Gas Phase
Photoemission
Beamline
CORE LEVEL SPECTROSCOPY AND
TAUTOMERISM OF KEY BIOMOLECULES
IN THE GAS PHASE
Vitaliy Feyer
Sincrotrone Trieste, Italy
OSU Symposium, June, 2010
Gas Phase
Photoemission
Beamline
Tautomerism of free molecules
in photoemission
- Tautomerism is the ability of a molecule to exist in more than one
chemical form.
- Many tautomers are formed by migration of a hydrogen atom,
accompanied by a switch of a single bond and neighboring
double bond.
OSU Symposium, June, 2010
Gas Phase
Photoemission
Beamline
Biomolecular Building Blocks
OSU Symposium, June, 2010
Gas Phase
Photoemission
Beamline
•
“Building blocks” interaction
Normal base pairing in DNA is A-T and G-C. The tautomers
forms are capable of unusual base pairing like T-G and C-A.
Tautomers can cause genetic mutations by pairing incorrectly with
complementary bases.
Mutations are the precursors to many molecular-based diseases, including
cancer.
OSU Symposium, June, 2010
Gas Phase
Photoemission
Beamline
Environment !!!
Study them in the
GAS PHASE !!!
Quantitative techniques !!!
Gas Phase
Photoemission
Beamline
Gas Phase beamline characteristic:
36 period, 12.5 cm period undulator.
Padmore type monochromator (variable angle spherical
grating).
Gas Phase Beamline
Coincidence Spectrometer
Experimental chamber
824 mm
Resolution: 2 meV @ 64 eV, with high
flux easily and reproducibly achieved.
< 40 meV @ 400 eV
< 50 meV @ 530 eV
< 80 meV @ 860 eV.
Refocusing chamber
3860 mm from defl.
X
Horizontal ReFocus Mirror
Plane
deflection
mirror
Exit Slit
Grating Chamber
Pre-Focus
Mirror
Entrance Slit
OSU Symposium, June, 2010
Vertical Re-Focus Mirror
Gas Phase
Photoemission
Beamline
Core level photoemission
Photoelectric effect: hv=EB+EK
Unoccupied
valence levels
C1s
C1s
C1s
Occupied
valence levels
Core level
Core ionization
Advantages:
296
296
296
294
292
294
292
294
292
Binding
energy
(eV)
Binding
energy
(eV)
Binding energy
(eV)
290
290
290
- chemical shifts;
- well above threshold, cross-sections of core electrons are equal, so the
peak intensities (areas) directly reflect population;
- thermal equilibrium.
OSU Symposium, June, 2010
Gas Phase
Photoemission
Beamline
Conformational/tautomeric investigation
of 2-mercaptopyridine
C-S-H
S2p
Core level photoemission
spectroscopy
C=S
Quantitative techniques:
population of C-S-H : C=S can be
directly extracted from spectra,
Free jet microwave spectroscopy
(Walther Caminati group)
High resolution:
three forms SHs, SHa and C=S are
observed
SHs
Population (%)
G/kJ·mol-1
OSU Symposium, June, 2010
95.5  1
XPS (339 K)
MW (403 K)
895
XPS (339 K)
MW (403K)
SHa
82
0.0
0.0
8.1
C=S
4.5  1
31
8.6
11.4
Gas Phase
Photoemission
Beamline
Cytosine tautomers
R.D. Brown, et al, J. Am. Chem. Soc. 111, 1989, 308.
(microwave spectroscopy ) 2b and 1, 3.
E.D. Radchenko, et al, J. Mol. Struct. 116, 1984, 387.
M. Szczesniak, et al J. Am. Chem. Soc. 110, 1988, 8319.
(matrix isolation infrared studies) 1 and 2b
G. Fogarasi, J. Phys. Chem. A. 106, 2002, 1381.
S. A. Trygubenko, et al Phys. Chem. Chem. Phys. 4, 2002, 4192.
(theoretical calculation) 2b, 2a, 1, and 3
Can XPS photoemission directly give us information about populations
of cytosine tautomers in the gas phase?
