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Table of Contents
Abstract 2
Introduction 3
Singlet and triplet oxygen 4
Formation of singlet oxygen 6
Type I and Type II oxidation pathways 8
Photosensitizers 10
Aromatic hydrocarbons and organic dyes 10
Phthalocyanines, porphyrins and other tetrapyroles 14
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Download file to see previous pages Transition metal complexes as photosensitizers 16
Semiconductors 17
Immobilized photosensitizers 17
Methionine oxidation 18
Determination of singlet oxygen 21
Aims 24
Materials and methods 25
General Information 25
Oxygen measurements 25
Singlet oxygen consumption at different methionine concentrations 26
Singlet oxygen consumption induced by laser. 27
Results and discussion 27
Conclusions 47
References: 49
The methionine oxidation reaction using singlet oxygen was studied. Initially this report is focused on presenting the overview of works associated with the topic. Singlet oxygen is described along with the ways it is formed. It was highlighted that singlet oxygen was a more powerful oxidant then triplet oxygen and the types of oxidation pathways are described. The practical aspect of this research is focused on using a photosensitizer, Rose Bengal, to generate singlet oxygen. This is the reason for giving a short overview of photosensitizers is given making focus on the behaviour of Rose Bengal and compounds similar to it in structure. Methionine oxidation mechanism is also described as well as function of oxygen electrode.
In order to research the topic of methionine oxidation by singlet oxygen two experiments were carried out. In the first experiment a series of methionine solutions with different concentrations were prepared. In each case Rose Bengal was added as a photosensitizer. As it was established, the rate of oxygen consumption depends on methionine concentration in the solution being the highest at the lowest concentration of methionine. The process was followed by Michaelis-Menten kinetics therefore the corresponding equations were used to construct Lineweaver-Burke plot and determine the maximum rate of the oxidation reaction as well as the line slope. The second experiment utilised a more vigorous approach. A laser pulse was employed to produce singlet oxygen molecules in the dye containing methionine solution. And by employing various concentrations of methionine and Rose Bengal as photosensitizer construct oxygen consumption plots along with determination of variation of centre-of mass distance and potential energy of the reacting molecules. Methionine oxidation was also described using SPARTAN calculations and the reaction mechanism was presented. This report is initially focused on describing the key literature associated with oxidation of methionine by singlet oxygen, highlighting relevant for the project issues and arguments, then moving on to presenting the research that has been done so far, making accent on the methods used and results achieved, before finally identifying the existing gaps in the study and setting up a plan for future work. Introduction Oxygen was discovered by Joseph Priestley in 1775 (Priestley, 1775). Later, Avagadro described the diatomic nature of oxygen, and the paramagnetic properties of this diatomic gas were studied by Faraday in 1811. Differences between oxygen and other gases such as helium or nitrogen were also investigated (Parkes, 1967). Later in 1928, using molecular orbital theory, it was established that oxygen is paramagnetic due to the presence of the parallel spins of two electrons occupying the outer shell. This form with uncoupled electron pair was named triplet oxygen. Spectroscopy was used to prove the existence of higher energy state, which later was called singlet oxygen (Herzberg, 1934). In the singlet form of this molecule outer-shell electrons are paired in antiparallel spins. Initially, the importance of singlet oxygen was not recognised. It was rediscovered in 1964 in photooxidation experiments and since then became intensively studied. Over the past twenty five years significant increase in data regarding singlet oxygen has led to the ...Download file to see next pagesRead More
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