What is the equilibrium constant for the reduction of ribofl avin with rubredoxin, a bacterial iron–sulfur protein, in the reaction ribofl avin(ox) + rubredoxin(red) 7 ribofl avin(red) + rubredoxin(ox) given that the biological standard potential of the rubredoxin couple is −0.06 V?
Rubredoxin perform one-electron transfer as central Fe atom changes between the +2 and +3 oxidation states.
rubredoxin(red) -e ↔rubredoxin(ox) Eo=+0.06V [oxidation half rxn]
The reduced and oxidized forms of riboflavin form a couple with
riboflavin(ox) ↔ riboflavin(red) +e, Eo= -0.21 [reduction half rxn]
Eorxn=Ered+Eox=+0.06-0.21=-0.15 V
∆Go=-RTlnKc=-nFEo
Where , ∆Go=std gibbs free energy
Kc=equilibrium constant
F=faraday’s constant=96458 C/mol
Eo=emf of the rxn=-0.15V
n=number of electrons exchanged in the redox rxn=1
ln kc=nFEo/RT=1 mol e*96458 C/mol*(-0.15V)/(8.314 J/K.mol*298K)=5.84
ln Kc=-5.84
kc=exp(-5.84)=0.0029
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