Motivated by recent experiments in gas-surface chemistry, we report our results from computational investigations of heterogeneous systems relevant to atmospheric chemistry and protection against chemical weapons. To elucidate findings of ultra-high vacuum experiments that probe the oxidation of carbon-carbon double bonds on model surfaces, we used electronic structure and QM/MM methods to study the reaction of ozone with C60-fullerene and the products of nitrate addition to a vinyl-terminated self-assembled monolayer. In the first system, we followed a reaction pathway beginning with primary ozonide formation through the formation of stable products. Theoretical vibrational spectra were used to identify a ketene product in prior experimental work. Next, through the construction of a multilayer model for the initial addition product of a nitrate radical to a chain embedded within a self-assembled monolayer, we report theoretical spectra that are consistent with experimental results. We then examined the fundamentals of the hydrolysis mechanism for nerve agents by a catalyst of interest in the development of filtration materials for chemical-warfare-agent defense. By following the gas-surface reaction pathway of the nerve agent Sarin on the Lindqvist polyoxoniobate Cs8Nb6O19, we determined that the rate-limiting step is the transfer of a proton from an adsorbed water molecule to the niobate surface, concomitant with the nucleophilic addition of the nascent hydroxide to the phosphorus atom in Sarin. Our results support a general base hydrolysis mechanism, though high product-adsorption energies suggest that thermal treatment of the system is required to fully regenerate the catalyst. We report similar mechanisms for the simulants dimethyl methylphosphonate and dimethyl chlorophosphate, though the latter may serve as a better simulant in studies of this type. Finally, an investigation of Sarin hydrolysis with solvated Cs8Nb6O19 shows an increase in the rate-limiting barrier relative to the gas-surface system, revealing the role of Cs counterions in the reaction. Then, we further increased explicit solvation to model the homogeneous solution-phase reaction, finding a different mechanism in which a water molecule adds to phosphorus in the rate-limiting step and protonation of the niobate surface occurs in a subsequent barrierless step. By examining the rate-limiting barrier for protonation, we suggest that specific base hydrolysis is also likely in the homogeneous system. / Ph. D.

he interactions of the chemical warfare agent sulfur mustard with amorphous silica were investigated using electronic structure calculations. In this thesis, the binding energies of sulfur mustard and mimic species used in the laboratory were calculated using density functional theory and fully ab initio calculations. The wB97XD and B97D functionals, which include functions to account for long-range dispersion interactions, were compared to experimental trends. The hydroxylated amorphous silica surface was approximated using a gas-phase silanol molecule and clusters containing a single hydroxyl moiety. Recent temperature programmed desorption experiments performed in UHV concluded that sulfur mustard and its less toxic mimics undergo molecular adsorption to amorphous silica. Hydrogen bonding can occur between surface silanol groups and either the sulfur or chlorine atom of the adsorbates, and the calculations indicate that the binding energies for the two hydrogen bond acceptors are similar. The adsorption of sulfur mustard and its mimics on silica also exhibits the presence of significant van der Waals interactions between alkyl of the adsorbates and the surface. These interactions, in combination with the formation of a hydrogen bond between a surface silanol group and the Cl or S atoms of the adsorbates, provide remarkably large binding energies. / Master of Science

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.

