Final Exam Flashcards
Best describes 1, n-ADEQUATE (4)
- 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
What 1, n-ADEQUATE and 1,1- ADEQUATE have in common
- initial 1JCH coupling in magnetization transfer pathways
- low sensitivity
best describes 1,1-ADEQUATE
developed prior to 1, n-ADEQUATE
advantage of running 1,n-ADEQUATE
-gives long-range heteronuclear correlation such as a psuedo-4JCH coupling which is especially useful for structure elucidation of proton-deficient molecules
disadvantage of running 1,n-ADEQUATE
-sometimes leak 2JCH correlation into the spectra, making the data ambiguous
JRES
2D NMR
f1 and f2 axes of JRES spectrum
-coupling on f1 axis, chemical shift on f2 axis
main use of JRES spectroscopy
-simplify 1D NMR spectra
True or False: JRES can involve either homonuclear couplings or heteronuclear couplings
True
JRES spectroscopy is limited to:
first order spin systems
What does WaterLOGSY stand for
Water-Ligand Observed via Gradient Spectroscopy
basic principle of WaterLOGSY (3)
- 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
How is Water LOGSY spectrum interpreted
-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
advantage of WaterLOGSY (3)
- detecting ligand binding due to high sensitivity and reliability
- provide structural information
- useful in developmental process of drugs
What pulse irradiates the protein-ligand complex in STD-NMR
Gaussian-shaped saturation pulse
size limit of protein that STD-NMR assays
-no size limit – larger the protein, the more effective
requirement for ligand size
-has to be big enough to adequately be saturated by pulse sequence
why STD-NMR is an improvement upon other NMR techniques
- far more sensitive
- doesn’t require a large sample
- can be directly detected from a mixture
What information can STD-NMR provide
-proximity of the ligand to the protein
2 main uses of solid state
- useful when only small amount of sample available
- useful for samples that don’t go into solution very well
most significant difference between solution NMR and solid state NMR
- in solution molecule can be tumbled rapidly and randomly
- solid state unable to be tumbled
3 methods used to produce sharp peaks in solid state
- Magic Angle Spinning
- Cross Polarization
- Combined Rotation and Multiple Pulse Sequence
Why do peaks appear split in solid state NMR
-split peaks indicate presence of two crystal environments in solid sample
what is importance of eliminating spinning sidebands
-mistakenly read as peaks in spectra
main application of 1D and 2D H-P coupled NMR
-goal was to determine pH of cell tissue samples containing phosphorous compounds
issue in determination of pH using 1D H NMR spectrum of biological sample HepG2.2.15
- reagent peak of TMSP was overlapping significant peaks
- presence of water was still apparent and difficult to completely remove
how was pH value for hydrogen spectrum in HBV sample obtained
-using 2D H-P HMQC to single out the exact chemical shift value of AMP
reagent used to center NMR
3-trimethylsilyl propionic acid sodium salt (TMSP)
3 samples used in experiment
- HepG2.2.15
- Urine
- Apple Juice
pathway for HNCA signal
Hydrogen-Nitrogen-alpha carbon
what kind of sample does HNCA examine
proteins
when was HNCA developed
1989
what dimension experiment is HNCA
3D
which is not a problem with the N nuclide that H-N HMBC overcame
short t1 relaxation time
what length of bonds between proton and nitrogen do you expect to see with the H-N HMBC
Both 2 and 3 bonds
is H-N HMBC proton detected or nitrogen detected
proton detected
what benefit did H-N HMBC have on alkaloid analysis
drastically reduced the number of possible structures for the alkaloids
why was H-N HMBC important for identifying nitrones rather than H NMR
proton NMR signal of nitrones is hidden under aromatic protons
why was there a need for NMR experiment to analyze large biomolecules when x-ray crystallography was already present
-X-ray crystallography only gives a snapshot of molecule and gives no details about interactions with the moelcule
How does TROSY help ratio of relaxation times in large biomolecules
-TROSY uses CSA and DD relaxation to its advantage to make T2 times longer to get better peak resolution
why were biomolecules over 30 kDa not being analyzed by NMR before 1997
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
Some methods to help the resolution of large biomolecule NMR are
isotope labeling
deuteration
TROSY NMR
TROSY stands for
Transverse Relaxation-Optimized Spectroscopy
What instruments does the LC-NMR-MS consist of
- HPLC
- NMR
- Mass Spec
benefits of using a cryoprobe
- increased signal-to-noise ratio
- reduction in sample amount
- increased sensitivity despite NMR limitations
what does a 4-fold increase to signal-to-noise ratio correspond to
-4-fold lower detection limit for a given amount of sample and the experiment time is reduced by a factor of 16
pulse wide utilized in APAP experiment using LC-NMR-MS
10.25 microseconds at 18 dB (90 degrees)
benefit to coupling an NMR to MS
Heteroatoms such as N, O, and Cl can be observed by MS data
