Yes / The stereochemical outcome of the epoxidation of Δ14–15 cholestanes with mCPBA is controlled by the steric bulk of a C17 substituent. When the C17 is in the β configuration, the epoxide is formed in the α face, whereas if the C17 is trigonal (flat) or the substituent is in the α configuration, the epoxide is formed in the β face. The presence of a hydroxyl substituent at C20 does not influence the stereochemical outcome of the epoxidation. / We thank University of Bradford for a bursary (MA).

The chemical aging of organic aerosols by OH-initiated heterogeneous oxidation was investigated using both model organic and ambient aerosol particles. Organic aerosol particles were exposed to OH radicals in an aerosol flow tube and the modification of their chemical composition and particle properties was studied. Overall, this work has shown that OH-initiated heterogeneous oxidation enhanced the degree of oxidation and the Cloud Condensation Nucleus (CCN) activity of organic aerosol particles for equivalent OH exposure timescales of a few days to a week. Aerosol Mass Spectrometer (AMS) measurements showed that the heterogeneous uptake kinetics of OH radicals onto model primary organic aerosols was efficient. The heterogeneous reaction of organic aerosols with OH led to the production of high molecular weight particle-phase species with the addition of multiple oxygenated functional groups. These results were consistent with the observed increase in particle density with OH exposure. With the exception of solid organic aerosols, the particle volume and mass of organic particles were reduced by less than 20% from OH oxidation at high OH exposures due to volatilization of particle-phase reaction products. The degree of oxidation of the organic fraction of urban ambient aerosols was significantly enhanced for an equivalent atmospheric OH exposure time of 4 days for a daily average atmospheric OH concentration of 2×106 cm-3. Ambient aerosol particles sampled from a sparsely populated, forested region were initially more oxygenated than the urban aerosol particles and did not become more oxidized from reaction with OH radicals. The modification of the hygroscopicity of model primary and secondary organic aerosols from chemical aging was investigated by measuring the CCN activity of organic aerosols exposed to OH radicals. Primary organic aerosols, initially CCN inactive, became as CCN active as secondary organic aerosols due to heterogeneous reaction, where surface tension reduction played a major role. The CCN activity for model secondary organic aerosols was also enhanced due to OH oxidation, but changes were less dramatic than for the model primary organic aerosols.

Choi, Lai Sheung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 111-115). / Abstracts in English and Chinese. / Contents --- p.i / Acknowledgements --- p.iv / Abstract --- p.v / Abbreviations --- p.viii / Chapter Chapter 1 - --- Introduction to Dendrimer / Chapter 1.1 --- Definition --- p.1 / Chapter 1.2 --- Synthetic Routes --- p.2 / Chapter 1.2.1 --- Divergent Growth --- p.2 / Chapter 1.2.2 --- Convergent Growth --- p.3 / Chapter 1.3 --- Applications --- p.4 / Chapter 1.4 --- Examples of Dendrimers --- p.6 / Chapter 1.4.1 --- Hydrocarbon Dendritic Species --- p.6 / Chapter 1.4.2 --- Aliphatic Polyether Dendritic Species --- p.8 / Chapter Chapter 2 - --- Synthesis of Novel Amphiphilic Hydrocarbon Dendrons / Chapter 2.1 --- Background - Hydrocarbon Dendrons (HCDs) --- p.11 / Chapter 2.2 --- Modification and Design of Synthetic Scheme --- p.13 / Chapter 2.3 --- Syntheses --- p.14 / Chapter 2.3.1 --- Convergent Synthesis --- p.14 / Chapter 2.3.2 --- Divergent Synthesis --- p.19 / Chapter 2.4 --- Characterizations --- p.22 / Chapter 2.4.1 --- 1H NMR Spectroscopy --- p.22 / Chapter 2.4.2 --- 13C NMR Spectroscopy --- p.25 / Chapter 2.4.3 --- Mass Spectrometry --- p.27 / Chapter 2.4.4 --- Gel Permeation Chromatography (GPC) --- p.29 / Chapter 2.4.5 --- Thin Layer Chromatography (TLC) --- p.31 / Chapter 2.4.6 --- Solubility --- p.31 / Chapter 2.5 --- Conclusions and Future Prospects --- p.33 / Chapter Chapter 3 - --- Hydrogen Bonding in Supramolecular Chemistry / Chapter 3.1 --- Background ´ؤ Supramolecular Chemistry --- p.35 / Chapter 3.1.1 --- Multiple Hydrogen Bondings --- p.37 / Chapter 3.1.2 --- Applications --- p.39 / Chapter 3.2 --- 2-Ureido-4[lH]-Pyrimidinone (UPy) --- p.40 / Chapter 3.2.1 --- Tautomerization and Dimerization Equilibria --- p.40 / Chapter 3.2.2 --- Examples of Dendronized UPy Dimers --- p.44 / Chapter 3.3 --- Effects of Substituents on the Dimerization Behavior of UPy --- p.46 / Chapter 3.4 --- Dimerization Studies on Our New UPy-Dendrons --- p.50 / Chapter Chapter 4 - --- "Synthesis, Characterizations and Dimerization Properties of Dendronized UPy Dimers" / Chapter 4.1 --- Synthesis --- p.51 / Chapter 4.2 --- Characterizations --- p.51 / Chapter 4.2.1 --- 1H NMR Spectroscopy --- p.51 / Chapter 4.2.1.1 --- Dimerization Behavior of Protected UPy Series (94-97) in CDC13 at 25 °C --- p.52 / Chapter 4.2.1.2 --- Temperature-Dependent Behavior of Protected UPy Series (94´ؤ97) in CDC13 --- p.59 / Chapter 4.2.1.3 --- Tautomeric Behavior of Protected UPy Series in (94-97) in Other Solvents --- p.60 / Chapter 4.2.1.4 --- Characterization of Deprotected UPy Series (98-101) in DMSO-d6 --- p.60 / Chapter 4.2.1.5 --- Dimerization Behavior of Deprotected UPy Series (98-101) in THF-d8 and Other Solvents --- p.63 / Chapter 4.2.1.6 --- Temperature-Dependent Behavior of Deprotected UPy Series (98´ؤ101) in THF-d8 --- p.67 / Chapter 4.2.1.7 --- Dimerization Constants of Both Protected and Deprotected UPy Series in DMSO-d6/CDCl3 Mixtures at 25 °C --- p.68 / Chapter 4.2.2 --- 13C NMR Spectroscopy --- p.71 / Chapter 4.2.3 --- Mass Spectrometry --- p.71 / Chapter 4.2.4 --- Gel Permeation Chromatography (GPC) --- p.73 / Chapter 4.2.5 --- Vapour Pressure Osmometry (VPO) --- p.74 / Chapter 4.2.6 --- Infrared Spectroscopy --- p.75 / Chapter 4.2.7 --- Polarity and Solubility --- p.76 / Chapter 4.3 --- Conclusions --- p.77 / Chapter Chapter 5 - --- Conclusions --- p.79 / Chapter Chapter 6 - --- Experimantal Procedures / Chapter 6.1 --- General Information --- p.81 / Chapter 6.2 --- Experimantal Procedures --- p.82 / References --- p.111 / Appendix 1 - Calculations of lower-limits of Kdim* in CDCI3 --- p.A-1 / Appendix 2 - Calculations of Kdim* in systems where both dimer(s) and 6[1H] monomer coexist --- p.A-4 / Appendix 3 - List of Spectra --- p.A-5

