Transcript Document

NMR Spectroscopy:
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Introduction – History of NMR
NMR Hardware and Software
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Superconducting Cryo-Magnet
Probe
RF Console
Computer + NMR Software
+ Printer/Plotter
Solution NMR
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Sample Preparation
Presentation of Data
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Important NMR Milestones
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1938 - NMR in molecular beams
Rabi (Columbia University)
1946 - NMR of Liquids and Solids
Purcell, Torrey, Pound (Harvard)
Bloch, Hansen, Packard (CalTech)
1952 - First commercial NMR spectrometer
1962 - First Superconducting Magnet for NMR
1968 - First Pulse Fourier Transform NMR
1969 - First Concept of MRI Scanners
1971 - First 2D NMR Experiment – COSY (Jean Jeener)
1985 - Protein Structures
2009 - First Gigahertz NMR Spectrometer
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NMR Nobel Prize Winners
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1944 Isador Rabi
1952 Felix Bloch
& Edwin Purcell
1991 Richard Ernst
2002 Kurt Wüthrich
2003 Paul Lauterbur
& Sir Peter Mansfield
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From: Bruker SpinReport, Vol 153
Laukien Prize Winners
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1999 Konstantin Pervushin, Roland Riek, Gerhard Wider, and Kurt Wüthrich;
TROSY
2000 Lucio Frydman;
Quadrupolar MQMAS
2001 Peter Boesiger, Klaas Prüßmann, Markus Weiger;
Sensitivity-encoded magnetic resonance imaging
2002 Ad Bax, Aksel Bothner-By and James Prestegard;
Residual dipolar couplings of weakly aligned molecules in solution
2003 Jacob Schaefer;
REDOR Technique for Solid State NMR
2004 Lewis E. Kay,
NMR of Biological Macromolecules
2005 Stephan Grzesiek,
J couplings across hydrogen bonds
2006 Thomas Szyperski, Eriks Kupce, Ray Freeman, and Rafael Bruschweiler;
Acceleration of Multi-dimensional NMR
by novel procedures for scanning data space and efficiently processing results to obtain a conventional spectral representation
2007 Robert G. Griffin;
High-field dynamic nuclear polarization (DNP) for sensitivity enhancement in solid-state MAS NMR
2008 Malcom H. Levitt;
Optimized pulses and pulse sequences to enhance the power of liquid & solid state NMR
2009 Daniel P. Weitekamp;
PASADENA and BOOMERANG
significantly improve NMR force detection by circumventing the problems of inhomogeneous magnetic fields
2010 Paul T. Callahan;
Contributions to the study of polymeric and heterogeneous materials by advanced NMR exchange, diffusion and relaxation techniques, and
for his innovative q-space-diffusion-related developments that were relevant in the context of the development of diffusion-tensor imaging.
2011 Daniel Rugar, John Mamin, and John Sidles;
Magnetic Resonance Force Microscopy (MRFM).
2012 Klaes Golman and Jan Henrik Ardenkjaer-Larsen:
Dissolution-DNP NMR
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Varian Prize Winners
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2012
2011
2010
2009
2008
2007
2006
2005
2004
2002
Ray Freeman and Weston A. Anderson
Gareth Alun Morris, The University of Manchester, UK
Martin Karplus, Harvard University, Cambridge, Massachusetts
Albert W. Overhauser, Purdue University, West Lafayette, IN
Alexander Pines, UC Berkeley, and Lawrence Berkeley National Laboratory
Alfred G. Redfield, Brandeis University, Waltham, Massachusetts
John S. Waugh, MIT, Cambridge, Massachusetts
Nicolaas Bloembergen, University of Arizona, Tucson, Arizona
Erwin L. Hahn, Professor Emeritus, University of California, Berkeley
Jean Jeener, Universite Libre de Bruxelles, Belgium
Nuclear Magnetic Double Resonance
INEPT
Karplus equations
NOE & Dynamic Polarization
Cross Polarization
Spin Dynamics
Average Hamiltonian Theory (AHT)
Nuclear Magnetic Relaxation
Spin Echoes
Two-dimensional NMR
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NMR Spectroscopy
NUCLEAR
MAGNETIC
RESONANCE
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Superconducting Cryo-Magnet
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Superconducting Cryo-Magnet
superconducting wire
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NMR Magnet Safety
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NMR magnets are always charged!
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NMR magnets may interfere with medical
devices (i.e. pacemakers, insulin pumps)
NMR magnets will erase credit cards, ID cards,
floppy disks, hard disks (some mp3 players).
