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NMR (PG503)

NMR (PG503). Solid-state NMR: Anisotropic interactions and how we use them. Dr Philip Williamson February 2009. Dipolar recoupling techniques and 2-dimensional NMR. Methods for transfer polarization and their application.

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NMR (PG503)

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  1. NMR (PG503) Solid-state NMR: Anisotropic interactions and how we use them Dr Philip Williamson February 2009

  2. Dipolar recoupling techniques and 2-dimensional NMR

  3. Methods for transfer polarization and their application Know how to manipulate anisotropic interactions to gain in resolution and sensitivity These anisotropic interactions contain lots of structural/dynamic information If we can selectively reintroduce these interactions we can obtain the information they encode Need methods that selectively reintroduce these interactions when we perform MAS

  4. Methods for transfer polarization and their application Overview dipolar recoupling under magic angle spinning: • Heteronuclear dipolar couplings: a) Cross Polarization (moving from HX to XY) b) REDOR 2) Homonuclear dipolar recoupling methods a) selective (rotational resonance) b) broadband (proton driven spin diffusion/C7)

  5. “Hahn’s Ingenious Concept1” (1) Normally two heteronuclear spins resonate at wI=gIB0and wS=gSB0 and pulses applied to I or S affect I or S. If we apply resonant fields to I and S they precess with a frequency WI=gIB1Iand WS=gSB1S We can make the precession frequencies match by adjusting the frequency B1 of individual nuclei. When these conditions match we obtain the so called Hartmann-Hahn condition: gIB1I=gSB1S z z y y x x MS MI WI WS BI BS 1) Principles of magnetic resonance, C.P. Slichter p277

  6. “Hahn’s Ingenious Concept1” (2) Fulfilled Hartmann-Hahn condition gIB1I=gSB1S I spin in close proximity to S spin so we have a strong heteronuclear dipolar coupling: Thus we can get resonant transfer of energy from the I to the S spin. z z yI yS xI xS MS MI WI WS BI BS 1) Principles of magnetic resonance, C.P. Slichter p277

  7. Experimentally what is observed(1) • The width of the matching condition is proportional to the strength of the dipolar coupling in both the static and MAS cross-polarisation experiment. 1H-13C 15N-13C

  8. Weaker couplings:Increased problems with relaxation Weaker couplings Slow buildup – transfer quenched Weaker couplings Slow buildup – transfer quenched

  9. Applications assignment NCA Experiment on microcrystalline ubiquitin.

  10. Rotational Echo Double Resonance (REDOR) Dephasing of X through the recoupling of the XY heteronuclear dipolar coupling Spin Lock Decouple (p/2)y 1H p X p p p p p p Y wr

  11. Averaging of anisotropic interactions Anisotropic interactions oscillate with a wr and 2wr dependence under MAS e.g. CSA If we want to selectively reintroduce them under MAS we want to find a way of selectively disrupting this averaging.

  12. Spin/Spatial Interactions Anisotropic interactions are time dependent under MAS Can interfere with MAS selectively disturbing averaging process Example apply p pulses during rotor cycle results in non-zero contribution from heteronuclear dipolar coupling wI2DIS(.. . sin(wr) + .. . sin(2wr)) . Ix

  13. Dephasing curves – distance measurements Example dephasing data here. 1.54Å 2.5Å 4.0Å

  14. Distances in biomolecules Murphy et al. 2001

  15. Transferred echo double resonance (TEDOR) INEPT in the solid-state? Spin Lock Decouple (p/2)y 1H p/2 X p p p p/2 p p p Y wr INEPT transfer

  16. Homonuclear recoupling methods • Dipolar assisted rotary recoupling (DARR) • Proton driven spin diffusion/Rotation resonance (selective) • Radio frequency driven recoupling • C7/POST-C7 • HORROR/DREAM

  17. Homonuclear recoupling under MAS • Rotation resonance (selective) Gain resolution sensitivity Loose structural information present in anisotropic interactions

  18. B0 Lineshape Distance wr=d2-d1  =54.7° Rotational resonance – lineshape wr

  19. wr=d2-d1 Rotational resonance Dd Same chemical shift Different chemical shift

  20. O + N O Magnetization exchange experiments 5 wr=d2-d1 1 4 3 13C /ppm 5 3 2 1 4

  21. Rotational resonance - selectivity Two active spins with chemical shift equal to MAS frequency, (n=1, rotation resonance condition) 1 2 Short distance, 1 bond coupling to passive spin 3 Distance (Å) 3 2 wr=DW12 wr=DW12 1

  22. 1 2 -62° 62° 128° -128° -53° 53° Rotational resonance - applications

  23. Rotation Resonance - Summary • Advantages • Recoupling selective • When sensitivity/analysis allows geometries can be determined with high resolution • Disadvantages • Only one spin pair recoupled at once • Makes analysis of large labelled molecules difficult • On resonance lines are broadened reducing resolution and sensitivity

  24. Proton driven spin diffusion • Interactions between 1H and low g nuclei remain • Transfer driven by: • heteronuclear coupling between 1H and low g nuclei • 1H-1H homonuclear interactions not averaged by MAS

  25. Spin diffusion Assignment and structure determination of SH3

  26. Problems with PDSD • At high fields/MAS frequencies • Chemical increases meaning 1H-1H couplings are no longer homogeneous • MAS more effectively averages 1H-1H couplings • Results in attenuation of PDSD • Requires longer mixing times • Reduced sensitivity due to T1 relaxation

  27. Dipolar assisted rotary resonance recoupling (DARR) Decoupled No-decoupling Rotary resonance recoupling of C-H dipolar interaction Takegoshi, 2001

  28. Comparison of PDSD and DARR

  29. Solid-state NMR spectra

  30. References Spin Dynamics: Basics of Nuclear Magnetic Resonance, Malcolm Levitt Biomolecular NMR, Jeremy Evans Principles of Magnetic Resonance, C.P. Slichter Proton driven spin diffusion Distance information from proton-driven spin diffusion under MAS, Andreas Grommek, Beat H. Meier, Matthias Ernst , Chemical Physics Letters 427 (2006) 404–409

  31. Appendix 1

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