Thiol reduction of arsenite and selenite: DFT modeling of the pathways to an as-se bond.
The reactivity of arsenite and selenite with biological thiols plays an important role in the toxicity of these elements. However, toxic effects are eliminated when the species are coadministered, due to the antagonistic relationship between selenium and arsenic. The reduction of arsenous acid and selenious acid by thiol and the formation of an As-Se species have been modeled using density functional theory (DFT) and solvent-assisted proton exchange (SAPE), a microsolvation technique that uses a network of water molecules to mimic the participation of bulk solvent in proton transfer processes. Activation barriers and relative energies were calculated for the stepwise thiol reduction of arsenite to form As(SR)3 and selenious acid to first form a selenotrisulfide (Se(SR)2) and then H2Se. Several pathways were explored for the formation of an As-Se bond: the nucleophilic attack of selenide or selenopersulfide on As(OH)3, (RS)As(OH)2, and (RS)2AsOH to form (RS)2AsSeH. On the basis of the lower activation barrier and bioavailability of (RS)2AsOH, the reaction of H2Se with (RS)2AsOH is deemed the most favorable, consistent with previous experimental studies.
Department of Chemistry and Biochemistry, Old Dominion University , Norfolk, Virginia 23529, United States.
Lenora K
LK
Harper
Sonia
S
Antony
Craig A
CA
Bayse
D018053:Arsenites / Q000737:chemistry*; D008962:Models, Theoretical; D010084:Oxidation-Reduction; D020887:Selenious Acid / Q000737:chemistry*; D013438:Sulfhydryl Compounds / Q000737:chemistry*
D018053:Arsenites; D013438:Sulfhydryl Compounds; D020887:Selenious Acid; C015001:arsenite