ZN ions

[Sergio Manzetti <sergio (+ at +) proinformatix.com>]

 Dear CCLrs I am trying to simulate a ZN peptidase. The problem is that
 the ZN ion, which is directed by an anterior sulphur atom to donate
 certain orbitals to one carboxylate oxygen and one carbonyl oxygen for
 polarization effect to carry out catalysis, is presented in the
 GROMOS96
 force fields as a structural ion. Indeed, you could say that I am
 expecting an EVB/QM model of the ZN ion in a MD program, however I was
 thinking it could be possible to reduce the current hexacoordinated
 state to tetra coordinated state somehow.
 I have been advised to create a topology of the tetra coordinated state
 manually, but this is rather tedious because of the state of the
 protein-inhibitor complex.
Are there options to modify the parameters in the GROMOS force field
 to
 your knowledge?
 Sergio