Thermodynamic stability versus kinetic lability of ZnS4 core

Delphine Picot (1) , Gilles Ohanessian (1) , Gilles Frison (1)

1 DCMR - Laboratoire des mécanismes réactionnels

Density Functional Theory and post-Hartree Fock calculations reveal an unusual energy profile for Zn-S and Zn-N bond dissociation reactions in several Zn(SR)4(2–) and Zn(Im)(SR)3(–) complexes. The Zn-S bond dissociation in tetrathiolate dianions, which is highly exothermic in the gas phase, proceeds through a late transition state which can be rationalised on the basis of an avoided-crossing resulting from Coulomb repulsion between the anionic fragments and ligand-to-metal charge-transfer in the Zn(SR)4(2–) complexes. When solvation models for water, DMSO or acetonitrile are included, some complexes become stable while others are metastable, so this constitutes the first theoretical model which is in full agreement with the experimental data for various Zn(SR)4(2–), Zn(SR)3(–) and Zn(Im)(SR)3(–) complexes. The analysis given here indicates that the Zn(Cys)4 and Zn(His)(Cys)3 cores of numerous proteins are metastable with respect to Zn-S and Zn-N bond dissociation respectively; this is consistent with the kinetic lability at the zinc-centres and illustrates that, in nature, thermodynamic stability is imparted upon the zinc cores by the protein environment.

Mots clés: zinc; metalloproteins; bond energy; computational chemistry; S ligands; density functional theory (DFT)

Domaines: Chimie théorique et/ou physique; Chimie de coordination; Chimie inorganique

Delphine Picot, Gilles Ohanessian, Gilles Frison. Thermodynamic stability versus kinetic lability of ZnS4 core. Chemistry - An Asian Journal, 2010, 5, pp.1445-1454. ⟨10.1002/asia.200900624⟩. ⟨hal-00467068⟩