OSU Symposium, June, 2010
Gas Phase
Photoemission
Beamline
150
120
125
100
X-ray Photoemission Spectroscopy
(a)
(a) Cytosine
OO1s1s Ionization
ionization
C
Enol forms
Experiment: XPS
Experiment: XPS
100
80
Keto forms
3 and 1 A
75
60
Intensity (arbitrary units)
50
40
Advantages of XPS:
-thermal equilibrium
-well above threshold cross-sections of
1s electron are equal, so the peak area
directly reflect population
B
25
20
00
542
0.6
541
540
539
538
537
536
535
C
(b)
Theory: ADC(4),
Boltzmann-weighted sum
0.4
3
A
(T2a + T2b) 63 %
B
4
0.2
Experiment:
T1 26 %
2
T3 11 %
1
0
543
542
541
540
539
538
537
536
Binding energy (eV)
OSU Symposium, June, 2010
Theory:
T1 32.8 %
T2a 17.7 %
T2b 34.4 %
T3 15 %
Gas Phase
Photoemission
Beamline
O 1s XPS
Keto and enol tautomeric
forms of cytosine and guanine
sufficiently populated under
present experiment conditions
For uracil and thymine only keto
form is observed.
O. Plekan et al. Chem. Phys. 347, 2008, 360.
J. Phys.Chem. A. 113, 2009, 9376.
V. Feyer et al. J. Phys.Chem. A. 113, 2009, 5736.
OSU Symposium, June, 2010
Gas Phase
Photoemission
Beamline
Conclusions….
•Tautomers of molecules have been clearly resolved in photoemission
spectra and their relative populations have been determined.
•Photoemission can be used as complementary technique to study
the shape of molecules.
• The gas-phase experimental data serve as benchmarks for quantum
chemical calculations.
Perspectives…
The study of biomolecules will benefit from the high flux of the
Free Electron Laser FERMI at ELETTRA.
OSU Symposium, June, 2010
Gas Phase
Photoemission
Beamline
Free Electron Laser FERMI@ELETTRA
Low-Density Matter beamline under construction
(free electron laser facilities )
Elettra LDM team: Carlo Callegari – coordinator
Angelica Moise – postdoc
Vitaliy Feyer – postdoc
Machine parameters
FEL-1
FEL-2
Photon energy
12-62 eV
62-413 eV
Pulse length
30-100 fs
< 100 fs
Repetition Rate
10-50 Hz
photon/ pulse
1014
10-50 Hz
1013
OSU Symposium, June, 2010
Gas Phase
Photoemission
Beamline
Future experiments
Helium nanodroplets machine is being constructed at the University of Freiburg
(Prof. F. Stienkemeier in collaboration with partners)
Photo electron spectroscopy of molecules in
liquid helium droplets
(small molecules, biomolecules, organic
nanostructures, organic semiconductors)
fs pump-probe studies (IR/UV –XUV)
- relaxation mechanism in superfluid helium,
- charge transfer in heterogeneous structures.
Imaging of gas-phase clusters and nanoparticles
Low-Density Matter beamline will be opened for users in 2011 !!!
OSU Symposium, June, 2010
Gas Phase
Photoemission
Beamline
I would like to thank…
Oksana Plekan
Robert Richter
Marcello Coreno
Monica de Simone
Kevin Prince
Gas Phase Photoemission Beamline
at Elettra, Trieste, Italy
B. M. Giuliano, S.Melandri,
L. Evangelisti, A. Maris,
W. Caminati
Chemistry department, University of
Bologna, Italy
V. Carravetta
Institute of Chemical Physical
Processes, Pisa, Italy
A.B.Trofimov
I.L.Zaytseva
Irkutsk State University,
Irkutsk, Russian Federation
E.V. Gromov
J. Schirmer
Theoretische Chemie, PhysikalischChemisches Institut, Heidelberg,
Germany
…and thanks a lot for your attention…
OSU Symposium, June, 2010