Subject: Interaction energy in host-guest complex

From: "Dr. Paolo Mencarelli" <[email-masked]>
Date: Fri, 23 Feb 1996 03:13:35 -0500 (EST)

Hi all,

I am an organic chemist interested in host-guest chemistry and I have a
question on a computational aspect of this topic.

The interaction energy (Delta E) of the host and the guest in a given
complex may be defined as:

Delta E = Esteric(complex) - Esteric(host) - Esteric(guest) 

where the steric energies may be evaluated by the molecular mechanics
approach.(For the time being I am neglecting the entropic and solvation
effects which are not taken into account by a molecular mechanics simulation
in the gas phase).
The interaction energies are useful in comparing the relative stabilities of
different conformations of the complex, for example different orientations
of the guest with respect to the host. 
Now comes my question: given two different complexes of the same host with
two different guests (or two hosts with the same guest), is it correct to
compare the interaction energies of the two complexes in order to find out
which is the better guest (or the better host)?
I am not sure that this is correct since, when the two guests (or the two
hosts) are not stereoisomers or not even isomers, the two complexes have
different chemical compositions.
Thanks to all who reply. I will summarize.

Paolo
*********************************************************
*   Dr. Paolo Mencarelli                                *
*   Dipartimento di Chimica  - Universita' La Sapienza  *
*   P.le Aldo Moro, 2  00185 Roma - ITALY               *
*   tel 06-49913697 fax 06-490631                       *
*   E-Mail [email-masked]                       * 
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