Publication: The cysteine radical cation: structures and fragmentation pathways
All || By Area || By Year| Title | The cysteine radical cation: structures and fragmentation pathways | Authors/Editors* | Junfang Zhao, K. W. Michael Siu and Alan C. Hopkinson |
|---|---|
| Where published* | Phys. Chem. Chem. Phys. |
| How published* | Journal |
| Year* | 2008 |
| Volume | 10 |
| Number | |
| Pages | 281-288 |
| Publisher | |
| Keywords | |
| Link | http://www.rsc.org/Publishing/Journals/CP/article.asp?doi=b712628j |
| Abstract |
A theoretical study on the structures, relative energies, isomerization reactions and fragmentation pathways of the cysteine radical cation, [NH2CH(CH2SH)COOH]+, is reported. Hybrid density functional theory (B3LYP) has been used in conjunction with the 6-311++G(d,p) basis set. The isomer at the global minimum, Captodative-1, has the structure NH2C(CH2SH)C(OH)2+; the stability of this ion is attributed to the captodative effect in which the NH2 functions as a powerful -electron donor and C(OH)2+ as a powerful -electron acceptor. Ion Distonic-S-1, H3N+CH(CH2S)COOH, in which the radical is formally situated on the S atom, is higher in enthalpy (H°0) than Captodative-1 by 6.1 kcal molâ1, but is lower in enthalpy than another isomer Distonic-C-1, H3N+C(CH2SH)COOH, by 8.2 kcal molâ1. Isomerization of the canonical radical cation of cysteine, [H2NCH(CH2SH)COOH]+, (Canonical-1), to Captodative-1 has an enthalpy of activation of 25.8 kcal molâ1, while the barrier against isomerization of Canonical-1 to Distonic-S-1 is only 9.6 kcal molâ1. Two additional transient tautomers, one with the radical located at C and the charge on SH2, and the other a carboxy radical with the charge on NH3, are reported. Plausible fragmentation pathways (losses of small molecules, CO2, CH2S, H2S and NH3, and neutral radicals COOH, HSCH2 and NH2) from Canonical-1 are examined. |
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