Physics behind NMRBY : E.SIVANAGI REDDY

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)

Out line of presentationIntroductionBirth of NMRPrinciple of NMRTypes of NucleiNMR SpectroscopyApplications SummaryReferences

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

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

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 .

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.

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.

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

Nuclear magnetic ResonanceResonant frequency depends on strength of

magnetic field and identity of nucleus.

Types of NucleiChemistry: 1H, 13C Bio-sciences: 1H, 13C, 15N, 19F, 31P, etc.Medicine: 1H, 17O

Nuclear Magnetic resonance Spectroscopy

NMR Spectrometer

Protons in a MoleculeDepending on their chemical environment,

protons in a molecule are shielded by different amounts

Number different kinds of protons

location shielded or dishielded

intensity number of protons of that type splitting number of protons on adjacent atoms

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

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 .

shielding

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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

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

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

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

NMR: Nobel work if you can get it