Thesis (Ph. D.)--University of Wisconsin--Madison, 1961. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographies.

Thesis (Ph. D.)--University of Florida, 1982. / Description based on print version record. Typescript. Vita. Includes bibliographical references (leaves 211-213).

Thesis (M.S.)--University of Missouri-Columbia, 2004. / Typescript. Includes bibliographical references (leaves 99-102). Also available on the Internet.

Recombination of chlorine atoms in the gas phase ; The effect of quaternary ammonium salts on the stabilities of initial and transition states in SN1 reactions.

The kinetics of the coordination reaction between the carboxyl group of the acetate radical and the trivalent chromium ion has been examined by independent methods at a temperature selected to yield reasonably accurate rate data. The study has been extended to an examination of the rate of chromium "fixation" by the carboxyl groups of hide collagen in a series of miniature tannages carried out under similar conditions for comparative purposes. The effect of olation of the chromium ions in solution on the kinetics of t he coordination reaction has also been examined. The rate of coordination of the acetate radical was followed by solvent extraction and spectrophotometric techniques over a range of concentration and pH levels. The rate data revealed a reaction having typical mass-action characteristics, the rate of reaction depending on the concentration levels of the chromium ion and the ionised acetate radical. An attempt made to distinguish a differential reaction rate in the case of a parallel reaction series using boiled and aged chromium nitrate reactant solutions, failed to reveal any significant differences between the series. The reactant solutions gave absorption spectra characteristic of the trivalent chromium ion with maxima in the 420 mµ and 570 mµ wavelength regions. The changes in optical density occurring in the vicinity of the maxima were followed spectrophotometrically, the height of the 570 mµ being found to increase during the course of reaction, while the height of the 420 mµ peak decreased. The variation in optical density at the 570 mµ peak was found to be directly related to the increase in concentration of the product complex in solution in accordance with the Baer-Bougher law, while the decrease in the height of the 420 mµ peak was related to the properties of unolated OH groups associated with the chromium complex as governed by pH and olation changes during the course of reaction. Boiled and aged chromium nitrate solutions gave reactant solutions having initial optical densities greater than those of the correspending fresh reactant solutions at the 570 mµ peak, and less than those of the fresh solutions at the 420 mµ peak. During the course of reaction, however, the two series converged to the same values. The equilibrium reaction solutions were subjected to paper electrophoretic study which indicated that all tho chromium was present in the form of cationic species. This finding was in accordance with stoicheiometric indications in the solvent extraction studies where coordination in a l : 1 ratio was reflected, giving rise to positively charged complex ions only. Making due allowance for band spreading the numbers of species predicted from the kinetic studies correspond with the electrophoretic patterns found. Application of the classical second order kinetic expression to the solvent extraction rate data, yielded plots having two distinctly linear sections, apparently indicating consecutive second order processes occurring in solution, contrary to the findings of previous workers who assign a first order mechanism to the reaction. This finding was consistent with the view that in the case of both the fresh and aged series, reaction consisted of successive coordination of an acetate radical to each chromium atom of a diol complex. Second order rate "constants" were calculated for each step and their dependency on pH level demonstrated. The findings of Hamm et al that these were first order reactions independent of acetate co'ncentration are believed to be due to their use of a large excess of acetate in their experiments. The kinetic study was further extended to an examination of the rate of "fixation"of trivalent chromium by the carboxyl groups of hide collagen under comparable conditions in a series of miniaturv tanning experiments in which the tannage substrate was provided in each of two physical forms:- (a) As hide powder where surface development was large, and (b) as prepared pelt pieces in which the fibrous weave pattern was retained. In view of the heterogeneity of the tannage systems, remarkable similarity was observed in the reaction course when compared with that of the acetate coordination studies, particularly in the case of the hide powder tannages. The dependency of the tannage rate data upon concentration and pH conditions was also found to be the same as in the case of the pure chemical system. The exact correlation between the rate data for the tannage and pure chemical systems was demonstrated by means of correlation plots. Close correlation was revealed in the case of hide powder tannage while the smaller degree of correlation observed in the case of the pelt tannage systems was attributed to the modifying effects of diffusion, particularly on the initial reaction velocity. The effect of using boiled and aged chromium solutions in the tannages was to increase the initial rate of chroniill!l "fixation" apparently due to tho coordination of a dial species at each coordination site. After the initial reaction period, the two series showed a tendency to converge as in the case of the spectrophotometric studies on the acetate reaction. The convergence trend was regarded as indicative of the tendency for the chromium in fresh solutions to under go rapid olation to the ame level as in the boiled and aged solutions. The experimental observations made on the various systems lead to the following conclusions:- (a) The mechanism of coordination of the acetate radical ttrivalent chromium appears to involve the successive coordination of ligand to each of the chromium atoms of a diol complex, both coordination steps proceeding by second order reaction mechanisms. (b) At the pH levels at which the reaction is carried out, the formation of elated bodios is rapid so that reaction in the case of both fresh and aged solutions essentially occurs between an elated species and the ionised acetate radical. (c) Modificati0ns in the absorption spectrum of the reactant solution at the 570 mµ peak are directly related to coordination, while changes at the 420 mµ peak are related to the formation of loosely-bound hydroxo chromium compounds, the concentrations of which depend on the pH level. (d) The mechanism of chromium fixation in hide is essentially similar to that operating in the case of coordination of the acetate radical to chromium, involving attachment of chromium to the side chain acid r sidues of collagen. (e ) The effect of olation is to enhance the rate of chromium fixation by hide protein during the initial reaction stages and to render possible bridge formation between adjacent side chains by secondary coordination during the latter reaction stages. (f) Where pelt pieces are used instead of hide powder, the initial rate of chromium fixation is dominated by the rate of diffusion of chromium into the fibrous structure. It should be stressed that the observations made on the various reaction systems cannot be regarded as exhaustive and the conclusions are subject to further confirmation. Consequently, the present study is essentially of a preliminary nature, but it is felt that the need for further investigation along similar lines has been demonstrated.

