physics behind nmr
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basics of NMR and its applicationsTRANSCRIPT
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Physics behind NMRBY : E.SIVANAGI REDDY
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NMR Nobel Prize Laureates
Richard Ernst (1990 c)
Otto Stern (1943)
Isidor I. Rabi(1944)
Kurt Wüthrich ( 2002c)Paul C. Lauterbur , Sir Peter Mansfield (2003M)
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Out line of presentationIntroductionBirth of NMRPrinciple of NMRTypes of NucleiNMR SpectroscopyApplications SummaryReferences
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IntroductionNMR –a technique for determining the
magnetic moments of nuclei by subjecting a substance to high-frequency radiation and a large magnetic field.
NMR = Nuclear: properties of atomic nuclei Magnetic: magnetic field is required Resonance: interaction between
magnetic field and radio frequency
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Birth of NMR1945 – Purcell, Torrey, and Pound (Harvard,
Cambridge, Massachusetts) detected weak radio- frequency signals generated by the nuclei of atoms in about 1 kg of paraffin wax placed in a magnetic field.
Simultaneously, Bloch, Hansen, and Packard (Stanford, Palo Alto, California) independently observed radio signals from atomic nuclei in water in a magnetic field.
E. M. Purcell, H.C. Torrey, and R.V. Pound, Phys. Rev., 1946, V69, p.37
F. Bloch, W.W. Hansen, and M.E. Packard, Phys. Rev., 1946, V69, p.127
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Birth of NMRPurcell, Torrey, and Pound described NMR as
observation of absorption by the nuclear spin system that produces an additional load that changes the quality factor Q of the circuit that drives the resonance.
Bloch, Hansen, and Packard described NMR as forced
precession of the nuclear magnetization in the applied
radio frequency field and the induction of detectable
electromotive force in a receiver coil .
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Principle of Magnetic ResonanceWhen molecules are placed in a strong magnetic
field , the magnetic moments of the nuclei align with the field
This equilibrium alignment can be changed to an excited state by applying radio frequency(RF) pulses
When the nuclei revert to the equilibrium ,they emit RF radiation that can be detected.
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The NMR Phenomenon
1. A spinning charge generates
a magnetic field
In the presence of an external magnetic field (B0), two spin states exist, +1/2 and -1/2.
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Nuclear magnetic ResonanceWhen oriented nuclei are subjected to E.M radiation at the proper frequencyEnergy absorption occurs Lower energy state nuclei “Spin-flip ” to the higher energy state Magnetic nuclei in resonance with applied field
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Nuclear magnetic ResonanceResonant frequency depends on strength of
magnetic field and identity of nucleus.
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Types of NucleiChemistry: 1H, 13C Bio-sciences: 1H, 13C, 15N, 19F, 31P, etc.Medicine: 1H, 17O
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Nuclear Magnetic resonance Spectroscopy
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NMR Spectrometer
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Protons in a MoleculeDepending on their chemical environment,
protons in a molecule are shielded by different amounts
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Number different kinds of protons
location shielded or dishielded
intensity number of protons of that type splitting number of protons on adjacent atoms
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Chemical shift Chemical shift is a measure of the degree to
which a nucleus in a molecule is shielded
Factors affecting
Electronegativity of nearby atoms
• Hybridization of adjacent atoms
• diamagnetic effects
• paramagnetic effects
• solvent effect
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Standard for Chemical ShiftIn NMR spectroscopy, the standard is often tetramethylsilane,
Si(CH3)4, abbreviated TMS
Tetramethyl silane (TMS) is used as reference because it is soluble in most organic solvents, is inert, volatile, and has 12 equivalent 1H and 4 equivalent 13C. TMS signal is set to 0 .
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shielding
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J
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Applications of NMRCHEMISTRYDetermine molecular structure of different chemical
compounds, including polymersIdentify products of chemical reactionsMeans to study dynamics, kinetics, and
thermodynamics of chemical systems
BIOLOGYProtein NMR
– Obtain structural information on complex proteins
– Multidimensional experiments needed to correlate frequencies with distinct nuclei
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Applications of NMR
MEDICINE Magnetic Resonance Imaging (MRI) – Insight into the structure of the human
body – Sharp contrast in soft tissueClinical applications – Cardiovascular system – Musculoskeletal system – Oncology – Neurology
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Summary Nuclear Magnetic Resonance (NMR): change in
alignment of atomic nuclei from preferred energy states due to intrinsic magnetic properties
Used to determine structural framework of chemical
compounds Applicable for multiple disciplines – Medicine –Chemistry – Biology
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REFERENCESJames Keeler ,Understanding NMR Spectroscopy,
Wiley International (2002) James N. Shoolery , A Basic Guide to NMR, Varian
Associates, Palo Alto, CA, USA, 1972J. Jon and H. S. Gutowsk, NMR IN CHEMISTRY
-AN EVERGREEN ,Ann. Re. Phys. Cher 1980. 31:1-27
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NMR: Nobel work if you can get it
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