Hydroxyl Radical (HO·) is a highly reactive radical species which is an important member of a class of chemical species known as Reactive Oxygen Species (ROS). Hydroxyl radical typically has an extremely short lifetime under most conditions and its highly reactive nature makes it hard to detect by conventional methods used for study of free radical kinetics. In this study we propose and develop an alternative method for relative reactivities and regioselectivities of hydroxyl radical reactions with aromatic compounds in organic solvents. Hydroxyl radical is generated by the thermolysis of a tert-butyl azohydroperoxide which dissociates to yield hydroxyl and tert-butyl radicals, nitrogen, and acetone. TMIO is used to trap the tert-butyl radical, but is less likely to trap hydroxyl radical, which is free to react with the target arene to yield a hydroxycyclohexadienyl species. These species undergo hydrogen abstraction with TMIO to yield phenols, which may be derivatized with an appropriate silylating agent (in this case BTFSA), and analyzed using gas chromatography with detection by flame ionization (GC-FID) and mass spectrometry (GC-MS). The reactivity and selectivity of reaction of hydroxyl radical with various aromatic compounds is determined at different temperatures to obtain relative reaction rates. In this work, the reactivities and selectivities for HO• reactions with simple arenes, such as toluene and naphthalene are investigated. / Department of Chemistry

Concern over the occurrence of micropollutants in drinking water and their health effects is increasing. Therefore, there is a growing interest in understanding micropollutant removal during drinking water treatment. Ozonation and advanced oxidation processes (AOPs) have been found to be effective in the degradation of many micropollutants. Ozonation involves reactions with both molecular ozone (direct pathway) and hydroxyl radicals (indirect pathway), while hydroxyl radicals are the main oxidants in advanced oxidation processes. Reaction rate constants of micropollutants with molecular ozone (kO3) and hydroxyl radicals (kOH) are indicators of their reactivity and are therefore useful in assessing their removal efficiency in ozonation and AOPs. However, to date, only a limited number of rate constants are available for micropollutants, especially emerging micropollutants such as endocrine disrupting chemicals (EDCs) and pharmaceuticals. Quantitative structure-property relationships (QSPR) are therefore desirable for predicting rate constants of numerous untested micropollutants without experimentation. The overall objective of this thesis was to develop predictive QSPR models which correlate the rate constants of a wide range of structural diverse micropollutants to their structural characteristics. To ensure the wide applicability of the QSPR models, the training set compound selection is critical and a group of heterogeneous compounds which are structurally representative of many others is preferred. A systematic compound selection approach which involves principal component analysis (PCA) and D-optimal onion design was applied for the first time in water treatment research. As a result, 22 micropollutants with diverse structures were selected as representatives from a large pool of micropollutants of interest (182 compounds). In addition, 12 molecular descriptors were identified which link relevant structural features to the removal mechanisms of oxidation processes. The kO3 and kOH values of the 22 selected micropollutants were then determined experimentally in bench-scale reactors at neutral pH using high performance liquid chromatography equipped with a photodiode array detector (HPLC-PDA). Three methods, competition kinetics, compound monitoring, and ozone monitoring were used for kO3 measurement, and competition kinetics was used for kOH measurement. As expected, kO3 values span a wide range from 10-2 to 107 M-1 s-1 because of the selective nature of molecular ozone. The general trends of micropollutant reactivity with ozone can be explained by the micropollutant structures and the electrophilic nature of ozone reactions. The kOH values range from 108 to 1010 M-1 s-1 because hydroxyl radicals are relatively non-selective in their reactions. For the majority of these micropollutants kO3 and kOH values were not reported prior to this study. Thus they provide valuable information for modeling and designing of ozonation and AOP treatment. QSPR models for kO3 and kOH prediction were then developed with special attention to model validation, applicability domain and mechanistic interpretation. With the experimentally determined rate constants, QSPR models were developed for predicting kO3 values using the selected 22 micropollutants as the training set and the 12 identified descriptors as model variables. As a result, two QSPR models were developed using piecewise linear regression (PLR) both showing an excellent goodness-of-fit. Model 1 was governed by average molecular weight and number of phenolic functional groups, and Model 2 was dominated by two principal components extracted from the descriptor matrix. The models were then validated using an external validation set collected from the literature, showing good predictive power of both models. Prior to applying these models to unknown micropollutants they need to be classified as high-reactive (logkO3 > 2 M-1 s-1) or low-reactive (logkO3  2 M-1 s-1), so that the appropriate submodel of the PLR can be applied. A classification function using linear discriminant analysis (LDA) was therefore developed which worked very well for both training and validation sets. With the help of additional compounds collected from the literature, and DRAGON molecular descriptors, a QSPR model for kOH prediction in the aqueous phase was developed using multiple linear regression. As a result, 7 DRAGON descriptors were found to be significant in modeling kOH, which related kOH of micropollutants to their electronegativity, polarizability, presence of double bonds and H-bond acceptors. The model fitted the training set very well and showed great predictive power as assessed by the external validation set. In addition, the model is applicable to a wide range of micropollutants. The model’s applicability domain was defined using a leverage approach. The main contributions of this thesis lie in the successful development of QSPR models for kO3 and kOH value prediction which, for the first time, can be used for a wide range of structurally diverse micropollutants. In addition, all QSPR models were externally validated to verify their predictive power, and the applicability domains were defined so that the applicability of the models to new compounds can be determined. Finally, the applicability of the model to natural water was explored by combining the QSPR models with the established Rct concept which predicts micropollutant removals during ozone treatment of natural water but requires kinetic data as input. Results show that the kinetic data from the QSPR model predictions worked well in the Rct model providing reliable estimations for most of the selected micropollutants. This approach can therefore be used in water treatment for initial assessment and estimation of ozonation efficiency.