NMR magnets and RF consoles may interfere with electronic and mechanical
devices and may damage them (cell phones, pagers, watches, I-pods, etc.)
NMR magnets will attract ferromagnetic objects of any size (i.e. paper clips, coins,
keys, pens, scissors, screw drivers, wrenches, metallic chairs, gas cylinders, etc.)
and spectrometer and people may sustain severe damage or injury, if handled
carelessly.
NMR magnets contain Cryogens (liquid Helium and Nitrogen)
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Cryogens can cause severe burns if handled improperly
(use eye protection and gloves during refills).
Cryogens evaporate and may cause asphyxiation if a lab is not properly ventilated.
During a magnet quench up to 100 liters of liquid Helium are vaporized in a
matter of minutes (2600 cu ft, 70,000 liters gas) and may cause asphyxiation, even
if the lab is well ventilated. If a magnet quenches, leave the lab immediately.
Don’t panic, helium gas will rise to the ceiling and escape through cracks.
During a refill the refill rubber tubing may shatter. Frozen rubber cuts like glass!!
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NMR Magnet Safety
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NMR magnets are always charged!
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NMR magnets contain Cryogens (liquid Helium and Nitrogen)
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NMR Console with Computer
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RF Signal Generator
Decoupler (1H):
Amplifier
Frequency Generator
Transmitter:
Amplifier
Frequency Generator
Frequency Generators and Signal Amplifiers are required for each RF channel.
Our spectrometers have 2 channels, modern spectrometers can have up to 8 channels.
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Magic angle
(54.7°)
NMR Probes
Solids
Liquids
Solids
Liquids
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NMR Signal Generation
Spectrometer:
RF Generation:
90°
Pulse (Sequences):
Receiver:
RD
180 °
τ
τ
DE
AQ
FT
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NMR Samples
Types of NMR sample holders
Sample preparation
Spectrum quality
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Types of NMR Sample Holders
Solution NMR
Sample Tube
Spinners
Solid State
Sample Rotors
NMR Sample
Tubes with Caps
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NMR Sample Preparation
Tubes and Caps:
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NMR tubes are a standard length (7 and 9 inch). When chipped (and reduced in
length) they should not be reused as an unbalanced tube will not spin.
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Always clean the tubes thoroughly after use.
First use the solvent you were using to recover your previous sample,
then rinse several times with acetone and finally dry the sample tube laying flat on a
layer of kimwipes or placed upside-down on a kimwipe in a beaker or Erlenmeyer
flask. Choose the container so the tubes stand vertically. Don’t heat the tubes above 50
°C, as the glass might warp.
Always store unused, clean tubes uncapped and laying on a flat surface.
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Tube caps are disposable and replacements can be easily obtained in bags of 100 ($5)
or 1000 ($40 at www.wilmad.com).
Degassing Samples:
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NMR spectra recorded using degassed solvents usually benefit from reduced halfheight line-width and thus better S/N. (O2 gas is paramagnetic!)
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There are several ways of degassing your sample:
 the best is the freeze-pump-thaw technique,
 placing the sample in a ultrasonic bath works moderately well,
 bubbling nitrogen through or over the sample less well.
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NMR Sample Preparation
Quantity:
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For proton NMR spectra of small organic compounds (up to MW=500) anything
between 1 and 20 mg of sample will be fine.
Concentrated solutions can be viscous and may result in broad signals.
Very dilute samples could be masked by impurities and solvent peaks.
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Carbon-13 is present at approximately 1.1 % natural abundance.
It is intrinsically less sensitive than protons (approx. six thousand times).
Please provide as much sample as possible, 50 - 100 mg (or more) is fine.
Preparing two samples - one dilute sample for proton NMR and one concentrated
sample for carbon NMR is a useful, but unnecessary practice.
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Solvent height (volume) should be uniform, 5 cm or 2 inches equal 0.5 ml.
The ends of the sample distort the field homogeneity, shimming on each sample
corrects this effect and takes just a minute or so. However, vastly different solvent
heights (volumes) prevent complete correction and require many minutes shimming
to achieve acceptable homogeneity.
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Samples prepared with too much solvent waste both time and money, and provide
poorer S/N. However, If you have limited amounts of sample (less than 1 mg), using
less solvent is permissible.
Minimum height: 1 cm, however, this requires special positioning of the sample tube
and very intensive shimming.
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NMR Sample Preparation
5 mm
• Use clean + dry NMR tubes and caps
(tubes can be re-used, caps should not!)
• 0.5 ml deuterated solvent
(i.e. CDCl3 ,C6 D6 , acetone-d6 ,etc.)