Doctor of Philosophy / Department of Chemical Engineering / Jennifer L. Anthony / Zeolites and zeolite-like materials have well-ordered structures and pores creating varying capacities for molecules based upon size, functional groups, polarity, and intermolecular forces making the materials useful for molecular sensing as well for molecules that are considered hazardous at very low concentrations with reproducible results because of these properties. This study will identify and characterize applications for zeolite and zeolite-like materials in gas and liquid phases based upon the dominating physical and chemical properties of the materials. The properties of interest include liquid phase ion exchange capacities, selectivities, gas/vapor phase adsorption capacity, and initial adsorption uptake rate. Zincosilicates have similar framework structures to aluminosilicate zeolites; however, they have distinct advantages over traditional zeolites. Zincosilicates typically have a higher ion density, lack “cages” in their structure which leads to all the cations being accessible for ion exchange, and have the ability to form three-membered rings which lead to large void spaces in their structure. These features lead to high capture capacities for divalent heavy metal mercury ions. In this work, the potential to use zincosilicates as ion exchangers such as VPI-7, VPI-9 and VPI-10 is presented. Results have shown that zincosilicates have capture capacities greater than traditional zeolites, even greater than those that have been synthesized with functional groups intended to increase metal sorption capacities. The selectivity coefficients in a binary ion exchange system were successfully modeled using the Gibbs-Donnan selectivity model. The selectivities for the zincosilicates were Pb>Na>Hg>K>Ca. Zeolites are also able to adsorb chemical species and therefore can be used as the recognition element in sensing devices. The sorption capacity of 2-chloroethyl ethyl sulfide, dimethyl methanephosphonate, ethanol, and n-butanethiol were examined with zeolites 13X, 4A, MCM-41, VPI-7, VPI-9, and ZSM-5. The zeolites selected provided very different framework composition, countercation, and surface area features for determining the most significant properties in adsorption. Zeolite 13X had the highest equilibrium and initial uptake rate for most compounds tested, whereas the low surface area zincosilicates, VPI-7 and VPI-9, had the lowest capacity. Based on these results, a piezoelectric device with an array of zeolites can be successfully employed as a sensor.

Prodigiosins and tambjamines are natural compounds from bacterial and marine sources belonging to a family containing a common 4-methoxy-2,2'-bipyrrole core. These compounds have received a lot of interest due to their promising biological activities. Studies have suggested DNA as a potential therapeutic target for the natural prodigiosin and tambjamine due to their ability to facilitate oxidative DNA cleavage in the presence of Cu2+. Based on this we sought to study the metal binding activity of new prodigiosin and tambjamine analogues. A new prodigiosin analogue was synthesized and complexed with Cu2+. This revealed 1:1 complex formation between the tripyrrole and Cu2+ that was confirmed by mass spectra and NMR spectra analysis. In addition in situ studies also revealed that our new analogues of prodigiosin cannot bind Zn2+ when the methoxy group on ring B is replaced by an alkyl group or when one of the ring nitrogens is methylated. Our UV-Vis experiments with calf thymus DNA showed that prodigiosins and tambjamines bind DNA mainly through an external mode, suggesting that hydrogen bonding between the pyrrole ring nitrogens and the bases of DNA takes precedence over stacking interactions. For the new Cu2+ complex synthesized however, we observed spectral changes that suggest intercalation into DNA. DNA cleavage experiments revealed that the prodigiosin-Cu complex is able to convert supercoiled DNA into its linear form. The data from the gel shift assays fit well to a first-order consecutive reaction model. In addition to preformed metal complexes, we showed DNA cleavage by in situ complexation of the ligands in the presence of Cu2+. However, although we showed Zn2+ complex formation with prodigiosin analogues, in situ studies did not show induction of DNA cleavage by Zn2+ complexes under our experimental conditions.

Thesis (Ph. D. (History))--Rhodes University, 2006.

Thesis (M.S.P.H.)--Uniformed Services University of the Health Sciences, 2006 / Typescript (photocopy)

