4 From Small Molecules to Complex Systems: A Survey of Chemical …
209
Fig. 4.23 Mössbauer spectra of PhrB taken at (a) T = 77 K, b T = 5 K with an external field of 20 mT
and c T = 5 K with an external magnetic field of 5 T. The magnetic fields were applied perpendicular
to the γ-beam. The solid lines are spin Hamiltonian simulations assuming a diamagnetic ground
state and all four iron being equivalent. PhrB has a [4Fe–4S] 2+ cluster the structural view is given
on the right. The diamagnetic ground state can be rationalized as follows: An electron is delocalized
between two mixed valent iron ions, resulting in a mean charge of Fe 2.5+ . The two Fe 2.5+ –Fe 2.5+
pairs have a spin of S = 9/2 each, but those couple antiparallel to each other and the total spin
becomes zero. Mössbauer data reprinted by permission from Springer-Nature: Hyperfine Interact.
Copyright (2013) [88]
assuming a diamagnetic S = 0 ground state. Such behavior is characteristic for a
diamagnetic [4Fe–4S]
2+ cluster. The cluster possesses two mixed-valence iron pairs
with two excess electrons each one delocalized over one pair (Fe
2.5+ –Fe
2.5+ ). The
spins of the two Fe
2.5+ –Fe
2.5+ pairs S 12 = 9/2 and S 34 = 9/2 are antiparallel coupled,
yielding a total cluster spin S = 0.
4.5.2 Exploration of the Unusual 4Fe–4S Center of the LytB
Protein
The LytB protein also called isoprenoid synthase (IspH) is an air sensitive iron sulfur
enzyme which is crucial for the biosynthesis of isoprenoids in many bacteria and in the
209
Fig. 4.23 Mössbauer spectra of PhrB taken at (a) T = 77 K, b T = 5 K with an external field of 20 mT
and c T = 5 K with an external magnetic field of 5 T. The magnetic fields were applied perpendicular
to the γ-beam. The solid lines are spin Hamiltonian simulations assuming a diamagnetic ground
state and all four iron being equivalent. PhrB has a [4Fe–4S] 2+ cluster the structural view is given
on the right. The diamagnetic ground state can be rationalized as follows: An electron is delocalized
between two mixed valent iron ions, resulting in a mean charge of Fe 2.5+ . The two Fe 2.5+ –Fe 2.5+
pairs have a spin of S = 9/2 each, but those couple antiparallel to each other and the total spin
becomes zero. Mössbauer data reprinted by permission from Springer-Nature: Hyperfine Interact.
Copyright (2013) [88]
assuming a diamagnetic S = 0 ground state. Such behavior is characteristic for a
diamagnetic [4Fe–4S]
2+ cluster. The cluster possesses two mixed-valence iron pairs
with two excess electrons each one delocalized over one pair (Fe
2.5+ –Fe
2.5+ ). The
spins of the two Fe
2.5+ –Fe
2.5+ pairs S 12 = 9/2 and S 34 = 9/2 are antiparallel coupled,
yielding a total cluster spin S = 0.
4.5.2 Exploration of the Unusual 4Fe–4S Center of the LytB
Protein
The LytB protein also called isoprenoid synthase (IspH) is an air sensitive iron sulfur
enzyme which is crucial for the biosynthesis of isoprenoids in many bacteria and in the