Gradients: Water suppression, DOSY

Question 1

Pulsed field gradients and diffusion editing

Answer 1

• Gradients add to the B0 field in a space dependant manner.
• A z-gradient causes a linear space-dependant change of B0 in the z-direction
• Gradients in a spin-echo:
• For magnetisation that has not observed the 180° pulse the second gradient causes dephasing
• magnetization which does experience the selective 180◦ pulse is rephased by the second gradient

Question 2

DOSY = Diffusion-ordered spectroscopy

Answer 2

90° -> tau -> 180° -> tau (detection)

Question 3

DOSY - gradient echo

Answer 3

• A pair of matched gradient pulses encodes the spins for displacement.
• Coherent mo7on preserves the signal amplitude, but leads to a phase shi;.
• Random mo7on results in an a=enua7on of the signal amplitude.

Question 4

Lipoproteins

Answer 4

• supramolecular assemblies of lipids, triglycerides, cholesterol and apolipoproteins
• part of a transport system for cholesterol and particles for steroid hormone and membrane synthesis
• relevant for processing of fatty acids
• Supramolecular assembly of lipids, triglycerides, and cholesterol and apolipoproteins.
• Significant diagnostic importance of LDL cholesterol
• increased concentrations of LDL cholesterol are associated with an increased risk of myocardial infarction and
  vascular death
• early exposure to excessive LDL cholesterol, which is often the result of mutations of the LDL receptor, results in markedly early atherothrombosis
• those who inherit two copies of a defective LDL receptor-related gene or who inherit combined genetic defects (homozygous familial hypercholesterolaemia) face myocardial infarction and stroke in their teens and early 20s
• more than a third of all middle-aged or older adults in the USA and the UK will be recommended for statin therapy

Question 5

NMR of blood

Answer 5

1) lipoproteins (phospholipids, cholesterol, triglycerides, apoproteins)
2) Metabolites 30-80
3) glycoproteins

Question 6

water suppression

Answer 6

• Presaturation (for short sequences)
• Jump-and-return and similar sequences
• Watergate using soft-pulses
• Excitation-sculpting
• Gradient echo-anti-echo-selection (in HSQCs)

Question 7

Pre-saturation

Answer 7

• Saturation of water signals by low-power continuos-wave irradiation between scans (1-2s)
• Depends on B0-homogeneity
• Works very well in 1D spectra (best as 1D-NOESY)

Question 8

Watergate

Answer 8

90° -> delta -> 90° (-y) -> 180° (y) -> 90° (-y)

• for signals not affected by the soft pulses
• für water the two frequency-selective soft 90° pulses cause dephasing

Question 9

Watergate with flip-back

Answer 9

90° (x) -> 90° (x) -> delta -> 90° (-y) -> 180° (y) -> 90° (-y)

• water aligned along z before any pulse is applied
• recovered water signal is further destroyed by Watergate

Question 10

Excitation sculpting

Answer 10

90° (x) -> delta -> 180° -> 180° -> delta -> 180° -> 180°

• two subsequent echos for solute
• for spins affected by the frequency-selective soft-pulse both echos cause dephasing

Question 11

Water Resonance Suppression in FT 1H NMR

Answer 11

1-1 Hard Pulse