A new portable flow tube technique, the Toronto Photo-Oxidation Tube v2.0 was developed and characterized to explore its potential to control and monitor the OH-initiated formation and chemical aging of secondary organic aerosol (SOA) in-situ. The first study investigated the different operational parameters of this flow tube technique. TPOT v2.0 can generate oxidizing conditions equivalent to ambient OH exposures of 2.3 – 10.8 days. The transmission efficiency of a model organic aerosol indicated negligible losses in the oxidation tube. Differences in the residence time distribution curves measured for a gas and model organic aerosol showed that particles were subjected to approximately half of the OH exposure compared to gases. The second study examined the capacity of the TPOT technique to generate secondary aerosols due to OH oxidation. High aerosol yield was observed for H2SO4 particles, whereas a low aerosol yield was observed for α-pinene SOA.

A new portable flow tube technique, the Toronto Photo-Oxidation Tube v2.0 was developed and characterized to explore its potential to control and monitor the OH-initiated formation and chemical aging of secondary organic aerosol (SOA) in-situ. The first study investigated the different operational parameters of this flow tube technique. TPOT v2.0 can generate oxidizing conditions equivalent to ambient OH exposures of 2.3 – 10.8 days. The transmission efficiency of a model organic aerosol indicated negligible losses in the oxidation tube. Differences in the residence time distribution curves measured for a gas and model organic aerosol showed that particles were subjected to approximately half of the OH exposure compared to gases. The second study examined the capacity of the TPOT technique to generate secondary aerosols due to OH oxidation. High aerosol yield was observed for H2SO4 particles, whereas a low aerosol yield was observed for α-pinene SOA.

