU et al (2003) Crystallographic and spectroscopic characterization of a nonheme
Fe(IV)-O complex. Science 299:1037–1039. https://doi.org/10.1126/science.299.5609.1037
24. Fukuzumi S, Morimoto Y, Kotani H, Naumov P, Lee Y-M, Nam W (2010) Crystal structure of
a metal ion-bound oxoiron(IV) complex and implications for biological electron transfer. Nat
Chem 2:756–759. https://doi.org/10.1038/nchem.731
25. McDonald AR, Que Jr L (2013) High-valent nonheme iron-oxo complexes: synthesis, structure,
and spectroscopy. Coord Chem Rev 257:414–428. https://doi.org/10.1016/j.ccr.2012.08.002
26. Swart M (2013) A change in oxidation state of iron: scandium is not innocent. Chem Commun
49:6650–6652. https://doi.org/10.1039/C3CC42200C
27. Swart M (2008) Accurate spin-state energies for iron complexes. J Chem Theory Comp
4:2057–2066
28. Perdew JP, Burke K, Ernzerhof M (1996) Generalized gradient approximations made simple.
Phys Rev Lett 77:3865–3868
29. Grimme S (2006) Semiempirical GGA-type density functional constructed with a long-range
dispersion correction. J Comput Chem 27:1787–1799
30. Swart M, Solà M, Bickelhaupt FM (2009) A new all-round DFT functional based on spin states
and S N 2 barriers. J Chem Phys 131:094103
31. Han W-G, Liu T, Lovell T, Noodleman L (2006) DFT calculations of 57 Fe Mössbaurer isomer
shifts and quadrupole splittings for iron complexes in polar dielectric media: applications to
methane monooxygenase and ribonucleotide reductase. J Comput Chem 27:1292–1306
32. Güell M, Solà M, Swart M (2010) Spin-state splittings of iron(II) complexes with trispyrazolyl
ligands. Polyhedron 29:84–93. https://doi.org/10.1016/j.poly.2009.06.006
33. MacBeth CE et al (2004) Utilization of hydrogen bonds to stabilize M-O(H) units: synthesis
and properties of monomeric iron and manganese complexes with terminal oxo and hydroxo
ligands. J Am Chem Soc 126:2556–2567. https://doi.org/10.1021/ja0305151