Re: Parametrization for Zinc / charges & vdW radius

 Hi Netters,
 We have been trying to develop parameters for the Zinc ion in the active
 site of an enzyme ( a fairly typical problem). The ion is surrounded by
 three neutral histidines, a charged carboxylate and a hydroxyl group of
 an inhibitor/ligand. We performed MOPAC6.0 (with AM1 & MNDO Hamiltonians)
 on a model system (single point calculation) and we obtain a value of
 approx. +0.7 on Zinc (Mulliken charge). Gaussian 94 calculations at
 3-21G* level indicate a higher Mulliken charge of approx. 1.0.
 I would like to use CHELPG charges which necessitates the use of right
 vdW radii. For neutral Zinc, the Bondi radius (J. Phys. Chem. 68. 441)
 is 1.39 A, which is clearly not appropriate. Can any one point to recent
 references or suggest a method? I will be happy to summarize the
 responses (with regard to vdW radii & modeling the charge in the active
 site of an enzyme for the Zinc ion).
 Vellarkad N. Viswanadhan
 vis $#at#$ gensia.com