Using Table 10-2 values, (a) what do you predict from the standard reduction potentials about the direction electrons will tend to flow between NADH and O2,

Question

and (b) using the equation calculate the standard free energy change (?G°) associated with the transfer of electrons between NADH and O2.
Reaction: O2 + 2 NADH + 2H+ = 2 H2O + 2 NAD+
Equation: ?G° = ?nF?E0' [n is the number of electrons transferred; F is the Faraday constant (23,062 cal/mol-V)

Answer 1

Answer:
a. The reduction potential is a measure of the oxidized form of a redox pair's electron affinity. A positive E0 means that the oxidized form has a high affinity for electrons (a good electron acceptor). The highly positive (+0.8 V) E0 for the O2/H2O pair means that O2 is a very good electron acceptor. The highly negative E0 value for the NAD+/NADH pair means that NAD+ is a poor electron acceptor but NADH is a good electron donor. Electron transfer from NADH to O2 is much more thermodynamically favorable than transfer of electrons from H2O to NAD+.
b. Transfer of electrons from NADH and O2 involves the following two half-reactions:
NADH → NAD+ + H + 2e−, E0' = +0.32 V [Note: this direction of the reaction changes the E0' sign to +] and ½ O2 + 2H + 2e−→ 2H2O, E0' = 0.82 V
ΔG° = −2(23,062 cal/mol-V)(+0.32 + +0.82= +1.1.36 V) = −52,397 cal/mol = −52.4 kcal/mol