1. Sincrotrone Trieste, Italy
CORE LEVEL SPECTROSCOPY AND TAUTOMERISM OF KEY BIOMOLECULES IN THE GAS PHASE
Vitaliy Feyer
Sincrotrone Trieste, Italy
OSU Symposium, June, 2010

2. 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

3. Biomolecular Building Blocks
OSU Symposium, June, 2010

4. “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

5. Environment !!!
Study them in the
GAS PHASE !!!
Quantitative techniques !!!

6. Gas Phase beamline characteristic:
36 period, 12.5 cm period undulator.
Padmore type monochromator (variable angle spherical grating).
Resolution: 2 64 eV, with high
flux easily and reproducibly achieved.
< eV
< eV
< eV.
OSU Symposium, June, 2010

7. Core level photoemission
Photoelectric effect: hv=EB+EK
Advantages:
- chemical shifts;
- well above threshold, cross-sections of core electrons are equal, so the peak intensities (areas) directly reflect population;
- thermal equilibrium.
Advantages:
- chemical shifts;
- well above threshold, cross-sections of core electrons are equal, so the peak intensities (areas) directly reflect population;
- thermal equilibrium.
Advantages:
- 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

8. Conformational/tautomeric investigation of 2-mercaptopyridine
Core level photoemission spectroscopy
Quantitative techniques: population of C-S-H : C=S can be directly extracted from spectra,
C-S-H
C=S
S 2 p
Free jet microwave spectroscopy
(Walther Caminati group)
High resolution:
three forms SHs, SHa and C=S are observed
SHs
SHa
C=S
Population (%)
XPS (339 K)
95.5  1
4.5  1
MW (403 K)
895
82
31
G/kJ·mol-1
0.0
8.6
MW (403K)
8.1
11.4
OSU Symposium, June, 2010

9. 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

10. X-ray Photoemission Spectroscopy
Advantages of XPS:
thermal equilibrium
well above threshold cross-sections of 1s electron are equal, so the peak area directly reflect population
Enol forms
Keto forms
3 and 1
Experiment:
T1 26 %
(T2a + T2b) 63 %
T %
Theory:
T %
T2a %
T2b %
T %
OSU Symposium, June, 2010

11. 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

12. Conclusions…. Perspectives…
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

13. 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 FEL-2
Photon energy eV eV
Pulse length fs < 100 fs
Repetition Rate Hz Hz
photon/ pulse
OSU Symposium, June, 2010

14. 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

15. …and thanks a lot for your attention…
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, Physikalisch-Chemisches Institut, Heidelberg, Germany
…and thanks a lot for your attention…
OSU Symposium, June, 2010