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Pulse Radiolysis and Spectral Resolutions

Pulse Radiolysis and Spectral Resolutions. Free Radical Problems in Biology and Medicine Spectral Resolution Technique Motivation for Transient Conductivity. Motivations. Oxidative stress Alzheimer’s disease Biological aging Basic issues Neighboring-group effects

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Pulse Radiolysis and Spectral Resolutions

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  1. Pulse Radiolysis andSpectral Resolutions • Free Radical Problems in Biology and Medicine • Spectral Resolution Technique • Motivation for Transient Conductivity

  2. Motivations • Oxidative stress • Alzheimer’s disease • Biological aging • Basic issues • Neighboring-group effects • Details of oxidative scheme

  3. N-Acetyl-L-Methionine Amide

  4. Gly-Met Met-Gly • STABILIZATION OF SULFURRADICAL CATIONS VIA INTRAMOLECULAR SULFUR-NITROGEN AND SULFUR-OXYGEN BOND FORMATION

  5. Three-electron bonds 2s,1s* -> 1s,2s* origin of 480 nm absorption in SS+ radical cations

  6. Advantage of Radiation Chemistry:Can convert all radicals to oxidizing (or reducing) ones Strongly reducing radical Strongly oxidizing radical Converting reducing to oxidizing G in units of radicals produced for every 100 eV of ionizing radiation absorbed

  7. Endo- and Exo-amides Neighboring group participation in compounds 3 but not in compounds 4?

  8. OPTICAL ABSORPTION SPECTRA USED FORSpectral Resolutions

  9. Endo-amide

  10. Endo-amide at pH 5

  11. Mathematics of Spectral Resolutions Knowns: the DAexp(lj) for all wavelengths j ei(lj) is the extinction coefficient of the i-th species at wavelength lj d = optical pathlength Unknowns: ci = concentration of i-th species DAexp(lj) = Siei(lj) cid Would like to solve for the ci’s But problem is over determined (too much data) and there is also noisy data Minimize Sum of Squares of the Deviation by varying the ci’s SSD = Si|DAexp(lj)  Siei(lj) cid|2

  12. Endo-amide pH 5 t = 650 ns SN included no SO

  13. Endo-amide pH 5t = 650 ns SO included no SN

  14. Time-resolved conductivity • N-Acetyl-L-Methionine Amide Formation of (SS)+ and (SO)+ species is paralled by a net decrease in equivalent conductivity

  15. Time-resolved conductivity • N-Acetyl-L-Methionine Amide +-OH Formation of (SN) species is not paralled by a net change in equivalent conductivity H2O - H+

  16. Concentration profiles Endo-amide at pH 5 Notes: No SO Only SS+ is conducting

  17. Alternative Concentration ProfilesEndo-amide pH 5 Notes: No SN Both SS+ and SO will conduct

  18. Conclusionsabout Endo-amide experiments • The expected transients account for the observed transient absorptions. • Whether or not SN or SO is present will depend on conductivity experiments yet to be made. • If SN, only the small amount of SS+ will contribute. • If SO, we expect a relatively large contribution to the conductivity at small times which decays into a smaller contribution as SO decays.

  19. Exo-amide

  20. Exo-amide pH 4 Notes: Same as pH 5 Namely little Neighboring Group Participation

  21. ConductivityExo-amide pH 4 Notes: Net decrease in conductivity, indicates SO or SS+ Since there was little Neighboring Group Participation in absorption, the conductive signal is probably SS+

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