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