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?