No description available.

No description available.

No description available.

<p> This thesis provides examples ~f new solid supports for Matrix-Assisted Laser Desorption Ionization Time-of-Flight (MALDI-TOF) in two parts. </p> <p> Firstly, mesoporous and macroporous silicas were developed as new supports for the elimination of low mass interference signals in the mass spectrum. Due to the complexity of the system, a variety of factors were studied, such as sol gel morphology, matrix crystallization, polymeric molecular weight and concentration. It was observed that the mesoporous silicas and higher matrix crystallization were advantageous for optimal signal intensity and signal-to-background ratio. </p> <p> Secondly, due to the inconsistencies in the literature apropos the role of the matrix in MALDI process, we have developed chemically modified compounds and studied these as alternative MALDI matrices. It was concluded that for optimal free matrix performance, the phenolic groups were desirable while crystallization was not required. Moreover, a highly selective covalently linked silicon-based matrix was developed, which yielded a superior signal-to-background ratio at moderate signal intensities. A chemical nature of matrix and sol gel processing methodology used were the relevant factors to be considered when optimizing a tethered matrix. It was demonstrated that requirements for free and surface-bound matrices were different; hence, suggesting the drastic difference in their operating mechanisms during MALDI process. </p> / Thesis / Master of Science (MSc)

The threat of chemical warfare agent (CWA) attacks has persisted into the 21st century due to the actions of terror groups and rogue states. Traditional filtration strategies for soldier protection rely on high surface area activated carbon, but these materials merely trap CWAs through weak physisorption. Metal-organic frameworks (MOFs) have emerged as promising materials to catalyze the degradation of CWAs into significantly less toxic byproducts. The precise synthetic control over the porosity, defect density, and chemical functionality of MOFs offer exciting potential of for use in CWA degradation as well as a wide variety of other applications. Developing a molecular-level understanding of gas-MOF interactions can allow for the rational design of MOFs optimized for CWA degradation. Our research investigated the fundamental interfacial interactions between CWA simulant vapors, specifically sulfur mustard (HD) simulants, and zirconium-based MOFs (Zr-MOFs). Utilizing a custom-built ultrahigh vacuum chamber with infrared spectroscopic and mass spectrometric capabilities, the adsorption mechanism, diffusion energetics, and diffusion kinetics of HD simulants were determined. For 2-chloroethyl ethyl sulfide (2-CEES), a widely used HD simulant, infrared spectroscopy revealed that adsorption within Zr-MOFs primarily proceeded through hydrogen bond formation between 2-CEES and the bridging hydroxyls on the secondary building unit of the MOFs. Through the study of 1-chloropentane and diethyl sulfide adsorption, we determined that 2-CEES forms hydrogen bonds through its chlorine atom likely due to geometric constraints within the MOF pore environment. Temperature-programmed desorption experiments aimed at determining desorption energetics reveal that 2-CEES remain adsorbed within the pores of the MOFs until high temperatures, but traditional methods of TPD analysis fail to accurately measure both the enthalpic and entropic interactions of 2-CEES desorption from a single adsorption site. Infrared spectroscopy was able to measure the diffusion of adsorbates within MOFs by tracking the rate of decrease in overall adsorbate concentrations at several temperatures. The results indicate that 2-CEES diffusion through the pores of the MOFs is a slow, activated process that is affected by the size of the pore windows and presence of hydrogen bonding sites. We speculate that diffusion is the rate limiting step in the desorption of HD simulants through Zr-MOFs at lower temperatures. Stochastic simulations were performed in an attempt to deconvolute TPD data in order to extract desorption parameters. Finally, a combination of vacuum-based and ambient-pressure spectroscopic techniques were employed to study the reaction between 2-CEES and an amine-functionalized MOF, UiO-66-NH2. Although the presence of water adsorbed within UiO 66 NH2 under ambient conditions may assist in the reactive adsorption of 2-CEES, the reaction proceeded under anhydrous conditions. / Doctor of Philosophy / Chemical warfare agents (CWAs) are some of the most toxic chemicals on the planet and their continued use by terror groups and rogue nations threaten the lives of both civilians and the warfighter. Our work was motivated by a class of high surface area, highly porous materials that have shown the ability to degrade CWAs, specifically mustard gas, into less harmful byproducts. By determining the adsorption mechanism (how and where mustard gas “sticks” to the material), diffusion rates (how quickly mustard gas can travel through the pores of to reach the binding sites), and desorption energies (how strongly mustard gas “sticks” to the binding sites), we can alter the structure of these materials and to efficiently trap mustard gas and render it harmless. In the research described in this dissertation, we examined these fundamental interactions for a series of molecules that mimic the structure of mustard gas. and linear alkanes within several metal-organic frameworks with varying pore size. We observed the size of the pore environment affects the orientation that a given molecule sticks to binding sites as well as how quickly these compounds diffuse through the MOF. While the majority of these studies were conducted in a low-pressure environment that eliminated the presence of gas molecules in the atmosphere, research that exposed a MOF to a mustard gas mimic in an ambient environment demonstrated that gas molecules present in the atmosphere, especially water, can greatly impact the chemical interactions between mustard gas and zirconium-based MOFs.

