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Protein structure and functions are tightly regulated. Studying the integration of multiple modifications in single systems is a novel approach. Hisactophilin protein from Dictyostelium discoideum, is an actin binding protein that serves to induce formation of actin filaments and is regulated by protonation and myristoylation. Utilizing hisactophilin as a model, I determined the effect of pH and myristoyl-switching on actin binding and filament induction using fluorescence spectroscopy, light scattering, and time-course electron microscopy. Results revealed the accessible myristoyl group slows binding and the rate of actin polymerization compared to when the group is sequestered. Hisactophilin induces pH-dependent actin aggregates before reorganizing them into filaments and bundles. Hisactophilin mutants impact initial actin binding and the kinetics of the aggregated state. I determined the cooperativity of myristoylation and protonation as interdependent protein regulatory mechanisms, their impact on actin binding and proposed a novel mechanism for actin polymerization as a result of these integrated regulators. / NSERC

La stabilité structurale et chimique de céramiques bien densifiées candidates pour leur utilisation comme électrolyte ou matériau d'électrode de piles à combustible, électrolyseur H2/air ou même de convertisseur CO2/Hydrocarbures a été étudiée vis-à-vis de l'eau sous pression (autoclave, eau pauvre ou saturée en CO2). La pressurisation maximise l'efficacité des dispositifs. Quatre familles de pérovskites ont été considérées: BaCe0.4Zr0.5Y0.1Zn0.04O3- (BCZYZ), SrZr0.9Er0.1O3- (SZE), Ln2NiO4+ (LNO, Ln = La, Pr, Nd), and La0.6Sr0.4Co0.2Fe0.8O3- (LSCF6428). Les céramiques denses sont traitées à 550°C en autoclave plusieurs jours à plusieurs semaines, soit dans des conditions de fonctionnement ( 20 bar, eau sans CO2, 550°C), soit en vieillissement accéléré ( 40 bar eau sans ou saturée de CO2, 550°C). Les céramiques ont été analysées avant et après 'protonation' par Microscopie Optique, Thermogravimétrie, Expansion Thermique, (micro/macro) ATR FTIR, Raman micro-Spectroscopie, diffraction des rayons X et des neutrons. En condition de fonctionnement ( 20 bar), la stabilité des matériaux d'électrodes LNO/LSCF6428 et de l'électrolyte SZE est bonne, alors que la céramique BCZYZ se corrode. La céramique LSFC6428 soumis à des conditions sévères (eau saturée en CO2, 40 bar) est 5 à 30 fois moins corrodée que les composés LNO and SZE. La corrosion s'initie en surface, aux joints de grains. La protonation modifie plus ou moins la symétrie, le volume et les paramètres de la maille unitaire ainsi que les transitions de phase en relation avec la modification de la distribution/organisation des lacunes d'oxygène. Le niveau de dopage en proton des différents matériaux est aussi discuté. / The chemical and structural stability of well-densified ceramics potentially used as H2/air fuelcell/electrolyzer (and perhaps in CO2/Hydrocabons Converter) electrolyte or electrodes vs. CO2-free/saturated pressurized water has been studied. The pressurization maximizes the efficiency of theenergy conversion systems. Four types of pervoskite-related oxide ceramics were concerned:BaCe0.4Zr0.5Y0.1Zn0.04O3-d (BCZYZ), SrZr0.9Er0.1O3-d (SZE), Ln2NiO4+d (LNO, Ln = La, Pr, Nd), andLa0.6Sr0.4Co0.2Fe0.8O3-d (LSCF6428). Dense ceramic samples were exposed at 550°C to water vaporpressure in an autoclave for days to weeks. The protonation treatments were performed in twodifferent conditions: operating condition (£20 bar of CO2-free water pressure, 550°C) and acceleratedaging conditions (³40 bar of CO2-free/CO2-saturated water pressure, 550°C). The pristine and‘protonated’ samples were characterized using various analysis techniques: Optical Microscopy,Thermogravimetry, Thermal Expansion, (micro/macro) ATR FTIR, Raman micro-spectroscopy, X-rayand Neutron Scattering. The study reveals that under the operating condition (£20 bar), the stability ofLNO/LSCF6428 electrode materials and of SZE electrolyte appears good, while the BCZYZelectrolyte exhibit significant corrosion. The superior stability of LSFC6428 exposed in extreme CO2-water vapor atmosphere was demonstrated about 5 to 30 times better than LNO and SZE homologues.The surface secondary phases form at the grain boundary. The protonation modifies more or less thestructure symmetry, the unit-cell volume/parameter and the phase transition sequence in relation withthe modification of the oxygen vacancy distribution. The proton doping level for different samples isalso discussed.

