title: Reinvestigation of the structure of protonated lysine dimer.
abstract: 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.
authors.affiliation: State Key Laboratory and Institute of Elemento-Organic Chemistry, Nankai University, Collaborative Innovation Center of Chemical Science and Engineering, 300071, Tianjin, China, kongxianglei@nankai.edu.cn.
authors.forename: Xianglei
authors.initials: X
authors.lastname: Kong
mesh_terms: D008239:Lysine / Q000737:chemistry*; D008958:Models, Molecular; D017434:Protein Structure, Tertiary; D011522:Protons; D013055:Spectrophotometry, Infrared; D013816:Thermodynamics
chemical_list: D011522:Protons; D008239:Lysine