No description available.

The chemical aging of organic aerosols by OH-initiated heterogeneous oxidation was investigated using both model organic and ambient aerosol particles. Organic aerosol particles were exposed to OH radicals in an aerosol flow tube and the modification of their chemical composition and particle properties was studied. Overall, this work has shown that OH-initiated heterogeneous oxidation enhanced the degree of oxidation and the Cloud Condensation Nucleus (CCN) activity of organic aerosol particles for equivalent OH exposure timescales of a few days to a week. Aerosol Mass Spectrometer (AMS) measurements showed that the heterogeneous uptake kinetics of OH radicals onto model primary organic aerosols was efficient. The heterogeneous reaction of organic aerosols with OH led to the production of high molecular weight particle-phase species with the addition of multiple oxygenated functional groups. These results were consistent with the observed increase in particle density with OH exposure. With the exception of solid organic aerosols, the particle volume and mass of organic particles were reduced by less than 20% from OH oxidation at high OH exposures due to volatilization of particle-phase reaction products. The degree of oxidation of the organic fraction of urban ambient aerosols was significantly enhanced for an equivalent atmospheric OH exposure time of 4 days for a daily average atmospheric OH concentration of 2×106 cm-3. Ambient aerosol particles sampled from a sparsely populated, forested region were initially more oxygenated than the urban aerosol particles and did not become more oxidized from reaction with OH radicals. The modification of the hygroscopicity of model primary and secondary organic aerosols from chemical aging was investigated by measuring the CCN activity of organic aerosols exposed to OH radicals. Primary organic aerosols, initially CCN inactive, became as CCN active as secondary organic aerosols due to heterogeneous reaction, where surface tension reduction played a major role. The CCN activity for model secondary organic aerosols was also enhanced due to OH oxidation, but changes were less dramatic than for the model primary organic aerosols.

Universiẗat, Diss.--Kiel, 2004.

Thesis (Ph. D.)--University of Nebraska, 1937. / Bibliography: p. 20.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1958. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 178-182).

Techn. Universiẗat, Diss., 2002--Berlin.

Thesis (Ph.D.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / We have constructed a database of hydroxyl radical (•OH) cleavage patterns of DNA in order to investigate the relationship between the sequence of a DNA molecule and its three-dimensional structure. The hydroxyl radical cuts DNA at every nucleotide, with the amount of cutting proportional to the solvent accessible surface area (SASA) of the deoxyribose hydrogen atoms. Cleavage fragments are quantified by a fluorescence sequencer, followed by normalization and deposition into the database. Our database currently contains 151 DNA sequences with lengths ranging from 35 to 41 nucleotides. These data have enabled us to develop some general rules regarding the sequence-dependence of DNA structure as well as to predict the cleavage pattern of any given DNA sequence with remarkable precision. Using this prediction algorithm, it is possible to construct structural maps of entire genomes. As there are many examples of DNA binding proteins with highly degenerate binding sites, the use of structural information to locate these sites may be helpful. There also exists other signals, including the signal for nucleosome positioning, which have no apparent consensus, making it likely that the structure of DNA is of critical importance. We have developed algorithms to identify regions of conserved structure using •OH cleavage intensity as a proxy. Within a set of DNase I hypersensitive sites (DHS) obtained from the ENCODE Consortium, we were able to identify a stretch of 12 nucleotides for which the structural conservation is much greater than the sequence conservation. These sites have been dubbed Conserved •OH Radical Cleavage Signatures, or CORCS. Upon further analysis, these CORCS were found to be 17-fold enriched for DHS as compared to shuffled elements. Through the continued analysis of hydroxyl radical cleavage data and development of algorithms to employ the data in biologically meaningful ways, we hope to further our understanding of the relationship between DNA sequence and structure, and how the local structural heterogeneity of genomic DNA contributes to biological function. / 2031-01-02