Spin Trapping Magnetic Resonance Determination of Atmospheric Species

101 Pages·2009·2.17 MB·English

Spin Trapping Magnetic Resonance
Determination of Atmospheric Species

Thesis submitted for the degree of
Master of Philosophy
at the University of Leicester

By

Michael Oladapo Ogunbowale
Department of Chemistry
University of Leicester

March 2009

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SPIN TRAPPING MAGNETIC RESONANCE DETERMINATION OF
ATMOSPHERIC SPECIES
Thesis submitted for the degree of Master of Philosophy
By Michael Oladapo Ogunbowale

March 2009

ABSTRACT
Spin trapping is a versatile technique for the detection of transient radicals with
applications in chemistry and biochemistry. The technique detects short-lived reactive
radicals by their addition reaction with a nitrone or nitroso compound which produces
aminoxyl radicals that are relatively more stable for detection than the free radicals.
This research was aimed at spin trapping gaseous peroxy radicals using solid and
solution phase spin traps; and Electron Paramagnetic Resonance (EPR) Spectroscopy to
detect the spin adducts formed. Known concentrations of PBN, nitrosobenzene and
nitrosobutane were used as spin traps for Di-tert-butylperoxide and EPR spectroscopy was
used for detection of the spin adducts which were used as reference and optimization of the
spectrometer used for this research and a medium of comparison and quantification for
gaseous peroxy radicals used for this research.
The results were promising as Nitrosobenzene demonstrated its ability to spin trap
gaseous peroxy radicals both in its solid and solution phases respectively by giving rise to
series of spectra that suggest that spin trapping has occurred. PBN on the other hand
showed its capability only in the solid phase while its solution seems not to spin trap
gaseous peroxy radicals in this research probably due to its high reactivity when exposed to
air, moisture and light.
The research found out that 1g each of PBN and Nitrosobenzene respectively were
probably capable of spin trapping reasonable amounts of gaseous peroxy radicals while 1ml
of 0.1M Nitrosobenzene will likely spin trap more radicals than the solid phase spin traps.
This result suggests that solution phase spin traps were probably more effective in spin
trapping gaseous peroxy radicals than solid phase spin traps.

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ACKNOWLEDGEMENT

My sincere gratitude and appreciation goes to my supervisors, Prof. Paul. S. Monks and Dr.
Jonathan. R. Woodward for their patience, support, encouragement, guidance and understanding
throughout the duration of this research. They have shown serious concern when I was troubled and
cheered me up when my moral was down. I will forever remember you for assisting me at all time
especially during my writing-up year. Thanks a lot.
I acknowledge my sponsor, Lagos State University (LASU), Ojo, Lagos, Nigeria for the travel grant
and study leave awarded me for the research. I am promising not to disappoint you as I am still willing
and ready to work for LASU as I have agreed before the commencement of this research.
I am indebted to my brothers and sister for all their concern and prayers for me although more is
expected from them morally and financially. Many thanks to my wife‟s family (Oguntala‟s) for their
relentless moral support to my children back in Nigeria when I was away. Mr & Mrs Adedotun
Oguntala have really shown me that I meant more than a son-in-law to them with their unmerited
support show towards the final payment of my fees. I pray that God should multiply your finances and
grant you long life so that you can enjoy the fruit of your labour.
I appreciate the favour received from The Redeemed Christian Church of God (R.C.C.G) a.k.a City
of Favour and members such as Dr. Sukanmi Osunsanmi, Mrs Balogun (Mummy Balogun), Mr. Remi
Olanrewaju and his family, Mr and Mrs Jide Aluko, Mr Sola Oni-Martins and Mr Daniel Anankhoma. I
thank GOD for the good work He is doing in the life of Pastor Taiwo Olugbenga and his family. I pray
that the anointing of GOD on your head should continue to flow forever in JESUS name. Words of
mouth alone could not express my thanks to Dr. Dare Asekun and his family for numerous gifts and
financial assistance. May you never lack good things and favour in JESUS name Amen.
My acknowledgement goes to the following staffs of Lagos State University for their support and
constant advice; Prof. Adeleke Adeniyi, Dr. Segun Ayejuyo (now in Unilag), Dr Femi Adeogun, Mr
Patrick Hunye, Prof. Babajide Elemo, Mr Adetola Onasanya, Mr Akin Lewis.
My sincere gratitude goes to Rev. Dr. & Dr. I. Olu Osokoya, Mrs Owolabi and all the
Ogunbowale‟s in general. My appreciation will not be complete without mentioning the contribution of
my Mr & Mrs Badejo (Daddy and Mummy Mile 2) and family. Your prayers, gifts, moral and financial
support to my family can not be quantified. The good GOD will repay your in several folds.
My utmost appreciation goes to my wife Elizabeth Abimbola and my children Raymond Olawale
and Monica Olamide for their prayers and understanding. They have been so supportive and
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understanding despite missing my absence. I will make-up for all the care that you have all missed. I
have carefully composed the statement below for my wife:
„Darling you have been a good example of a faithful wife and a caring mother for my children; I can
not repay you for your support which has been wonderful. I promise to continue to love and cherish
you for the rest of my life till death do us part. I really thank you for taking care of the gifts GOD has
given us. I join Raymond and Monica in saying „Thank you Mummy‟.
Finally, my acknowledgement goes to all members of the Molecular properties research group for
their support and encouragement. I will continue to remember all of you and I wish you good luck in
you future.