Late transition metal complexes bearing nitrogen-containing ligands have many applications in biotechnology or industrial catalysis. Imidazole is one of the most common biofunctional ligands to play critical roles in meta1loenzymes, since the imidazole moiety of the histidyl residues often constitutes all or part of the binding sites of various transition metal ions. We use the newly synthesized tetradentate ligand containing the imidazolyl and pyridyl functional group to react with zinc, copper, nickel, and iron ions in order to carry out biomimetic studies. We have obtained two crystal structures via different methods of crystallization. One of them is a mononuclear complex while the other is a polymeric structure. The polymeric structure has demonstrated the spontaneous deprotonation on the imidazolyl nitrogen on binding to the metal ion followed by the intermolecular self-assembly process.We believe that the imidazolate -bridged complexes undergo the pH-dependent interconversions between mononuclear (protonated ligand) and self-assembled oligomer (deprotonated ligand). In addition, we have measured the titration curves of the tetradentate ligand and its corresponding metal complexes to determine the preferential binding sites at varying pH. From the titration processes, we got the protonation constant of ligand and stability constants of its corresponding metal complexes.

This thesis is an investigation into the development of amidine and guanidine based compounds to be employed as switchable surfactants. The surface activity of these molecules can be triggered by reaction with a benign gas, CO2. The ultimate application of these surfactants was to be used as emulsifying and demulsifying agents of crude oil and water emulsions. Synthesis and characterization of the following desired bases: N’-octyl-N,N-dimethylacetamidine (1), 2-octyl-2-imidazoline (2), 1-methyl-2-octyl-2-imidiazoline (3), N’-(4-heptylphenyl)-N,N-dimethylacetamidine (4), N’-(4-(octyloxy)phenyl)-N,N-dimethylacetamidine (5), N’-(4-(methyloxy)phenyl)-N,N-dimethylacetamidine (6), and N-octyl-N',N',N",N"-tetramethylguanidine (7) was carried out. Their solubility in water was quantified with NMR spectroscopy. All bases were reacted with CO2 and H2O to form bicarbonate salts, of which in situ characterization was achieved by IR and NMR spectroscopy. Percent conversion to the protonated forms at elevated temperatures was determined using NMR spectroscopy. A direct correlation between switchability and basicity was observed, as the strongest bases possessed the largest conversions to the protonated species, even at higher temperatures. The enthalpy of protonation was determined for each base through calorimetry experiments. These compounds were tested as demulsifying surfactants of crude oil and water emulsions. Demulsifying ability was determined to differ greatly with the head group structure of the various surfactants. / Thesis (Master, Chemistry) -- Queen's University, 2009-10-27 16:56:13.631