• substrate requirements for routine spectra:
10 mg for proton NMR
100 mg for carbon-13 NMR
• min. filling height of tube: 2 inches (5 cm)
• Cleaning of tubes:
1. rinse with solvent you were using
2. rinse with acetone
3. dry in (vacuum-)oven at low temperature
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NMR Sample Preparation
Clean
clear
solution
GOOD!
Suspension
or opaque
solution
Precipitate
Concentration
gradient
Two
phases
Bad Samples!
Not
enough
solvent
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NMR Sample Preparation
Shimming
improves the
magnetic field
homogeneity
If the magnetic field is not uniform within the sample, molecules in
different positions will experience different field strengths.
This will produce broad, distorted, or additional signals.
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Good and bad NMR Spectra
… are the result of:
Homogeneity of magnetic field
Sample preparation
Choice of solvent
Data acquisition parameters
Processing procedures
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Good spectrum
ppm
ppm
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Good spectrum
ppm
Peak picking
Integrals
ppm scale
ppm
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Good spectrum
ppm
ppm
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Bad spectrum ?
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Bad spectrum !
No units specified for
axis and peak picking
Signal/Noise
ratio bad
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Bad spectrum ?
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Bad spectrum !
Tall signals
are cut off
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Bad spectrum ?
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Bad spectrum !
Signals too small
(only allowed when trying to
compare signal intensities between
different spectra)
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Bad spectrum ?
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Bad spectrum !
Broad signals
Possible reasons:
poor shimming
viscous sample
sample too concentrated
suspended particles in sample
excessive line broadening may
have been used during processing
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Bad spectrum ?
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Bad spectrum !
Signals are distorted
Excessive peak picking
(automatic phase correction
is often insufficient)
(low p.p. threshold,
also due to improper phasing)
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Bad spectrum ?
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Bad spectrum ?
Areas without signals should be excluded.
(If you want to print all your spectra with a
default range, i.e. 0-10 ppm, don’t forget to
print detailed expansions.)
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1.
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Instrument:
600 300 100
3x2 hrs x
2x2 hrs x
2x2 hrs x
3 hrs x
2 hrs
2 hrs x
3 hrs x
2 hrs x
3 hrs d
2 hrs x
2 hrs x
Lab Assignments
x x Comprehensive 1H NMR and Indirect 13C Observation
25%
x
Pulse Width Calibration and B1
100 mg
x
Rare spin NMR (13C, 17O, 29Si)
80%
Decoupling 1H from 13C and B2
100 mg
x
Spin Echo and Spin/Spin Relaxation, 13C - T2
100 mg
x
Spin/Lattice Relaxation, 13C - T1
100 mg
x
Nuclear Overhauser Effect
10 mg
Polarization Transfer and DEPT
10 mg
13C CP/MAS in Solids
x
(sample provided)
HETCOR (1H/13C HSQC)
10 mg
1H COSY / NOESY
25 mg
Use your own samples, if possible. Familiarize yourselves with the procedures
for each experiment, before you come to the lab. Print the manuals.
http://nmr.binghamton.edu
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In all assignments you are expected to report on the following information:
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Signal-to-noise ratio
Chemical shifts and method of reference in relation to structure
J coupling (homo and heteronuclear) in relation to structure
Peak intensity and area in relation to concentration and structure/dynamics/relaxation
Effect of B0 / lab magnetic field strength, Larmor frequency and gyromagnetic ratio
Effect of B0 inhomogeneity
Pulse width and tip angle
Magnitude of B1 and B2 fields / rf field strengths used
Effect of B1 and B2 inhomogeneity
Effects of O1 and O2 / frequency offsets
Effects of sample spinning and location of spinning sidebands
Method of decoupling if used as well as effectiveness
Solvent and temperature used
Pulse sequence and instrument control programming
All critical instrument or data processing parameters
Vector and spin diagrams, as needed.
Note any experimental or instrumental anomalies
The spectrometer manual to be used in this course can be downloaded from:
http://www.chem.binghamton.edu/staff/schulte/CHEM585f/Chem585f-Bruker.doc
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A letter in the New Scientist of 17 April 1999, signed by Terry McStea, Whitburn, Tyne and Wear:
Your article on MRI (This Week, 3 April, p 7) reminded me of a story, probably untrue, related by a doctor friend.
MRI used to be known in hospitals as nuclear magnetic resonance, or NMR.
Unfortunately, patients who arrived at the hospital asking for "an NMR" often received a treatment that they were not expecting.
Hence the change to MRI.
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