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Solid state NMR
- Chapter 13, on web site: http://www.chem.ubc.ca/faculty/straus/c518_09.html
A) Introductioni) Challenges of solid stateii) What can we study?iii) Review of NMR interactions
B) Averaging – Magic angle sample spinning
C) Polarization transfer - CP
Linewidth comparison
Solution State: 1H 12-25 Hz13C 5-15 Hz15N 4-7 Hz
Solid State: 1H ca. 10 000 Hz13C ca. 5000 Hz15N ca. 7000 Hz
α
β
α
α
H = Hz + Hcs + HJ + HD (+ HQ)
Hz=-γB0IzZeeman --
Hcs=-γσB0IChemicalShift
• environment• orientation
Scalar • connectivities• dihedral angles
HJ = ΣΣ 2π Jkj Ik.Ijk j
Dipolar • distances (<6A)• orientation
HD=b12[(I1.I2)r-3–3(I1.r)(I2.r)r-5]
b12=µ0γ1γ2h2
16π3
Only the isotropic part of Hcs and HJ remain
Averaging due to isotropic tumbling
H = Hz + Hcs + HJ + HD (+ HQ)
Solution State
These interactions are on the order of Hz, thereforehigh resolution can be achieved.
Solid StateNo averaging
Single crystal
Powder
H = Hz + Hcs + HJ + HD (+ HQ)
The interactions of interest are on the order of 10-1000 Hz (106 Hz in the case of HQ) and conserve their anisotropic character.
Intermediate Regime: Residual Dipolar Couplings
H = Hz + Hcs + HJ + HD
The dipolar coupling is not fully averaged and is on the order of Hz.
Resolution in the Solid State
Use the angular dependence of some of the Interactions to:
1) Average Magic Angle Sample Spinning (MAS)
P2(cosθ) = (3 cos2θ -1)H = Hz + Hcs + HJ + HD (+ HQ)
For θ=54.7o,
<P2(cosθ)> =0
2) Make use of the angular dependence
Oriented Methods
For θ=θi,
P2= (3cos2θi -1)
MAS
Solution State: 1H 12-25 Hz13C 5-15 Hz15N 4-7 Hz
Solid State: 1H ca. 100 Hz13C ca. 100 Hz15N ca. 40 Hz
Oriented Methods
Solution State: 1H 12-25 Hz13C 5-15 Hz15N 4-7 Hz
Solid State: 1H ca. 1000 Hz13C ca. 300 Hz15N ca. 300 Hz
So why bother with solid state NMR?
if resolution is poor and (as we will see) the theory is complex!
Solid State NMR of Membrane Proteins
1) Membrane proteins constitute 20-40%of the proteins encoded by knowngenomes and are important drug targets (e.g. dopamine receptors, ABCtransporters)
YET
Only 368 out of a total of 20057 (1.8%)structures determined and deposited in the Protein Databank are of membraneprotein structures
STRUCTURAL INFORMATION IS NEEDED TO GAIN INSIGHT INTO FUNCTION
Recent developments in solid stateNMR have made it possible to undertake structural studies of peptidesand proteins.
Hagfish slime is 99.996% seawater, 0.002% mucin (glycoprotein) and 0.002%protein fibre. The fibres were hypothesized to contain both rigid and mobileregions. 13C spectra collected with and without cross-polarization show verydifferent carbonyl carbon lineshapes, supporting the two-phase model for thefibres.
CPBloch decay
Bloch decay spectra clearly show a sharp feature in the carbonyl region,while CP spectraclearly show a broad component.
Solution or solid?
Ubiquitin
1998
Straus, S.K. et al. 1998 J. Biomol. NMR, 12, 39-50.
2004
180 140 100 60 20
Igumenova, T.I. et al. 1998 JACS 126, 6720-27; ibid, 5323-31.
What has made this possible?
Sample preparation: - labelling strategies- recrystallization/precipitation
Assignment strategies: - 13C-13C correlation experiments- 13C-15N correlation experiments- 13C-1H or 15N-1H correlation experiments
Structural parameters from: - chemical shifts- torsion angle measurements- distance measurements
Straus, S.K. Phil. Trans. B. 2004
Interactions in solid state
Chemical shift:
Spherical tensor notation:
where
Scalar coupling:
Spherical tensor notation:
Dipolar interaction:
Spherical tensornotation:
Quadrupolar interaction:
Spherical tensornotation:
Spatial parts in arbitrary frame:
