A thorough understanding of the chemical and physical properties of small molecules involves spectroscopy, thermodynamics, kinetics and dynamics of the system. This thesis highlights the use of photochemistry to measure these properties for Au+(C2H4), Pt+ (C2H4) and ethylbenzene cation as well as for deposition of zeolite films. Chapter 1 highlights the principles behind photodissociation and the information that can be obtained from spectroscopy. Also discussed is what the appearance of the photodissociation spectrum and time-of-flight profile implies about the molecular dynamics and kinetics. Chapter 2 examines gas-phase photodissociation of the classic π complexes Au+(C2H4) and Pt+(C 2H4). Spectroscopic onsets provide upper limits to the metal-ligand bond strengths of 344 kJmol−1 and 230 kJmol−1 for Au+(C2H4) and Pt +(C2H4) respectively. The spectrum of Au +(C2H4) features an extended progression in the metal-ligand stretch with a frequency of 176 cm−1 that drops to 160 cm−1 in Au+(C 2D4). Hybrid density functional theory (DFT) calculations and TD-DFT calculations are used to explore the structures, bonding and electronic spectroscopy of the two complexes. The photodissociation pathways and kinetics of the ethylbenzene radical cation are investigated in Chapter 3. The energy dependence of the various pathways are investigated. The most abundant dissociation channel is C 7H7+ + CH3 at all wavelengths, but C6H4+ + C2H6 and C6H6+ + C2H4 are also important in the near-UV. The C6H4+ + C2H6 pathway is especially interesting as it exhibits a significant peak broadening with ∼0.6 eV kinetic energy release. Later studies using vibrationally cold ions examined the dissociation rate, k(E), at various photon energies. Simulations of the time of flight profile show that the k(E) increases from 0.97 × 106 s−1 at 2.38 eV to 2.6 × 106 s −1 at 2.67 eV internal energy. An alternate application of molecule-light interaction to surface science is explored in Chapter 4. Here, the technique of pulsed laser deposition has been employed in efforts to improve thin film growth for ETS-4 molecular sieves. Characterization using X-Ray Diffraction and Transmission Electron Microscopy confirm that the zeolite structure is unaltered during the deposition process. Recommendations for further studies are discussed in Chapter 5.

Sulfur and selenium participate in a variety of essential biological functions. The investigation of two non-heme iron dioxygenases with sulfur-containing substrates is reported along with studies of seleno-compounds by gas chromatography with atomic emission detection (GC-AED). Cysteine dioxygenase (CDO) catalyzes the oxidation of cysteine to cysteine sulfinic acid, which is the first major step in cysteine catabolism in mammalian tissues. Rat liver CDO was cloned and expressed in E. coli as a 26.8 kDa fusion protein bearing a poly-histidine tag. Kinetics studies revealed a Km value of 2.5 ± 0.4 mM at pH 7.5 and 37 °C, with no requirement for secondary proteins or cofactors. Fe was demonstrated to be the only metal that is essential for activity. Inhibition studies with cysteine analogs along with the use of x-ray absorption spectroscopy (XAS) allowed for the characterization of the active site. Acireductone dioxygenases (ARDs) are enzymes involved in the methionine recycle pathway. Klebsiella produces two ARD enzymes that share a common polypeptide sequence and differ only in the metal ion present. In the presence of Fe-containing ARD (ARD'), reaction of acireductone with dioxygen produces formate and the ketoacid precursor of methionine. In the presence of the Ni-bound form (ARD) the same substrate produces formate, methylthiopropionate and CO, an off-pathway shunt. XAS study of the structure of the catalytic Fe center in resting state enzyme shows a six coordinate Fe site composed of N/O-donor ligands including 3-4 histidine residues. The substrate binds to the Fe center in a bidentate fashion by displacing two ligands, at least one of which is a histidine ligand. Cancer prevention attributed to the properties of selenium is widely recognized, but the mechanism of tumor inhibition by this element is still not known. The determination of Se-metabolites and the understanding of their fate are indispensable. Liver extracts from rats administered with selenized yeast were examined by GC-AED. Organoseleno compounds have been observed, including selenomethionine, and possibly the newly-discovered S-(methylseleno)-cysteine molecule. Aromatic Se-compounds have been recognized as antitumorigenic alternatives with lower toxicity. Gas chromatographic behavior of several aryl diselenide derivatives were analyzed.

A multiplexed method for performing MS/MS on multiple ions simultaneously in a miniature rectilinear ion trap (RIT) mass spectrometer has been developed. This method uses an ion encoding procedure that relies on the mass bias that exists when ions are externally injected into an RIT operated with only a single phase RF applied to one pair of electrodes. The ion injection profile under such conditions ions is Gaussian-like over a wide range of RF amplitudes, or low mass cutoff (LMCO) values, during ion accumulation. We show that this distribution is related to ion m/z, and is likely caused by ions having an optimal range of pseudo-potential well depths for efficient trapping. Based on this observation, precursor ion intensity changes between two different injection LMCO values can be predicted, and these ion intensity changes are found to be carried through to their corresponding product ions, enabling multiplexed MS/MS spectra to be deconvoluted. The gas-phase reactions of a series of coordinatively unsaturated [Ni(L) n]y+ complexes, where L is a nitrogen-containing ligand, with chemical warfare agent (CWA) simulants in a miniature rectilinear ion trap mass spectrometer were investigated as part of a new approach to detect CWA. Results show that the metal complex ions can react with low concentrations of several CWA simulants, including dipropyl sulfide (simulant for mustard gas), acetonitrile (simulant for the nerve agent tabun), and diethyl phosphite (simulant for nerve agents sarin, soman, tabun, and VX), thereby providing a sensitive means of detecting these compounds. The [Ni(L)n] 2+ complexes are found to be particularly reactive with the simulants of mustard gas and tabun, allowing their detection at low parts-per-billion (ppb) levels. These detection limits are well below the median lethal doses for these CWAs, which indicates the applicability of this new approach, and are about two orders of magnitude lower than electron ionization detection limits on the same mass spectrometer. The use of coordinatively unsaturated metal complexes as reagent ions offers the possibility of further tuning the ion-molecule chemistry so that desired compounds can be detected selectively or at even lower concentrations. Mass spectrometry has become a tool for studying noncovalently bound complexes. Specifically, electrospray ionization mass spectrometry (ESI-MS) has found increasing use for the determination of affinity (Ka) or dissociation (Kd) constants. Direct measurement of the equilibrium components by ESI-MS is the most straightforward approach for determining binding equilibrium constants, but this approach is prone to error and has some inherent limitations. Transferring complexes from solution to the gas phase may perturb the equilibrium concentrations and/or different ionization efficiencies may cause the resulting ion signals not to reflect actual solution concentrations. Furthermore, ESI only works under a limited range of solvent conditions (i.e. low ionic strengths), which limits the broad applicability of this approach. We propose an approach based on covalent labeling in the context of metal-catalyzed oxidation (MCO) reactions that, when combined with MS, overcomes such limitations when determining metal-ligand binding constants. The MCO-MS approach will provide concurrent information regarding metal binding site and metal-protein binding affinity. Optimization of the MCO reaction through isotopic mass tags will permit enhanced identification of modified residues. Application of this method to study the affinity and binding interactions of other divalent metals with β2m are likely to provide insight into the specificity of copper for causing β2m amyloid formation.

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