The hydroxyl (OH) radical is a common intermediate species in any hydrogen- or hydrocarbon-based flame. Investigating OH at elevated temperatures and pressures is not a trivial task, and many considerations must be made to fully study the molecule. Shock tubes can provide the experimenter with a wide range of temperatures and pressures to investigate a variety of combustion characteristics including, but not limited to, OH kinetic profiles. Described in this dissertation is the diagnostic used to measure OH within a shock tube using UV absorption spectroscopy from an enhanced UV Xenon lamp passed through a spectrometer. OH absorption was made over a narrow range of wavelengths around 309.551 nm within the widely studied OH X→A ground vibrational transition region. Experiments have been performed in the shock-tube facility at Texas A&M University using this OH absorption diagnostic. A calibration mixture of stoichiometric H2/O2 diluted in 98% argon by volume was tested initially and compared with a well-known hydrogen-based kinetics mechanism to generate an absorption coefficient correlation. This correlation is valid over the range of conditions observed in the experiments at two pressures near 2 and 13 atm and temperatures from 1182 to 2017 K. Tests were completed using the absorption coefficient correlation on stoichiometric mixtures of methane, methane and water, ethane, ethylene, and acetylene to compare against a comprehensive, detailed chemical kinetics mechanism which considers up through C5 hydrocarbons. Measurements of methane show good agreement in peak OH formation and ignition delay time when compared with the mechanism. Improvements can be made in the shape of the methane-oxygen OH profile, and sensitivity and rate of production analyses were performed with the mechanism to identify key reactions for tuning. Similar results were found for methane-water-oxygen mixtures with no difference in profile shape or ignition delay time noted. There is room for improvement between the mechanism and measured values of OH for ethane-, ethylene-, and acetylene-based mixtures, although interesting pre-ignition features are nonetheless captured relatively well by the mechanism. Uncertainty in the measurement comes from the inherent noise in the photomultiplier tube signal and is ±25-150 ppm for the 2-atm experiments and ±6-25 ppm for the 13-atm experiments.

Thesis (Ph.D.)--Michigan State University. Environmental Engineering, 2008. / Title from PDF t.p. (viewed on Mar. 30, 2009) Includes bibliographical references. Also issued in print.

Thesis (M. Phil.)--University of Hong Kong, 1998. / Cover title. Includes bibliographical references (leaves 169-192).

High-resolution techniques to characterize the three-dimensional structure of nucleic acids are critical for understanding the mechanisms of action of biologically important RNA and DNA molecules. Methods based on chemical probing have been particularly useful in gaining insight into the structures of nucleic acids in solution. The hydroxyl radical has been widely adopted as a chemical probe for DNA and RNA structure since its first application to protein-DNA footprinting. This dissertation describes efforts to improve upon the current model of how the hydroxyl radical cleaves the RNA backbone, through the use of specifically deuterated ribonucleoside triphosphates (NTPs). The synthesis and purification of deuterated NTPs are described in detail, as well as their application to the study of two RNAs: the sarcin-ricin loop (SRL) RNA - a biologically active region of ribosomal RNA - and a short RNA designed to lack secondary structure. Measurement of deuterium kinetic isotope effects (KIEs) on the cleavage of these RNAs suggests that it is possible to use this experiment to identify the GUA base triple structural motif that is commonly found in RNA. Abstraction of a 5' ribose hydrogen atom in RNA yields a fragment containing a 5'-aldehyde terminus with the sugar and base intact. Comparison of primer extension products of cleaved SRL RNA with or without deuterium substituted at the C5' ribose position of uracil residues demonstrated that the 5' aldehyde-terminated fragment can serve as a template for reverse transcription. Implications of the presence of a 5'-aldehyde terminus on hydroxyl radical cleavage analysis are discussed in the context of reverse transcriptase-mediated primer extension, a commonly used method. Structural features of naked DNA molecules with known protein binding sequences were explored using hydroxyl radical cleavage analyzed by capillary gel electrophoresis. An application was written in MATLAB to deconvolute and integrate cleavage intensities of hundreds of peaks in an electropherogram. In many cases, comparison of the cleavage profile to the minor groove width found in an X-ray co-crystal structure of the DNA-protein complex revealed a high degree of correlation.

