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Several low-lying levels in the exotic N = Z nucleus 62Ga have been observed for the first time using a new fast β-decay tagging system at the Argonne National Laboratory. The system provides enhanced selectivity on proton-rich nuclei, produced in heavy-ion fusion-evaporation reactions, that exhibit ‘fast’ β decays compared with isobaric contaminants. A 103 MeV beam of 40Ca ions, produced by the Argonne Tandem-Linac Accelerator System (ATLAS), was used to bombard an isotopically enriched 24Mg target, allowing 62Ga nuclei to be produced via the evaporation of one proton and one neutron in heavy-ion fusion evaporation reactions. Prompt γ rays were detected by the Gammasphere array, and recoiling reaction products dispersed by their mass-to-charge ratio by the fragment mass analyzer (FMA). New β-tagging capabilities were provided by the installation of a 1 mm thick, highly segmented 160×160 double-sided Silicon strip detector (DSSD) at the focal plane of the FMA, which allowed implanted reaction residues to be correlated in both space and time with subsequent β+ decays. The experiment was carried out with the benefit of digital acquisition systems for the Gammasphere, FMA and DSSD. The exotic nucleus 62Ga has a β-decay half-life of ∼ 100 ms. The main contaminants in the 40Ca + 24Mg fusion-evaporation reaction are 62Zn, which has a ∼ 9 hour half-life, and 58Ni, which is stable. A clean ‘singles’ γ-ray spectrum of 62Ga transitions was made permissible for the first time by the high levels of selectivity achieved, through requiring the detection of a β particle in the DSSD in close proximity to implanted reaction residues within 400 ms of implantation. Several low-lying low-spin states are reported in this thesis work, and discussed in the context of previous experimental results and theoretical predictions made using shell model, deformed shell model and IBM-4 calculations.

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Thesis (M.A.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / N-methylacetamide reacts with hypobromous acid to form N-bromo-N-methylacetamide and water. The kinetics of the reaction were studied spectrophotometrically using a Cary 14 spectrophotometer to observe the absorption of hypobromous acid at 3300 A. The reaction in aqueous solution is reversible under the mildly basic conditions at which it was studied and is of the type A + B --> C if water is disregarded since its concentration remains constant. Borate and carbonate buffers, pH 8.5-10.0, were used to keep the pH constant. An analysis of the kinetic data showed that the undissociated hypobromous acid reacts with N-methylacetamide in a second order reaction. Extinction coefficients of hypobromous acid were determined using concentrations known from iodometric titrations. The values increase with pH from 111 liters/mole at pH 8.5 to 265 liters/mole at pH 10 in borate buffers at 26.5°C. Extinction coefficients of N-bromo-N-methylacetamide were determined by forcing the reaction to completion using excess N-methylacetamide which does not absorb at 3300 A. Values of 24-26 liters/mole in borate buffers at 26.5°C were found. Extinction coefficients in carbonate buffer are of the same order of magnitude. [TRUNCATED] / 2031-01-01

No presente trabalho descrevemos a preparação dos compostos de adição entre hexafluorofosfatos dos lantanídeos e a DMA. Foram obtidos os compostos de toda a série lantanídica, e através de análises elementares foi possível estabelecer que os mesmos apresentam as fórmulas gerais: Ln(PF6)3.7DMA (Ln= La-Ho) e Ln(PF=La-Ho) e Ln(PF6)3 .6DMA (Ln= Er-Lu, Y). Os produtos são cristalinos, não apresentam higroscopicidade e fundem numa faixa de temperatura entre 115 e 125°C; são solúveis em água, nitrometano, acetonitrila, metanol, nitrobenzeno e acetona. Além da análise química elementar, os compostos foram caracterizados por espectroscopia de absorção na região do infra-vermelho, medidas de condutância molar em nitrometano e acetonitrila, medidas de condutância equivalente de alguns compostos representativos, registros de difratogramas de raios-X (método do pó). Foram obtidos espectros na região do visível dos compostos de praseodímio, neodímio, hôlmio e érbio. Os espectros de absorção na região do infra-vermelho mostraram que a coordenação do ligante se dá através do oxigênio do grupo carbonila e que o ânion PF6- não deve estar coordenado ao íon lantanídeo tripositivo, mantendo sua simetria octaédrica. Os valores obtidos para as medidas de condutância molar evidenciaram que os compostos comportam-se como eletrólitos 1:3 em acetonitrila e nitrometano. As medidas de condutância equivalente de alguns compostos em várias concentrações em acetonitrila, confirmaram a existência deste tipo de eletrólito e indicaram um comportamento de eletrólito fraco neste solvente, sugerindo a existência de pares iônicos, em solugões concentradas. Os difratogramas de raios-X obtidos pelo método do pó, permitiram verificar a existência de três séries isomorfas distintas: a primeira constituída apenas do composto de lantânio, a segunda formada pelos compostos Ln(PF6)3.7DMA e a última com preendendo os compostos de composição Ln(PF6)3.6DMA. Os espectros de absorção eletrônica em acetonitrila e DMA são muito semelhantes, sugerindo que a simetria em torno do íon central é a mesma nesses solventes e diferentes da dos correspondentes hexafluorofosfatos dos lantanídeos em solução aquosa. Os espectros de soluções dos compostos de praseodímio, neodimio, hôlmio e érbio em acetonitrila, em diferentes concentrações não são substancialmente modificados, apresentando absortividades molares praticamente iguais para as diversas bandas observadas na região do visível, mesmo em soluções concentradas, indicando que quando há formação de pares iônicos, a proximidade do ânion não modifica o arranjo ao redor do cátion complexo, volumoso, contendo sete ou seis moléculas de DMA. / The preparation and characterization of adducts between lanthanide hexafluorophosphates and DMA are described. According to elemental analysis the compounds present two general compositions: Ln(PF6)3.7DMA (Ln= La-Ho) and Ln(PF6)3.6DMA (Ln= Er-Lu, Y). The compounds are crystalline, not hygroscopic and melt between 115-125°C. They are soluble in water, nitromethane, acetonitrile, methanol, nitrobenzene and acetone. The adducts were characterized by infrared spectra, molar conductance measurements in nitromethane and acetonitrile, equivalent conductance and X-ray powder patterns. The electronic spectra of the compounds of praseodimium, neodymium, holmium and erbium were also obtained in different conditions. According to infrared spectra, the ligand is coordinated to the lanthanides through the carbonyl oxygen and the PF6- ions are not coordinated, maintaining its octahedral symmetry. Conductance data of millimolar solutions in nitromethane and acetonitrile indicate a behaviour of 1:3 electrolytes. Equivalent conductances of some compounds in acetonitrile showed a behaviour of weak electrolytes, suggesting the existence of ion pairs in concentrated solutions. According to X-ray data three types of patterns were observed, corresponding to: a) the compound of lanthanum; b) compounds from cerium to holmium; c) compounds from erbium to lutetium and yttrium. The electronic spectra of the compounds in acetonitrile and in DMA are practically identical, suggesting that the environment around the lanthanide ion is maintained in these solvents, but are different of the corresponding lanthanide hexafluorophosphates in aqueous solution. The spectra of solutions of the compounds of praseodymium, neodymium, holmium and erbium at different concentrations in acetonitrile are not considerably modified presenting about the same molar absorptivities. This fact may be explained in terms that vicinity of the anion does not modify the environment around the bulky, tripositive lanthanide cation complex.

