Subject: cation-pi interaction

From: Mark Ripley <[email-masked]>
Date: Mon, 25 Nov 2002 10:59:38 +0000

Dear CCLers,

my studies concern molecular dynamics simulation of protein-protein complex where main interactions are of the cation-pi type. As far as I know common force fields like that of Amber are not able to 'handle' that interaction. Is anyone aware of force fields capable of dealing with cation-pi interaction?

Thanks in advance, Mark.
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From: Per-Ola Norrby <[email-masked]>
Date: Mon, 25 Nov 2002 16:13:17 +0100

>Dear CCLers,
>
>my studies concern molecular dynamics simulation of protein-protein 
>complex where main interactions are of the cation-pi type. As far as 
>I know common force fields like that of Amber are not able to 
>'handle' that interaction. Is anyone aware of force fields capable 
>of dealing with cation-pi interaction?
>
>Thanks in advance, Mark.

	Dear Mark,

	We've looked a bit at ammonium-benzene interactions, mostly 
QM, but also some force field checks.  In our experience, the 
interaction can be at least partially modelled by standard force 
fields, provided that the aromatic ring has a negatively charged core 
and positive hydrogens (as in Amber and MM3, but not standard MM2). 
With the force fields in MacroModel (among them Amber*), we find that 
roughly half the interaction energy is captured by the force field.

	I believe that Peter Kollman studied solvated cation-pi 
systems in some detail using AMBER, but I don't have the reference 
handy.

	Allinger added some terms for using sp2 carbons as hydrogen 
bond acceptors in MM3.  Such a potential could capture the rest of 
the interaction, also for a benzene-M+ system, but not all programs 
allow you to add this potential.  Some programs will only allow 
hydrogen bond potentials for heteroatom-hydrogen...heteroatom.

	Best,

	Per-Ola
-- 
Per-Ola Norrby, Assoc. Professor, http://compchem.dfh.dk/PeO/
Technical University of Denmark, Deptartment of Chemistry
Building 201, Kemitorvet, DK-2800 Kgs. Lyngby, Denmark
Email: [email-masked]  tel +45-45252123,  fax +45-45933968