PEP activity has been described in several locations and has mostly been linked to a variety of neurological disorders such as schizophrenia, amnaesia, depression as well as other disease states such as anorexia nervosa, bulimia nervosa and blood pressure regulation. The enzyme has also been previously isolated from a variety of archae, microorganisms and several eukaryotic species but no prolyl endopeptidases have been isolated from plants. Plants have high levels of proline and glutamine rich peptides in seeds. We therefore hypothesize plants must express PEPs during germination. Bioinformatics tools were used to identify known PEPs and putative plant PEPs. A global sequence alignment of putative plant PEPs and other known PEPs indicated that the active site amino acids Ser, His and Asp are conserved in putative plant PEP sequences. Furthermore, putative plant PEPs showed similar secondary structures to known PEPs and when a rice PEP was modelled onto porcine brain PEP structure, a high degree of similarity was found. Germination studies of wheat seed showed an increase of PEP activity over time with maximum PEP activity reached after 4 days of germination, which remained at this level until 9 days of germination, implying a function for PEP in plant seed germination. Wheat PEP was purified using ion exchange and gel filtration chromatography with a final yield of less than 1 percent and a relative purity (only 2 bands detected by SDS-PAGE). The purified wheat PEP had a molecular weight of approximately 55kDa, substrate specificity for chymotrypsin-like substrates (N-Suc-Ala-Ala-Pro-Phe-pNa, Km value of 0.58 mM, Kcat of 29.37 s–1; Kcat /Km 50813.14s–1 M–1); a pH optimum of 7.9; temperature optima of 37oC and a high sensitivity to temperature as indicated by loss of activity at temperatures above 40oC. Inhibition studies using E64, Leupeptin and PMSF confirmed that the wheat PEP is from the Serine protease family and is most likely a trypsin-like protease.