This thesis explores changing curatorial strategies at the Museum of Fine Arts, Houston. This is preceded by an assessment of the Museum of Modern Art’s earlier role in systematizing and defining this field throughout the 1930s and 1940s. Three exhibitions of art from Latin America and Latino art will illustrate how the MFAH contributed to shifts in this field proposing parallel and expanded readings to those first introduced at MoMA. Firstly, the Gulf-Caribbean Art Exhibition (1956) was a collaboration with the Pan American Union. This exhibition was framed by Cold War modernist approaches and a re-imagined geographical conception of the Gulf region. Secondly, Hispanic Art in the United States- Thirty Contemporary Painters and Sculptors (1987) sought to include Latino art and reflect the community in Houston within this mainstream institution. This lead to traditional museum practices emphasising the quality of artworks, while the criteria for selection was based on the ethnicity of the artists. Finally, Inverted Utopias- Avant-Garde Art in Latin America (2004) revised curatorial structures that were based upon the geographical and national survey format. Six constellations emphasising nodal connections between movements from Latin America disrupted established narratives of this field. The extensive use of archival documents further aided this historical review. I will answer how political, diplomatic, social, and art historical contexts have influenced the curation of these exhibitions and the outcomes of each. I will argue that through the location of the MFAH in the south of the United States, this institution is able to experiment with curatorial approaches and contribute to reviewed readings of art and art history in the United States.

The introduction to this thesis examines the importance of N-dealkylation in pharmaceutical studies and considers the scope of microbial transformations and their possible role in effecting N-dealkylation. The experimental section is in eight parts, Chapters 2 and 3 are concerned with the screening of selected Pseudomonads, Streptomyces and fungi for their ability to N-dealkylate drug molecules. The development of qualitative analytical techniques is also detailed. A 'model' transformation system in which the alkaloid codeine is N-demethylated by C. echinulata was selected. Chapter 4 describes quantitative transformation studies in chemically defined growth media with the model transformation system. The effect of growth media components on codeine transformation is investigated and parameters which may influence microbial transformations, such as substrate concentration, are optimised. In Chapter 5, factors likely to affect the transformation process are characterised. These include microbial growth, carbon source depletion, extracellular protein levels and cell lysis. Chapter 6 investigates the feasibility of batch culture transformations in laboratory fermenters and examines the effect of culture pH on N-demethylation. Chapter 7 describes experiments with resting cells, and cell-free extracts prepared from C. echinulata aimed at establishing the type of catabolic regulation operative during transformations and the optimum pH, temperature and cofactor requirements for the N-dealkylation reaction. Studies using specific enzyme inhibitors, in an attempt to characterise the N-demethylase enzyme system, are also reported. Investigations into the microbial transformation of diazepam, a substrate with low aqueous solubility, are described in Chapter 8. Various pharmaceutical solubilisation techniques are investigated in an attempt to increase the diazepam solubility and transformation. The effect of two different fungal growth forms on diazepam transformation is also examined. Chapter 9 examines the effect of structural variations in the codeine molecule on N-demethylation and ability of C. echinulata to cleave more complex N-alkyl functions in 6,7, benzomorphans. In the discussion, the data are considered with reference to current microbial transformation literature and are compared to mammalian biotransformations utilising similar pathways.