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1 Influence of Microhydration on the Ionization Energy Thresholds of Thymine University of Southern California Department of Chemistry Kirill Khistyaev,

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Presentation on theme: "1 Influence of Microhydration on the Ionization Energy Thresholds of Thymine University of Southern California Department of Chemistry Kirill Khistyaev,"— Presentation transcript:

1 1 Influence of Microhydration on the Ionization Energy Thresholds of Thymine University of Southern California Department of Chemistry Kirill Khistyaev, Prof. Anna I. Krylov 64th OSU International Symposium on Molecular Spectroscopy June 22-26, 2009

2 2 Importance of ionization processes in DNA 1 1 Bernd Giese, Annu. Rev. Biochem. 2002. 71:51–70 DOI: 10.1146/annurev.biochem.71.083101.134037

3 3 Experimental data 2. PIE curves. a.thymine b.thymine−H 2 O c.thymine−(H 2 O) 2 d.thymine−(H 2 O) 3 Photoionization efficiency (PIE) curves recorded for 2 Leonid Belau, Kevin R. Wilson, Stephen R. Leone, and Musahid Ahmed, Vacuum-Ultraviolet Photoionization Studies of the Microhydration of DNA Bases (Guanine, Cytosine, Adenine, and Thymine), J. Phys. Chem. A 2007, 111, 7562-7568

4 4 Experimental results. Appearance Energies of Four DNA Bases and Complexes with Water monomermonohydratedihydratetrihydrate thymine8.90 ± 0.058.75 ± 0.058.6 ± 0.1 adenine8.30 ± 0.058.20 ± 0.058.1 ± 0.1 guanine8.1 ± 0.18.0 ± 0.1 8.0 cytosine8.65 ± 0.058.45 ± 0.058.4 ± 0.18.3 ± 0.1

5 5 Theoretical studies. Thymine + H 2 O tautomers. 2 2 Jaroslav Rejnek, Michal Hanus, Martin Kabela, Filip Ryjaek and Pavel Hobza,Phys, Chem. Chem. Phys., 2005, 7, 2006–2017

6 6 Thymine + H 2 O geometry optimization. 1.351 1.378 1.386 1.215 1.383 1.405 1.219 1.466 1.456 1.221 1.400 1.375 1.227 1.371 1.372 1.352 1.017 1.006 0.001 -0.006 -0.016 -0.008 -0.005 0.002 -0.01 0.011 0.002 Thymine Thymine + H 2 O Δ rimp2/ccPVTZ

7 7 Ionization Energies, eV A'' 9.01 (9.13 for Thymine) A' 10.10 (10.13) A'' 10.51 (10.52) A' 11.10 (11.04) Thymine + H 2 O (Thymine) EOM-CCSD/cc-PVTZ ΔIE = 0.12 eV ΔIE = 0.03 eV ΔIE = 0.01 eV ΔIE = -0.06 eV

8 8 Ionization Energies, eV Thymine + H 2 O (Thymine) A'' 12.30 (12.39 for H 2 O) A'' 12.53 (12.67 for Thymine) A' 13.70 (13.82 for Thymine) EOM-CCSD/cc-PVTZ

9 9 IE of Thymine at geometry of Thymine + H 2 O cluster  IP of Thymine at the equilibrium geometry is 9.13 eV  IP of Thymine at the equilibrium geometry of Thymine + H 2 O complex is 9.16 eV  ΔIP = 0.03 eV due to the geometry change EOM-CCSD/cc-PVTZ

10 10 Charge distribution. First Ionization Energy Element# NutralIonizedΔ C2 -0.1900.066 0.256 N4 -0.658-0.456 0.202 O9 -0.599-0.437 0.162 O10 -0.679-0.504 0.175 O16-1.020-1.026-0.006 H170.5180.509-0.009 H180.5000.5270.027 ∑H 2 O -0.0020.009 0.011 0.256 0.202 0.162 0.175 ΔIP = 0.12 eV 0.011 NBO/EOM-CCSD/6-31+G(d)

11 11 Charge distribution. Second Ionization Energy Element# NutralIonizedΔ O9 -0.599-0.105 0.494 O10 -0.679-0.520 0.159 O16-1.020-1.0170.004 H170.5180.506-0.012 H180.5000.5220.022 ∑H 2 O-0.0020.011 0.013 0.494 0.159 ΔIP = 0.03 eV 0.013 NBO/EOM-CCSD/6-31+G(d)

12 12 Charge distribution. Third Ionization Energy Element# NutralIonizedΔ N6-0.301-0.679 0.377 O9-0.336-0.599 0.263 O10-0.418-0.679 0.261 O16-1.011-1.0200.009 H170.5000.518-0.017 H180.5240.5000.024 ∑H 2 O-0.0020.014 0.016 0.377 0.263 0.261 ΔIP = 0.01 eV 0.016 NBO/EOM-CCSD/6-31+G(d)

13 13 Charge distribution. Fourth Ionization Energy Element# NutralIonizedΔ O9-0.336 -0.448 0.151 O10-0.418 -0.148 0.531 O16-1.011 -0.987 0.034 H170.5010.478 -0.040 H180.524 0.534 0.034 ∑H 2 O-0.0020.025 0.027 0.531 0.151 ΔIP = -0.06 eV 0.027 NBO/EOM-CCSD/6-31+G(d)

14 14 Correlation between ΔIE and charge transfer between H 2 O and Thymine

15 15 Charge-dipole interaction. -δ’-δ’ +δ’’

16 16 Correlation between charge-dipole interaction and ionization energy. IE1 IE2 IE3 IE4

17 17 Geometry of the first ionized state (omegaB97X-D/cc-pvtz) 1.456 1.221 1.400 1.375 1.227 1.3711.372 1.352 1.017 1.040 1.379 1.192 1.369 1.288 1.338 1.408

18 18 IE of different structures of Thymine + H 2 O

19 19 IE of different structures of Thymine + H2O Thymine Th+H2O t1 ΔIE Th+H2O t2 ΔIE Th +H2O t3 ΔIE 9.139.010.129.050.089.080.05 10.1310.10.0310.17-0.049.970.16 10.5210.510.0110.360.1610.340.18 11.0411.1-0.0610.870.1711.030.01 12.3912.30.0912.58-0.1912.63-0.24 12.6712.530.1411.940.7311.970.7 13.8213.70.1213.60.2213.550.27 13.8413.760.0813.780.0613.670.17

20 20 IE of different structures of Thymine + H2O

21 21 Conclusions:  First calculated IE of thymine + H 2 O cluster is 9.01 eV which is 0.12 eV lower than IE of thymine.  Charge distribution between thymine and water for the fist 3 ionized states can’t explain change in IE.  Geometry change can’t explain the difference in IP.  Change in IE can be explained by charge-dipole interaction between thymine and water molecule.  Oxygen atom of water molecule stabilize a positive charge on nearest atoms

22 22 Acknowledgments Prof. Anna I. Krylov group Prof. Anna I. Krylov group Dr. Ksenia Bravaya Dr. Ksenia Bravaya iOpenShell center for computational studies iOpenShell center for computational studies QChem ab initio package QChem ab initio package

23 23 Thank you for your attention

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