Tesis (MPhil) -- Universiteit van Stellenbosch, 2000. / ENGLISH ABSTRACT: When rumours started circulating in 1998 that former president Nelson Mandela and Mrs Graca Machel were about to get married, Mandela's spokesman at the time, Parks Mankahlana, vehemently denied them. Mankahlana was the gatekeeper who decided what information about Mandela' s impending marriage would be made available to the rest of the world. The entire incident became somewhat of an embarrassment for Mandela's office, resulting in the former president trying hard to cover for Mankahlana at subsequent media conferences. In the end it became a case of trying to unravel who had lied to whom, who had given whom instructions to say what, and who had been in the know and at what stage, etc. A similar incident ensued following an assassination attempt on former American president Ronald Reagan in 1981. Initially his media office kept the gates firmly shut by alleging he had been only slightly injured. Later it emerged he'd been much more seriously injured than the White House had initially intimated. Between 1996 and 1998 South Africa's Truth and Reconciliation Commission investigated human rights violations since 1960. The South African and foreign media were faced with the challenge of presenting witness accounts of the numerous attrocities in a palatable form. Despite these attempts media managers at Cape Town's two English-language dailies in particular detected a measure of reader resistance to "bad news" which made readers feel" powerless", and they consequently had to adopt a careful approach. The TRC could not be ignored, but the often gruesome details which came to light could not willy nilly be stuffed down readers' throats. Gatekeeping had to be exercised with the greatest circumspection and the news filters prudently regulated. This study attempts to illustrate the concept of gatekeeping by analysing the coverage the three Cape Town dailies, the Cape Argus, Cape Times and Die Burger, gave the most sensational sessions of the Truth and Reconciliation Commission. In June and July 1998 about 10 men, each of them doctors or generals, gave evidence about their involvement in the stockpiling of chemical and biological weapons for South Africa's arsenal. Reporters were confronted with a major challenge to comply with the journalistic rigours set by this session. This study concentrates on reports of the different version of events given by four prominent witnesses, Dr Wouter Basson, former project leader of South Africa's chemical and biological weapons programme, his commanding officer and former surgeon general Lieutenant General Niel Knobel, General Lothar Neethling, former head of the police's forensic laboratory, and Dr Jan Lourens, biomedical engineer and the first witness to take the stand. To illustrate the phenomenon of gatekeeping interviews were held with nine journalists at the three newspapers to determine their views and perceptions, and the effect of these on the phenomenon of gatekeeping. Aspiring media managers, media managers, reporters and anyone performing a gatekeeping role may find the findings of this study useful. / AFRIKAANSE OPSOMMING: Toe gerugte in 1998 die rondte begin doen het dat oudpres. Nelson Mandela en mev. Graca Machel trouplanne het, het Mandela se woordvoerder, Parks Mankahlana, dit heftig ontken. Mankahlana was die hekwagter wat besluit het watter inligting oor Mandela se trouplanne aan die wereld deurgelaat word. Die hele episode het op 'n halwe verleentheid vir die president se kantoor uitgeloop met Mandela wat op daaropvolgende mediakonferensies verwoed probeer skerm het vir Mankahlana en dit 'n geval geword het van wie het gelieg en wie het vir wie opdrag gegee om sus of so te se en wie het wat in watter stadium geweet, ens. 'n Soortgelyke episode het hom afgespeel met 'n sluipmoordaanval op pres. Ronald Reagan van Amerika in 1981. Aanvanklik het sy mediakantoor ook die hekke redelik styftoe gehou deur te beweer hy is net lig beseer. Later het dit geblyk hy was veel ern stiger beseer as wat die Wit Huis aanvanklik bereid was om te erken. Suid-Afrika se Waarheids-en-versoeningskommissie het tussen 1996 en 1998 kragtens wet menseregteskendings sedert 1960 ondersoek. Die Suid-Afrikaanse en buitelandse media het 'n stewige uitdaging op hande gehad om talle gruwels uit die monde van getuies in verteerbare dosisse die wereld in te stuur. 'n Mate van lesersweerstand vir "slegte nuus" wat lesers "magteloos" laat voel het, is nietemin deur mediabestuurders by veral Kaapstad se twee Engelstalige dagblaaie bespeur en 'n versigtige aanslag moes gevolg word. Die WVK kon nie geignoreer word nie, maar die dikwels bloederige besonderhede wat daar aan die lig gekom het, kon nie blindelings in lesers se keel gate afgedruk word nie. Hekwagterskap moes met groot omsigtigheid gepleeg word. Die nuusfilters moes delikaat reguleer word. In hierdie studie word gepoog om hekwagterskap te illustreer by wyse van 'n ontleding van die dekking wat die drie dagblaaie in Kaapstad, die Cape Argus, Cape Times en Die Burger, verleen het aan een van die Waarheids-enversoeningskommissie se opspraakwekkendste sittings. In Junie en Julie 1998 het sowat tien mans, op een na almal dokters, doktore of generaals, getuig oor hul betrokkenheid by die opbou van Suid-Afrika se chemiese en biologiese wapenarsenaal. Verslaggewers het voor 'n groot uitdaging te staan gekom om by te bly met die joernalistieke eise wat tydens hierdie sitting gestel is. In hierdie studie word gekonsentreer op beriggewing oor vier prominente getuies se weergawes, naamlik dr. Wouter Basson, gewese projekleier van Suid-Afrika se chemiese en biologiese wapenprogram, sy bevelvoerder, It.-genl. Niel Knobel, voormalige geneesheer-generaal, genl. Lothar Neethling, oud-hoofvan die polisie se forensiese laboratorium, en dr. Jan Lourens, biomediese ingenieur en die eerste een wat sy plek in die getuiestoel ingeneem het. Gesprekke is gevoer met nege joernaliste by die drie koerante ten einde hul beskouings en persepsies te peil ter illustrasie van hekwagterskap en hoe dit hekwagterskap beinvloed het. Aspirant-mediabestuurders, sowel as mediabestuurders, verslaggewers - almal wat hekwagtersrolle vertolk - sal hierdie studie straks leersaam vind ter verfyning van hul kundigheid.

