No description available.

The selectivity and sensitivity of ion mobility spectrometry (IMS) to explosives was first demonstrated by Karasek in 1974.1 Airport security has always been a concern in the United States, especially since September 11th, 2001, and as a result IMS is commonly used to screen airline passengers and their luggage at all major airports. Portable IMS systems are now widely available for a variety of applications, but as the overall size of the IMS instrumentation decreases, the sensitivity typically decreases as well. A new ion detector read out technology, a capacitive trans-impedance amplifier (CTIA), coupled to a traditional Faraday plate has shown increased sensitivity over a Faraday plate read by a conventional current to voltage converter when used in mass spectrometry. Sandia National Laboratories sponsored a project to determine whether the CTIA technology could be coupled to an IMS, and to determine the potential increase in sensitivity that could be provided to a miniature IMS equipped with the new read out technology.Sandia first provided a full size IMS, a Phemto-Chem PCP-110, which was modified to support the first generation of CTIA (CTIA1). The CTIA1 was coupled to the IMS and was successfully used to detect explosives. Next, Sandia provided miniature IMS drift tubes, but incompatibilities necessitated the design of new miniature systems. At first, only the drift tube itself was redesigned, but eventually a complete miniature IMS, including the ionizer, circuitry, and read out, was designed and built. During the design phase a new ion-beam shutter capable of increased resolution was also implemented. The second generation of CTIA was coupled to a custom drift tube and the system demonstrated increased resolution and drastically increased sensitivity to the common explosives TNT and RDX when compared to the sensitivity of the system provided by Sandia. A custom miniature drift tube coupled to a CTIA will be placed into the peripheral equipment for Sandia's MicroHound II instrumentation to provide a portable IMS with sensitivity equal to or better than bench top IMS systems.

Thesis (Ph. D.)--Washington State University, August 2009. / Title from PDF title page (viewed on Aug. 4, 2009). "Department of Chemistry." Includes bibliographical references.

Thesis (Ph. D.)--Washington State University, December 2006. / Includes bibliographical references.

Thesis (M.S. in mechanical engineering)--Washington State University, December 2006. / Includes bibliographical references (p. 66-77).

Thesis (Ph.D.) -- Virginia Commonwealth University, 2004. / Title from title-page of electronic thesis. Prepared for: Dept. of Chemistry. Bibliography: p. 181-191.

β-defensins are a class of mammalian defence peptides with therapeutic potential because of their ability to kill bacteria and attract host immune cells. In order to realise this potential, it is necessary to understand how the functions of these peptides are related to their structures. This thesis presents biophysical analysis of β- defensins and related peptides in conjunction with biological assays. These studies provide new insights into the structure-activity relationships of β-defensins. Ion mobility-mass spectrometry (IM-MS) is used throughout this thesis to probe the tertiary structure of peptides in vacuo and, by inference, make conclusions about their conformations in solution prior to ionisation. Where appropriate, IM-MS is complemented by other techniques, including high performance liquid chromatography and circular dichroism spectroscopy. First, the importance of a C-terminal cysteine residue within the murine β-defensin Defb14 is investigated. The functional and structural implications of chemically modifying the cysteine residue are examined. Second, the N-terminal region of Defb14 is modified by the substitution and deletion of amino acids. Again, the effects on biological activity and structure are discussed. Finally, the functional and structural overlap of β-defensins with another family of proteins – the chemokines – is considered. The oligomerisation of β-defensins and their interaction with glycosaminoglycans is of particular interest: structural data for human β-defensins 2 and 3 in the absence and presence of polysaccharides are presented.

The ability to characterize the interactions between ions and solvent molecules plays a critical role in understanding fundamental aspects of thermodynamics in solution chemistry. These interactions are often difficult if not impossible to observe in solution due to the number of solvent molecules far exceeding that of the ions. However, this challenge can be circumvented in the gas phase which enables the isolation and study of reactions between a single ion and single solvent molecule. Within the field of ion-molecule chemistry are two sub-categories of interactions known as ionic hydrogen bonds (IHBs) and ionic halogen bonds (IXBs). In these interactions, the incorporation of a charged species permits ion-dipole interactions which are innately stronger than those found in dipole-dipole interactions among neutral molecules. This dissertation describes and explains the interactions which take place between halogenated benzenes (F-, Cl-, Br-, and Iodobenzene) and neutral polar molecules (water, acetonitrile, acetone, and methanol). Additional studies on ionic hydrogen bonding involve the exploration of protonated benzonitrile monomer and dimer solvated by methanol. All systems were examined using the mass-selected ion mobility technique using the VCU mass selected ion mobility mass spectrometer. Thermochemical equilibrium measurements, in conjunction with density functional theory (DFT) calculations, were performed, enabling comparison between experimentally and theoretically determined binding energies. Additionally, the DFT calculations were able to validate hypothetical predictions for the lowest energy structures of each interaction. Furthermore, the averaged collision cross sections of the benzonitrile dimer radical cation, protonated benzonitrile dimer, and benzonitrile solvated hydronium ion were elucidated using the technique of ion mobility where experimentally determined cross sections were compared with theoretical collision cross section calculations on predetermined geometries that were optimized using DFT calculations.

Thesis (M.S.)--Washington State University, December 2007. / Includes bibliographical references.

Thesis (Ph. D.)--Brigham Young University. Dept. of Chemistry and Biochemistry, 2006. / Includes bibliographical references.