Solvent effects on ion pairing and photoionization in water

1. Solvent effects on ion pairing and photoionization in water hn e- - + - + Eva Pluhařová École Normale Supérieure Paris Advisor:PavelJungwirth Charles University in Prague Faculty of Science Institute of Organic Chemistry and Biochemistry

2. Ion pairing : Motivation • Ion pairing • Coulomb attraction x solvation contact shared separated ion pair - + - + + • Ion specific effects on proteins - protein • Salt bridges + - • Phenomenological models • Neutron scattering, atomistic simulations Solvent effects on ion pairing and photoionization in water

3. Ion pairing by molecular dynamics simulations Newton equations of motion: • Classical • Empirical force fields • Fixed partial charges(not explicitly polarizable) • Thousands of atoms • Hundreds of nanoseconds • Ab initio • Density functional theory • Pseudopotentials for core electrons • Hundred(s) of atoms • Tens of picoseconds Solvent effects on ion pairing and photoionization in water

4. Ion pairing in concentrated salt solutions Classical MD simulations • Lithium salts 1.5M Li2SO4 Polarization included by ECC nonpolarizable force field EP et al. J. Phys. Chem. B2013, 117, 11766. EP et al. Mol. Phys. 2014, 112, 1230. air • Aqueous interfaces M. Vazdar, EP et al. J. Phys. Chem. Lett2012, 3, 2087. Solvent effects on ion pairing and photoionization in water

5. Ion pairing by ab initio molecular dynamics • LiF g • Sources of uncertainties • Electronic structure method • Simulation length EP et al. J. Phys. Chem. Lett2013, 4, 4177. Solvent effects on ion pairing and photoionization in water

6. Ion pairing by ab initio molecular dynamics • N-methylacetamidewith Na+ and Ca2+ exposed EP et al. J. Phys. Chem. Lett2014, 5, 2235. + - + - • Salt bridge buried EP et al. J. Chem. Phys. 2012, 137, 185101. Solvent effects on ion pairing and photoionization in water

7. Switching gears Solvent effects on ion pairing and photoionization in water

8. Radiation damage of DNA Radiation energy excitation or ionization UVB pyrimidine crosslinks UVA Less efficient Secondary photoreactions 260 nm Can solar photon ionize DNA? • Radiotherapy of cancer • Fukushima, flight personnel Solvent effects on ion pairing and photoionization in water

9. Exposure of DNA to ionizing radiation . direct hn indirect Mechanisms: + d-Rib d-Rib G C Localization of the “hole”: OH. P P OH. d-Rib T A d-Rib P P Solvent effects on ion pairing and photoionization in water

10. The first step of indirect damage Delocalized “hole” H2O+. OH. and H3O+ ~ 31 fs units of fs, but recrossings O. Marsalek, ..., EP et al. J. Chem. Phys. 2011, 135,  224510. Solvent effects on ion pairing and photoionization in water

11. Photoionization of DNA Definitions Photoelectron spectroscopy in solution Winter, B.; Flaubel, M. Chem. Rev.2006, 106, 1176. electron analyzer Energy VIEe AIE0 AIEe skimmer nozzle liquid jet geometry change Solvent effects on ion pairing and photoionization in water

12. Modeling photoelectron spectrum Cross-section: nonionized ground state: ionized state: IE0 MP2/aug-cc-pVDZ PMP2/aug-cc-pVDZ TDDFT/BMK/6-31+g* IE of tighter bound electrons = excitation to SOMO + IE0 Ionization of nucleic acid components

13. Modeling solvation + e- solute er er hybrid model polarizable dielectric continuum (PCM) microhydration ? Solvent effects on ion pairing and photoionization in water

14. Differently charged species unstable EP et al. J. Phys. Chem. B 2011, 115, 1294. EP et al. J. Phys. Chem. B 2012, 116, 13254. Solvent effects on ion pairing and photoionization in water

15. Nucleic acid bases Calculated lowest ionization energy of NA bases at PMP2/aug-cc-pVDZ level: relaxation 0.2 - 0.4 eV solvation 0.9 - 1.4 eV solvent nuclear relaxation 1.1 – 1.3 eV solute nuclear relaxation 0.2- 0.35 eV • Guanine remains the base with the lowest VIE in solution. EP et al. J. Phys. Chem. B 2011, 115, 1294. Solvent effects on ion pairing and photoionization in water

16. Photoelectron spectra nucleotide base nucleoside water gas phase Solvent effects on ion pairing and photoionization in water C. Schroeder, EP et al. J. Am. Chem. Soc. 2015, 137, 201.

17. From VIE to redox potentials? • Initial electron transfer • Disagreement about E0 • Follow-up reactions C. Schroeder, EP et al. J. Am. Chem. Soc. 2015, 137, 201. Solvent effects on ion pairing and photoionization in water

18. Ionization of a piece of DNA Dickerson dodecamer MP2/PM6/PCM Guanine in DNA 7.1 eV Guanine in GMP- 7.0 – 7.3 eV Guanine in guanosine 7.4 eV Guanine 7.3 eV EP et al. J. Phys. Chem. Lett2013, 4, 3776. EP et al. Acc. Chem. Res. 2015, asap. Solvent effects on ion pairing and photoionization in water

19. DNA conclusions • Ionization of DNA bases, nucleosides, nucleotide and even a piece of DNA modeled by ab initio calculations employing non-equilibrium polarizable continuum model of solvent. Lowest VIE just above 7 eV. • Screening effect of water • Simpler description than in the gas phase, nucleotides are relevant. • From VIE to redox potentials Solvent effects on ion pairing and photoionization in water

20. Conclusions • Methodological • Computationally cheap treatment of polarizability in an effective way for concentrated salt solutions. • DFT based ab initioMD can be combined with enhanced sampling methods. • The non-equilibrium polarizable continuum model of solvation performs well in context of photoionization. • Chemical • Ionization energies of aqueous nucleic acid components • Ability of water to screen interactions between building blocks • Small influence of the DNA environment on the VIE of the base • Established values for nucleotides can be directly used for DNA Solvent effects on ion pairing and photoionization in water

21. Acknowledgements PavelJungwirth (ÚOCHB Praha) Petr Slavíček(VŠCHT Praha) Stephen E. Bradforth (USC L. A.) Bernd Winter (HZ Berlin) Christopher J. Mundy (PNNL Richland) Burkhard Schmidt (F.U. Berlin) CP2K and Gromacs developers Institute of Organic Chemistry and Biochemistry Center for Biomolecules and Complex Molecular Systems, Prague Solvent effects on ion pairing and photoionization in water