The Interaction Of Singlet Oxygen With The Unsaturated Organic Compounds And The Subsequent Chemiluminescence Reactions

Singlet oxygen is a unique reactive oxygen species and its chemical reactivity derives from its characteristicelectronically-excited state. The involvement of singlet oxygen in many important atmospheric, physical,chemical, biological, and therapeutic processes has attracted intense research interest in recent years.Photosensitized generation of singlet oxygen is a simple, controllable method, requiring only oxygen, light of anappropriate wavelength, and a photosensitizer capable of absorbing and using light energy to excite oxygen to itssinglet state.In this work, the interaction of singlet oxygen with the unsaturated organic compounds and the subsequentchemiluminescence (CL) reactions were studied. The transformation conditions of various unsaturated substrates,including unsaturated fatty acids, chlorophenols and synthetic musks were optimized to enhance thephototransformtion efficiency of substrates. Quantum dots were used as the photosensitizer in thephototransfomation process, the mechanism of quantum dot-induced phototransformation and its subsequent CLreaction were studied in detail. Furthermore, the primary and final products in the transformation reactionsbetween singlet oxygen and six chorophenols were studied by quantum theory calculation. Based on thesefindings, the relationship between photodegradation rates and the number of chlorine substitutions was illustratedtheoretically. Finally, the dye-sensitized photodegradation method was preliminarily studied for the removal ofsynthetic musks in real samples. This study is not confined to prompt the understanding of these reactions, moreimportantly, the principle proposed in this study is expected to have a general significance. The contents weresummarized as follows:1. The basic properties, the production and the determination methods of singlet oxygen are reviewed.Applications of singlet oxygen in CL system and quantum theory calculations on the reaction mechanism ofsinglet oxygen with unsaturated organic compounds are addressed.2. The influence of surfactant micelles on hydrogen peroxide and sodium hypochlorite CL system wasinvestigated. The micellar media based on anionic, cationic and non-ionic surfactants were employed as thesimple models to mimic more complex biological environments. The formation of surfactants cage canimprove the CL quantum yield of singlet oxygen by protecting singlet oxygen from solvent quenching. Theresults showed that the CL emission is related to the hydrophobic group of surfactant medium, which isfurther confirmed by the enhancing effect of the alcohol solvent on the CL intensity. The involvement ofsinglet oxygen was characterized by the quenching effect of a specific singlet oxygen scavenger sodiumazide and chemical trapping of singlet oxygen with the sodium1,3-cyclohexadiene-1,4-diethanoate.Moreover, the CL spectrum of the sodium hypochlorite/hydrogen peroxide system was measured. The lightemission is observed in a wavelength range from435to475nm, which may attributes to the singlet oxygendimol species (1O2)*2.3. A dye-sensitized phototransformation method was developed for the evaluation of oxidation damage tounsaturated fatty acids induced by singlet oxygen. The singlet oxygen was generated in thephotosensitization process. Results showed that the order of phototransformation rate of three unsaturatedfatty acids is α-Linolenic acid>Linoleic acid>Oleic acid. The participation of singlet oxygen during thephototransformation process was confirmed by the changes in the UV spectra of a chemical trap CHDDE.The CL spectrum indicates that the excited state of rose bengal was responsible for the light emission.Kinetic studies showed the formation rate of singlet oxygen (vf) is1.74×10-6M-1s-1in the photosensitizedprocess.4. We have studied the CdTe quantum dot-induced phototransformation of2,4-dichlorophenol (2,4-DCP) andits subsequent CL reaction. Quantum dots (QDs) of different sizes and capped with thioglycolic acid were prepared and characterized by molecular spectroscopy, X-ray diffraction and transmission electronmicroscopy. In the presence of QDs,2,4-DCP is photochemically transformed into a long-living1ightemitting precursor which can react with N-bromosuccinimide (NBS) to produce CL. The CL spectra indicatethat the singlet oxygen dimol species and the excited state of QDs were responsible for the light emission.The formation of singlet oxygen during the phototransformation process was confirmed by the enhancementeffect of deuterium oxide on the CL reaction and the changes in the UV spectra of a chemical trap. The CLintensity is linearly related to the concentration of2,4-DCP in the range from0.36to36μmol L-1, and thedetection limit (at3σ) is0.13μmol L-1.5. With the intention of finding certain predictors to be used for the determination of the most probable reactionpath and estimating the dye-sensitized photodegradation rates of chlorophenols, the reactions of1O2with sixchorophenols (CPs), including2-chlorophenol (2-CP),3-chlorophenol (3-CP),4-chlorophenol (4-CP),2,4-dichlorophenol (2,4-DCP),2,4,6-trichlorophenol (2,4,6-TCP) and pentachlorophenol (PCP), wereinvestigated in aqueous solution by using the density functional theory. Results suggested that1,3-addition toa double bond connected to a hydrogen-carrying group, resulting in the formation of allylic hydroperoxides,and1,4-addition to chlorophenols to form of hydroperoxide ketones are thermodynamically more likely totake place. Furthermore, the reaction barrier of the former one is higher than that of later one, which tends toconclude that1,4-addition to chlorophenols to form of hydroperoxide ketones is the most likely route inaqueous solution. The computational results are in agreement with previous experimental results. Also it wasobserved that with the increase of chlorine substitutions, the reactions become less exergonic and kineticallyless favorable due to the increase in reaction barriers. The relationship between photodegradation rates andthe number of chlorine substitutions was illustrated theoretically by using the energies of frontier molecularorbitals and the ionization potentials, which are further confirmed that monochlorophenols are more readilyreact with singlet oxygen.6. The removal of synthetic musks in aqueous solution by means of a dye-sensitized photodegradation methodwas preliminarily studied. Two polycyclic musks (HHCB and AHTN) and two nitro musks (MX and MK)were selected as the model compounds due to their wide applications. Important factors that may affect thedegradation process were investigated and the result showed that the optimum performance can be achievedwith rose bengal as the sensitizer (1.0mg L-1) in aqueous solution at pH9.0. Room temperature (25oC) wasfound to be suitable for the degradation of the four musks. The degradation percentages obtained for HHCB,AHTN, MX and MK were84.6%,86.1%,77.7%and49.2%, respectively. The experiment data suggestedthat the kinetics of the dye-sensitized photodegradation followed pseudo first-order reaction. Furthermore,the photodegradation in natural water was simulated and the results were compared with the degradationpercentages in pure water. It was found that the degradation percentages obtained in pure water were lowerthan that in natural water, suggesting that the approach of the dye-sensitized photodegradation could beapplied for the removal of the synthetic musks from water resources.