The kinetics of the electron transfer reaction U(IV) + T1(III) → U(VI) + T1(I) were examined in aqueous perchloric acid solution. The rate law was found to be of the form [ Formula omitted ] The two rate constants were identified with reaction paths involving activated complexes of the compositions (U.OH.T1)⁶⁺ and (U.O.T1)⁵⁺ , respectively. The corresponding heats and entropies of activation, evaluated from rate measurements over the temperature range 16 to 25°, are ΔH₁± = 24.6 kcal/mole, ΔH₂± = 21.7 kcal/mole, ΔS₁±= 16 e.u. and ΔS₂±= 7 e.u. The effect of ionic strength and the specific effects of various anions and cations on the rate were examined. The results suggest, but do not prove, that the reaction occurs through a single two-equivalent step rather than through successive one electron changes. The homogeneous oxidation of carbon monoxide by metal ions in aqueous solutions was studied. At temperatures below 80° only Hg²⁺ and MnO₄¯ were found to oxidize carbon monoxide. The ions Cu²⁺ , Ag⁺ , Hg₂²⁺ , Fe³⁺ , T1³⁺ and Cr₂O₇²¯, were inactive. Kinetic measurements of the reaction 2Hg²⁺+ CO + H₂O → Hg₂²⁺+ + CO₂ + 2H⁺ in dilute perchloric acid over the temperature range 26 to 54° yielded the rate law [ Formula omitted ] The activation parameters are ΔH± = 14.6 kcal/mole and ΔS± =-13 e.u. It is believed that the reaction proceeds by a mechanism which involves the insertion of CO between Hg²⁺ and a coordinated water molecule [ Formula omitted ] The oxidation of carbon monoxide by MnO₄¯ was found to proceed readily over the temperature range 28 to 50°. The rate law was found to be [ Formula omitted ] with ΔH± = 13 kcal/mole and ΔS± = -17 e.u., both substantially constant over the pH range 1 to 13. The rate determining step is considered to be the formation of hypomanganate MnO₄¯+ CO + H₂O → MnO₄³¯ + CO₂ + 2H which then undergoes further fast reactions to yield MnO₄²¯ in basic solution and MnO₂ in acid and neutral solutions. A remarkable feature of the latter reaction is its very marked sensitivity to catalysis by Ag⁺ and Hg²⁺ (but not by Cu²⁺, Cd²⁺, Fe³⁺, or T1³⁺ ). The rate law of the catalyzed path is, in each case, [ Formula omitted ] where M = Ag⁺ or Hg²⁺. For Ag⁺, k at 0° is 1.10 x 10⁵ M¯² sec¯¹ with ΔH± = 1.3 kcal/mole and ΔS± = -30 e.u. For Hg²⁺, k at 0° is 1.09 x 10³ M¯² sec¯¹ with ΔH± = 6.5 kcal/mole and ΔS± = -21 e.u. It is suggested that the remarkably high reactivities exhibited by carbon monoxide in these catalytic reactions are related to favourable oxidation paths involving intermediates such as [ Formula omitted ] / Science, Faculty of / Chemistry, Department of / Graduate

Three aspects of the isomerization reaction of cyclopropane to propylene were explored, in order to evaluate the suitability of this rearrangement for use as a model reaction in studying the effects of pore diffusion on the rates of chemical change in porous solids. First, kinetic data for this reaction were extended from 555°C to 620°C, with good agreement being obtained with data of others at temperatures below 555°C For the results of this work, as well as for all other published results, the first order homogeneous rate constant at infinite pressure can be represented by log₁₀ k =15.38 [formula omitted] (T in degrees Kelvin) with an accuracy of ± 15% over the temperature range 470°- 620°C. Second, the isomerization was shown to proceed homogeneously in the presence of Pyrex surfaces, even with 60-fold changes in-the surface to volume ratio. Third, the only side reaction of any importance was the decomposition of propylene, which was found to be about 20-50 times slower than the cyclopropane isomerization. These results indicate that the cyclopropane reaction is a satisfactory one for the purposes of studying diffusion controlled processes, but the propylene pyrolysis may restrict the range of desirable experimental conditions. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

The rate constants of the abstraction reaction Mu + HBr —• MuH + Br were measured using the well established μSR technique at TRIUMF. Measurements were made at various temperatures between 170 and 480 K, and fit to the Arrhenius equation both with and without an additional T½ dependence. The rate constants obtained were k(T) = (5.101 ± 0.106) x 10⁻¹¹ exp{-(0.560 ± 0.110) kcal mol⁻¹/RT} and k(T) = (0.183 ± 0.005) x 10⁻¹¹T½exp{-(0.286± 0.014) kcal mol⁻¹/RT} cm³ molecule⁻¹ s⁻¹. The low activation energy for such an exothermic reaction indicates that the barrier on the Mu + HBr surface is early. Kinetic isotope effects of the H/Mu + HBr reactions along with a lack of curvature in the Mu + HBr Arrhenius plot suggest that tunneling is relatively unimportant down to 170 K. / Science, Faculty of / Chemistry, Department of / Graduate

The etching of silicon by atomic and molecular chlorine and bromine was studied as a function of etchant pressure and reaction temperature. Various types of silicon were employed in the etching experiments including intrinsic and n-type polycrystalline silicon as well as the (100) face of intrinsic single crystal silicon. The pressures of Cl₂ and Br₂ varied from 0.1 to 30 Torr and the partial pressure of Cl and Br atoms was between 0.08 and 0.2 Torr. Temperatures of between 365 and 600°C were required for CI₂ and Br₂ etching, while lower temperatures of 25 to 470°C were sufficient for the more reactive Cl and Br atoms. The reaction between silicon and Br atoms was shown to be first order with respect to the partial pressure of atoms and a first order dependence was assumed for Cl atom etching. The rate constants were determined for the Cl and Br atom etching of intrinsic and n-type polycrystalline silicon, with a dopant concentration of 5x10¹⁸ atoms cm⁻³. The reactivity of Cl atoms with n-type silicon was approximately 90 times greater than with intrinsic silicon. This enhancement in reaction rate is primarily due to an increase in the preexponential factor in k₁, with the activation enthalpy for the process remaining unchanged at approximately 28 kJ mol⁻¹. For Br atom etching, the reaction rate for the n-type silicon was over 300 times greater than for intrinsic silicon and was characterized by activation enthalpies of 55 and 63 kJ mol⁻¹ respectively. The enhancement in reactivity can also be attributed principally to an increase in the preexponential factor. The preexponential factors for the rate constants are larger than those expected, based on the collision frequencies of Cl and Br atoms. This is interpreted as evidence for a preadsorption step in these reactions. The reactions of silicon with CI₂ and Br₂ were found to display a complex pressure dependence. The etch rates varied linearly with (etchant pressure)¹′² and the intercepts from a linear regression of the data were slightly negative. To account for the half order pressure dependencies observed in these etching reactions, a reversible dissociative adsorption mechanism is proposed whereby Br₂ (or CI₂) is dissociatively adsorbed, in a reversible reaction, onto the silicon surface yielding two atoms bound to the surface. This step is then followed by a first order reaction leading to the formation of a species which is either gaseous product or some precursor which forms that product in a subsequent non rate-determining step. From the slopes of etch rate versus (pressure)¹′² plots, composite half order rate constants were calculated and from the intercepts it was possible to evaluate the rate constant for dissociative adsorption of the halogen molecules. At high etchant pressures, where the reaction was half order with respect to Br₂ (or CI₂), a half order "composite" rate constant characterized the etching reaction. Values for the half order rate constant were determined for a number of wafers at various temperatures. From the temperature dependencies of these rate constants, activation enthalpies of 131±8 and 116±7 kJ mol⁻¹ were calculated for Br₂ and CI₂ etching of intrinsic polycrystalline silicon respectively. A value of 121±7 kJ mol⁻¹ was deterrnined for the Br₂ etching of silicon (100). Higher reaction rates were observed for the etching of n-type polycrystalline silicon, with greater enhancements observed for Br₂ relative to Cl₂ etching. The enhancements in etch rates were found to be principally due to a lower activation enthalpy for the half order rate constant. An activation enthalpy for the composite rate constant of 82±3 kJ mol⁻¹ was determined for Cl₂ etching of n-type silicon with a dopant atom concentration of 5x10¹⁸ atoms cm⁻³. Br₂ etching of the same wafer yielded an activation enthalpy of 86±3 kJ mol⁻¹. At low pressures, the reaction becomes first order and the temperature dependence of the corresponding first order rate constant yielded activation enthalpies of 109 and 83 kJ mol⁻¹ for intrinsic and n-type polycrystalline silicon. / Science, Faculty of / Chemistry, Department of / Graduate