NMR Nobel Prize LaureatesOtto Stern (1943) Isidor I. Rabi(1944)Richard Ernst (1990 c) Kurt Wüthrich ( 2002c) Paul C. Lauterbur , Sir Peter Mansfield (2003M)
Out line of presentation Introduction Birth of NMR Principle of NMR Types of Nuclei NMR Spectroscopy Applications Summary References
Introduction NMR –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 NMR 1945 – 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 NMR Purcell, 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 Resonance When 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 Phenomenon1. A spinning charge generates In the presence of an external magnetic field a magnetic field (B0), two spin states exist, +1/2 and -1/2.
Nuclear magnetic Resonance When oriented nuclei are subjected to E.M radiation at the proper frequency Energy absorption occurs Lower energy state nuclei “Spin-flip ” to the higher energy state Magnetic nuclei in resonance with applied field
Nuclear magnetic Resonance Resonant frequency depends on strength of magnetic field and identity of nucleus.
Protons in a Molecule Depending 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 shieldedFactors affecting Electronegativity of nearby atoms• Hybridization of adjacent atoms• diamagnetic effects• paramagnetic effects• solvent effect
Standard for Chemical Shift In 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 .
Applications of NMRCHEMISTRY Determine molecular structure of different chemical compounds, including polymers Identify products of chemical reactions Means to study dynamics, kinetics, and thermodynamics of chemical systemsBIOLOGY Protein NMR – Obtain structural information on complex proteins – Multidimensional experiments needed to correlate frequencies with distinct nuclei
Applications of NMRMEDICINEMagnetic 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
REFERENCES James Keeler ,Understanding NMR Spectroscopy, Wiley International (2002) James N. Shoolery , A Basic Guide to NMR, Varian Associates, Palo Alto, CA, USA, 1972 J. Jon and H. S. Gutowsk, NMR IN CHEMISTRY -AN EVERGREEN ,Ann. Re. Phys. Cher 1980. 31:1-27