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The world of The world of “ “ tiny nuclear magnets tiny nuclear magnets” ”
- T. G. Ajithkumar
The world of The world of tiny nuclear magnets tiny nuclear - - PowerPoint PPT Presentation
The world of The world of tiny nuclear magnets tiny nuclear - - PowerPoint PPT Presentation
The world of The world of tiny nuclear magnets tiny nuclear magnets T. G. Ajithkumar Scientist, Central NMR Facility National Chemical Laboratory Why Nuclear Magnetic Resonance Spectroscopy (NMR) ? The most powerful
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Why Nuclear Magnetic Resonance Spectroscopy (NMR) ?
The most powerful analytical tool for synthetic chemists.
Study of reaction kinetics.
Three dimensional structural studies (protiens, RNA/DNA complexes).
Structure function relationships for drug design.
In medicine, magnetic resonance imaging (MRI) has become a very important diagnostic tool.
Solids state NMR to study structure and dynamics of a variety of materials like polymers, catalysts, nanomaterials.
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MRI
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Data sources : Left - The Whole-brain Atlas, K. A. Johnson and J. A. Becker, Harvard; Right - SMIS UK Ltd.
MRI of human brain
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Magnetism
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Magnetic Field
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B µ B µ
Low Energy High Energy
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The atom
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The origin of magnetism
electron
- rbital
motion proton
- rbital
magnetic moment
+
magnetic field generated by orbital motion
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+
electron magnetic moment nuclear magnetic moment
- Magnetic moments
The nuclear magnetic moment is many orders of magnitude weaker than the electron magnetic moment.
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In the absence of a Magnetic Field, the magnetic moments are aligned in all random directions and thus the net magnetic moment is zero
No external Field
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On application of external Field
B B
N S N S
A bar magnet aligns itself in the direction of the magnetic field !
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Larmour Precession
B B
Precession/Larmour Frequency = -B Larmour Frequency (MHz/T) of important nuclei
1H 42.576 13C 10.705 31P 17.235
Usually, an NMR spectrometer is named based on the 1H Larmour Frequency Thus, a spectrometer which has a field of 7.05 T is called a 300MHz spectrometer 9.4 T is called the 400 MHz spectrometer, 11.74T called a 500MHz spectrometer
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B
B Thermal Equilibrium Net Magnetic Moment
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Resonance
An experiment to demonstrate Resonance using a spring and motor.
The Larmour Frequency is in the Radio Frequency Range.
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Electricity from magnetism
The experiment where an oscillation magnet in a coil generates a alternating current.. Very similar to the NMR signal !!!
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Application of Radio Frequency
B
x y z
Net Moment
B
x y z x y z x y z
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NMR signal
t t My Mx
B
x y z
NMR Signal Coil
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Re Im Im ADCs Im Post-Dig Phase Shifter Computer Re Re Synthesizer Pulse Gate Amplifier Duplexer Signal Amplifier Receiver Phase Shifter
1 2 3 5 6 7 8 9 10 11
Pulse Programmer
4
Display, Plot Magnet Probe
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Magnet
bore liquid He superconducting solenoid liquid N2
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Probe
Sample Sample Coil Capacitor C
M
Capacitor CT Rotation (Optional)
B
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Chemical Shift
B
electrons The field experienced by the nucleus in a molecule will depend on the electron environment..
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NMR Imaging
Along with the external field, a field gradient which is propotional to the geometry is applied
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Physics Chemistry Biology Medicine Bloch Purcell Ernst Wuthrich Lauterbur Mansfield
Nobel Glories of NMR
1954 1990 2002 2003
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In the winter of our first experiment….looking on snow with new eyes. There the snow lay around my door step….great heaps
- f protons quietly precessing in the Earth’s magnetic field.
To see the world for a moment as something rich and strange is the private reward of many a discovery. Ed Purcell, 1946
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Acknowledgements
- Dr. T. S. Mahesh, IISER for his help in
setting up the demo experiments.
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