+ current, cathodic i c - current, anodic i a + potential, v - potential, v

+ current, cathodicic

- current, anodicia

+ potential,

V

- potential,

V

+ current, cathodicic

- current, anodicia

+ potential,

V

- potential,

V

Reduction

Oxidation

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

When no electroactive species is present, no current flows, no ic nor ia

This is what backgroundelectrolyte should look like.

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

Starting at a + V,Initially no current flows

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

If a reducible species is present ic will increase

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

And continue to increase

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

Until all of the species is reduced. ic has reached a maximum.

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

Then ic decreases until…

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

It again reaches the background current level.

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

Now the potential is reversed

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

And as V is more positive, The reduced species can beRe-oxidixed

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

So ia decreases to a maximum

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

Where all has been oxidized,

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

Then ia decreases, back to thebackground level.

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

Important features:

Ec

Ea

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

E1/2 is ~ EoRed

Ec

Ea

E1/2

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

All Fe(3+)

Using an Fe(3+) heme,Fe is electroactive,(and also the heme!) …

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

A little Fe(2+) formed

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

more Fe(2+) formed

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

Largest cathodic current,Max rate of Fe(2+) formed

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

Little Fe(3+) left; Less Fe(2+) forms;Decrease in ic

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

all Fe(2+) now

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 VA little Fe(2+) isre-oxidized toFe(3+)

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

Nearly all Fe(2+) has been oxized

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

All back to Fe(3+).

Cycle could be runagain, many times.

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

Important features:

Ec

Ea

+ current, cathodicic

- current, anodicia

+ V - V

+1.0 V -1.0 V

E1/2 for Fe(3+/2+) reduction

Ec

Ea

E1/2

theblackbox Working

Electrode:

Where the redox reaction action occurs

theblackbox

Reference Electrode:

Defines “0” potential for the cell.

We use Ag/AgCl

Working Electrode:

Where the redox reaction action occurs

theblackbox

Auxilliary Electrode:

Needed to complete circuit.

We use a Pt wire

Reference Electrode:

Working Electrode:

Where the redox reaction action occurs

theblackbox

Fe(3+)Fe(3+) Fe(3+) Fe(3+)

Fe(3+)Fe(3+)Fe(3+)

Fe(3+) Fe(3+) Fe(3+)Fe(3+)

Fe(3+)

Fe(3+) Fe(3+) Fe(3+)

Fe(3+)

Fe(3+)Fe(3+) Fe(3+)

Fe(3+)

At start of CV experiment…

Working Electrode:

Where the redox reaction action occurs

theblackboxWorking

Electrode:

Where the redox reaction action occurs

Fe(2+)Fe(3+) Fe(3+) Fe(3+)

Fe(3+)Fe(3+)

Fe(3+)

Fe(3+) Fe(3+) Fe(3+)Fe(3+)

Fe(3+)

Fe(3+) Fe(3+) Fe(3+)

Fe(3+)

Fe(3+)Fe(3+) Fe(3+)

Fe(3+)

Fe(3+)

Moving up the cathodic current peak…

theblackboxWorking

Electrode:

Where the redox reaction action occurs

Fe(2+)Fe(3+) Fe(3+) Fe(3+)

Fe(3+)Fe(3+)

Fe(2+)

Fe(3+) Fe(3+) Fe(3+)Fe(3+)

Fe(3+)

Fe(3+) Fe(3+) Fe(3+)

Fe(3+)

Fe(3+)Fe(3+) Fe(3+)

Fe(3+)

Fe(3+)

Still moving up the cathodic current peak…

theblackboxWorking

Electrode:

Where the redox reaction action occurs

Fe(2+)Fe(2+) Fe(3+) Fe(3+)

Fe(3+)Fe(3+)

Fe(2+)

Fe(3+) Fe(3+) Fe(3+)Fe(3+)

Fe(3+)

Fe(3+) Fe(3+) Fe(3+)

Fe(3+)

Fe(3+)Fe(3+) Fe(3+)

Fe(3+)

Fe(3+)

After the maximum cathodic current peak…

theblackboxWorking

Electrode:

Where the redox reaction action occurs

Fe(2+)Fe(3+) Fe(3+) Fe(3+)

Fe(3+)Fe(3+)

Fe(2+)

Fe(3+) Fe(3+) Fe(3+)Fe(3+)

Fe(3+)

Fe(3+) Fe(3+) Fe(3+)

Fe(3+)

Fe(3+)Fe(3+) Fe(3+)

Fe(3+)

Fe(3+)

Moving down the anodic current peak…

theblackboxWorking

Electrode:

Where the redox reaction action occurs

Fe(2+)Fe(3+) Fe(3+) Fe(3+)

Fe(3+)Fe(3+)

Fe(3+)

Fe(3+) Fe(3+) Fe(3+)Fe(3+)

Fe(3+)

Fe(3+) Fe(3+) Fe(3+)

Fe(3+)

Fe(3+)Fe(3+) Fe(3+)

Fe(3+)

Fe(3+)

Sill moving down the anodic current peak…

theblackboxWorking

Electrode:

Where the redox reaction action occurs

Fe(3+)Fe(3+) Fe(3+) Fe(3+)

Fe(3+)Fe(3+)Fe(3+)

Fe(3+) Fe(3+) Fe(3+)Fe(3+)

Fe(3+)

Fe(3+) Fe(3+) Fe(3+)

Fe(3+)

Fe(3+)Fe(3+) Fe(3+)

Fe(3+)

At end of CV experiment…

+ ic

- ia

- V

In your CV scans of Fe(porphyrin)Cl, you will see:

InterpretationInterpretation????

+ V

How is the range of Heme Potentialsin Respiration adjusted?

N

N

NN Fe

ClN

N

NN Fe

Cl

CH3

CH3H3C

H3C

N

N

NN Fe

Cl

Cl

ClCl

Cl

The Question asked: Can changing Heme substituents vary Fe(3+/2+) redcution potentials?