核磁共振光譜與影像導論. Introduction to NMR Spectroscopy and Imaging Lecture 06 Nuclear Overhauser Effect (NOE) and NOESY (Spring Term, 2011) Department of Chemistry National Sun Yat-sen University. Nuclear Overhauser Effect (NOE) and NOESY. Population Transfer.
Introduction to NMR Spectroscopy and ImagingLecture06Nuclear Overhauser Effect (NOE) and NOESY(Spring Term, 2011)Department of ChemistryNational Sun Yat-sen University
In population manipulations, the most commonly used technique is
selective population transfer (SPT):
Whenever a polarization or a transition of a spin is inverted or saturated, the polarization or transition of the other spins that are coupled to it will be affected.
Perturbation on a Spin (Saturation/Inversion) + Cross Relaxation
The Polarization of Another (Coupled) Spin Is Altered.
Depending on the relative magnitudes of W2 and W0, NOE factor can be
Larger or smaller than 1 and can be both negative and positive.
Black: NOE affected peak
1001D Homonuclear Transient NOE
A single spin is inverted and the spin system response is
read using a 90° pulse after a “mixing” time delay of variable duration. In the transient mode, the NOE builds up due to cross-relaxation of nearby spins by the inverted spin as the entire spin system.
Neither have to be steady
Nor have to be equilibrium
Whenever the polarization of one of two coupled spins deviates from its equilibrium value, the polarization of the other spin is affected by cross relaxations. The NOE factor (the extent that the polarization of the unperturbed spin is affected) depends on cross relaxation rates and longitudinal relaxation rates.
When the distance between spins A and B is smaller than ~ 5 Å, NOE
cross peaks are observable.
90o1D Homonucelar ROE
A single transition is inverted using a selective 180° pulse (along the x axis), and
then a hard 90° x pulse is immediately applied to the spin system.
This has the effect of placing the “inverted” magnetization along the -y axis while
the rest of the magnetization is aligned along +y. Then, a low-power rectangular
pulse is applied long the y-axis.
This pulse is applied parallel to the magnetization (in the rotating frame) and effects
no net rotation. Instead, it “locks” the magnetization along the y axis, and is referred
to as a spin lock pulse. The magnetization is said to be spin locked because
it doesn’t precess about B0, but the spins now precess aboutB1(the spin lock pulse).
Therefore, under these conditions, the magnetization can be considered to being
analogous to alignment along the z axis in the presence of B0 alone.
Finally, the spins will relax towards a new equilibrium in the presence of B1;
the characteristic time constant for this decay is called T1ρ forT1in the rotation frame.
100ROE Mechanism:All relaxation rates are changed into rotating frame.
Note that both W2 and W0 promote ROE!
W2 promotes NOE while W0
Both W2 and W0 promote ROE
Hydration of biomolecules
Structure determination of biomacromolecules
Principle of CORMA
Example of CORMA
NOESY of Poly(N-vinyl-carbazole): CHCl3, mixing time:450 ms, 500 MHz, 303 K
--- G. Otting, E. Liepinsh, K. Wuthrich, Science1991,254,974
Residues : 58
Internal water : 4
--- G. Otting,J. Progr. NMR. Spectrosc. 1997, 31 , 259
Glu1-190 ( mix=0.4 ms )
CTX II: 44-60