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DEDICATION

This write-up is dedicated to the Almighty GOD for His guidance and protection throughout my
research in the University of Leicester. I just want to say, “Thank you GOD” for being faithful to me.
The dedication is also extended to my Late parent Pa Stephen Olaitan Ogunbowale and Chief (Mrs)
Josephine Ore-oluwa Ogunbowale whom we planed this study together but could not wait to see the
end of the study. I know they will be happy for me getting to this stage despite the ups and downs I
experienced. May their gentle souls rest in perfect peace. Amen

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TABLE OF CONTENTS

Abstract 2
Acknowledgement 3-4
Certification 5

CHAPTER ONE
Introduction 9
1.1 The Atmosphere 9
1.1.1 The Troposphere 9
1.1.2 The Stratosphere and the ozone layer 9
1.1.3 The Mesosphere 10
1.1.4 The Thermosphere 10
1.1.5 The Ionosphere 11
1.2 History of Air pollution 11-13
1.3 Ozone chemistry in the troposphere 14-17
References 18
CHAPTER TWO
2.1 Peroxy radicals 19-20
2.2 Determination of Atmospheric peroxy radicals 21-24
2.3 Other techniques 24-26
References 27-29
CHAPTER THREE
Electron Paramagnetic Resonance (E.P.R.) Spectroscopy 30
3.1 Continuous Wave E.P.R. Spectroscopy 30-34
3.2 Hyperfine interaction 34-38
3.3 The E.P.R Spectrometer 38-39
3.4 Choice of experimental conditions 39-40
3.5 Typical E.P.R Spectrometer 40-44
3.6 Spin trapping 44-46
3.7 Applications of Spin Trapping 46-47

3.8 Spin Trapping and E.P.R detection of gaseous molecules 47-49
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and radicals
References 50-51

CHAPTER FOUR
Experimental
4.1 Aims 52
4.2 Equipments and chemicals 52-54
4.3 Experimental procedure for liquid spin traps 54
4.3.1 Preparation of solution 54
4.3.2 Initial Spin Trapping in solution 55
4.3.3 Determination of maximum irradiation time 55
4.3.4 Lowest detection limit of the spectrometer 55
4.3.5 Use of different lamps 55
4.3.6 Oxygenated and deoxygenated solutions 56
4.4 Experimental procedure for gas phase Spin trapping 56
4.4.1 Aims 56
4.4.2 Designing the sample tube 56-57
4.4.3 Gaseous peroxy radical source 57-59
4.4.4 Preliminary gas phase experiment 59
4.4.5 Other experiments 59-61
4.4.6 Trapping of gas phase peroxy radicals 61-62
References

