oxidation and reduction

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Lecture 4 Slides

Oxidation and

Reductionas it pertains to biochemistry

Read The Slow Burnplease read

fig 13-22

fig 13-22

fig 13-23

reduction potentialcan be measured

testcell

ref.cell

Redox reactions as pairs of half-reactions

Fe2+ + Cu2+Fe3+ + Cu+

The half-reactions:

Fe3+ + e- Fe2+

Cu2+ + e- Cu+ E'o = -.18

E'o = .77

always reductions!rh

Energetics calculated from half-reactions

Fe2++ Cu2+Fe3+ + Cu+

Cu2+ + e-Cu+ E'o =.18

what is E'o for this reaction ?

E'o = (.18 +.77)

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Fe2+ + Cu2+Fe3+ + Cu+

Fe3+ + e- Fe2+ E'o = .77

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DG'o = -nFE'o

one confusing thing: by the convention, positive E means spontaneous reaction… or negative DG.

relationship between free energy and reduction potential

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Energetics calculated from half-reactions

Fe2++ Cu2+Fe3+ + Cu+

Cu2+ + e-Cu+ E'o = .18

what is E'o for this reaction ?

E'o = 0.95

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Fe2+ + Cu2+Fe3+ + Cu+

Fe3+ + e- Fe2+ E'o = .77

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DG'o = -nFE'o

nFE'o

glucose

Fe2+ + Cu2+ Fe3+ + Cu+

familiar from earlier chemistry classes…

BUT WHAT ABOUT SOMETHING LIKE THIS?:

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Oxidation of a "model" sugar molecule: CH2O

glucose

general:

let's make n=1, to aid understanding

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Oxidation of a "model" sugar molecule: CH2O

1) removal of electrons from sugar

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Oxidation of a "model" sugar molecule: CH2O

2) reduction of oxygen

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Oxidation of a "model" sugar molecule: CH2O

3) production of CO2

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TOP

MID

DLE

BO

TTO

MTable of Standard Reduction Potentials

fig 13-24

NAD+ and NADH

The business end of NAD and NADP

this moiety is from the vitamin niacinrh

this moiety is from the vitamin niacinrh

moi·e·ty (moi-t)n.One of two or more parts into which something may be divided, such as the various parts of a vitamin or molecule.

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table 13-8

fig 13-27

FAD and FADH2 (and FMN and FMNH2)

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The business end of FAD or FMN

this moiety is from the vitamin riboflavin

isoalloxazinering

fig 13-9