In
chemistry and
biochemistry, a measure of the
electron affinity of a particular
molecule. This is a somewhat arbitrary measure, as it is measured and reported as a
potential difference between the molecule in question and that of the
standard hydrogen electrode, which has been
pronounced to be 0. Most redox potentials (denoted E
0) are tabulated under a set of (also arbitrary) standard conditions: 1
molar HCl (a
pH of 0), 1 molar oxidant, 1 molar reductant and 25 degrees
Celsius. Since
biomolecules fall apart at extremes of pH, biologically important redox potentials are measured and reported at pH 7 (denoted E
0'.)
These values are for one-electron transfer processes. For multiple electron processes the individual one-electron values are averaged and this average is called a
redox midpoint potential.
Redox potentials are measured in
volts, and a good way to compare them is to remember that electrons always want to go to the molecule with the highest potential. So, for example if you were trying to figure out if
NADPH (with a redox midpoint potential of -320 mV) would give it's two electrons to
flavin mononucleotide (-205 mV), you could just by comparing the two values predict that it should happen
spontaneously.
The probability of it
actually happening depends
inversely on how bad you need your experiment to work. But that is meat for another node.