NUCLEAR MAGNETIC RESONANCE in medical field By –Vivek singh Department of Biochemistry King George’s Medical University Lucknow.

Contents Introduction Principle and instrumentation Resonance( Flipping) Population density The chemical shift and shielding Magnetic anisotropy Spin-spin splitting( origin and n+1 rule) Application

INTRODUCTION Nuclei studied by NMR techniques. NMR gives information the no. of magnetically distinct atoms. Radiofrequencies have low energy; only cause nuclear spin[ nmr].

Nmr electromagnetic spectrum

PRINCIPLE AND INSTRUMENTATION The nucleus has magnetic moment generated by its charge & spin. A hydrogen nuclear may have clockwise [+1/2] or counterclockwise[-1/2]. Spin state +1/2 has lower energy and aligned with magnetic field; -1/2 higher energy opposite to magnetic field. In NMR, entities are nuclear magnetic spins which populate energy level a/c to quantum chemical rule.

Alligned and opposed arrangement of bar [from pavia]

The basic elements of nmr spectrometer[from google]

Resonance[flipping] When frequency of oscillating ef component of the incoming radiation just match the frequency of ef generated by precessing nucleus, two field can couple, energy can transferred from incoming radiation to the nucleus and causing spin change.

POPULATION DENSITY A slight excess nuclei in lower energy spin state. Magnitude of this difference calculated by BOLTZMANN DISTRIBUTION LAW. Saturation achieved if power of RADIOFREQENCY signal is too high.

CHEMICAL SHIFT AND SHIELDING Electron surrounds the proton produces magnetic field which oppose the field DIAMAGNETIC SHIELDING. Standard reference is TETERAMETHYLSILANE[TMS]-proton are more shielded than other compounds. The CHEMICAL SHIFT is amount by which proton resonance is shifted from TMS.

Chemical shift data Different kinds of protons come at different chemical shifts.shown below is a chart of some common kinds of protons that appear in delta scale.

LOCAL DIAMAGNETIC SHIELDING depends on: Area under each peak is proportional to no. of hydrogens generating that peak. Eletronegativity. Hybridisation. Acidic and exchangeable proton; hydrogen – bonding.

Shift of group on delta scale Downfield= deshielded molecule Up field=shielded molecule

MAGNETIC ANISOTROPY Example- benzene; It placed in magnetic field, pie electron of aromatic ring are induced to circulate around ring. Circulation of electron is called ring current(shielded region). Moving electrons generate magnetic field much like generated in the loop of wire. A proton attached to benzene ring is influenced by three magnetic field(more deshielded hydrogen).

Splitting patterns with multiple neighbouring If a proton has n neighbouring protons that are equivalent, that proton will split into n+1 lines.

SPIN-SPIN SPLITTING It arises because hydrogens on adjacent carbon atoms can SENSE one another. n+1 rule-each type of proton senses the no. of equivalent proton on the carbon atoms next to the one to which it is bonded and its resonance peak splits into n+1 components.

More 1H-1HCoupling When there is more than one proton splitting a neighbouring proton, we get more lines. Consider the molecule shown below where we have 2 protons on one carbon and one proton on another.

Applications of nmr Molecular structure determination. Solution structure of protiens and peptides. Magnetic resonance imaging. Identification of protien-protien interaction sites is crucial for understanding the basis of molecular recognition.

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