Page 355 - Thermodynamics of Biochemical Reactions

Redox Reactions 355

9.1 Calculate the standard apparent reduction potentials for 298.15 K at pHs 5,6, 7, 8, and 9 and ionic strengths 0, 0.10, and
0.25 M for the following biochemical half reactions and plot their pH dependencies at 0.25 M ionic strength.
0, (aq) + 4e-= 2H2 0
0, (8) + 4e-= 2H2 0
O2 (sq) + 2e-= 2H2 O2
o2 (g) + 2e-= 2H2 O2
cytochrome cox+ e-= cytochrome cred
pyruvate + 2e-= lactate
acetaldehyde + 2e-= ethanol
Fm,, + 2e-z FMNred
retinal + 2e-= retinol
(1 0) acetone + 2e- = 2-propanol
(1 1) NAD,, + 2e-= NADred
(12) NADP,, + 2e-=NADPred
(13) f erredoxin,, + e-= f erredoxinred
(14) acetylcoA + 2e-= coA + acetaldehyde
(15) 2e-= H2 (8)
(16) 2e-= H2 (aq)

(BasicBiochemData has to be loaded)

calcappredgot [eL, nu-, pHlist-, islist-] : =
Module[{energy), (*Calculates the standard apparent reduction potential of
a half reaction at specified ~HS and ionic
strengths for a biochemical equation typed in the form
nadox+de==nadred. The names of the reactants call the corresponding
functions of pH and ionic strength. nu is the number of
electrons involved. pHlist and islist can be lists.*)
energy = Solve [eq, de] ;
(-l*energy[[l, 1, 211 / (nu*96.485)) /. pH-ipHlist /. is-iislist
1

TableFonn[Transpose[calcapgredpot[nadox+de == nadred, 2, (5, 6, 7, 8, 9}, {0, .l, .25}]],
TableHeadings + { { "I=O MI1, "I=O. 10 MI', llI~O. 25 Mml},
{"pH 5", "pH 6" "pH 7", "pH 8", "pH 9")}, TableSpacing+ {I, I}]
PH 5 PH 6 PH 7 PH 8 PH 9
1=0 M -0.265275 -0.294855 -0.324435 -0.354015 -0.383595
1~0.10 M -0.258932 -0.288512 -0.318092 -0.347672 -0.377252

1~0.25 M -0.256884 -0.286464 -0.316044 -0.345624 -0.375204
plot11 = Plot [calcappredpot [nadox+de == nadred, 2, pH, .25],
{pH, 5, 9}, AxesLabel + (I1pHIm, llEio/Vn}];