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Theory of NMR > Final Exam > Flashcards

Final Exam Flashcards

1
Q

Best describes 1, n-ADEQUATE (4)

A
  • proton-detected
  • “out and back” experiment
  • correlates proton to carbon four bonds in a psuedo-4JCH coupling
  • useful in structure elucidation of highly substituted aromatic ring molecule
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2
Q

What 1, n-ADEQUATE and 1,1- ADEQUATE have in common

A
  • initial 1JCH coupling in magnetization transfer pathways

- low sensitivity

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3
Q

best describes 1,1-ADEQUATE

A

developed prior to 1, n-ADEQUATE

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4
Q

advantage of running 1,n-ADEQUATE

A

-gives long-range heteronuclear correlation such as a psuedo-4JCH coupling which is especially useful for structure elucidation of proton-deficient molecules

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5
Q

disadvantage of running 1,n-ADEQUATE

A

-sometimes leak 2JCH correlation into the spectra, making the data ambiguous

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6
Q

JRES

A

2D NMR

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7
Q

f1 and f2 axes of JRES spectrum

A

-coupling on f1 axis, chemical shift on f2 axis

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8
Q

main use of JRES spectroscopy

A

-simplify 1D NMR spectra

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9
Q

True or False: JRES can involve either homonuclear couplings or heteronuclear couplings

A

True

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10
Q

JRES spectroscopy is limited to:

A

first order spin systems

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11
Q

What does WaterLOGSY stand for

A

Water-Ligand Observed via Gradient Spectroscopy

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12
Q

basic principle of WaterLOGSY (3)

A
  • one-dimensional NMR technique dependent on NOESY technique
  • involves transfer of magnetization by an intramolecular NOE and spin diffusion caused by protein and ligand
  • RF irradiation causes magnetization of bulk of water molecules to become excited
  • transferred to bound ligand during NOESY mixing time
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13
Q

How is Water LOGSY spectrum interpreted

A

-positive resonances given by compounds that bind to target protein and negative resonance are given by compounds that have no interaction with the protein ligand

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14
Q

advantage of WaterLOGSY (3)

A
  • detecting ligand binding due to high sensitivity and reliability
  • provide structural information
  • useful in developmental process of drugs
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15
Q

What pulse irradiates the protein-ligand complex in STD-NMR

A

Gaussian-shaped saturation pulse

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16
Q

size limit of protein that STD-NMR assays

A

-no size limit – larger the protein, the more effective

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17
Q

requirement for ligand size

A

-has to be big enough to adequately be saturated by pulse sequence

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18
Q

why STD-NMR is an improvement upon other NMR techniques

A
  • far more sensitive
  • doesn’t require a large sample
  • can be directly detected from a mixture
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19
Q

What information can STD-NMR provide

A

-proximity of the ligand to the protein

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20
Q

2 main uses of solid state

A
  • useful when only small amount of sample available

- useful for samples that don’t go into solution very well

21
Q

most significant difference between solution NMR and solid state NMR

A
  • in solution molecule can be tumbled rapidly and randomly

- solid state unable to be tumbled

22
Q

3 methods used to produce sharp peaks in solid state

A
  • Magic Angle Spinning
  • Cross Polarization
  • Combined Rotation and Multiple Pulse Sequence
23
Q

Why do peaks appear split in solid state NMR

A

-split peaks indicate presence of two crystal environments in solid sample

24
Q

what is importance of eliminating spinning sidebands

A

-mistakenly read as peaks in spectra

25
Q

main application of 1D and 2D H-P coupled NMR

A

-goal was to determine pH of cell tissue samples containing phosphorous compounds

26
Q

issue in determination of pH using 1D H NMR spectrum of biological sample HepG2.2.15

A
  • reagent peak of TMSP was overlapping significant peaks

- presence of water was still apparent and difficult to completely remove

27
Q

how was pH value for hydrogen spectrum in HBV sample obtained

A

-using 2D H-P HMQC to single out the exact chemical shift value of AMP

28
Q

reagent used to center NMR

A

3-trimethylsilyl propionic acid sodium salt (TMSP)

29
Q

3 samples used in experiment

A
  • HepG2.2.15
  • Urine
  • Apple Juice
30
Q

pathway for HNCA signal

A

Hydrogen-Nitrogen-alpha carbon

31
Q

what kind of sample does HNCA examine

A

proteins

32
Q

when was HNCA developed

A

1989

33
Q

what dimension experiment is HNCA

A

3D

34
Q

which is not a problem with the N nuclide that H-N HMBC overcame

A

short t1 relaxation time

35
Q

what length of bonds between proton and nitrogen do you expect to see with the H-N HMBC

A

Both 2 and 3 bonds

36
Q

is H-N HMBC proton detected or nitrogen detected

A

proton detected

37
Q

what benefit did H-N HMBC have on alkaloid analysis

A

drastically reduced the number of possible structures for the alkaloids

38
Q

why was H-N HMBC important for identifying nitrones rather than H NMR

A

proton NMR signal of nitrones is hidden under aromatic protons

39
Q

why was there a need for NMR experiment to analyze large biomolecules when x-ray crystallography was already present

A

-X-ray crystallography only gives a snapshot of molecule and gives no details about interactions with the moelcule

40
Q

How does TROSY help ratio of relaxation times in large biomolecules

A

-TROSY uses CSA and DD relaxation to its advantage to make T2 times longer to get better peak resolution

41
Q

why were biomolecules over 30 kDa not being analyzed by NMR before 1997

A

large biomolecules give a lot of resonances which causes signal overlap and a large magnetic field is needed which causes problems with T2 relaxation times

42
Q

Some methods to help the resolution of large biomolecule NMR are

A

isotope labeling
deuteration
TROSY NMR

43
Q

TROSY stands for

A

Transverse Relaxation-Optimized Spectroscopy

44
Q

What instruments does the LC-NMR-MS consist of

A
  • HPLC
  • NMR
  • Mass Spec
45
Q

benefits of using a cryoprobe

A
  • increased signal-to-noise ratio
  • reduction in sample amount
  • increased sensitivity despite NMR limitations
46
Q

what does a 4-fold increase to signal-to-noise ratio correspond to

A

-4-fold lower detection limit for a given amount of sample and the experiment time is reduced by a factor of 16

47
Q

pulse wide utilized in APAP experiment using LC-NMR-MS

A

10.25 microseconds at 18 dB (90 degrees)

48
Q

benefit to coupling an NMR to MS

A

Heteroatoms such as N, O, and Cl can be observed by MS data

Theory of NMR (4 decks)

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