Or
Quack…. Quack….I see a duck

[Cu(OH
2
)
5
] 2+ (aq)
[Cu(NH
3
)
4
] 2+ (aq)
0.3
0.2
0.1
0
-0.1
-0.2
0
0.8
0.7
0.6
0.5
0.4
[Cu(OH
2
)
2
] + (aq) Cu
Cu(NH
3
)
4
]
2+
1
Oxidation Number
[Cu(NH
3
)
2
] + (aq)
2
Cu

Now we react the Cu(II) with a series of phenanthroline-based ligands
N
N
N
N
N
N phenanthroline 4,7-dimethylphenanthroline 2,9-dimethylphenanthroline
2,9-di-Mephen
4,7-di-Mephen phen
E o for [CuL
2
] 2+ /[CuL
2
] + (Volts)
0.823 V
0.256 V
0.322 V

Now we react the Cu(II) with a series of phenanthroline-based ligands
N
N
N
N
N
N phenanthroline 4,7-dimethylphenanthroline 2,9-dimethylphenanthroline
2,9-di-Mephen
4,7-di-Mephen phen
E o for [CuL
2
] 2+ /[CuL
2
] + (Volts)
0.823 V
0.256 V
0.322 V

Ligand’s Influence on
Redox Potential

Influence of coordinated atoms on redox potential

Electron transport chain
Follows Krebs Cycle
Results in oxidative phosphorylation
Yes! Every Step uses a metalloenzyme

Redox Potential for Electron
Transport Proteins

Rubredoxin (Rd)
Oxidized rubredoxin ( 1IRO ) from Clostridum pasterurianum at 1.1Å

[2Fe] Ferredoxin oxidized Spinach ferredoxin ( 1A70 ) from Spinacia oleracea at 1.7Å

[4Fe] Iron Proteins
( 1BLU ) from Chromatim vinosum at 2.1Å ( 1IUA ) from Thermochromatium tepidum at 0.8Å

250
FMN
200
NADH
150
100 cyt b
CoQ cyt c
1 cyt c cyt a
50
0
O
2
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1

So, the more negative the reduction potential is, the easier a reductant can reduce an oxidant and
The more positive the reductive potential is, the easier an oxidant can oxidize a reductant
The difference in reduction potential must be important

Reduction Potential Difference =  Eº 
 Eº  = E ° (acceptor) E ° (donor)
 measured in volts.
 The more positive the reduction potential difference is, the easier the redox reaction
 Work can be derived from the transfer of electrons and the ETS can be used to synthesize ATP.

 The reduction potential can be related to free energy change by:


F 
 where n = # electrons transferred =
1,2,3
F = 96.5 kJ/volt, called the Faraday constant

********************************************************************
Table of Standard Reduction Potentials
--Oxidant + e  reductant
-- e.g., M&vH, 3rd ed., p. 527
Note:
 oxidants can oxidize every compound with less positive voltage -- (above it in Table)
 reductants can reduce every compound with a less negative voltage -- (below it in Table)
**********************************************************************

Oxidant Reductant n Eº, v
NAD + NADH 2 -0.32
acetaldehyde ethanol 2 -0.20
pyruvate lactate 2 -0.19
oxaloacetate malate 2 -0.17
1/2
O
2
+2H + H
2
O 2 +0.82

Redox Function
Thermodynamics = redox potential: (

G = -nF E 0 )
• ionization energy - electronic structure a) HOMO/LUMO - redox active orbital energy
(stronger metal-ligand bonding
 raises the orbital energy
 easier to oxidize
 potential goes down) b) metal Z eff
- all orbital energy levels
(stronger ligand donation
 lower Z eff
 raised d-orbitals ...) c) electron relaxation - allow for orbital reorg. after redox
(creation of a hole upon oxidation
 passive electrons shift
 larger thermodynamic driving force
 potential goes down)

-- Electrons can move through a chain of donors and acceptors
-- In the electron transport chain, electrons flow down a gradient.
-- Electrons move from a carrier with low reduction potential (high tendency to donate electrons) toward carriers with higher reduction potential (high tendency to accept electrons).

Superoxide Dismutase
[CuZnSOD]

12 Influenceson
Redoxpotential: 1)Metalcenter2
)Electrostatic (ligand charge)3)σ/π-Donor strength of ligand (pKa)4)π-Acceptor strength of ligand5)Spin state6)Steric factors/ constraints
(enthatic state)How can a protein chain generate these diverse redox potentials?