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Magnetic Resonance

Magnetic Resonance. MSN 506 Notes. Overview. Essential magnetic resonance Measurement of magnetic resonance Spectroscopic information obtained by magnetic resonance 1D 2D Correlation and spin transfer related MR. Magnetic Resonance.

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Magnetic Resonance

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  1. Magnetic Resonance MSN 506 Notes

  2. Overview • Essential magnetic resonance • Measurement of magnetic resonance • Spectroscopic information obtained by magnetic resonance • 1D • 2D Correlation and spin transfer related MR

  3. Magnetic Resonance • Nuclei and electrons carry spin (magnetic dipole moment) g is called the gyromagnetic ratio or g-factor Nuclear magneton (unit for nuclear magnetic spins) μN = 5.050 783 × 10-27J·T-1 Bohr magneton (unit for electron magnetic spins) μB = 9.274 009 × 10-24J·T-1

  4. Energy of dipole in an external magnetic field

  5. NMR spectrometer

  6. Free Induction Decay • The spins that are in a non-equilibrium initial position lose energy by radiating and return to equilibrium state The released electromagnetic energy is picked up by coils

  7. Free Induction Decay • Field generated per spin is very small • Large number of atoms/molecules (1023) can produce measurable signal if they add up coherently Bolztmann Factor Small portion of spins have net effect at room temperature Field Uniformity If B field is not uniform, spins at different locations oscillate at different frequencies Solvents should be chosen so as not to confuse the experiment

  8. Couplings • Local magnetic field of a nuclei is affected by its surroundings Nuclei produce fields at each others location Electrons in bonds produce fields at nuclei locations Atom 2 Atom 1

  9. Couplings are used to identify bond structure of molecules

  10. Dephasing There are characteristic times for energy loss and phase loss, which can also be measured by MR

  11. 2D NMR • Measures correlations between NMR lines by pulsed excitation • Correlations indicate closely placed nuclei The complicated 1D NMR spectrum of a protein molecule does not say much about the molecular structure

  12. Correlation measurement

  13. 2D correlations help you estimate structure

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