Hydrogen bonds are arguably the most important reversible intermolecular forces. However, surprisingly few studies of their fundamental nature at the gas-surface interface have been performed. Our research investigated sulfur mustard (HD) adsorption by characterizing interfacial hydrogen bonding and dispersion forces for the simulant molecules 2-chloroethyl ethyl sulfide (2-CEES) and methyl salicylate on well-characterized hydroxyl-functionalized surfaces (silica and UiO-66). Our approach utilized infrared spectroscopy to study specific surface-molecule interactions and temperature-programmed desorption to measure activation energies of desorption. 2-CEES has two polar functional groups, the chloro and thioether moieties, available to accept hydrogen bonds from free surface silanol groups. Diethyl sulfide and chlorobutane were investigated to independently assess the roles of the chloro and thioester moieties in the overall adsorption mechanism and to explore the interplay between the charge transfer and electrostatic contributions to total hydrogen bond strength. The results indicate that both SiOH---Cl and SiOH---S hydrogen bonds form when 2-CEES adsorbs to silica or hydroxylated UiO-66. However, a more stable configuration in which both polar groups interact simultaneously with adjacent silanol groups likely does not form. A systemaic study of chloroalkanes revealed that dispersion forces involving the methylene units in 2-CEES contribute to nearly half of the total activation energy for desorption from silica. Methyl salicylate possesses aromatic, hydroxyl, and ester functional groups, each of which is a potential hydrogen bond acceptor. We found that uptake on silica is mainly driven by the formation of carbonyl-silanol and hydroxyl-silanol hydrogen bonds with additional contributions from weaker interactions. In an effort to learn more about the SiOH---π bond, the adsorption of simple substituted benzene derivatives on silica was investigated to probe the effects of electron withdrawing and donating substituents. Results indicate that the substituted benzene derivatives adsorb to silica via a cooperative effect involving SiOH---π hydrogen bonds and additional substituent-surface interactions. The strength of the SiOH---π bond is enhanced by electron donating groups and weakened by electron withdrawing groups. / Ph. D.

Polyethylene pipes and epoxy or polyurethane linings are increasingly used in drinking water infrastructure. As a recent introduction to the water industry, there are still many unknowns about how polymers will behave in the distribution system specifically relating to sorption and desorption of chemical contaminants. This study is in response to a spill of 4-methylcyclohexane methanol (MCHM) that occurred in January 2014 contaminating the drinking water of nine counties in West Virginia. This study investigated sorption and desorption of the odorous chemical MCHM into polymer drinking water infrastructure and granular activated carbon (GAC). Experiments for sorption of non-polar toluene and polar 1-butanol were conducted as a comparison for MCHM sorption. Additionally, a brief odor analysis was done on the ability of activated carbon to remove odor from contaminated water and on leaching of MCHM from pipe material into clean water. The results show that MCHM diffusion and solubility in polyethylene pipe materials is low. Solubility in polyethylene ranged from 0.003-0.008 g/cm3 and was more similar to the polar contaminant n-butanol than the non-polar contaminant toluene. Desorption experiments indicated that MCHM sorbed to polyethylene diffused back into water at levels that produced odor. MCHM diffused very quickly into epoxy; its solubility was similar to polyethylene pipe. MCHM caused the polyurethane lining to swell and deform. Granular activated carbon effectively sorbed MCHM to below its odor threshold. The sorption properties of MCHM indicate the potential for contamination of infrastructure and the desorption indicates subsequent recontamination of drinking water. / Master of Science

