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Electron Spin Resonance - It's Principles and Applications

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Electron Spin Resonance (ESR) also known as Electron Magnetic Resonance (EMR) or Electron Paramagnetic Resonance (EPR) is a branch of absorption spectroscopy in which radiations having frequency in the microwave region (0.04 – 25 cm) is absorbed by paramagnetic substances to induce transitions between magnetic energy levels of electrons with unpaired spins.ESR is shown by atoms having odd number of electrons.
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1 A Seminar on A Seminar on Principle and Applications of Principle and Applications of Electron Spin Resonance (ESR) Electron Spin Resonance (ESR) Spectroscopy Spectroscopy Prepared by – Prepared by – Mr. Mohit G. Dewani (M.Pharm Q. A. – I Mr. Mohit G. Dewani (M.Pharm Q. A. – I Semester) Semester) Under the Guidance of - Under the Guidance of - Prof. (Mrs.) Mrinalini C. Damle Prof. (Mrs.) Mrinalini C. Damle At - At - AISSMS College of Pharmacy, Kennedy Road, AISSMS College of Pharmacy, Kennedy Road, Near RTO, Pune. Near RTO, Pune.
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11

A Seminar onA Seminar on

Principle and Applications of Principle and Applications of Electron Spin Resonance (ESR) Electron Spin Resonance (ESR)

SpectroscopySpectroscopyPrepared by –Prepared by –

Mr. Mohit G. Dewani (M.Pharm Q. A. – I Semester)Mr. Mohit G. Dewani (M.Pharm Q. A. – I Semester)

Under the Guidance of -Under the Guidance of -

Prof. (Mrs.) Mrinalini C. DamleProf. (Mrs.) Mrinalini C. Damle

At -At -AISSMS College of Pharmacy, Kennedy Road, AISSMS College of Pharmacy, Kennedy Road,

Near RTO, Pune.Near RTO, Pune.

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CONTENTSCONTENTS

Introduction to ESRIntroduction to ESR Paramagnetism & DiamagnetismParamagnetism & Diamagnetism Principle of ESRPrinciple of ESR The g – ValueThe g – Value Maxwell – Boltzmann distributionMaxwell – Boltzmann distribution Presentation of ESR spectrumPresentation of ESR spectrum Hyperfine splittingHyperfine splitting Multiple Resonance techniquesMultiple Resonance techniques ESR and NMRESR and NMR Applications of ESRApplications of ESR

Introduction to ESRIntroduction to ESR Paramagnetism & DiamagnetismParamagnetism & Diamagnetism Principle of ESRPrinciple of ESR The g – ValueThe g – Value Maxwell – Boltzmann distributionMaxwell – Boltzmann distribution Presentation of ESR spectrumPresentation of ESR spectrum Hyperfine splittingHyperfine splitting Multiple Resonance techniquesMultiple Resonance techniques ESR and NMRESR and NMR Applications of ESRApplications of ESR

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IntroductionIntroduction Electron Spin Resonance (ESR) also known as Electron Electron Spin Resonance (ESR) also known as Electron

Magnetic Resonance (EMR) or Electron Paramagnetic Magnetic Resonance (EMR) or Electron Paramagnetic Resonance (EPR)Resonance (EPR) is a branch of absorption spectroscopy in is a branch of absorption spectroscopy in which radiations having frequency in the microwave region which radiations having frequency in the microwave region (0.04 – 25 cm) is absorbed by paramagnetic substances to (0.04 – 25 cm) is absorbed by paramagnetic substances to induce transitions between magnetic energy levels of induce transitions between magnetic energy levels of electrons with unpaired spins.electrons with unpaired spins.

ESR is shown by atoms having odd number of electrons.ESR is shown by atoms having odd number of electrons. ESR is based on the fact that atoms, ions, molecules or ESR is based on the fact that atoms, ions, molecules or

molecular fragments which have an odd number of electrons molecular fragments which have an odd number of electrons exhibit characteristic magnetic properties. An electron has a exhibit characteristic magnetic properties. An electron has a spin and due to spin there is magnetic moment.spin and due to spin there is magnetic moment.

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Substances with unpaired electronsSubstances with unpaired electrons

Stable Paramagnetic substances –Stable Paramagnetic substances –

E.g. NO, NOE.g. NO, NO22

Unstable Paramagnetic substances -Unstable Paramagnetic substances -

E.g. E.g. Free radicals or radical ionsFree radicals or radical ions which can be which can be produced either as intermediates in a chemical produced either as intermediates in a chemical reaction or by irradiation of a stable molecule with reaction or by irradiation of a stable molecule with a beam of nuclear particles or with UV or X-ray a beam of nuclear particles or with UV or X-ray radiation.radiation.

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Paramagnetism & DiamagnetismParamagnetism & Diamagnetism Paramagnetic substances exhibit an ESR spectrum

because the molecules contain an odd number of electrons and hence the number in the two spins states is not identical. The spin of an unpaired electron induces a field that reinforces the applied field.

e.g; Iron oxide, platinum, tungsten, sodium, lithium. Some molecules fail to exhibit an ESR spectrum

because they contain an even number of electrons and the number in the two spin states is identical or spins are parallel. Hence magnetic effects of electron spin are cancelled. Such substanes are Diamagnetic.

e.g.; water, mercury, lead, copper, silver, bismuth.

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Principle of ESRPrinciple of ESR In ESR, energy levels are produced by the interaction of In ESR, energy levels are produced by the interaction of

the magnetic moment of an unpaired electron in a the magnetic moment of an unpaired electron in a molecule ion with an applied magnetic field. molecule ion with an applied magnetic field.

Every electron has a Every electron has a magnetic moment and and spin quantum number (1/2), with magnetic components (1/2), with magnetic components

mmss = +1/2 and m = +1/2 and mss = -1/2. In presence of an external = -1/2. In presence of an external magnetic field, electron's magnetic moment aligns itself magnetic field, electron's magnetic moment aligns itself either parallel (meither parallel (mss = -1/2) or antiparallel (m = -1/2) or antiparallel (mss = +1/2) to the = +1/2) to the field field (Zeeman Levels),(Zeeman Levels), each alignment having a specific each alignment having a specific energy. The parallel alignment corresponds to lower energy. The parallel alignment corresponds to lower energy state and the difference between this two energy energy state and the difference between this two energy levels (levels (Zeeman SplittingZeeman Splitting) is given by –) is given by –

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ΔE = hΔE = hνν = g = gββHH

Existence of 2 Zeeman levels and the possibility of inducing transitions from lower energy level to higher energy level, is very basis of ESR spectroscopy.

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The g - ValueThe g - Value g is proportionality factor / spectroscopic splitting g is proportionality factor / spectroscopic splitting

factor / Lande’s spitting factor.factor / Lande’s spitting factor. It is a measure of ratio between frequency and It is a measure of ratio between frequency and

magnetic field.magnetic field. The value of g for free electrons is 2.0023, which The value of g for free electrons is 2.0023, which

may vary by 0.0003.may vary by 0.0003. In ionic crystals, value of g vary from 0.2 – 0.8. The In ionic crystals, value of g vary from 0.2 – 0.8. The

reason is that unpaired electrons are localized in a reason is that unpaired electrons are localized in a particular orbital of the atom and orbital angular particular orbital of the atom and orbital angular momentum couples with spin angular momentum momentum couples with spin angular momentum giving rise to a low value of g in ionic crystals. giving rise to a low value of g in ionic crystals.

The g-factor in ESR is analogous to chemical shift in The g-factor in ESR is analogous to chemical shift in NMR.NMR.

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Maxwell – Boltzmann DistributionMaxwell – Boltzmann Distribution

If a sample containing unpaired electrons is in If a sample containing unpaired electrons is in thermodynamic equilibrium in a magnetic field, there thermodynamic equilibrium in a magnetic field, there will be a population difference between the two will be a population difference between the two energy levels given by Boltzmann law,energy levels given by Boltzmann law,

nn11 / n / n22 = exp (–ΔE / kT) = exp (–g = exp (–ΔE / kT) = exp (–gββH / kT)H / kT) where,where, nn1 1 and nand n22 are the populations in the upper and lower are the populations in the upper and lower

level respectively, leading to an excess population in level respectively, leading to an excess population in lower level,lower level,

k is the Boltzmann’s constant,k is the Boltzmann’s constant, T is temperature (in Kelvins).T is temperature (in Kelvins).

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Presentation of ESR SpectrumPresentation of ESR Spectrum

For Absorption -Intensity against strength of magnetic fieldFirst Derivative curve –First derivative (slope) of absorption curve Vs strength of magnetic field.

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Hyperfine SplittingHyperfine Splitting

The ESR spectrum exhibits hyperfine splitting which The ESR spectrum exhibits hyperfine splitting which is caused by the interactions between the spinning is caused by the interactions between the spinning electrons and adjacent spinning magnetic nuclei.electrons and adjacent spinning magnetic nuclei.

When a single electron interacts with one nucleus, the When a single electron interacts with one nucleus, the number of adjacent splittings will be equal to (2I + 1), number of adjacent splittings will be equal to (2I + 1), where I is the spin quantum number of the nucleus.where I is the spin quantum number of the nucleus.

For n equivalent nuclei, the electron signal will split For n equivalent nuclei, the electron signal will split up into (2nI + 1) multiplet.up into (2nI + 1) multiplet.

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a)a) Effect of External field on the energy states for an electron Effect of External field on the energy states for an electron

b)b) Effect of a nuclear spin ½ of proton on these energy statesEffect of a nuclear spin ½ of proton on these energy states

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Fig : The spectrum of a free electron showing the single peak corresponding to a transition between the energy levels (w.r.t. a)

Fig : The ESR spectrum showing two peaks corresponding to two transitions (w.r.t b)

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For a radical having NFor a radical having N11 equivalent nuclei, each with equivalent nuclei, each with a spin of Ia spin of I11, and a group of N, and a group of N22 equivalent nuclei, equivalent nuclei, each with spin of Ieach with spin of I22, the number of lines expected is , the number of lines expected is

(2N(2N11II11 + 1) (2N + 1) (2N22II22 + 1) + 1) As an example,As an example, CHCH33 – O - CH – O - CH33 CHCH22 – O – CH – O – CH33 + + HH The methoxymethyl radical, HThe methoxymethyl radical, H22C(OCHC(OCH33), has two ), has two

equivalent 1H nuclei each with I = 1/2 and three equivalent 1H nuclei each with I = 1/2 and three equivalent 1H nuclei each with I = 1/2, and so the equivalent 1H nuclei each with I = 1/2, and so the number of lines expected is;number of lines expected is;

(2N(2N11II11 + 1) (2N + 1) (2N22II22 + 1) + 1) = [2(2)(1/2) + 1][2(3)(1/2) + 1] = [3][4] = 12= [2(2)(1/2) + 1][2(3)(1/2) + 1] = [3][4] = 12 Hence, 12 peaks have been observed.Hence, 12 peaks have been observed.

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Figure: ESR Spectrum (First Derivative) for H2C(OCH3) radical

The two equivalent methyl hydrogens will give an overall 1:2:1 EPR pattern, each component of which is further split by the three methoxy hydrogens into a 1:3:3:1 pattern to give a total of 3 x 4 = 12 lines, a triplet of quartets. The smaller coupling constant is due to the three methoxy hydrogens, while the larger coupling constant is from the two hydrogens bonded directly to the carbon atom bearing the unpaired electron.

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Multiple Resonance TechniquesMultiple Resonance Techniques

Multiple resonance techniques are used to improve Multiple resonance techniques are used to improve the effective resolution of an ESR spectrum.the effective resolution of an ESR spectrum.

In this techniques, the change in intensity of the ESR In this techniques, the change in intensity of the ESR line upon irradiation with a second frequency are line upon irradiation with a second frequency are observed.observed.

It includes ENDOR, ELDOR & TRIPLE.It includes ENDOR, ELDOR & TRIPLE.

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ENDORENDOR Electron Nuclear Double ResonanceElectron Nuclear Double Resonance In this technique, the sample is irradiated In this technique, the sample is irradiated

simultaneously with a microwave frequency and a simultaneously with a microwave frequency and a radiofrequency. The radiofrequency is then swept radiofrequency. The radiofrequency is then swept while observing the ESR spectrum under microwave while observing the ESR spectrum under microwave frequency conditions.frequency conditions.

Most suitable when there occurs broadening of Most suitable when there occurs broadening of normal ESR lines due to large variety of nuclear normal ESR lines due to large variety of nuclear energy levels.energy levels.

Also suitable, when more precise values of hyperfine Also suitable, when more precise values of hyperfine couplings are desired. couplings are desired.

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TRIPLETRIPLE

ENDOR experiment can be extended to the ENDOR experiment can be extended to the use of two simultaneous radiofrequency fields, use of two simultaneous radiofrequency fields, called TRIPLE experiment. called TRIPLE experiment.

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ELDORELDOR

Electron Double ResonanceElectron Double Resonance In this techniques, the sample is irradiated In this techniques, the sample is irradiated

simultaneously with two microwave frequencies and simultaneously with two microwave frequencies and the signal height thus obtained is the measure of the the signal height thus obtained is the measure of the

difference of the two microwave frequenciesdifference of the two microwave frequencies..

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Sr. Sr. No.No.

ESRESR NMRNMR

1.1. Transition occurs at Transition occurs at frequencies in the microwave frequencies in the microwave region (0.04 – 25 cm). region (0.04 – 25 cm).

Transition occurs in the radio Transition occurs in the radio frequency region (>25cm). frequency region (>25cm).

2.2. Applicable to those molecules Applicable to those molecules which have their which have their electrons electrons unpairedunpaired..

Applicable to those molecules Applicable to those molecules having all their having all their electrons electrons paired.paired.

3.3. The two different energy The two different energy states are produced due to the states are produced due to the alignment of the alignment of the electron electron magnetic momentsmagnetic moments relative to relative to the applied field and transition the applied field and transition between these 2 energies takes between these 2 energies takes place on the absorption of a place on the absorption of a quantum of radiation in the quantum of radiation in the microwave region.microwave region.

The two different energy The two different energy states are produced due to states are produced due to alignment of the alignment of the nuclear nuclear magnetic momentsmagnetic moments relative to relative to the applied field & transition the applied field & transition between these two energies between these two energies takes place upon application takes place upon application of of radio frequencyradio frequency field to the field to the appropriate frequency. appropriate frequency.

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ApplicationsApplications

In Biological Systems In Biological Systems Study of Free Radicals Study of Free Radicals Study of CatalystsStudy of Catalysts Spin Labels Spin Labels Study of Inorganic Compounds Study of Inorganic Compounds Reaction Velocities & Mechanisms Reaction Velocities & Mechanisms Naturally Occurring SubstancesNaturally Occurring Substances Conducting Electrons Conducting Electrons Analytical Applications Analytical Applications

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In Biological SystemsIn Biological Systems Presence of free radicals in healthy and diseased tissues Presence of free radicals in healthy and diseased tissues

has been studied by ESR.has been studied by ESR. Transition metal ion if present, can also be studied.Transition metal ion if present, can also be studied. e.g; In case of Fee.g; In case of Fe3+ 3+ ions of Hemoglobin, change in its ions of Hemoglobin, change in its

valence state may be studied by ESR.valence state may be studied by ESR. Some typical systems which have been studied by ESR Some typical systems which have been studied by ESR

are hemoglobin, nucleic acids, enzymes, irradiated are hemoglobin, nucleic acids, enzymes, irradiated chloroplasts, riboflavin (before and after UV irradiation), chloroplasts, riboflavin (before and after UV irradiation), and carcinogens. and carcinogens.

Role of free radical in photosynthesis, has been provided Role of free radical in photosynthesis, has been provided by the observation of a sharp ESR resonance line.by the observation of a sharp ESR resonance line.

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Study of Free RadicalsStudy of Free Radicals

A free radical is a compound which contains an A free radical is a compound which contains an unpaired spin such as methyl radical produced unpaired spin such as methyl radical produced through the break up of methane.through the break up of methane.

CHCH44 CHCH33 + H + H

Methyl radical, has three 1H nuclei each withMethyl radical, has three 1H nuclei each with

II = 1/2, and so the number of lines expected is, = 1/2, and so the number of lines expected is,

22nInI + 1 = 2(3)(1/2) + 1 = 4 + 1 = 2(3)(1/2) + 1 = 4

4 peaks are observed in the proportion of 1:3:3:1.4 peaks are observed in the proportion of 1:3:3:1.

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Figure: ESR Spectrum (First Derivative) for methyl radical

In case of I = 1/2 nuclei (e.g., 1H, 19F, 31P), the line intensities produced by a population of radicals, each possessing N equivalent nuclei, will follow Pascal's triangle.

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RadicalRadical HyperfinHyperfine linese lines

Relative IntensitiesRelative Intensities

CHCH22OHOH 33 1 : 2 : 11 : 2 : 1

CHCH33CHOHCHOH 55 1 : 4 : 6 : 4 : 11 : 4 : 6 : 4 : 1

(CH(CH33))22COCOHH

77 1 : 6 : 15 : 20 : 15 : 6 : 1 : 6 : 15 : 20 : 15 : 6 : 11

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Study of Inorganic CompoundsStudy of Inorganic Compounds E.g; [NO(SOE.g; [NO(SO33))22]]2-2- yields a triplet in its ESR spectrum yields a triplet in its ESR spectrum

in chloroform. This arises from the interaction in chloroform. This arises from the interaction between the spin of the unpaired electron and the spin between the spin of the unpaired electron and the spin of a of a 1414N nucleus (I=1), conforming that this electron N nucleus (I=1), conforming that this electron is mainly localised on the nitrogen atom.is mainly localised on the nitrogen atom.

(2I + 1) = 2 x 1 + 1 = 3(2I + 1) = 2 x 1 + 1 = 3

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Study of CatalystsStudy of Catalysts In a study of heterogeneous catalysis, the spin In a study of heterogeneous catalysis, the spin

trapping technique has been used to prove the trapping technique has been used to prove the presence of radical species on a catalyst surface.presence of radical species on a catalyst surface.

e.g; In a study of palladium metal catalyst supported e.g; In a study of palladium metal catalyst supported on alumina, it was shown that hydrogen is on alumina, it was shown that hydrogen is dissociatively chemisorbed by trapping hydrogen dissociatively chemisorbed by trapping hydrogen atoms with PBN (atoms with PBN (αα-phenyl-N-t-butyl nitrone).-phenyl-N-t-butyl nitrone).

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Spin LabelsSpin Labels There are number of free radicals called Spin Labels which There are number of free radicals called Spin Labels which

can attach themselves to particular sites in biological systems can attach themselves to particular sites in biological systems and produce spectra which provide information on changes and produce spectra which provide information on changes in the chemical and physical characteristics in the in the chemical and physical characteristics in the neighborhood of the site. neighborhood of the site.

They can also be inserted into a cell membrane which They can also be inserted into a cell membrane which provides information on the activities of the membrane at provides information on the activities of the membrane at various depths below the surface.various depths below the surface.

Label must have chemical activity & a group of atoms to Label must have chemical activity & a group of atoms to form bridges between free radical and a particular group.form bridges between free radical and a particular group.

Spin label must contain a nitroxyl group or a transition metal Spin label must contain a nitroxyl group or a transition metal complex providing unpaired electrons.complex providing unpaired electrons.

E.g; 2,2,6,6 tetramethyl-4-piperadone-1-oxyl (TEMPOL) has E.g; 2,2,6,6 tetramethyl-4-piperadone-1-oxyl (TEMPOL) has an unpaired electron on NO group.an unpaired electron on NO group.

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Group on the Group on the MacromoleculeMacromolecule

Spin LabelsSpin Labels

HemeHeme RCN (cyanide)RCN (cyanide)

MyosinMyosin ATP-RATP-R

LysozymeLysozyme CH3CO-NHRCH3CO-NHR

MethionineMethionine BrCH2CO-NHRBrCH2CO-NHR

Cystein ImmidazoleCystein Immidazole I-CH2CO-NHRI-CH2CO-NHR

Table: Selected spin labels and the groups on macromolecules to which spin label is attached

The unpaired electron on oxygen of NO group of a nitroxyl compound strongly interacts with nuclear spin of nitrogen atom to produce a 3 line hyperfine spectrum. As for Nitrogen (I=1), it has one equivalent proton so, (2nI + 1) = 2 x 1 x 1 + 1 =3

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XX + ST = XST + ST = XST

Transient Spin long-livedTransient Spin long-lived

Free radical trap spin adductFree radical trap spin adduct (paramagnetic) (Diamagnetic) (paramagnetic)(paramagnetic) (Diamagnetic) (paramagnetic)

Spin trap must react at relatively fast trapping rates.Spin trap must react at relatively fast trapping rates. The radical adduct must have a reasonable half-life. The radical adduct must have a reasonable half-life.

Commonly used spin traps :Commonly used spin traps :

DMPO (Dimethyl pyridine N-oxide)DMPO (Dimethyl pyridine N-oxide)

PBN (PBN (αα-phenyl-N-t-butyl nitrone).-phenyl-N-t-butyl nitrone).

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In ToxicologyIn Toxicology – –

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Conducting ElectronsConducting Electrons

ESR spectroscopy has been used to detect conduction ESR spectroscopy has been used to detect conduction electrons in solutions of alkali metals in liquid electrons in solutions of alkali metals in liquid ammonia, alkaline earth metals, alloys (e.g; small ammonia, alkaline earth metals, alloys (e.g; small amounts of paramagnetic metal alloyed with another amounts of paramagnetic metal alloyed with another metal). metal).

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Reaction Velocities & Reaction Velocities & MechanismsMechanisms

ESR is also found to be useful for determination of ESR is also found to be useful for determination of mechanisms and kinetics of reaction.mechanisms and kinetics of reaction.

The molecular interactions that exist e.g; between The molecular interactions that exist e.g; between solvent and solute (environment) can also be studied solvent and solute (environment) can also be studied by ESR spectroscopy.by ESR spectroscopy.

Special cells have been used in ESR spectroscopy, in Special cells have been used in ESR spectroscopy, in which radicals are produced by irradiation with UV, which radicals are produced by irradiation with UV, gamma or X-rays or by electrolytic redox reactions.gamma or X-rays or by electrolytic redox reactions.

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Fig; ESR Spectrum (First Derivative) for ethyl radicalFig; ESR Spectrum (First Derivative) for ethyl radical E.g; Ethyl radicals are produced when ethyl alcohol is E.g; Ethyl radicals are produced when ethyl alcohol is

irradiated with X-ray radiation. Spectrum shows five irradiated with X-ray radiation. Spectrum shows five lines which conforms the formation of ethyl radicals.lines which conforms the formation of ethyl radicals.

The 5 lines thus obtained are in the proportion of The 5 lines thus obtained are in the proportion of 1 : 4 : 6 : 4 : 11 : 4 : 6 : 4 : 1

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(…contd)(…contd)

This technique can also be used to study very This technique can also be used to study very rapid electron exchange reactions.rapid electron exchange reactions.

e.g; addition of naphthalene to a solution of e.g; addition of naphthalene to a solution of naphthalene radical anion.naphthalene radical anion.

This causes the broadening of the hyperfine This causes the broadening of the hyperfine component of ESR resonance line, which can component of ESR resonance line, which can thus be employed to calculate the rate constant thus be employed to calculate the rate constant for the exchange between naphthalene and for the exchange between naphthalene and naphthalene radical anion. naphthalene radical anion.

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Analytical ApplicationsAnalytical Applications Determination of MnDetermination of Mn2+2+ –– ESR spectrum of MnESR spectrum of Mn2+2+ ions ions shows six lines. The shows six lines. The

multiplicity is given by 2I + 1, where I is 5/2. multiplicity is given by 2I + 1, where I is 5/2. i.e; 2 x 5/2 + 1 = 6. This ions can be measured and i.e; 2 x 5/2 + 1 = 6. This ions can be measured and

detected even when present in trace quantities.detected even when present in trace quantities. Determination of Vanadium –Determination of Vanadium – Traces of vanadium in petroleum oils cause corrosion Traces of vanadium in petroleum oils cause corrosion

in combustion engines and furnaces and alter the in combustion engines and furnaces and alter the catalytic cracking of petroleum during processing.catalytic cracking of petroleum during processing.

ESR spectrum shows an 8 line spectra (I is 7/2);ESR spectrum shows an 8 line spectra (I is 7/2); 2I + 1 = 2 x 7/2 + 1 = 8. 2I + 1 = 2 x 7/2 + 1 = 8.

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(…contd)(…contd)

Determination of Polynuclear hydrocarbons –Determination of Polynuclear hydrocarbons – ESR spectroscopy has been used to estimate ESR spectroscopy has been used to estimate

polynuclear hydrocarbons which are first converted polynuclear hydrocarbons which are first converted into radical cations and then absorbed in the surface into radical cations and then absorbed in the surface of an activated silica-alumina catalyst. Free radicals of an activated silica-alumina catalyst. Free radicals so formed are then analysed. so formed are then analysed.

E.g; Naphthalene, anthracene, dimethylanthracene, E.g; Naphthalene, anthracene, dimethylanthracene, perylene, etc.perylene, etc.

In case of Naphthalene negative ion, there are two In case of Naphthalene negative ion, there are two sets (alpha & beta) of 4 equivalent protons each.sets (alpha & beta) of 4 equivalent protons each.

(2nI+1)(2nI+1) = (4+1)(4+1) = 25 lines.(2nI+1)(2nI+1) = (4+1)(4+1) = 25 lines.

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Naturally Occurring SubstancesNaturally Occurring Substances

Minerals with transition elements Minerals with transition elements

[e.g; ruby (Cr/Al[e.g; ruby (Cr/Al22OO33)])] Minerals with defects (e.g; quartz)Minerals with defects (e.g; quartz) Hemoglobin (Fe)Hemoglobin (Fe) PetroleumPetroleum CoalCoal RubberRubber

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BibliographyBibliography1. Cazes J.; Ewing’s Analytical Instrumentation Handbook (2005), 31. Cazes J.; Ewing’s Analytical Instrumentation Handbook (2005), 3 rdrd

edition, Marcel Dekker Publication, New York, pp. 349-390.edition, Marcel Dekker Publication, New York, pp. 349-390.

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3. Conners K. A.; A Textbook of Pharmaceutical Analysis (1932), 33. Conners K. A.; A Textbook of Pharmaceutical Analysis (1932), 3 rdrd edition, John Wiley & Sons, A Wiley – Interscience Publication, edition, John Wiley & Sons, A Wiley – Interscience Publication, New York, P. 299.New York, P. 299.

4. Khopkar S. M., Basic Concepts of Analytical Chemistry (2008), 34. Khopkar S. M., Basic Concepts of Analytical Chemistry (2008), 3 rdrd edition, New Age International Publishers, New Delhi, p. 400edition, New Age International Publishers, New Delhi, p. 400

5. Anjaneyulu Y., Chandrashekhar K., Manickam V.; A Textbook of 5. Anjaneyulu Y., Chandrashekhar K., Manickam V.; A Textbook of Analytical Chemistry (2006), published by – Pharma Book Analytical Chemistry (2006), published by – Pharma Book Syndicate, Hyderabad, pp. 719-742.Syndicate, Hyderabad, pp. 719-742.

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Bibliography (…contd)Bibliography (…contd)66. . Banwell C. N.; Fundamentals of Molecular Spectroscopy

(1983), 3rd edition, published by – Mc-Graw Hill Book Company, London, pp. 299-311.

7. Chatwal G. R., Anand S. K.; Instrumental Methods of Chemical Analysis (2007), 5th edition, Himalaya Publishing House, Mumbai, pp. 2.245-2.271.

8. Sharma B. K.; Instrumental Methods of Chemical Analysis (2006), 25th edition, Goel Publishing House, Meerut, pp.s-737 – s-773.

9. www.uottawa.ca/publications/interscientia/inter.2/spin.html (accessed on - 12-09-2009).

10 http://en.wikipedia.org/wiki/Electron_paramagnetic_resonance (accessed - 12-09-2009).

11 http://www.ncbi.nlm.nih.gov/pubmed/3039940 (accessed on - 23-09-09))

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