dG0' calculation for a reaction

[songcan chen]

Hello administrator,

I sent this Email to ask how dG0' for the following reactions was calculated:

C04628 + C03920 <=> C04832 + C01438

When I search this reaction at eQuilibrator, I got dG0' of -24.9 kJ mol-1. I assume this value is determined from biological standard Gibbs energy of formation of each compound (ΔfG'°). However, no ΔfG'° for C03920 and C04832 was found on the website (it says 'Cannot estimate ΔfG'° for C03920 and C04832 because the uncertainty is too high'). May I ask how dG0' for the reaction was calculated in this case?

Best,

Songcan.

[Elad Noor]

Hi Songcan,

Sorry for missing your question for so long. I hope this is still somewhat relevant, so I'll try to answer briefly.

The ΔrG'0 is actually not calculated from the formation energies, but using the group-contribution method. Since the two compounds you mentioned have groups that cancel out in the reaction (i.e. they don't change and therefore we can ignore their energy). The algorithm focuses only on the things that change, which in this case have empirically determined information. That is why we can still predict the reaction ΔG'0, but not each reactant individually.

Best,

Elad