4-(12-mercaptododecyloxy)phenol (1), 3-(12-mercaptododecyloxy)phenol (2), 4-(12-mercaptododecyl)phenol (3), 4-(12-mercapto-dodecyl)phenol (4), 12-phenyldodecyl-mercaptan (5), 12-phenylundecyoxymercaptan (6), 4-(6-mercapto-hexyl)phenol (7), and 4-(12-mercaptododecyloxy)phenol (8) were synthesized. The thiol products were characterized by NMR, HRMS, and elemental analysis. Self-assembled monolayers (SAMs) on gold substrates were prepared from thiols 1-8, and the resulting monolayer surfaces were analyzed using Reflectance Absorbance Infrared Spectroscopy (RAIRS), contact angle goniometry, ellipsometry, reductive desorption cyclic voltametry, and impedance spectroscopy. Several aromatic C-C vibrational frequencies in the RAIRS spectra, for SAMs of 1-8, reveal a dependence of peak intensity on substitution regiochemistry of the aromatic ring. This result suggests that the orientation of the aromatic ring changes with substitution. Peak intensity, and peak widths of alkyl C-H vibrational features in the RAIRS spectra also reveal a dependence of the environment of the alkyl chain on structure of thiols 1-8. Meta-substitution seems to significantly alter the projection of the terminal -OH group relative to para-substitution. Contact angles were obtained for each SAM surface using water, glycerol, and ethylene glycol. From the contact angle data, Zisman and Fowkes analyses were performed in order to determine surface free energy values and also to determine the dispersive contribution to the surface energy. The energy values obtained from the Zisman plots as well as the dispersive contributions obtained from the Fowkes plots suggest a dependence of surface energy on substitution regiochemistry of the aromatic ring. The results are consistent with the interpretation of the RAIRS spectra as they relate to the effect substitution regiochemistry has on SAM structure and interfacial properties. The results of the reductive desorption measurements performed on each monolayer surface, indicate that changes in substitution regiochemistry do not seem to affect the surface coverage of SAMs 1-8. Desorption potentials however, are affected by the structure of the thiols composing the SAM, which suggests that the lateral stability resulting from interactions of the terminal groups and alkyl chains, is different for each monolayer surface. Specifically SAMs of 12-phenyldodecylmercaptan (5) and SAMs of 4-(12-mercaptododecyloxy)phenol (1) seem to be more stable due to interactions of the terminal aromatic ring in SAMs of (5) and due to an increase in van der Waals interactions in SAMs of (1). Film thicknesses, as determined by ellipsometry, also suggest that meta-substitution of the aromatic ring results in lower thicknesses for SAMs of (4), which is consistent with the interpretation of the structural changes resulting from meta-substitution, suggested by the interpretation of the RAIRS spectrum of SAMs of (4). Thickness measurements also indicate that most of the functionalized SAMs (1-4, 7, 8) react with OTS, which suggests the terminal -OH group is not shielded at the interface and is available for reaction. Following reaction with OTS the RAIRS spectra of the reacted surfaces reveal structural changes to the underlying SAM. Impedance spectroscopic measurements performed on SAMs of 1-8 reveal what seems to be a correlation between the orientation of the aromatic ring and the resistance properties of the SAM. It appears meta-substitution of the ring lowers the monolayers ability to resist electron transfer. These data suggest that meta-substitution of the aromatic ring has a significant impact upon the structure of the resulting monolayer relative to monolayers composed of para-substituted molecules. The data also suggests that there is a correlation between molecular structure and interfacial properties particularly as it relates to surface energy and reactivity. Small atomic changes in the molecules composing the SAM result in measurable differences in macroscopic properties of the interface. It is important to recognize the need for understanding structure-property relationships in self-assembled monolayers particularly if logical design of surfaces is to be achieved and applied towards solving problems associated with corrosion and adhesion of metal surfaces. / Ph. D.

Trace metal concentrations in soil solution, and hence trace metal bioavailability and toxicity, are primarily controlled by sorption/desorption reactions at the mineral-water interface. While numerous studies have been conducted to understand the initial adsorption of these metals to soil minerals, less in known about long-term adsorption/ desorption processes. The objective of this study was to examine the influence of residence time and organic acids on the desorption of Pb2+and Cd2+ from goethite. Adsorption experiments were conducted at pH 6.0. Lead adsorption was nearly completed after 4 hours, with very little additional sorption during a 20-week period. In contrast cadmium showed a continuous slight increase in the amount of adsorption over the 20-week period. Desorption experiments were conducted at pH 4.5 and similar to previous studies examining trace metal desorption from oxide surfaces, the desorption kinetics for Pb2+and Cd2+ were slow compared to the sorption reaction. None of the experiments were completely reversible after an eight-hour desorption period. For all experiments except long-term Pb2+ desorption, the quantity of metal desorbed from goethite followed the order salicylate >NaNO3 > oxalate. Based on differences in cation affinity for the iron oxide surface one would expect a greater quantity of Cd2+ to be removed compared to Pb2+, for each of the extracting solutions. However at a pH of 4.5 we did not find a statistically significant trend. We observed a difference between the amount of metal removed for short and long-term experiments in five of six experiments, but these differences were only significant for Pb2+ experiments in the presence of salicylate. Two first order rate equations best fit the kinetics of trace metals desorption, with R2 values greater than 0.910 in all cases. Although our results show a decrease in rate coefficients (expect k1 for oxalate) with increased residence time, statistical analysis indicates that these results were only significant for Pb2+ experiments in the presence of salicylate. However raw and transformed data both suggest that desorption values are diverging as a function of aging time. Similar to other researchers we believe that Pb2+ and Cd2+ are sequestered by the goethite surface with an increase in residence time. These results suggest that residence time effects observed by many researchers are much less prevalent at low pH values. Therefore a reduction in soil pH created by natural anthropogenic processes may reduce the ability of soils to naturally sequester metals over time. / Master of Science

京都大学 / 新制・課程博士 / 博士(農学) / 甲第25320号 / 農博第2586号 / 京都大学大学院農学研究科森林科学専攻 / (主査)教授 髙野 俊幸, 教授 上髙原 浩, 教授 和田 昌久 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM