Theoretical models based on the structure excerpted from the literature for Ni-C state of [NiFe] hydrogenase from Desulfovulgaris (Miyaszaki F) were considered. These models mainly possess either CO,CN and SO or CO,CO and SO ligands on the iron site. All the cysteinyl moieties of the models are in the amide form. In addition to the neutral forms, -/+1 charged forms of these models have been subjected to semiempirical quantum chemical analysis (PM3 (UHF)). After strict geometry optimization, certain quantum chemical and thermodynamic properties were calculated. The calculations have revealed that all the models are thermodynamically stable and exothermic. However, the heat of formation data indicate that negatively charged systems are more exothermic than the neutral ones and they are more exothermic than the positively charged ones. Variation of some bond lengths and bond angles as the charge develops were investigated. Also the effect of charge on the fronlier molecular orbitals, their energies and the interfrontier molecular orbital energy gaps were studied. (C) 2003 Elsevier B.V. All rights reserved.