Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references. Available also in a digital version from Dissertation Abstracts.

The factors that determine RNA structure formation, stability, and dynamics are inexorably linked to RNA function. The Hammerhead ribozyme (HHRz) has long served as a model for studying metal-dependent folding and catalysis in RNA. The HHRz consists of three helices meeting at a common junction of conserved nucleotides that form the active site of the ribozyme. Current models of metal-dependent HHRz function involve a requirement for divalent metals to globally fold the ribozyme at low metal concentrations, followed by a second metal-dependent process which activates the HHRz for catalysis. The exact role of metal ions in activating HHRz catalysis is still a subject of investigation. We used 2-aminopurine substitutions near the active site of the ribozyme to determine if this second metal-dependent process involves a conformational rearrangement in the core of the ribozyme. We find evidence for a conformational change beyond global folding in the core of the ribozyme that not only correlates with metal activated catalysis but is also sensitive to the identity of the metal ions used for folding. Though phosphorothioate substitutions indicate that a ground-state coordination of a catalytic metal to the scissile phosphate is required for efficient catalysis, our folding studies show that this coordination event is not absolutely required for folding of the HHRz core. To investigate possible roles for metal ions in general acid-base catalysis, we tested the pH dependence of the HHRz rate using a variety of metal ions. We find the pH dependent rate profile of the ribozyme is shifted by transition metal ions, whereas other group II metals show similar profiles to Mg

A series of bis [e] and [a] fused dibenzannulenes/cyclophanes have been synthesized for the first time using benzyne-like intermediates (annulynes). These include the dibenzannulene trans-2,9-di-t-butyl-14c, 14d-dihydro-14c-14d-dimethyldibenzo[fg,op]naphthacene 82b, and the metacyclophanedienes anti-[1,2;9,10]- dibenzo-5, 13-di-t-butyl-8,16-dimethyl[2.2]metacyclophane 82a, and anti-[1,2-b; 9,10-b]- dinaphtho-5,13-di-t-butyl-8,16-dimethyl[2.2]metacyclophane 85a. From these compounds several metal complexes including trans-{μ- [( 1,2,3,4,4a, 14b-η:8a,9,10,11,12,12a-η)-12c, 12d-dihydro-12c-12d-dimethylbenzo[ rst]pentaphene]]hexacarbonyldichromium 100, have been synthesized. Among the bis [e] fused compounds, pairs 82a/82b and 95a/95b show reversible and repeatable photo-switching properties both in solution and in the solid state. The pyrene forms 82b and 95b are characterized at low temperature and they thermally return to their cyclophane forms 82a and 95a at room temperature. A polystyrene based film of 82 shows a much better bistability required for photo-switching units. These properties make them potential candidates for optical memory units. For the similar naphtho[e] fused compound 95a, no pyrene isomer 95b was detected upon irradiation with UV light. Based on the NMR data, relative bond fixing abilities (RBFA) of several species are measured. The order is: [special characters omitted] > Benzene > Oxanorbomadiene > lU Norbomadiene The reduced species, oxanorbomene and norbomene, do not induce any significant bond localization on the [14] annulene ring. / Graduate

Previous work on crystal field aspects of the vibrational spectra of metal β-ketoenolates has been extended here to metal tropolonate complexes. The crystal field trends have been used to assist in the assignment of metal sensitive vibrations to the transition metal tropolonate complexes. A study has been made of the effects of spin state and Jahn-Teller distortion on the vibrational spectra of the metal tropolonates. Of particular interest is the octahedral divalent metal tropolonate adducts, where the distortion of the copper complex is small, and the metal 2-thiotroponates where the Jahn-Teller- distortion is absent. The spectra of the lanthanide tropolonates are of interest, as a plot of the metal sensitive vibrations show the 'double-humped' curve indicating that crystal field effects are present in the lanthanide ions. This has not previously been shown. Further, from the vibrational spectra of the various lanthanide tropolonates, various conclusions are made regarding structure. The non-transition metal tropolonates provide a system devoid of crystal field effects and afford the opportunity to investigate the influence of other factors on the vibrational spectra. Of interest is the strong influence of the ionic radius and ionization potential on the metal sensitive vibrations and the remarkably small influence of the mass of the metal ion on these vibrations. Although the vibrational spectra of complexes of ethylenediamine and N- substituted ethylenediamines were studied, difficulty with, assignment of the metal sensitive vibrations and the complicating influence of substituents on the spectra, prevents any observations made, from being conclusive.

No description available.

No description available.

Call number: LD2668 .T4 1959 G63

The hydrolysis of 4-Nitrophenylphosphate (NPP) as model substrate in the presence of several cobalt (III) amine [N4Co(OH)(H2O)]2+ and copper bipyridyl [Cu(bpy)(H2O)2]2+ complexes in oil in water microemulsion media was investigated. The reaction was monitored by measuring the absorbance of the nitrophenolate ion produced in the reaction aliquots with time under the experimental conditions. The order of effectiveness of the microemulsion systems towards the hydrolysis of NPP in the presence of these metal ions were found to be cationic > anionic > aqueous at neutral pH. The results of the present investigation exhibits stoichiometric turnovers for the 1:1, 2:1 and 3:1 cobalt to NPP ratio and catalytic turnovers for the [Cu(bpy)2+ to NPP ratio of 1:20. Catalysis in the microemulsion mediated reaction solutions was evident even in low concentrations of the metal ions in 1:2000 metal to NPP ratio. An explanation for the enhanced catalytic activity of the [Cu(bpy)(OH)(H2O)]2+ complex for the hydrolysis of NPP is afforded and the application of the above model systems for possible environmental decontamination of toxic organophosphates is anticipated. / Chemistry / M.Sc. (Chemistry)

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

No description available.