Nitrilotriacetic Acid (NTA) is an organic ligand which has been extensively studied due to its biological significance and excellent chelating properties. Nitrilotripropionic Acid (NTPA) is a ligand that is believed to possess similar properties to NTA, but has not been as extensively studied. It has been experimentally determined that metal complexes of NTA are orders of magnitude stronger than those formed with NTPA. This is surprising, especially considering that the ligands do not differ that much from each other. NTPA contains an additional –CH2– group in each of the acid containing arms as compared to NTA. The aim of these studies were to explain, theoretically, why this is the case. Analyses were conducted with a number of software programs including, Gaussian 03, Schrödinger Maestro and AIM 2000. All Density Functional Theory (DFT) studies were conducted in solvent at the RB3LYP/6-311+G(d,p) level of theory in conjunction with a number of different solvation models. En route to explaining why the complexes differ in stability a new methodology was utilized (isodesmic reactions) in which the four stepwise protonation constants of both NTA and NTPA were successfully predicted; in fact these were the most accurate values predicted to date by DFT methods. The final step of these studies focused on predicting stability constants of metal (Zn2+ and Ni2+) complexes of NTA and NTPA. These predictions were not as accurate as those achieved for the prediction of protonation constants; however, success was achieved in predicting the trend – complexes with NTA are orders of magnitude stronger than complexes formed with NTPA. The most important observation revealed that H–clashes and C–H∙∙∙O hydrogen bonds present in M(NTPA) complexes, which are not present in M(NTA) complexes, result in the formation of additional rings which contributes to the formation of a cage. It was discovered that the H-clashes present in the M(NTPA) complexes were contributing to the overall stability of the molecule. This is completely contradictory to a previous explanation in which H-clashes, being a result of steric crowding, resulted in destabilization of a complex. If the H-clashes were not present in the M(NTPA) complexes there would not be enough stabilizing factors present in the molecule which will inevitably result in the non-existence of M(NTPA) complexes. Copyright / Dissertation (MSc)--University of Pretoria, 2010. / Chemistry / unrestricted

The incorporation of the trifluoromethyl and perfluoroalkyl motifs into organic compounds has been a hot topic in synthetic organofluorine chemistry. There is a plethora of methods for the introduction of the CF3 moiety at carbon, oxygen and sulfur centers. In sharp contrast, methods for synthesizing N-trifluoromethyl and N-perfluoroalkyl compounds are very limited and new approaches are highly sought-after. The scarcity of these compounds prompted us to develop reagents capable of transferring the perfluoroalkyl unit to nitrogen atom. To fulfil this purpose, we have regarded azidoperfluoroalkanes as ideal reagents, therefore, this thesis is concerned with the synthesis and applications of these azides. The first part describes the preparation of azidoperfluoroalkanes. Upon activation by cesium fluoride, TMSCF3 transfers the trifluoromethyl group to an electrophilic azide to produce the desired azidotrifluoromethane. Longer carbon chain azidoperfluoroalkanes were prepared in a similar way, starting from the corresponding organosilane. A different synthetic strategy was applied for the preparation of azidopentafluoroethane where the perfluoroalkyl anion was generated from pentafluoroethane with n BuLi, followed by the addition of tosyl azide. The isolation of these fluorinated azides was...

To define the overall kinetic and chemical mechanism of adenosine 3',5'-monophosphate dependent protein kinase catalytic subunit, the mechanism in the direction of MgADP phosphorylation was determined, using studies of initial velocity in the absence and presence of dead-end inhibitors. The kinetic mechanism was determined as a function of uncomplexed Mg^2+ (Mg_f) at pH 7.2 and as a function of pH at low (0.5 mM) Mg_f. At pH 7.2 data are consistent with a random kinetic mechanism in the direction of MgADP phosphorylation with both pathways allowed: the pathway in which MgADP binds to enzyme prior to phosphorylated peptide (PSP) and that in which PSP binds before MgADP. One or the other pathway predominates, depending on Mg_f concentration. At 0.5 mM Mg_f, the mechanism is steady-state ordered with the pathway where PSP binds first preferred; at 10 mM Mg_f, the mechanism is equilibrium ordered, and the pathway in which MgADP binds first preferred. This change in mechanism to equilibrium ordered is due to an increase in affinity of enzyme for MgADP and a decrease in affinity for PSP. There is also a pH-dependent change in mechanism at 0.5 mM Mg_f. At pH 6 the mechanism is equilibrium ordered with the pathway where PSP binds first preferred. At pH 7.6 the mechanism is ordered with MgADP binding first. The log V/E_t vs. pH profile is pH-independent, suggesting only the correctly protonated form of each substrate binds to enzyme. The log V/K_MgADP vs. PH profile gives a pK of 7, likely that of a general acid, which must be protonated for activity. The pK_iPSP vs. pH profile gives a pK of 6.5, likely reflecting the peptide phosphoryl group, which must be unprotonated for activity.

