NMR 5 Flashcards
(29 cards)
What is T_1-relaxation?
It is the developement of magnetization back to its equlibrium.
What is the formula for T_1-relaxation/longitudinal relaxation (difference in magnetization from the equlibrium is going to decay exponentially)?
M_z−M_0=e^(−(t/T_1))
T_1=relaxation time
What happens when the relaxation gets slower?
When T₁ relaxation is slower (i.e., T₁ is longer), it takes more time for the net magnetization to return to equilibrium along the z-axis after excitation. This means signal recovery is slower, which affects how quickly you can repeat scans and may reduce signal intensity in fast experiments.
Describe the inversion-recovery
Inversion-recovery is a pulse sequence used to measure T₁ relaxation times. It starts with a 180° pulse to invert the magnetization, followed by a variable delay time (τ), and then a 90° pulse to detect how much magnetization has recovered along the z-axis. By changing τ and recording the signal, a T₁ relaxation curve can be created.
How can T_1 be interpret from a spectrum?
when tau is plottet against the intensity, it is possible to interpret T_1 from the linarization:
I(τ)=1−2∗e^(−τ/T_1 )
What is the formula for the longitudinal relaxation rate?
R(1)=1/T_1
Select all correct statements from below!
T1 relaxation affects only z-magnetization.
T1 relaxation leads to a loss of measurable magnetization.
T1 relaxation affects both x,y and z-magnetization.
T1 relaxation leads to a re-establishment of equilibrium magnetization.
too fast T1 relaxation causes problems for NMR spectroscopy
too slow T1 relaxation causes problems for NMR spectroscopy
T1 relaxation leads to a loss of measurable magnetization.
T1 relaxation affects both x,y and z-magnetization.
T1 relaxation leads to a re-establishment of equilibrium magnetization.
too fast T1 relaxation causes problems for NMR spectroscopy
too slow T1 relaxation causes problems for NMR spectroscopy
After running an inversion-recovery sequence on your sample, you obtain the following intensity values depending on the delay τ:
τ [s]…..intensity [a.u.]
0.1…….-0.753
0.2…….-0.623
0.5…….-0.162
1.0……..0.456
2.0……..0.767
5.0……..1.160
10.0…….1.002
- Which quantity is determined by the Inversion-Recovery Sequence?
T1, T2 or NOE
T1
After running an inversion-recovery sequence on your sample, you obtain the following intensity values depending on the delay τ:
τ [s]…..intensity [a.u.]
0.1…….-0.753
0.2…….-0.623
0.5…….-0.162
1.0……..0.456
2.0……..0.767
5.0……..1.160
10.0…….1.002
- Which T_1 quantity is determined by the Inversion-Recovery Sequence?
0.85
What is T_2-relaxation (transverse/ spin-spin- relaxation)
T₂-relaxation describes the loss of coherence among nuclear spins in the xy-plane, which leads to a decay of the observed NMR signal over time.
Why is T_2-relaxation annoying?
Because it kills your signal and it will not reach equilibrium the same as T_1- relaxation.
What is the formula for T_2-relaxation?
M_xy (t)=e^(−t/T_2 )
What is the formula for transverse relaxation rate?
R_2 [s^(−1) ]=1/T_2
Why is it difficult to work with bigger molecules in NMR?
Because the larger molecules relax faster, especially via T2-relaxation leading to broader peaks and lower signal resolution.
Choose all terms of magnetization that are affected by T2 relaxation
Ix
-Iz
2IxSz
2IxSy
Ix
2IxSz
2IxSy
You are running a CPMG experiment with n repetitions of a spin-echo.
Each spin echo consists of a delay τ=6 ms, followed by a 180 degree pulse of 24 µs, followed by a delay τ=6 ms.
Depending on the number of repetitions (n) of the spin-echo, you get the following intensities:
n……….intensity
1……….0.96
2……….0.95
4……….1.01
8……….0.82
16………0.53
32………0.36
64………0.08
128……..0.01
What is the value of T2 for this atom?
0.33
What is molecular mobility?
It is expressed as correlation tome τ_c [s]. τ_c is defined as the time it takes an intramolecuar vector to reorient by 1 rad (57.3°) on average. The higher the mobilty, the shorter τ_c.
A small value for a correlation time means that the underlying molecular motion is….
slow or fast
fast
If both T1 and T2 relaxation of a hydrogen atom are slow, it belongs to a …
- large molecule (more than 2 kDa)
- small molecule (less than 1 kDa)
small molecule (less than 1 kDa)
If the values of both time constants T1 and T2 are large for a hydrogen atom, it belongs to a …
- large molecule (more than 2 kDa)
- small molecule (less than 1 kDa)
small molecule (less than 1 kDa)
Proteins have:
fast T2 and slow T1
fast T1 and slow T2
slow T2 and slow T1
fast T2 and fast T1
fast T2 and slow T1
What is the nuclear overhauser effect (NOE)?
The NOE is an NMR phenomenon where the intensity of one nucleus’s signal is affected by the relaxation of a nearby nucleus, due to dipole–dipole interactions.
What does NOE describe?
The observation that the signal of one nucleus changes its intensity if a nearby nucleus is saturated.
What is the formula for NOE?
η=I/I_0 −1