CHAPTER FIVE
Results Discussion and Conclusions
Background information 63-66
5.1 Solution phase reactions 66-67
5.1.1 Peroxy radical formation 67-74
5.2 Optimization of the EPR Spectrometer 7-78
5.3 E.P.R saturation effect 78-82
5.4 Gas phase peroxy radical trapping 82-87
5.5 Solid and solution phase peroxy radical trapping 87-95
5.6 Conclusions and Future work 95-97
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References 98-99
5.7 Postgraduate record 100
5.7.1 Induction/training sessions attended 100
5.7.2 Undergraduate lecture courses attended 100
5.7.3 Departmental seminars 1007-101
5.7.4 Conferences/meetings attended with dates 101
5.7.5 Departmental presentations 101

CHAPTER ONE
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INTRODUCTION
1.1: THE ATMOSPHERE.

The atmosphere is a layer of gases surrounding the planet earth and retained by the earth‟s
gravity. The present atmosphere of the earth is probably not its original atmosphere. The atmosphere
was lost to space, and replaced by compounds out gassed from the crust and other planetesmals rich in
volatile materials. This mixture of gases is commonly known as air. It reaches over 560 kilometres (348
miles) from the surface of the Earth, so we are only able to see what occurs fairly close to the ground.
Earth is believed to have formed about 5 billion years ago. These gases may have consisted of
hydrogen (H ), water vapours, methane (CH ), and carbon oxides. Prior to 3.5 billion years ago the
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atmosphere probably consisted of carbon dioxide (CO ), carbon monoxide (CO), water (H O),
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nitrogen (N ), and hydrogen. The present composition of the atmosphere is 79% Nitrogen, 20%
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oxygen and 1% other gases. [1]
The Earth's atmosphere contains several different layers that can be defined according to air
temperature. Figure 1.1 displays these layers in an average atmosphere.

1.1.1 The Troposphere
The troposphere is where all weather takes place; it is the region of rising and falling packets of
air. It is the closest to the earth [2]. The air pressure at the top of the troposphere is only 10% of that at
sea level (0.1 atmospheres). It is a region in which temperature decreases with altitude [3]. There is a
thin buffer zone between the troposphere and the next layer called the tropopause. The tropopause and
the troposphere are known as the lower atmosphere.

1.1.2 The Stratosphere and Ozone Layer
Above the troposphere is the stratosphere, where air flow is mostly horizontal. The thin ozone
layer in the upper stratosphere has a high concentration of ozone, a particularly reactive form of
oxygen. This layer is primarily responsible for absorbing the ultraviolet radiation from the Sun [2]. The
formation of this layer is a delicate matter, since only when oxygen is produced in the atmosphere can
an ozone layer form and prevent an intense flux of ultraviolet radiation from reaching the surface,
where it is quite hazardous to the evolution of life. Chlorofluorocarbons used as cooling agents in
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refrigeration have been found to react with ozone in the stratosphere. These man made fluorocarbon
compounds have been depleting the ozone layer, with dire future consequences for life on the Earth [3].

Figure 1.1: The atmospheric temperature profile as it corresponds to the different regions [2].

1.1.3 The Mesosphere
Above the stratosphere is the mesosphere where temperature decreases with height.
1.1.4 Thermosphere
This region starts from between 200 and 250 kilometres. [4] The thermosphere starts just above
the mesosphere and extends to 600 kilometres (372 miles) high. The temperature goes up as altitude
increases due to increase intensity of the Sun's energy. Temperatures in this region can be as high as
1,727 oC. Chemical reactions occur much faster here than on the surface of the Earth. This layer is
known as the upper atmosphere [3].
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