Reinvestigation of the structure of protonated lysine dimer

J Am Soc Mass Spectrom. 2014 Mar;25(3):422-6. doi: 10.1007/s13361-013-0801-z. Epub 2014 Jan 14.


To better understand inconsistencies between the predicted infrared (IR) spectra of previously suggested isomers of Lys2H(+) reported by Wu et al. (J. Am. Soc. Mass Spectrom. 22:1651-1659, 18) and the experimental IR photon dissociation (IRPD) spectrum obtained by Oh et al. (J. Am. Chem. Soc. 127:4076-4083, 4), the structure of Lys2H(+) was reinvestigated using IRPD spectroscopy in the extended region 2700-3700 cm(-1) and theoretical calculations. The new experimental IRPD spectrum is in good agreement with Oh's spectrum in the corresponding wavelength range. Based on calculations at the MP2/6-311++G(d,p)//B3LYP/6-311++G(d,p) and MP2/6-31 + G(d,p)//MP2/6-31 + G(d,p) levels, a new salt-bridged isomer, ZW1, was found to be the most stable isomer; it is more energetically favored than the previously suggested charge-solvated isomer LL-CS01 by 10 or 26 kJ mol(-1). Although the calculated IR spectrum of ZW1 is in good agreement with the experimental one in the range 2700-3700 cm(-1), it is in poor agreement with the previous IRPD spectrum in the range 1000-1900 cm(-1). This investigation shows that the intermolecular interactions inside the dimer are more complex than previously supposed. It is possible that both salt-bridged and charge-solvated isomers of Lys2H(+) are stable in the gas phase, and the isomers generated during ionization are sensitive to the experimental conditions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Lysine / chemistry*
  • Models, Molecular
  • Protein Structure, Tertiary
  • Protons*
  • Spectrophotometry, Infrared
  • Thermodynamics


  • Protons
  • Lysine