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Which comes first in one-electron-reduction? The Electron or the Proton?

Which comes first in one-electron-reduction? The Electron or the Proton?. Einar Uggerud University of Oslo. Park City, Utah, 2 July, 2007. Part 1. Cation-Electron Recombination Small molecule models of electron capture dissociation. The green colour of Aurora Borealis.

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Which comes first in one-electron-reduction? The Electron or the Proton?

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  1. Which comes first in one-electron-reduction?The Electron or the Proton? Einar Uggerud University of Oslo Park City, Utah, 2 July, 2007.

  2. Part 1. Cation-Electron Recombination Small molecule models of electron capture dissociation

  3. The green colour of Aurora Borealis Solar wind (”day time”):O2 O2++ e- Night: O2++ e- (O2)* O + O

  4. One of the O atoms is exited: O2++ e-  (O2)* O + O 1S hn 1D n = 557,7 nm O2

  5. Electron capture dissociation (ECD) of proteins/peptides MHnn+ + e– MHn(n-1)+  fragments Zubarev, R. A.; Kelleher, N. L.; McLafferty, F. W. Electron Capture Dissociation of Multiply Charged Protein Cations - a Nonergodic Process J. Am. Chem. Soc.1998, 120, 3265-3266.

  6. Characteristics of ECD of multiply protonated proteins/peptides • Specific for dissociation of backbone N-Ca bond • Cleaves disulfide bridges • Leaves most side-groups untouched • Fast (non-ergodic ?) • Loss of H

  7. Electron capture of protonated side group (Lys): Release of ”hot” H

  8. Collisions between hot H and peptide ?

  9. CRYRING in Stockholm 10-12 mbar 17 m Reaction zone Ion energy: E(NH4+)= 4.5 MeV Velocity =2 % of c Andersson et al., in preparation

  10. Small scale models of relevance to ECD: NH4++ e-NH3 + H CH3SSHCH3+ + e-→CH3SH + CH3S CD3COHNHCH3+ + e-→ CD3C(OH)NH + CH3 A. Al-Khalili, et al. J. Chem. Phys., 121(12) 5700-5708 (2004). P. Andersson et al., in preparation.

  11. NH4+ HF/aug-cc-pVDZ 388 kJ/mol MP2/aug-cc-pVDZ 429 kJ/mol CCSD(T)/aug-cc-pVQZ 436 kJ/mol NH4 HF/aug-cc-pVDZ 389 kJ/mol MP2/aug-cc-pVDZ 431 kJ/mol CCSD(T)/aug-cc-pVQZ 436 kJ/mol HF/aug-cc-pVDZ 66 kJ/mol MP2/aug-cc-pVDZ 52 kJ/mol CCSD(T)/aug-cc-pVQZ 50 kJ/mol NH3 + H HF/aug-cc-pVDZ 89 kJ/mol MP2/aug-cc-pVDZ 53 kJ/mol CCSD(T)/aug-cc-pVQZ 40 kJ/mol V. Bakken, T. Helgaker, and E. Uggerud European Journal of Mass Spectrometry, 10 (2004), 625 – 638.

  12. Direct reaction dynamics • Ab initio potential energy surface • genereated in situ. • Initial conditions sampled from • Boltzmann distribution. • 20 – 100 trajectories Helgaker, T.; Uggerud, E.; Jensen, H. J. A. Chem. Phys Lett.1990, 173, 145-150.

  13. V. Bakken, T. Helgaker, and E. Uggerud European Journal of Mass Spectrometry, 10 (2004), 625 – 638.

  14. Trajectory calculations, NH4+ + e– NH4 HF/aug-cc-pVDZ RC energy corresponds to ≈ 7000 K 25 trajectories: NH4 NH3 + H <T> = 221 kJmol-1 (50 %) V. Bakken, T. Helgaker, and E. Uggerud European Journal of Mass Spectrometry, 10 (2004), 625 – 638.

  15. ch3cohnch3 + h (298K,1500meV,traj0001) b3lyp/4-31g V. Bakken, T. Helgaker, and E. Uggerud European Journal of Mass Spectrometry, 10 (2004), 625 – 638.

  16. Part 2. Electron-bound dimers Fine-tuning H2 bond activation on a gliding scale from weak dihydrogen interaction to covalent H–H

  17. 2H+ + 2e- = H2 Aqueous solution: Ered = 0.000 V Gas phase: H° = -3060 kJmol-1 Two steps: 2H+ + e- = H2+ H2+ + e- = H2

  18. Hydrogen Fuel Cell Wikipedia

  19. Solvated electrons Boag and Hart, Nature1963, 197, 45. Keene, Nature1963, 197, 47. Laubereau, et al. TU München www.e11.ph.tum.de/forschung/ projekte/esolv.en.htm

  20. Electron solvated by two water molecules is not stable (HOH)e-(HOH)  H2O + H2O + e-H°= -152 kJmol-1 mp2/6-311+g(d,p)

  21. Surprise: Electron solvated by two HBr (or two HCl) molecules is stable (HBr)2- mp2/6-311+g(d,p) Rauk, A.; Armstrong, D. A. J. Phys. Chem. A2002, 106, 400-403. SOMO

  22. Among the hydrides of the main group elements (EHn) only HBr and HCl and form stable electron bound Dimers. What about the isoelectronic (EHn)H+ ? ((EHn)H+)2-= [HnE–H–H–EHn]+.

  23. [HnE–H–H–EHn]+.

  24. [HnE–H–H–EHn]+. *TZVPP

  25. [HnE – H–H – EHn]+. H–H [H3As – H–H – AsH3]+. [H3P – H–H – PH3]+. H–H+. [H3N – H–H – NH3]+.

  26. Alternative point of view, electron donation to H2+ 2HnE + H2+ HnE–H–H–EHn+Ecom

  27. Stability considerations a) Gain in energy for 2HnEH++ e- HnE–H–H–EHn+, b) Gain in energy for 2HnE + H2+ HnE–H–H–EHn+. c) Proton affinity, data from ref Uggerud2006, d) Data from NIST web site. e) Energy of reaction for HnE–H–H–EHn+  E2H2n+ + H2. f) Critical energy for HnE–H–H–EHn+  E2H2n+ + H2. g) Energy of reaction for HnE–H–H–EHn+  E2H2n–H–H+. h) Critical energy for HnE–H–H–EHn+  E2H2n–H–H+. i) Energy of reaction for HnE–H–H–EHn+ HnE–H–EHn+ + H, j) Critical energy for HnE–H–H–EHn+ HnE–H–EHn+ + H.

  28. 2H+ + 2e- = H2 Two steps: 2HnE–H+ + e-HnE–H–H–EHn+ HnE–H–H–EHn+ 2HnE + H2

  29. Thank you for your attention! Thanks are due to: Patrik Andersson Vebjørn Bakken Trygve Helgaker Andreas Krapp Gernot Frenking

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