Post on 12-Jan-2016
Glucose Spectroscopy in the Gas Phase with Cryogenic Ion Vibrational SpectroscopySTEVE KREGEL
GARAND GROUP-UW MADISON
6/17/2014
Background and Motivation Sugar mixtures extracted from glycoproteins are very complex All hexoses yield the same information via mass spectrometry Typically separated with HPLC to determine isomeric ratio
◦ Slow◦ Requires significant molecular modifications
Gas phase spectroscopy could potentially identify isomeric mixtures without separation
Alley, William R. Jr.; Mann, Benjamin F.; Novotny, Milos V.; Chemical Reviews 2013, 113 2668-2732
Instrumental Setup-CIVS
1) ESI sugar solution with ~1mM NaCl
2) Trap ions and attach D2 tag
5) Acquire MS of detagged ions
3) Remove untagged ions from TOF path
4) Excite vibrational modes and remove tag
Glucose Background Anomeric ratio is 44% α and 56% β in solution phase
◦Interconverts through ring opening deprotonation mechanism at C1
◦Requires solvent to interconvert◦α and β anomers must be considered distinct species in gas phase
Multiple Na+ binding sites possible - yields a distribution of conformers
Fishman, P.H. and Bailey, J. Martyn. American Journal of Physiology Vol. 226, No.4 April 1974
Experimental and Calculated Spectrum of Sodiated Glucose
72% α0 (+0cm-1) 9% α1 (+717cm-1)
9% α2 (+731cm-1) 5% β0 (+370cm-1)
5% β1 (+504cm-1)
All calculations were done at the cam-B3LYP/6-311+G(d,p) level
3500 3550 3600 3650 3700012345
(Na-
Glu
cose
)+
3500 3550 3600 3650 3700012345
Cal
cula
ted
3500 3550 3600 3650 3700012345
Ove
rlay
Frequency (cm-1)
Glucose-6-Phosphate Background
Addition of a phosphate group greatly expands the PES Anomeric conversion IS possible in gas phase due to the dual acid-base nature of the phosphate group◦ α and β G6P cannot be considered separately
Naturally charged, requires no Na+ atom to become an ion◦ Phosphate group can move to lowest energy position before
cryogenic trap◦ Implies that only a single conformer should be present
Phosphorylation Simplifies the Spectrum…
3300 3350 3400 3450 3500 3550 3600 3650 37000.0
0.5
G6P
-
3300 3350 3400 3450 3500 3550 3600 3650 37000.0
0.5
1.0
(Na-
Glu
cose
)+
Frequency (cm-1)
… But it’s Still Complicated
3300 3350 3400 3450 3500 3550 3600 3650 37000.0
0.5
G6P
-
3300 3350 3400 3450 3500 3550 3600 3650 37000
250
500
Alp
ha
3300 3350 3400 3450 3500 3550 3600 3650 37000
250
500
Bet
a
3300 3350 3400 3450 3500 3550 3600 3650 37000
250
500
Bes
t M
atch
Frequency (cm-1)
α-G6P (+0 cm-1)
β-G6P (+324 cm-1)
Best Match (+1555 cm-1)
Conclusions Gas phase spectroscopy has the potential to identify mixtures of hexoses Multiple (Na-Glucose)+ conformers complicate the spectrum◦Could lead to difficulty in creating a hexose spectral library
G6P is likely not in its low energy conformation
Acknowledgements
Brett Marsh
Jon Voss
Etienne Garand
Jia Zhou
Erin Duffy