<p>The protonation for several classes of weak bases has been studied by n.m.r. techniques and the structure of the conjugate acids determined. The rates of proton transfer and the activation energies for some of the processes have been calculated and in the cases of the methylbenzene-HSO₃F systems the mechanism of the proton transfer process has been elucidated.</p> <p>The acidity function (H₀) for the HSO₃F/SbF₅ system has been redetermined and extended to higher concentrations of SbF₅• The application of some n.m.r. methods to the measurement of H₀ is discussed.</p> <p>The behaviour of the n.m.r. spectra of sulphuric and fluorosulphuric acids upon the addition of electrolytes has been studied and the results interpreted.</p> / Thesis / Doctor of Philosophy (PhD)

Une double dynamique traverse l’œuvre de Mongo Beti, et ce dès 1953 et ses débuts en littérature : en premier lieu, un engagement inflexible, intransigeant, que l’écrivain brandit comme un signe identificateur de son esthétique romanesque et de son action citoyenne. En second lieu, un courant d’échanges souvent fructueux s’instaure entre « prose latérale » (écrits journalistiques et politiques, essais, pamphlets) et production fictionnelle. Autant dire que l’homme et l’œuvre, pour reprendre une formule désuète, sont indissociablement liés et que les combats de l’un trouve toujours un écho et une transposition, plus ou moins distanciée selon les périodes, dans l’autre. Dans le sillage de Sartre et fidèle en cela à la volonté affichée par les promoteurs de la revue Les Temps modernes, Beti refuse le silence du clerc. Et si trahison il y a, elle se niche, selon lui, dans le refus obstiné de dire l’injustice criante et les manquements aux droits de l’homme. C’est cette ligne de conduite idéologique et scripturaire qui unit tous les ouvrages de Mongo Beti, de la « chronique coloniale » aux « romans d’un retour au pays natal » que ce travail souhaite mettre en évidence, tout en s’interrogeant sur les limites et les tensions qu’engendre une telle posture. Mais, parce qu’il n’est pas un propagandiste appointé mettant son œuvre au service d’une cause qui la transcenderait, Beti évite le piège du roman à thèse - même si certains textes, ceux du « cycle Dzewatama » en particulier, témoignent d’un didactisme pesant - et livre une œuvre qui est avant tout le témoignage passionné et ironique sur plus de soixante-dix ans de l’histoire, souvent douloureuse et tragique, parfois drolatique, de l’Afrique. / Two tendencies underpin the works of Mongo Beti, right from his literary beginnings in 1953. First, an inflexible, uncompromising commitment that the writer raises as a sign identifying his novelistic aesthetics and his action as a public figure. Second, a channel permitting frequently productive exchanges between “secondary prose” (journalistic and political writing, essays, political pamphlets) and fictional production. All of which means, as the hackneyed saying goes, that the man and his works cannot be dissociated and that the struggles of the former are always echoed in the latter, and transposed, at a distance varying from great to small depending on the period. Following in the steps of Sartre and thus respectful of the ideal promoted by those who defended the literary review Les Temps modernes, Beti refused to be a silent cleric. If there be betrayal, in his view, it is to be found in the stubborn refusal to denounce patent injustice and failures to respect human rights. It is this ideological and scriptural line of conduct which unites all the works of Mongo Beti, from the “Colonial Chronicles” to the “Returned to Homeland” cycle. However, since he is not an official propagandist dedicating his works to a cause that might transcend him, Beti avoids the pitfalls of thesis novels, even if some texts, particularly those of the “Dzewatama Cycle”, are weightily didactic. His works are above all the impassioned and ironic testimony of more than 70 years of African history: often painful and tragic, sometimes droll.