The syntheses of siloxyl and hydroxyl chain end functionalized polystyrene and poly(methyl methacrylate) by Atom Transfer Radical Polymerization (ATRP) were effected by the following methods: (a) α-Siloxyl functionalized polymers were prepared in quantitative yields via a one-pot ATRP synthesis method for the polymerization of styrene or methyl methacrylate using a new siloxyl functionalized initiator adduct, formed in situ by the reaction of (1-bromoethyl)benzene with 1-(4-t-butyldimethylsiloxyphenyl)-1- phenylethylene in the presence of CuBr/bpy or CuBr/PMDETA as catalysts in diphenyl ether at 90 -110 oC. The polymerizations proceeded via controlled living radical polymerization methods and α-siloxyl functionalized polymers with predictable number average molecular weights (Mn = 1.8 x 103 - 17.40 x 103 g/mol), narrow molecular weight distributions (Mw /Mn = 1.03 - 1.41) and regiospecificity of the functional groups were obtained in quantitative yields. Similarly, the one-pot ATRP synthesis method for the preparation of α-bis(siloxyl) functionalized polymers were effected by the initiation of styrene or methyl methacrylate polymerization with a new bis(siloxyl) functionalized initiator adduct, formed by the in situ reaction of 1,1-bis(4-t-butyldimethylsiloxylphenyl)- ethylene with (1-bromoethyl)benzene in the presence of CuBr/bpy or CuBr/ PMDETA as catalytic systems in diphenyl ether at 90 -110 oC. Each polymerization reaction proceeded via a controlled living fashion to afford quantitative yields of the corresponding α-bis(siloxyl) functionalized polymers with predictable number average molecular weights (Mn = 1.7 X 103 - 15.00 x 103 g/mol), narrow molecular weight distributions (Mw /Mn = 1.03 - 1.35) and good control of chain end functionality. The acid catalyzed hydrolysis of α-siloxyl and α-bis(siloxyl) chain end functionalized polymers afforded the corresponding α-hydroxyl and α-bis(hydroxyl) chain end functionalized polymers, respectively. Polymerization kinetic data was employed to determine the controlled/living character of each ATRP reaction leading to the formation of different siloxyl functionalized chain end functionalized polymers. Polymerization kinetic measurements show that the polymerization follows first order rate kinetics with respect to monomer consumption and the number average molecular weight increases with percentage monomer conversion, resulting in the formation of polymers with narrow molecular weight distributions. Thin layer chromatography (TLC), 1H and 13C Nuclear Magnetic Resonance Spectrometry (NMR), Fourier Transform Infrared Spectroscopy (FTIR), Size Exclusion Chromatography (SEC), Gas Chromatography (GC) and non - aqueous titrations were used to determine the structures and purity of the siloxyl functionalized initiator precursors as well as the siloxyl and hydroxyl functionalized polymers.

Galactitol and cis,cis,cis-1,3,5-cyclohexanetriol are polyols that are ideal examples of model compounds for ligands with lanthanide ions as they have their hydroxyl groups in favourable steric arrangement. Several complexes were synthesised with both lanthanide chloride and lanthanide nitrate salts with galactitol, and a variety of structures, both polymeric and monomeric, were observed. In all these complexes, galactitol acted as a bridging molecule between the lanthanide ions. A notable difference was the lanthanum chloride–galactitol complex that showed both chloride and galactitol bridging. The lanthanide nitrate salts formed only polymeric complexes with galactitol. Not all of the complexes showed nitrate ions coordinated to the metal centre, and in the neodymium nitrate– galactitol complex, which shows both monodentate and bidentate coordination of the nitrate groups. The coordination of the nitrate ions was confirmed using both XRD and IR analysis. Two complexes with lanthanide chloride salts and cis,cis,cis-1,3,5-cyclohexanetriol were synthesised and analysed. Lanthanum chloride formed a polymeric complex, which showed extensive chloride bridging between the metal centres. Praseodymium chloride formed a dimeric complex. All complexes were analysed with single-crystal X-ray diffraction, 1H NMR, 13C NMR and IR spectroscopy.