Reactivity of zinc fingers in oxidizing environments: insight from molecular models through activation strain analysis.

The reactivity of Zn2+ tetrahedral complexes with H2O2 was investigated in silico, as first step for the process of their disruption. The substrates were chosen to represent the cores of three different zinc finger protein motifs, i.e., a Zn2+ ion coordinated to four cysteines (CCCC), to three cysteines and one histidine (CCCH), and to two cysteines and two histidines (CCHH). The cysteine and histidine ligands were further simplified to methyl thiolate and imidazole, respectively. H2O2 was chosen as oxidizing agent because of its biological role as metabolic product and species involved in signaling processes. The mechanism of oxidation of a coordinated cysteinate to sulfenate-κS and the trends for the different substrates were rationalized through activation strain analysis and energy decomposition analysis in the framework of scalar relativistic DFT calculations at ZORA-M06/TZ2P ae // ZORA-BLYP-D3(BJ)/TZ2P. CCCC is oxidized most easily, an outcome explained considering both electrostatic and orbital interactions. The isomerization to sulfenate-κO was attempted to assess whether this step may affect the ligand dissociation; but it was found to introduce a kinetic barrier without improving the energetics of the dissociation. Lastly, ligand exchange with free thiolates and selenolates was investigated as trigger for ligand dissociation, possibly leading to metal ejection.

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