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From: David A Case <david.case.rutgers.edu>

Date: Wed, 21 Sep 2016 07:38:36 -0400

On Wed, Sep 21, 2016, Trang Nguyen wrote:

*>
*

*> I've been noticed that in many of my MM-PBSA calculations, the
*

*> electrostatic and solvation energy are compensated with each other; i.e.,
*

*> when one is negative, the other would be positive with relatively close
*

*> absolute values. It's pretty straightforward to explain why the
*

*> electrostatic energy is negative would lead to positive solvation energy.
*

*> But I'm not quite sure about the positive electrostatic and negative
*

*> solvation energy. Any comment or explanation in the later situation is
*

*> appreciated.
*

Your observation is correct. Think about it this way: solvation screens

electrostatic interactions between atoms. So the electrostatic interaction

terms in the gas-phase are very much smaller in solution, which implies that

the solvation energy is close to being the opposite of the electrostatic

energy. Doesn't matter whether the gas-phase term is positive or negative:

the solvation term will always be of the opposite sign.

This analysis ignores the "self-energy" terms, where i=j, which reflect the

penalty for burial of charges. There is no such contribution in the

gas-phase, but a significant contribution to the solvation free energy. This

means that the anti-correlation between electrostatics and solvation energy is

less perfect that it would have been for just the cross terms.

...dac

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Received on Wed Sep 21 2016 - 05:00:02 PDT

Date: Wed, 21 Sep 2016 07:38:36 -0400

On Wed, Sep 21, 2016, Trang Nguyen wrote:

Your observation is correct. Think about it this way: solvation screens

electrostatic interactions between atoms. So the electrostatic interaction

terms in the gas-phase are very much smaller in solution, which implies that

the solvation energy is close to being the opposite of the electrostatic

energy. Doesn't matter whether the gas-phase term is positive or negative:

the solvation term will always be of the opposite sign.

This analysis ignores the "self-energy" terms, where i=j, which reflect the

penalty for burial of charges. There is no such contribution in the

gas-phase, but a significant contribution to the solvation free energy. This

means that the anti-correlation between electrostatics and solvation energy is

less perfect that it would have been for just the cross terms.

...dac

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Received on Wed Sep 21 2016 - 05:00:02 PDT

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