Chemical warfare agents continue to pose a global threat despite the efforts of the international community to prohibit their use in warfare. For this reason, improvement in the detection of these compounds remains of forensic interest. Protein adducts formed by the covalent modification of an electrophilic xenobiotic and a nucleophilic amino acid may provide a biomarker of exposure that is stable and specific to compounds of interest (such as chemical warfare agents), and have the capability to extend the window of detection further than the parent compound or circulating metabolites. This research investigated the formation of protein adducts of the nitrogen mustard chemical warfare agents mechlorethamine (HN-2) and tris(2-chloroethyl)amine (HN-3) to lysine and histidine residues found on the blood proteins hemoglobin and human serum albumin. Identified adducts were assessed for reproducibility and stability both in model peptide and whole protein assays. Specificity of these identified adducts was assessed using in vitro assays to metabolize common therapeutic drugs containing nitrogen mustard moieties. Results of the model peptide assays demonstrated that HN-2 and HN-3 were able to form stable adducts with lysine and histidine residues under physiological conditions. Results for whole protein assays identified three histidine adducts on hemoglobin, and three adducts (two lysine residues and one histidine residue) on human serum albumin that were previously unknown. These protein adducts were determined to be reproducible and stable at physiological conditions over a three-week analysis period. Results from the in vitro metabolic assays revealed that adducts formed by HN-2 and HN-3 are specific to these agents, as metabolized therapeutic drugs (chlorambucil, cyclophosphamide, and melphalan) did not form the same adducts on lysine or histidine residues as the previously identified adducts formed by HN-2 and HN-3. Results obtained from the model peptide and full protein work were enhanced by comparing experimental data to theoretical calculations for adduct formation, providing further confirmatory data. This project was successful in identifying and characterizing biomarkers of exposure to HN-2 and HN-3 that are specific and stable and which have the potential to be used for the forensic determination of exposure to these dangerous agents.

abstract: As experiencing hot months and thermal stresses is becoming more common, chemically protective fabrics must adapt and provide protections while reducing the heat stress to the body. These concerns affect first responders, warfighters, and workers regularly surrounded by hazardous chemical agents. While adapting traditional garments with cooling devices provides one route to mitigate this issue, these cooling methods add bulk, are time limited, and may not be applicable in locations without logistical support. Here I take inspiration from nature to guide the development of smart fabrics that have high breathability, but self-seal on exposure to target chemical(s), providing a better balance between cooling and protection. Natural barrier materials were explored as a guide, focusing specifically on prickly pear cacti. These cacti have a natural waxy barrier that provides protection from dehydration and physically changes shape to modify surface wettability and water vapor transport. The results of this study provided a basis for a shape changing polymer to be used to respond directly to hazardous chemicals, swelling to contain the agent. To create a stimuli responsive material, a novel superabsorbent polymer was synthesized, based on acrylamide chemistry. The polymer was tested for swelling properties in a wide range of organic liquids and found to highly swell in moderately polar organic liquids. To help predict swelling in untested liquids, the swelling of multiple test liquids were compared with their thermodynamic properties to observe trends. As the smart fabric needs to remain breathable to allow evaporative cooling, while retaining functionality when soaked with sweat, absorption of water, as well as that of an absorbing liquid in the presence of water were tested. Micron sized particles of the developed polymer were deposited on a plastic mesh with pore size and open area similar to common clothing fabric to establish the proof of concept of using a breathable barrier to provide chemical protection. The polymer coated mesh showed minimal additional resistance to water vapor transport, relative to the mesh alone, but blocked more than 99% of a xylene aerosol from penetrating the barrier. / Dissertation/Thesis / Doctoral Dissertation Chemical Engineering 2020