Synthesizing proteins containing unnatural amino acids inserted at specific positions within the protein sequence has been a longstanding goal of biological chemists. This poses unique challenges, as aminoacyl tRNA synthetases, the enzymes responsible for protein synthesis, are highly specific. To overcome this, a lanthanum-catalyzed, biomimetic tRNA aminoacylation method has been developed(1). However, due to unproductive lanthanum coordination of ethyl phosphate, a reaction byproduct, a full equivalent of lanthanum must be added to each reaction. This may threaten the integrity of tRNA, as lanthanides are known to catalyze the hydrolysis of RNA (2, 3). Using uridine as a simplified tRNA mimic, magnesium, which is known to coordinate strongly with phosphate ions, has been utilized to optimize this reaction and increase the selectivity of lanthanum towards esterification. In the presence of magnesium, ester yield is substantially increased. In addition to this, optimal pH and buffer reaction conditions were determined.

Synthesizing proteins containing unnatural amino acids inserted at specific positions within the protein sequence has been a longstanding goal of biological chemists. This poses unique challenges, as aminoacyl tRNA synthetases, the enzymes responsible for protein synthesis, are highly specific. To overcome this, a lanthanum-catalyzed, biomimetic tRNA aminoacylation method has been developed(1). However, due to unproductive lanthanum coordination of ethyl phosphate, a reaction byproduct, a full equivalent of lanthanum must be added to each reaction. This may threaten the integrity of tRNA, as lanthanides are known to catalyze the hydrolysis of RNA (2, 3). Using uridine as a simplified tRNA mimic, magnesium, which is known to coordinate strongly with phosphate ions, has been utilized to optimize this reaction and increase the selectivity of lanthanum towards esterification. In the presence of magnesium, ester yield is substantially increased. In addition to this, optimal pH and buffer reaction conditions were determined.

Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references.

No description available.

Thesis (M.S.)--Oregon Graduate Center, 1985.

The temperature dependence of the ⁵D₄ Tb ³⁺ level in crystalline Tb(dpm)3 has been determined and its anomalous behaviour has been interpreted in terms of thermal depopulation to a low lying triplet level in the solid complex, Comparisons are made with the behaviour shown by the adducts of this compound in the solid state and in solution. In solution molecular weight and conductance measurements indicate some dissociation of the monomeric units. Large variations in the quantum efficiency of Tb³⁺ tetrakis compounds differing only in the nature of the cation, have been observed. Thermal depopulation of the ⁵D₄ Tb³⁺ level to the ligand triplet level has been established in two series of terbium β-diketoenolates (hfaa and tfaa). This is insufficient to completely explain the quantum efficiency differences. Relative quantum yields of these compounds and related europium compounds in solution and in the solid state have been measured and these results are discussed. Spectroscopic and analytical evidence of 9-coordination in adducts of tetrakis β-diketoenolate compounds is presented and the isolation of some such compounds is reported. The ability of tetrakis compounds to increase their coordination sphere to nine in solution is demonstrated using an nmr technique. The occurrence of intermolecular energy transfer in solution containing lanthanide chelates has been observed. The possibility of triplet- triplet transfer has been investigated and the data indicate that this is possible over relatively short distances. Lanthanide- lanthanide transfer has been established and the results Eire consistent with a diffusion controlled process. The efficiency of this process is relatively low. Intermolecular energy transfer in some crystalline chelates has been observed and is interpreted in terms of triplet-triplet and lanthanide-lanthanide transfer processes.

Made available in DSpace on 2014-06-11T19:32:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2003Bitstream added on 2014-06-13T20:42:56Z : No. of bitstreams: 1 marques_rfc_dr_araiq.pdf: 3201564 bytes, checksum: 52e1050410ca60bb9191ed79b606558e (MD5) / Manganita de lantânio dopada com estrôncio (La1-xSrxMnO3) tem recebido atenção da comunidade científica por apresentar propriedades elétricas e magnéticas, com funções para sensores de campo, catalisadores, eletrodos em células combustíveis, entre outras. A substituição de La3+ por Sr2+ resulta em uma transição de um estado isolante antiferromagnético para um estado metálico ferromagnético em composições de x³0,17 com valência mista Mn3+-Mn4+ responsável pelos portadores de carga. Na presença de campo magnético externo as manganitas dopadas exibem a propriedade magnetoresistência negativa gigante (GMR) e a resistividade do material varia com a temperatura e com o campo magnético aplicado. Este trabalho descreve a síntese de nanopartículas de La1-xSrxMnO3 (x=0,1; 0,2 e 0,3) pelo método da coprecipitação homogênea usando uréia como agente precipitante. Neste método, novos ligantes, tais como NH4 +, OH- e CO3 2-, podem substituir as moléculas de água nas posições de coordenação delas com os íons metálicos. Este método leva a uma nucleação homogênea prevenindo o crescimento das partículas precursoras. A dependência da magnetização DC com a temperatura para as amostras La1-xSrxMnO3 (x=0,1; 0,2 e 0,3) forneceu valores de temperatura crítica (TC) iguais a 140 K, 316 K e 357 K, respectivamente. A dependência da resistividade elétrica com a temperatura para pastilhas destes materiais apresentaram a transição metal-isolante e os valores encontrados para TC são similares aos valores de TC observados em monocristais destas manganitas. Espectroscopia infravermelho foi realizada para estudar as propriedades de transporte... / Lanthanum strontium-doped manganite (La1-xSrxMnO3) has attracted renewed attention at present due to the observation of interesting electrical and magnetic properties such as a giant negative magnetoresistance (GMR), catalytic, oxygen cathode reduction, field-sensing, among others. The substitution of La3+ ions by Sr2+ results in a transition from antiferromagnetic insulating state to a ferromagnetic metallic state at x ³ 0.17 with a Mn3+-Mn4+ mixed valence state responsible for the mobile charge carriers. This work describes the La1-xSrxMnO3 (0.1, 0.2 and 0.3) nanoparticle synthesis by the homogenous coprecipitation method using urea as precipitant agent. In this method, some new ligands like NH4+, OH- and CO3 2- can substitute the water molecules coordinating the metallic ions. This method allows the homogenous nucleation and prevents the particle precursors to grow. The temperature dependence of DC magnetization of the samples La1-xSrxMnO3 and critical temperature (TC) values were found to be 140 K, 316 K and 357 K, respectively for x = 0.1, 0.2 and 0.3. Temperature dependence of the electrical resistivity exhibits a metalinsulator transition at Tc in pellet samples and Tc values were found to be similar to those observed in single crystals of these manganitas. Infrared spectroscopy was performed to study spin dependent transport properties using the magnetorefractive effect (MRE), which probes the change of reflection in the infrared (IR) spectral region due to the change in electrical conductivity in the presence of a magnetic field. In the IR spectral region, the free carrier dispersion mechanism often dominates and MRE have been used to study intraband transitions of the conduction...(Complete abstract, click electronic access below)

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published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy