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DR.S.ARAVAMUDHAN
http://www.ugc-inno-nehu.com/
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Dr.S.Aravamudhan   

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  I had submitted my thesis on "Overhauser effect Studies" at 3300G Magnetic Field Strength, in the year 1974. And, currently the DNP at High Fields is gaining importance for Sensitivity Enhancemnet and I had corresponded to be able to participate in the recently held DNP School on Enhanced NMR, but finally could not attend. The organizers have sent an EMAIL with Photographs (link: http://www.weizmann.ac.il/conferences/DNP/photos/gallery.html ) after the School and I thank the organizers with these few photographs in my website for the synopsis of my thesis.                Aravamudhan... 7th December 2009
CLICK HERE and JUMP to view a cartoon on D.N.P.-19/02/2012
Top of the Webpage of the DNP School

The DNP (of nuclei due to free radicals) with dominating scalar interaction mechanism can give positive enhancements while dipolar interaction results in negative enghancements. When both mechanisms are operating, then if Scalar interaction predominates the result would be a positive enhancement. The image above has a positively enhanced spectrum: the enhancements depend on the magnetic fields of the experiment. All the protons in a molecule undergoing quantitatively enhancements to the same extent can happen only if the free-radical interactions (scalar & dipolar) with every one of the protons is to the same extent independent of the topology of the molecule/differential D.N.P. effects, differing from one proton location to another proton location is usually observed.
Happy New year A view at venue At the lounge

     Can we meet again?
http://aravamudhan-s.ucoz.com/

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from the gallery Happy New Year

Video Lectures by Prof. Aravamudhan


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DOWNLOAD LINKfrom Digital Library of India  for the thesis of DR.S.Aravamudhan
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Web Page updated on May 13, 2017
The thesis is documented at the website of DIGITAL LIBRARY OF INDIA


EXPERIMENTAL STUDIES IN OVERHAUSER EFFECT

A Thesis Submitted

In Partial Fulfillment of the Requirements for the Degree of

DOCTOR OF PHILOSOPHY

 

By

S.ARAVAMUDHAN

 

TO THE
DEPARTMENT OF CHEMISTRY

INDIAN INSTITUTE OF TECHNOLOGY, KANPUR

DECEMBER 1974

 

 

Synopsis of the Contents of Thesis

 

The thesis consists of six chapters. In Chapter I, a brief review of the recent Overhauser effect studies of "free radicals in solution" is given and the scope of the present work is also discussed. 

Chapter II deals with the construction of an X-band Overhauser effect spectrometer for use at a magnetic field of 3300G in which a broad-band r.f. hybrid junction is employed for NMR detection. Due to difficulties in obtaining several associated equipments and components it has been necessary to make the fullest use of whatever equipment was available in our Institute for this study. Since a dual-purpose Varian EPR/ wide-line NMR spectrometer system was available we have built our Overhauser effect spectrometer around this unit. 

A coil-in-the cavity arrangement is used for the Overhauser effect probe. The cavity is connected to a Varian V-4502 EPR spectrometer system, which constitutes the ESR part of the Overhauser effect set-up. A Varian VF-4210 variable frequency r.f. transmitter-receiver unit in conjunction with the V-4270B output unit and the associated sweep units are used in the NMR part. The original crossed-coil NMR probe has been replaced by a single coil system using the broad-band r.f. hybrid junction for the NMR detection. Field modulation at 20 Hz and field scanning are used to record the NMR spectra. 

The mode of recording NMR spectra under Overhauser effect conditions, monitoring of microwave power and recording relaxation data are discussed in detail. It is pointed out here that the maximum microwave power available in our klystron was only 300 mW and the power reaching the sample cavity was even less. Nonetheless the enhancement factors extrapolated to infinite microwave power yielded U~ values in agreement with literature values for several proton containing_ systems. The effect of sti­mulated emission on these enhancement factors has been consider­ed and it was found that under these experimental conditions the correction factors were within the experimental error. In Chapter III some results of Overhauser effect studies on protons in solutions of free radicals at room Chapter III some results of Overhauser effect studies on protons in solutions of free radicals at room m temperature are reported. These studies were made using the set-up described in Chapter II. Tri-tertiary butyl phenoxyl (TBP) radical has been used as the solute to observe the signal enhancement for protons of cyclohexane, o-, m-, and p-xylenes, n-pentane and n-hexane. These results have not been so far reported in the literature. In all these cases a  dominant dipolar interaction  has been noticed. U values for these systems are reported. Results have been interpreted assuming a pure translation diffusion modulating the dipolar interaction. 

The construction of an Overhauser effect spectrometer with higher NMR resolution capabilities at 3300 G is described in Chapter IV. The spectrometer described in chapter II does not have the capability to resolve chemically shifted NMR peaks. It was felt desirable to have a better resolving power NMR spectrometer for the Overhauser effect studies. A V-4311 fixed frequency (25.1 MHz) r.f. transmitter-receiver unit for 13C studies using the high resolution HA-100 NMR spectrometer was available to us. We therefore designed our new system incorporating this unit. The ESR part and the Overhauser effect probe are the same as in the earlier set-up described in Chapter II. The Varian V-4311 fixed frequency (25.1 MHz) unit has r.f. phase sensitive detection capabilities. The output of the r.f. phase-sensitive detector is available for recording or presenting on the Oscilloscope. But at 3300G the operating frequency of NMR for 1H is ~14 MHz. Moreover, slightly variable frequency for the NMR is required due to the variability of the ESR frequency depending on the nature of the solvents and free radicals. Since V-43l1 is only a fixed frequency unit at 25.1 MHz a mixing scheme with an external local oscillator has been adopted to suit the NMR frequency requirements. With this scheme it was possible to detect not only 1H resonance but 19F resonances also by altering the L.O. frequency appropriately. A set of homogeneity coils mounted on the magnet pole faces were used to improve the magnetic field homogeneity at the sample. With this set-up we could achieve a moderate resolution for protons, which are chemically, shifted by ~ 10 Hz even without sample spinning. A field-frequency lock system suitable for incorporation in this spectrometer has also been constructed and tested. The sensitivity and performance of this set-up was significantly superior to our earlier set-up. 

In Chapter V some of the results of our Overhauser effect studies at room temperature under moderate resolution conditions are reported. Some of the systems which have been studied using the earlier set-up have been reinvestigated with the new spec­trometer and good agreement for U values was obtained. The studies on 0-, m- and p-xylenes show that the signal enhance­ment factors for the methyl protons and the ring protons are nearly equal. Studies made on mixtures of some proton containing solvents with TBP radical show that for these systems the variation in enhancement factors can be understood on the basis of the changes in the viscosity of the medium. Enhancement of the t-butyl protons of tri-tertiary butyl phenol could be observed when tritertiary butyl phenol was dissolved in carbon tetra chloride and a small fraction of this was reduced to tritertiary butyl phenoxyl radical. The interaction in this case has been reported earlier to be of the scalar type and this could be confirmed. 19F resonance could be observed using this set-up by changing the L.O. frequency. 1, 2, 2-Trifluoro trichloro ethane showed two chemically shifted 19F peaks in the intensity ratio 1:2. When Overhauser effect studies were carried out on this solvent with TBP radical as the solute a dominant dipolar inter­action was observed for both the peaks. The two peaks, however, enhanced to different extents. This has been attributed to the differences in the scalar interaction between the solvent 19F nuclei and TBP radical due to the presence of different number of chlorine atoms in the neighborhood of the two types of 19F nuclei. A model based on molecular orbital theory has been discussed in Chapter V to explain the trends observed in 1,2,2-­ Trifluoro trichloro ethane. In the last chapter of this thesis suggestions are made for further possible improvement of the present Overhauser effect spectrometer system.


Typing of the text document for the contents of this page: by staff at BIC,NEHU
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Table of Contents

 

 

 

page

CERTIFICATE I

 

ii

CERTIFICATE II

 

iii

STATEMENT

 

iv

PREFACE

 

v

ACKNOWLEDGEMENTS

 

vii

CHAPTER I

INTRODUCTION

I.1

General

1

I.2

Electron-Nuclear Interaction

2

I.3

Correlation Function, Spectral Density and Relaxation Transi­tion Probabilities

6

I.4

Origin of DNP and the Relevant Parameters

10

I.5

Experimental Determination of Relevant Parameters­

15

I.6

Models for the Calculation of

19

I.6.1

Models for Dipole-Dipole Interaction

23

I.6.2

Models for Mixed Scalar and Dipolar Interaction

28

I.6.3

Use of the Theoretical Models in the Analysis of Data Obtained from DNP and Other Relevant Measure­ments

35

I.7

Experimental Techniques

40

I.8

A Survey of Experimental Results

48

I.8.1

Studies on Protons

48

I.8.2

Studies on 19F Nuclei

55

I.8.3

Studies on 3lp Nuclei

60

I.8.4

Studies 'on 13c Nuclei

64

I.8.5

Studies on other Nuclei

68

I.9

Scope of the Present Work

69

 

References

75

CHAPTER II

CONSTRUCTION OF' AN X-BAND OVERHAUSER EFFECT SPECTROMETER USING AN RF INBRID JUNCTION FOR NMR DETECTION

II.1

Introduction

80

II.2

The Overhauser Effect Probe

87

II.3

R.F. Hybrid junction for NMR Detection

91

II.4

The NMR Spectrometer

94

II.5

Relaxation measurements

97

II.6

Microwave Power measurements

97

II.7

Performance Evaluation of the Set-up

101

II.8

Concluding remarks

106

 

References

108

CHAPTER III

RESULTS OF OVERHAUSER EFFECT STUDIES ON SOME PROTON--CONTAINING SOLVENTS

WITH TBP

III.1

Introduction

109

III.2

Theory and the Method of cal­culation of Distance of Closest Approach

110

III.3

Experimental

113

III.4

Results and Discussion

114

III.5

Concluding Remarks

122

 

References

123

CHAPTER IV

CONSTRUCTION OF AN X-BAND OVERHAUSER SPECTROMETER WITH MODERATE NMR RESOLU­TION CAPABILITY

IV.1

Introduction

124

IV.2

The Varian V-4311 R.F. Unit

125

IV.3

A Description of the Overall Set-up

126

IV.4

Some Details of the Mixers and R.F. Amplifiers Employed in this set-up

129

IV.5

The Local Oscillator

135

IV.6

NMR Field Sweep

136

IV. 7

NMR Stabilization of the Magnetic Field

138

 

References

145

CHAPTER V

SOME RESULTS OF OVERHAUSER EFFECT STUDIES ON 1H AND19F NUCLEI UNDER MODERATE NMR RESOLUTION CONDITIONS AT 3300G

V.l

Introduction

146

V.2

Studies on 1H Nucleus

147

V.2.1

Xylenes with TBP

147

V.2.2

Mixtures of Solvents with TBP

150

V.2.3

Tritertiarybutylphenol with TBP

155

V.3

Studies on 19F Nucleus

156

V.3.1

Experimental Studies on l, 2, 2-Trifluorotrichloro­ethane

156

V.3.2

A Molecular Orbital Treat­ment of Spin Density Pertur­bations in l, 2, 2-Trifluoro­trichloroethane due to TBP

158

 

References

174

CHAPTER VI

SUGGESTIONS FOR FURTHER IMPROVEMENT IN THE PRESENT OVERHAUSER EFFECT SPECTROMETER

VI.1

Introduction

175

VI.2

ESR Part

175

VI.3

Overhauser Effect Probe

176

VI.4

NMR Part

177

VI.5

Concluding Remarks

178

 

References -

180

VITAE
http://in.geocities.com/saravamudhan2002/biodata.html

 


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Below displayed are scanned images of photographs from thesis
depicting the Instrument and Measurements


NMR-Coil in ESR-Cavity

( Chapter-II Fig.II.4 )

 


Overhauser enhancements
of Proton signals

(Chapter-IV Fig.IV.3)

upper: Unenhanced

lower: Negatively enhanced

 

Additional Scanned images of Figures from the thesis
Images below: scanned at Dept. of Biohemistry, N.E.H.U
Fig.II.8 on page 95 of thesis: CLICK on this thumbnail to display the full view
Refer Para #2 & para 3 in
synopsis above
Fig.II.10 on page 100 of thesis: CLICK on this thumbnail to display the full view
Refer Para #4 in
synopsis above
Fig.IV.1 on page 127 of thesis: CLICK on this thumbnail to display the full view
Refer Para #5 in
synopsis above
Fig.II.9 on page 98 of thesis: CLICK on this thumbnail to display the full view
Recording Relaxation:
Refer Para-4 in synopsis above
Fig.IV.2 on page 130 of thesis: CLICK on this thumbnail to display the full view
A view of the Spectrometer:
for Overhauser-Effect measurements
Refer Para-5 in synopsis above
Fig.IV.8 on page 140 of thesis: CLICK on this thumbnail to display the full view
Field-frequency lock system
Refer Para-5 in synopsis above
Fig.II.1 on page 83 of thesis: CLICK on this image to display the full view
A Marginal Oscillator circuit of FNH Robinson
Eventhough NMR and the Overhauser enhancements could be observed, the entire effort had to become 'not-useful'
for the reason that, no reproducible quantitative measurement was possible.
Image installed on 4th August 2015-sa-NEHU campus-Shillong         Click on image below to view in actual size         Click on image below to view in actual size
Click on image for viewing actual size
link for the original full paper on energies (in figure above) in pdf format (from internet resources):sa-thesis-design-energies-07-04316.pdf
link for the original full paper on Wireless Power Transfer(in figure above) in pdf format (from internet resources):WirelessPower-321203.pdf

ISMAR1974 Abstract

ISMAR-CA98;Link1                     ISMAR-CA98;Link2                  ISMAR-2013

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The Scanned (at Biochem,NEHU) Image of the Abstract for the oral presentation (by S.Aravamudhan) at the Internatioanl Conference of ISMAR held at T.I.F.R. Mumbai in Jan. 1974

CLICK HERE   to download a publication illustrating the current APPLICATION of the BLOCK SIEGERT SHIFT in Magnetic Resonance.The SUBJECT of the Cartoon----> on the right hand side column is this  "Block Siegert Effect"---->

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The Scanned (at Biochem,NEHU) Image of the Ph.D., Degree Certificate
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The Certificate by Ph.D.Superviser Prof.P.T.Narasimhan
Photo image from the thesis bound volume

This Table with the contents of 2 columns was insetrted on Friday,October 27, 2006 4:07PM at Deptt. of Chemistry, N.E.H.U. -
 The CARTOON below was drawn and furnished on 18th Feb.2012 by Dr.Aravamudhan
at Chennai after the 99th ISC / events_2012

CARTOON

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