NMR Spectroscopy. Relaxation Time Phenomenon & Application. Relaxation- Return to Equilibrium. t. t. x,y plane. z axis. Longitudinal. Transverse. 0. 0. 1. 1. t. t. 2. 2. E -t/ T 2. 1- e -t/ T 1. 8. 8. Transverse always faster!. Relaxation.
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Phenomenon & Application
Transverse always faster!
magnetization vector's trajectory
The initial vector, Mo, evolves under the effects of T1 & T2 relaxation and from the influence of an applied rf-field. Here, the magnetization vector M(t) precesses about an effective field axis at a frequency determined by its offset. It's ends up at a "steady state" position as depicted in the lower plot of x- and y- magnetizations.
The T2 relaxation causes the horizontal (xy) magnetisation to decay. T1 relaxation re-establishes the z-magnetisation. Note that T1 relaxation is often slower than T2 relaxation.
1. Dipole-Dipole interaction "through space"
2. Electric Quadrupolar Relaxation
3. Paramagnetic Relaxation
4. Scalar Relaxation
5. Chemical Shift Anisotropy Relaxation
6. Spin Rotation
180y (or x)
Range of interaction (Hz)
104 - 105
- abundance of magnetically active nuclei- size of the magnetogyric ratio
106 - 109
- size of quadrupolar coupling constant- electric field gradient at the nucleus
concentration of paramagnetic impurities
10 - 103
size of the scalar coupling constants
Chemical Shift Anisotropy (CSA)
10 - 104
- size of the chemical shift anisotropy- symmetry at the nuclear site
6- Spin rotation
line width at half-height=1/T2
Two factors contribute to the decay of transverse magnetization.
( lead to a pure pure T2 molecular effect)
( lead to an inhomogeneous T2 effect)
180y (or x)
For peptides in aqueous solutions the dipole-dipole spin-lattice and spin-spin relaxation process are mainly mediated by other nearby protons