Browsing by Subject "aromatic"
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Item Chemisorption of Aromatic Compounds on Well-Defined Palladium Surfaces: Studies by Electron Spectroscopy and Electrochemistry(2010-10-12) Li, DingThe chemisorption of aromatic compounds, derivatized with different functional groups, on well-defined Pd(111) surfaces was studied by a combination of Auger electron spectroscopy (AES), low energy electron diffraction (LEED), high resolution electron energy loss spectroscopy (HREELS), and electrochemistry (EC). The results of this work led to the following trends and conclusions: (a) At low concentrations, 2,5-dihydroxythiophenol (DHT) chemisorbs on a Pd surface through both diphenolic ring and thiol group. At high concentrations, it chemisorbs only through the thiol group. (b) There is extensive intermolecular attraction between the co-adsorbed thiolated quinone and thiolated hydroquinone molecules. The interaction occurs through the Pd substrate and not through space. (c) The chemisorption properties of Nheteroaromatic compounds are pH-dependent. When the nitrogen heteroatom is protonated, it becomes very weakly surface-active. When the nitrogen heteroatom is deprotonated, surface activity stronger than the diphenolic ring is exhibited. (d) On a palladium surface, the binding strengths of ligands increase in the order: phenyl ring < quinonoid ring, < N-heteroatom < I < -SH.Item Development of an Intact Muscle Pork Flavor Lexicon(2015-02-27) Chu, Sarah KatherineA fresh intact muscle pork flavor lexicon was developed by obtaining cuts of pork (pork loins, shoulders, picnics, tenderloins, fresh ham legs, bellies, enhanced picnics and pork chops) from retail grocery stores. Varying cooking temperatures, cooking techniques, and cuts induced differences in flavors and aromas. These cuts were cooked to various internal temperature endpoints (57.2?C, 62.7?C for roasts, 68.3?C, and 79.4?C) utilizing a high temperature cooking method for chops, and roasting and/or braising for whole muscle cuts. Five highly trained panelists identified and defined twenty-four aroma and flavor attributes. Pork identity, brown/roasted, bloody/serumy, metallic, and fat-like flavor aromatics, and astringent feeling factors, and 4 of the 5 basic tastes were most prevalent in samples. Validation of the pork lexicon was performed. Trained panelists evaluated tenderloin medallions, and loin chops, inside ham chops, and shoulder chops cooked to four internal endpoint temperatures (62.7?C, 68.3?C, 73.8?C, and 79.4?C). Pork identity, brown/roasted, fat-like, bloody/serumy, metallic, liver-like, and nutty flavor aromatics, and astringent feeling factors, and sweet, sour, salty, bitter, and umami basic tastes were present in samples. All attributes but bitter basic taste (P > 0.05) differed across cuts (P < 0.05). All samples had moderate levels of pork identity flavor aromatics. Umami basic taste and liver-like, nutty, and fat-like flavor aromatics and astringent feeling factors were barely detectable. Shoulder chops were higher in pork identity and fat-like flavor aromatics and umami basic taste. Inside ham chops were higher in astringent feeling factors and metallic flavor aromatics, and sour and bitter basic tastes. Brown/roasted, bloody/serumy, and metallic flavor aromatics, and astringent feeling factors, and sour and bitter basic tastes differed across internal endpoint temperatures (P < 0.05). As internal endpoint temperatures increased, brown/roasted flavor aromatics increased, while bloody/serumy flavor aromatics and astringent feeling factors, and sour and bitter basic tastes decreased. Gas chromatography with olfactory sniff ports detected volatile aromatic compounds (n=157) found in the samples. Stepwise linear regression equations and simple correlation coefficients were calculated. Stepwise equations used 50, 42, 43, 58, 33, 37, 75, 53, and 42 compounds to account for 93, 91, 83, 94, 77, 87, 96, 88, and 83% of pork identity, brown/roasted, fat-like, bloody/serumy, and metallic flavor aromatics, and astringent feeling factors, and sour, salty, and bitter basic tastes, respectively which determined volatile aroma compounds that may explain variance of trained descriptive attributes. Sulfur-containing compounds, nitrogen-containing compounds, aldehydes, ketones, acids, alkanes, alkenes, furans, pyrazines, and benzenes influenced pork flavor. Aldehydes were quantitatively higher than other compound classes. Aromatic compounds that clustered with treatments and flavor aromatic attributes varied in partial least squares regression biplots, with a large number of treatments and attributes that clustered with aldehydes and alcohols, and treatments that were cooked to higher internal endpoint temperatures clustered with compounds such as pyrazines and thiazoles.Item Photochemistry of aromatic hydrocarbons: implications for ozone and secondary organic aerosol formation(Texas A&M University, 2006-08-16) Suh, InseonAromatic hydrocarbons constitute an important fraction (~20%) of total volatile organic compounds (VOCs) in the urban atmosphere. A better understanding of the aromatic oxidation and its association in urban and regional ozone and organic aerosol formation is essential to assess the urban air pollution. This dissertation consists of two parts: (1) theoretical investigation of the toluene oxidation initiated by OH radical using quantum chemical and kinetic calculations to understand the mechanism of O3 and SOA precursors and (2) experimental investigation of atmospheric new particle formation from aromatic acids. Density functional theory (DFT) and ab initio multiconfigurational calculations have been performed to investigate the OH-toluene reaction. The branching ratios of OH addition to ortho, para, meta, and ipso positions are predicted to be 0.52, 0.34, 0.11, and 0.03, respectively, significantly different from a recent theoretical study of the same reaction system. Aromatic peroxy radicals arising from initial OH and subsequent O2 additions to the toluene ring are shown to cyclize to form bicyclic radicals rather than undergoing reaction with NO under atmospheric conditions.Isomerization of bicyclic radicals to more stable epoxide radicals possesses significantly higher barriers and hence has slower rates than O2 addition to form bicyclic peroxy radicals. At each OH attachment site, only one isomeric pathway via the bicyclic peroxy radical is accessible to lead to ring cleavage. Decomposition of the bicyclic alkoxy radicals leads primarily to formation of glyoxal and methyl glyoxal along with other dicarbonyl compounds. Atmospheric aerosols often contain a considerable fraction of organic matter, but the role of organic compounds in new nanometer-sized particle formation is highly uncertain. Laboratory experiments show that nucleation of sulfuric acid is considerably enhanced in the presence of aromatic acids. Theoretical calculations identify the formation of an unusually stable aromatic acid-sulfuric acid complex, which likely leads to a reduced nucleation barrier. The results imply that the interaction between organic and sulfuric acids promotes efficient formation of organic and sulfate aerosols in the polluted atmosphere because of emissions from burning of fossil fuels, which strongly impact human health and global climate.