Infrared photodissociation spectroscopy of electrosprayed ions in a Fourier transform mass spectrometer.
Previous gas-phase methods for infrared photodissociation spectroscopy (IRPD) require sample volatility. Our method instead uses electrospray ionization to introduce even large nonvolatile molecules into a Fourier transform mass spectrometer, where extended (>15 s) ion storage makes possible high sensitivity spectral measurements with an OPO laser over a range of 3050-3800 cm(-1). The spectra of 22 gaseous proton-bound amino acid complexes are generally correlated with the H-stretching frequencies established for O-H and N-H functional groups in solution. For theoretical structure predictions of the Gly2H+ and N-acylated Asp2H+ dimers, IRPD spectra clearly differentiate between the predicted lowest energy conformers. In contrast to solution, in the gas phase the glycine zwitterion is approximately 20 kcal/mol less stable than the neutral; however, glycine is clearly zwitterionic in the gaseous GlyLysH+ dimer. The level of theory is inadequate for the larger Lys2H+ dimer, as all low energy predicted structures have free carboxyl O-H groups, in contrast to the IR spectrum. IRPD appears to be a promising new technique for providing unique information on a broad range of biomolecular and other gaseous ions, especially on noncovalent bonding involving O-H and N-H groups.
Oh
Han-Bin
HB
Department of Chemistry, Sogang University, Seoul 121-742, South Korea.
Lin
Cheng
C
Hwang
Harold Y
HY
Zhai
Huili
H
Breuker
Kathrin
K
Zabrouskov
Vladimir
V
Carpenter
Barry K
BK
McLafferty
Fred W
FW
D001224:Aspartic Acid / Q000737:chemistry; D004151:Dipeptides / Q000737:chemistry*; D005583:Fourier Analysis; D005998:Glycine / Q000737:chemistry*; D008958:Models, Molecular; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D013055:Spectrophotometry, Infrared / Q000379:methods*
D004151:Dipeptides; D001224:Aspartic Acid; C035809:glycyllysine; D005998:Glycine