This document provides an introduction to electron spin resonance (ESR) spectrometry, also known as electron paramagnetic resonance (EPR). ESR detects paramagnetism by exciting unpaired electrons in atoms, ions, or free radicals to a higher energy state using microwaves under a magnetic field. The instrument works by measuring microwave absorption as a function of the magnetic field. ESR can be used to study metalloproteins, monitor enzyme activity through metal oxidation states, examine free radicals caused by irradiation, and determine free radical concentrations in samples.

1. ELECTRON SPIN RESONANCE
SPECTROMETRY
Presented
By
Kamlesh Patade

2. INTRODUCTION
• It is a branch of absorption spectroscopy in which
radiation having frequency in microwave region.
• Electron spin resonance (ESR) is also known as
Electron Paramagnetic Resonance(EPR).
• This is a technique for detecting paramagnetism.
• The technique may be used for detecting transitional
metal ion and their complexes, free radicals and their
excited states.
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3. ESR Phenomenon is shown by
• Atoms having odd number of electrons.
• Ions having partly filled inner electron shells
• Free radicals having unpaired electrons.
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4. PRINCIPAL
• The unpaired electrons are excited to a high energy state
under the magnetic field by the absorption of microwave
radiations.
• The excited electron changes its direction of spin and
relaxes in to the ground state by emitting its energy.
• The transition between two different energy levels takes
place by absorbing a quantum of radiation of frequency
in the microwave region.
• Microwave absorption is measured as a function of the
magnetic field by ESR Spectroscopy.
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5. • In ESR the energy levels are produced by the
interaction of magnetic moment of an unpaired
electron in a molecule with an applied magnetic
field.
• The ESR spectrum results in due to the transitions
between these energy levels by absorbing radiations
of microwave frequency.
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6. INSTRUMENTATION
• Source
• Sample Cavity
• Magnet System
• Crystal Detector
• Auto amplifier and Phase sensitive Detector
• Oscilloscope
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7. • Klystron Source
• It is a vacuum tube which can produce microwave
oscillations centered on a small range of frequency
• The frequency of the monochromatic radiation is
determined by the voltage applied to Klystron.
• Isolator: It is a device which minimizes vibrations in
the frequency of microwaves produced by Klystron
oscillator.
• Isolator is a strip of ferrite material
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8. • Wave meter
• It is fixed in between the isolator and attenuator to
know the frequency of microwaves produced by
Klystron oscillator.
• Attenuator
• Attenuator is used to adjust the level of the
microwave power incident upon the sample.
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9. • Sample Cavity:
• This resonant cavity which contains the sample is
called the heart of ESR.
• Magnet System:
• The sample cavity is placed between the pole pieces
of an electromagnet
• This provides a homogenous magnetic field and can
be varied from zero to 500 gauss.
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10. • Crystal Detectors
• The most commonly used detector is a silicon crystal
which acts as a microwave rectifier.
• This converts microwave power into a direct current
input.
• Oscilloscope
• The signal from phase sensitive detector and sweep
unit is recorded by the oscilloscope.
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13. APPLICATION
• ESR spectroscopy is one of the main methods used
to study metalloproteins, particularly those
containing molybdenum, copper, iron, etc.
• Both copper and non-haem iron do not absorb
radiation in visible and ultra violet range, posses ESR
absorbance peak in one of their oxidation state .
• Hence their appearance and disappearance of their
ESR signal are used to monitor their activity in multi
enzyme system
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14. • In metalloproteins, the metal atom has characteristic
number of ligands coordinated to it in a definite
geometrical arrangement. Studies using ESR have
shown that their geometry is frequently distorted.
• The technique ESR has been extended by spin
labeling . Thus spin labeling glycerophosphatides
with a suitable nitrox free radical the laterate
diffusion of the labelled molecules can be studied.
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15. • Electron spin resonance is also extensively used to
study the free radicals caused by irradiation of
biological material.
• The concentration of free radicals in samples can also
be determined.
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16. THANK YOU
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