Jump to main content
Jump to site search
Access to RSC content Close the message box

Continue to access RSC content when you are not at your institution. Follow our step-by-step guide.

Issue 2, 2008
Previous Article Next Article

The cysteine radical cation: structures and fragmentation pathways

Author affiliations


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 π-electron donor and C(OH)2+ as a powerful π-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 (ΔH°0) than Captodative-1 by 6.1 kcal mol–1, but is lower in enthalpy than another isomer Distonic-C-1, H3N+C˙(CH2SH)COOH, by 8.2 kcal mol–1. 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 mol–1, while the barrier against isomerization of Canonical-1 to Distonic-S-1 is only 9.6 kcal mol–1. Two additional transient tautomers, one with the radical located at Cα 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.

Graphical abstract: The cysteine radical cation: structures and fragmentation pathways

Back to tab navigation

Article information

16 Aug 2007
11 Oct 2007
First published
22 Oct 2007

Phys. Chem. Chem. Phys., 2008,10, 281-288
Article type

The cysteine radical cation: structures and fragmentation pathways

J. Zhao, K. W. M. Siu and A. C. Hopkinson, Phys. Chem. Chem. Phys., 2008, 10, 281
DOI: 10.1039/B712628J

Social activity

Search articles by author