Protonolysis of the Hg-C bond of chloromethylmercury and dimethylmercury. A DFT and QTAIM study.
Possible mechanisms for degrading chloromethylmercury (CH(3)HgCl) and dimethylmercury [(CH3)2Hg] involving thiol and ammonium residues were investigated by DFT and atoms-in-molecules (QTAIM) calculations. Using H2S and HS- as models for thiol and thiolate groups RSH and RS-, respectively, we obtained transition states and energy barriers for possible decomposition routes to Hg(SH)2 based on a model proposed by Moore and Pitts (Moore, M. J.; Distefano, M. D.; Zydowsky, L. D.; Cummings, R. T.; Walsh, C. T. Acc. Chem. Res. 1990, 23, 301. Pitts, K. E.; Summers, A. O. Biochemistry 2002, 41, 10287). Demethylation was found to be a multistep process that involved initial substitution of Cl- by RS-. We found that successive coordination of Hg with thiolates leads to increased negative charge on the methyl group and facilitates the protonolysis of the Hg-C bond by H-SH. This was also found to be the case for (CH3)2Hg. We found that NH4(+) readily protonolyzes the Hg-C bond of these thiolate complexes, suggesting that ammonium residues of protonated amino acids might also act as effective proton donors.
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Boris
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Department of Chemistry, McMaster University, Hamilton, Ontario L8S 4M1, Canada.
Kramer
James R
JR
Bell
Russell A
RA
Werstiuk
Nick H
NH
D002244:Carbon / Q000737:chemistry*; D003198:Computer Simulation; D008628:Mercury / Q000737:chemistry*; D008767:Methylmercury Compounds / Q000737:chemistry*; D011522:Protons; D011789:Quantum Theory
D008767:Methylmercury Compounds; D011522:Protons; D002244:Carbon; C073972:dimethyl mercury; D008628:Mercury; C004925:methylmercuric chloride