1 / 23

Spectroscopie RPE

Spectroscopie RPE. Résonance Paramagnetique Electronique. Introduction and principles. Paramagnetic species (in biology). Spin S = 1/2 systems. hyperfine coupling anisotropy. Spin S > 1/2 systems. half-integer integer polynuclear systems. Bio-EPR spectroscopy.

gur
Télécharger la présentation

Spectroscopie RPE

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Spectroscopie RPE RésonanceParamagnetiqueElectronique

  2. Introduction and principles • Paramagnetic species (in biology) • Spin S = 1/2 systems hyperfine coupling anisotropy • Spin S > 1/2 systems half-integer integer polynuclear systems • Bio-EPR spectroscopy

  3. Introduction and principle

  4. History of (bio)EPR 1944- discovery of the EPR effect E.K. Zavoisky concomitantly: solid-state physicists: quantum theoretical bases 1952- first detection of an EPR spectrum (radical) 1956- J.E. Bennett and D.J.E. Ingram : single crystal EPR studies of Hemoglobin 1959- R.H. Sands H. Beinert : EPR studies of frozen solutions of heart tissue 1959- B.G. Malmström and T. Vänngard : EPR studies of frozen solutions of multicentre metalloenzymes

  5. History Two and a half decades after the first observation of EPR signal : EPR Spectroscopy became a practical research tool for non specialists Powerful tool to study paramagnetic systems unpaired electrons « EPR signal intensity and Powder Shapes: A Reexamination » R. Aasa, T. Vänngård, J. Magn. Res. 1975, 19, 308-315

  6. Electronspin electron: magnetic moment and spin quantum number S = 1/2 with magnetic components ms = +1/2 and ms = –1/2 Stern and Gerlach experiment: Otto Stern and Walther Gerlach - 1922

  7. Zero field field B0 B0 Electron Spin - classical view Electron spin: angular momentum S = 1/2 Classical view: E = - . B0

  8. Some definitions Electron spin: angular momentum S = 1/2 Magnetic moment • ge = 2,002319304386 •  = Bohr magneton • e : gyromagnetic constant of the electron

  9. Electron Spin - quantum mechanical view Applied magnetic field along z. Projection of S along z : -S  ms S i.e. ms = -1/2 ; + 1/2 ms = +1/2 E = 1/2 geB0 Energy ms = -1/2 E = -1/2 geB0 B0 B0 = 0

  10. Bohr magneton9,2740154 10-24 J T-1 Free electron ge2,002319304386 Magnetic fieldTesla T perpendicular mode: B1 B0 Planck constant6,6260755 10-34 J s Frequency of the radiation EPRtransitions E = 1/2 geB0 Energy E = - 1/2 geB0

  11. EPRtransitions h Energy B0 Br

  12. EPRspectrometers Energy: 0.3 cm-1 Units: 1 T = 10000 G 336 mT = 3360 G

  13. EPRspectrometers Diode gun -waves source) -waves bridge Magnet CPU

  14. EPRspectrometers

  15. Intensity of EPR signal Depends on: • Sample concentration (spin concentration) • Power of the microwaves • Temperature • (Modulation) Experimental key parameters !

  16. EPR SAMPLES -powder -solution typical biological samples • frozen solutions: • cylindrical quartz tube • 100-200 L • 3-4 mm inner diameter room temperature experiments: water - high dielectric constant flat cells or capillary

  17. Paramagnetic species

  18. Organic radicals • Inorganic radicals: NO, O2 • metal ions and metal complexes (metalloproteins) • defect centers in crystals or semiconductors • metallic conductors

  19. 3d7 3d8 TRANSITION METAL IONS

  20. TRANSITION METAL five d orbitals:

  21. low spin (S = 1/2) high spin (S = 5/2) dz2 dx2-y2 dx2-y2 dz2 0 0 dyz dxz dxy dxy dxz dyz CASE of IRON FeII (3d6) FeIII (3d5) FeIV (3d4) FeV (3d3)

  22. dx2-y2 dxy dz2 dxz dyz CASE of COPPER CuI (3d10) CuII (3d9) CuIII (3d8)

More Related