AMBER Archive (2007)

Subject: AMBER: equilibrium constants via MMPBSA

From: Sean Rathlef (sean_at_syncitium.net)
Date: Fri Jun 01 2007 - 11:57:46 CDT

Dear Amber,

A quick question regarding Keq computations via MMPBSA. I have an association reaction (A + B --> AB). I am modeling the free energies for AB, A, and B, and generating my deltaG from:

1 delG(AB) - [delG(A) + delgG(B)].

Keq is then computed via:

2 Keq = e^(-delG/RT).

In this instance, Keq will have units of M-1, because of the relationship to the concetrations of the species, i.e.,

3 Keq = [AB] / [A]*[B]

The Keq leveraged from equation 2 however is unitless, so would it be appropriate to simply divide this value by standard state concentraion, C_0, of 1M?

Thanks for any responses,
Sean

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