1. Principles of Bioinorganic Chemistry - 2004

2. Magnetic Splitting of Line in 63/65Cu EPR Spectroscopy

8. The Research Yard at SLAC

9. Electron Transfer (ET) in Living Systems
PRINCIPLES:
M-binding sites tailored to minimize structural changes upon ET
One-electron transfer processes preferred
Coupling of H+ with electron transfer controls redox potential
ET can occur over long distances; ~ Å is most common
Parameters: distance, driving force, reorganizational energy, path
TOPICS:
Three major bioinorganic ET units: FenSn clusters; Cu; hemes
Long-distance electron transfer: dependence on distance, driving force, reorganization energy
Electron supply in the methane monooxygenase system

10. The Major Metal Units in ET Proteins (1)
Iron-Sulfur
Clusters

11. Properties of Iron-Sulfur Clusters
(A) Rubredoxin
Fe–S, Å in oxidized (FeIII) and reduced (FeII) states
Reduction potentials: - 50 to + 50 mV
(B) 2Fe-2S Ferredoxins (Fd)
Reminder:
eo =
-RT/nF lnQ + pH,
where Q =
[Mn]/[Mn-1]
Thus, at pH 7, the
biological H2/2H+
standard couple
is mV.
FeII FeII
FeII FeIII
FeIII FeIII
reduced
mixed-valent
oxidized
all physiological uses
Reduction potentials: -490 to mV
(C) 3Fe-4S Ferredoxins (cube missing a corner)
FeIII 3S4
FeIII 2 FeII S4
Reduction potentials: -700 to mV

12. Properties of Iron-Sulfur Clusters, cont’d
(D) 4Fe-4S Ferredoxins and High-potential Iron Proteins (HiPIPs)
The three state hypothesis:
FeII3 FeIII
FeII2 FeIII2
FeII FeIII3
Ferredoxin
HiPIP
Reduction potentials: -650 to mV (Fd); mV (HiPIP)
minimal reorganizational energy

13. The Physical Properties of Iron-Sulfur Clusters

14. Structure of an 8Fe-8S Ferredoxin
Primary structure (sequence)
does not dictate the tertiary
structure of a metalloprotein,
as revealed by this 8-iron
ferredoxin crystal structure.

15. The Major Metal Units in ET Proteins (2)
Blue Copper and CuA
Depicted at the right are the three copper sites in the enzyme ascorbate oxidase. Type 1, or blue, copper is the ET center. Below is depicted CuA .
Blue Copper
CuA

16. The Physical Properties of Blue Copper Centers
The deep sky blue
color of these
proteins facilitated
their purification on
columns; the optical
band is Cu–S C.T.

17. Structure of Poplar Plastocyanin
The copper(II) thiolate center is difficult to model.
The oxidized, reduced and apo plastocyanin structures are nearly identical.

18. EPR Spectra Distinguish the Three Types of Copper Found in Metalloproteins

19. CuA Model Chemistry: Reversible 1-Electron Transfer
These complexes demonstrate that constrained dicopper(I/II) units afford good 1-electron reversible transfer centers and display the possible environments that could be encountered in biology.
LeCloux
Chuan He

20. The Major Metal Units in ET Proteins (3)
Cytochrome c from tuna showing coordination of the iron porphyrin group by the protein side chains from Met (left) and His (right) residues.

21. Electronic Properties of Low-Spin Metalloporphyrins
Note again, minimal reorganization energy upon electron transfer