Physical 3

Physical 3

1. 1 dimensional

   • pulse acquire
     • RF pulse, FID, fourier transform
   • frequency x-axis

2. pseudo 2D

   • inversion recovery
   • spin echo
   • DOSY
   • x-axis= frequency; Y-axis= time

3. 2 dimensions

   • NOESY
   • EXSY
   • X-axis=frequency; y-axis=frequency
   • pulse sequence
     • preparation
       • Evolution
         • mixing
           • acquisition
           • magnetisation transfer
         • nuclear precession
       • excitation
     • 2 pulse sequence
       • measures magnetisation transfer
         • off diagonal peaks

4. applications

   • molecular dynamics
     • proton transfer
     • molecular rearrangement
   • structure elucidation
     • bond & space interactions

5. isolated spins=diagonal peaks

   • other nuclei-coupling

6. nuclear overhauser effect

   • no J coupling
     • 2 separate peaks
   • transfer of nuclear spin
     • via cross relaxation
     • mixing time
   • change in intensity
     • caused by saturation in another
       • stronger
       • weaker
       • invert
   • dipolar coupling <3.5A
   • Saturation Na=Nb
   • lowest energy state is when both nuclei are aa
     • highest energy state is when both nuclei are bb
   • same pulses used

7. saturation of a nuclei

   • too many in beta states
     • want to flip to alpha state

8. W2 process

   • bb-aa
   • increase population difference
   • net increase in spin resonance intensity
   • Positive NOE
   • dominates at faster τ values

9. w0

   • ba-ab
   • decrease population difference
   • net decrease in spin resonance intensity
   • negative NOE
   • starts to dominate as it goes to slower τ values

10. structural NOE

    • large molecules
      • slow tumbling rate
      • reduction in NMR intensity of neighbouring proton
    • small molecules
      • quick tumbling rate
      • increase in NMR intensity of neighbouring proton

11. chemical exchange

    • conformational change cis to trans
      • occurs in mixing stage
    • frequency can change from t1 to t2

12. PGSE

    • gradient amplitude reduced signal

13. contrast agents

    • paramagnetic ions
    • T1 or T2 relaxation time of water is what it relys on