Post on 12-Jan-2016
An Introduction to An Introduction to Electrochemistry in Inorganic Electrochemistry in Inorganic
ChemistryChemistry
OrOr
Quack…. Quack….I see a duckQuack…. Quack….I see a duck
[Cu(NH3)4]2+ (aq) [Cu(NH3)2]
+ (aq) Cu
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 1 2
Oxidation Number
-G
/F =
nE
o
Cu(NH3)4]2+
[Cu(OH2)5]2+ (aq) [Cu(OH2)2]
+ (aq) Cu
N
N
N
NN
N
phenanthroline 4,7-dimethylphenanthroline 2,9-dimethylphenanthroline
Now we react the Cu(II) with a series of phenanthroline-based ligands
Eo for [CuL2]2+/[CuL2]
+ (Volts)
2,9-di-Mephen 0.823 V
4,7-di-Mephen 0.256 V
phen 0.322 V
N
N
N
NN
N
phenanthroline 4,7-dimethylphenanthroline 2,9-dimethylphenanthroline
Now we react the Cu(II) with a series of phenanthroline-based ligands
Eo for [CuL2]2+/[CuL2]
+ (Volts)
2,9-di-Mephen 0.823 V
4,7-di-Mephen 0.256 V
phen 0.322 V
Ligand’s Influence on Redox Potential
Influence of coordinated atoms on redox potential
THERE’S THERE’S METALS METALS
IN IN THERE!!!!!!!THERE!!!!!!!
!!!!!!
Follows Krebs CycleResults in oxidative phosphorylation
Electron transport chain
Yes! Every Step uses a metalloenzymeYes! Every Step uses a metalloenzyme
Redox Potential for Electron Transport Proteins
Oxidized rubredoxin (1IRO) from Clostridum pasterurianum at 1.1Å
Rubredoxin (Rd)
oxidized Spinach ferredoxin (1A70) from Spinacia oleracea at 1.7Å
[2Fe] Ferredoxin
[4Fe] Iron Proteins
(1BLU) from Chromatim vinosum at 2.1Å (1IUA) from Thermochromatium tepidum at 0.8Å
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
G
o' (
kJ
mo
l-1 r
ela
tiv
e t
o O
2)
0
50
100
150
200
250
E'o
(v
olt
s)
FMN
CoQ
NADH
cyt b
cyt c1
cyt a
cyt c
O2
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 Reduction Potential Difference ==EºEº
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 ETScan be used to synthesize ATP.
The reduction potential can be related to free energy change by: Gº = -nFEº
where n = # electrons transferred = 1,2,3F = 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 negativevoltage -- (below it in Table)**********************************************************************
Standard Reduction Potential
Oxidant Reductant n Eº, vNAD+ NADH 2 -0.32acetaldehyde ethanol 2 -0.20pyruvate lactate 2 -0.19oxaloacetate malate 2 -0.171/2 O2+2H+ H2O 2 +0.82
Redox Function
Thermodynamics = redox potential: (G = -nFE0)
• 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 Zeff - all orbital energy levels(stronger ligand donation lower Zeff 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 carrierwith low reduction potential (high tendency to donate electrons)toward carriers with higherreduction potential (high tendencyto accept electrons).
Superoxide Dismutase[CuZnSOD]
12Influenceson 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?