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: