The structures and properties of proton- and alkali-bound cysteine dimers
Résumé
The proton-, lithium-, and sodium-bound cysteine dimers have been investigated in a joint computational and experimental infrared multiple photon dissociation (IRMPD) study. IRMPD spectra in the 1000-2000 cm$^{-1}$ region show that protonation is localized on an amine group, and that intermolecular hydrogen bonding occurs between the protonated amine and the carbonyl oxygen of the neutral Cys moiety. Alkali-bound dimers adopt structures reminiscent of those observed for the monomeric Cys.Li$^+$ and Cys.Na$^+$ species. Calculations of the heavier Cys$_2$.M$^+$ (M = K, Rb or Cs) species suggest that these are significantly less strongly bound than the lighter (M = H, Li, or Na) dimers.
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