Subject: Problems related to selectivity calculations

From: Girish Ssr Suravajhula <gss006 :: LaTech.edu>
Date: Wed, 16 Mar 2005 18:56:26 -0600

Dear all,

I was doing calculations using G03 on calix[4]arene crown-6 in cone and 1,3
alternate conformations.
I was trying to see the slectivity of that this molecule in both the above said
conformations with differnt alkali metal ions using Guassian-03.

I was doing bindning energy calculations$$$ by placing cesium and potassium in
crown strucutre of the molecule.

According to literature the molecule in 1,3 alternate conformation is more
selective towards cesium than potassium.  So we expected the cesium binding
energy$$$ to be higher than potassium.  But what we got is exactly opposit to
that.

Please correct me if I am doing any thing thats not right or
I would be glad to receive any suggestion from you on how to calculate the
selctivity of a molecule towards a perticular atom when compared to another
atom.

Regards,

Girish Suravajhula.

$$$[Method we used to perform binding enrgy calculation:
We made the optimization on the molecule with out the atom.  Then placed the
atom at the center of the crown ad then did the opt again and obtained the
enrgy of the whole strcuture(a).

Then we removed the atom from inside the crown and made the strcture converge
and then we obtained the energy of the molecule alone with out the atom in the
crown ring(b).

We obatined the atom anergy alone(c)

After that we did b+c-a to obtain the bindning energy of the atom and the
molecule.]

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