Thesis (Ph. D.)--University of Texas at Austin, 2005. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Chicago, 1913. / "Reprinted from the Physical review, vol. XXXIV, no. 2, February 1912." Also available on the Internet.

The motivation of this dissertation is to provide insight towards primary ionization mechanisms within MALDI mass spectrometry. Albeit MALDI-MS is an extensively used analytical technique, the mechanism in which primary ions are created is still under scrutiny. Two current models of primary ionization exist which claim to elucidate the ion formation mechanisms within MALDI. In this work, excited state dynamics of MALDI matrices are shown to play an important role in the ionization mechanism. Upon inspection of the thermodynamic properties of commonly used MALDI matrices, no correlation was observed when plotted against their respective analyte ion yields. However, the excited state singlet lifetimes of these matrices seem to correlate well with their respective analyte ion yields. In the broadest sense, this correlation further supports the fact that photophysical properties of the matrix should be included in current UV-MALDI models. Investigation of a claim which stated singlet energy pooling reactions were absent in the MALDI matrix 2,4,6-trihydroxyacetophenone (THAP) resulted in the discovery of a new energy pooling mechanisms. Characteristic of aromatic ketones such as THAP, intersystem crossing is an efficient process in solution, which gives way to fluorescence in the solid state. Triplet pooling mechanisms from two neighboring THAP molecules are proposed and appear to be dependent on the preparation solvent used. These triplet pooling reactions are thought to play an important role in the primary ion formation mechanism within MALDI. To further investigate the theory of triplet species playing a vital role in MALDI ionization, the internal heavy-atom effect was employed to determine the effect of the triplet species. MALDI mass spectra and excited state decays of these heavy-atom substituted matrices were collected to demonstrate the relationship between triplet species and analyte ionization efficiency. Gas-phase thermodynamics and absorption at 337 nm were also examined to determine if these properties affected the analyte ion signal observed in the MALDI mass spectrum. Using the information collected from the previous study, an advanced MALDI matrix is synthesized. Addition of covalently bound iodine to the gold standard matrix, α-cyano-hydroxycinnamic acid, should drastically improve the performance of the non-substituted matrix due to the increase in triplet species present for pooling reactions. Sample preparation methods in MALDI are examined as are the effects of crystal morphology on the overall signal observed in the mass spectrum. Exciton hopping and pooling rates are highly dependent on intermolecular interactions, so it is expected that crystal packing will affect MALDI. As noted for THAP, preparation solvent plays a significant role in not only crystal morphology, but also the excited state dynamics for all matrices studied.

The greater part of the experimental research, described in this thesis, has been devoted to an investigation, by direct electrical methods, of the formation of ionised molecules in mercury vapour and helium. […] This thesis is divided into four parts. The first contains a brief outline of the quantum theory of the atom and the molecule, a summary of our present knowledge of the interchange of energy in various collision processes, and a discussion of the theory of the thermionic emission from a heated filament and its applications. Particular reference for the development of the experimental research described in Parts 2, 3 and 4.

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The acidities of 37 amino-substituted heterocyclic compounds have been determined using measurements of degree of ionization in DMSO/ water/0.011 M hydroxide ion and recently developed extrapolative procedures which are based on the Bunnett-Olseh (B.O.) and the Marziano-Cimino-Passerini (M.C.P.) methods. The compounds studied include 19 aminopyridines and pyrimidines and 18 derivatives of the biologically important nucleotide bases, cytosine, adenine and guanine. The UV/vis spectra of the neutral and anionic forms of the amino-pyridines and pyrimidines are well separated so that in evaluating the ionization ratios, changes of the spectra with medium composition were accounted for by measuring at the wavelength of maximum anionic absorption in each solution and by assuming that eA- and eHA vary linearly with HN . For the majority of the nucleotide derivatives, the neutral and anionic spectra were closely overlapping although different in shape. The ionization ratios were best evaluated by using the area under the spectral curve; spectral changes with solvent composition were accounted for by an adaptation of the method described above. Ionization ratios evaluated by the area method agreed well with those calculated by other methods as long as the anionic area was at least one and one-half times as great as the neutral area (or vice versa). The aminopyrimidines and purines define a new acidity function Hp . This function covers the range from water to 87.6 mole % DMSO and was established using 15 aminopyrimidines and purines. When Hp plotted against mole % DMSO, it rises less steeply than HN. This has been attributed to less extensive derealization of charge in the aminopyrimidine anion relative to that of an aniline (usually a nitroaniline) ionizing at the same solvent composition. The B.O. pKHA values of unsubstituted 2- and 4-aminopyridine, 2- and 4-aminopyrimidine and 2-amino-s-triazine, ranging from 23.50 to 14.91 are well-correlated by a Hammett plot using a values recently established for aza substituents and assuming the additivity of aza substituent effects, p. 4.99. The B.O. pKHA values of five substituted anilines, ranging from 25.50 to 23.13, fall close to this plot. All ten compounds are accommodated by a straight line, p value 5.10, which suggests that the aminoheterocycles may be considered to be aza-substituted anilines. It appears that the sensitivity of aniline and diphenylamine acidity to substituent effects is greater than previously believed. The findings in this work suggest that transmission of substituent effects through a heterocyclic and a benzene nucleus are equal and that an aza group may be regarded as a normal ring substituent. From the acidities of substituted aminopyridines and pyrimidines it appears that, to a first approximation, aza groups do not perturb the effects of other substituents on the same nucleus, although there may be a small resonance interaction between a +R group, such as chloro, and an aza group lying para to it. The same conclusion was reached from examination of the basicities of these compounds. / Science, Faculty of / Chemistry, Department of / Graduate

<p> Conductivity measurements on liquid hydrogen fluoride solutions of some simple bases and fluoroanion salts were carried out, and a set of equivalent ionic conductivities have been determined. The conductivities of electrolytes in hydrogen fluoride have been compared to those of analogous electrolytes in water and strong acid solvents. A method for the investigation of more complex electrolytes was developed.</p> <p> The mode of ionization of adducts of sulfur tetrafluoride, thionyl tetrafluoride and selenium tetrafluoride with fluoride acceptors in hydrogen fluoride has been investigated by conductivity and nmr spectroscopy. The structures of the solid adducts have also been investigated by Raman spectroscopy. The structure and stability of other sulfur-oxide-fluoride adducts have been investigated and found to differ from adducts of thionyl tetrafluoride. </p> / Thesis / Doctor of Philosophy (PhD)

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