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+ current, cathodic i c - current, anodic i a + potential, V - potential, V.

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Presentation on theme: "+ current, cathodic i c - current, anodic i a + potential, V - potential, V."— Presentation transcript:

1 + current, cathodic i c - current, anodic i a + potential, V - potential, V

2 + current, cathodic i c - current, anodic i a + potential, V - potential, V Reduction Oxidation

3 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V -1.0 V When no electroactive species is present, no current flows, no i c nor i a This is what background electrolyte should look like.

4 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V Starting at a + V, Initially no current flows

5 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V If a reducible species is present i c will increase

6 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V And continue to increase

7 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V Until all of the species is reduced. i c has reached a maximum.

8 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V Then i c decreases until…

9 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V It again reaches the background current level.

10 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V Now the potential is reversed

11 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V And as V is more positive, The reduced species can be Re-oxidixed

12 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V So i a decreases to a maximum

13 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V Where all has been oxidized,

14 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V Then i a decreases, back to the background level.

15 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V Important features: EcEc EaEa

16 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V E 1/2 is ~ E o Red EcEc EaEa E 1/2

17 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V All Fe(3+) Using an Fe(3+) heme, Fe is electroactive, (and also the heme!) …

18 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V A little Fe(2+) formed

19 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V more Fe(2+) formed

20 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V Largest cathodic current, Max rate of Fe(2+) formed

21 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V Little Fe(3+) left; Less Fe(2+) forms; Decrease in i c

22 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V all Fe(2+) now

23 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V

24 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V A little Fe(2+) is re-oxidized to Fe(3+)

25 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V

26 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V Nearly all Fe(2+) has been oxized

27 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V All back to Fe(3+). Cycle could be run again, many times.

28 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V Important features: EcEc EaEa

29 + current, cathodic i c - current, anodic i a + V- V- V +1.0 V-1.0 V E 1/2 for Fe(3+/2+) reduction EcEc EaEa E 1/2

30 the black box Working Electrode: Where the redox reaction action occurs

31 the black box Reference Electrode: Defines “0” potential for the cell. We use Ag/AgCl Working Electrode: Where the redox reaction action occurs

32 the black box Auxilliary Electrode: Needed to complete circuit. We use a Pt wire Reference Electrode: Working Electrode: Where the redox reaction action occurs

33 the black box Fe(3+) At start of CV experiment… Working Electrode: Where the redox reaction action occurs

34 the black box Working Electrode: Where the redox reaction action occurs Fe(2+)Fe(3+) Moving up the cathodic current peak…

35 the black box Working Electrode: Where the redox reaction action occurs Fe(2+)Fe(3+) Fe(2+) Fe(3+) Still moving up the cathodic current peak…

36 the black box Working Electrode: Where the redox reaction action occurs Fe(2+) Fe(3+) Fe(2+) Fe(3+) After the maximum cathodic current peak…

37 the black box Working Electrode: Where the redox reaction action occurs Fe(2+)Fe(3+) Fe(2+) Fe(3+) Moving down the anodic current peak…

38 the black box Working Electrode: Where the redox reaction action occurs Fe(2+)Fe(3+) Sill moving down the anodic current peak…

39 the black box Working Electrode: Where the redox reaction action occurs Fe(3+) At end of CV experiment…

40 + ic+ ic - ia- ia - V- V In your CV scans of Fe(porphyrin)Cl, you will see: Interpretation???? + V

41 How is the range of Heme Potentials in Respiration adjusted?

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

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