Realizamos dentro do formalismo ab-initio do funcional da densidade e pseudopotenciais com conservação da norma, estudos detalhados da geometria atômica e estrutura eletrônica das superfícies Si (001) com a deposição de Cl atômico sobre as reconstruções (2x1) e (4x2), e disposição de Cl molecular sobre a superfície (001) com reconstrução (2x1). Estudamos também a superfície Si (111) com reconstruções (1x1), (2x1) e (4x2) com a deposição de Cl atômico. A superfície Si (001)-(2x1) com deposição de CI molecular mostrou evidências da não desorção do composto SiCI2. Os resultados para a deposição de Cl atômico sobre as superfícies Si (001)-(2x1) e Si (001)-(4x2) foram os mesmos para a geometria atômica e energia total por átomo de superfície. Os átomos de CI posicionam-se a 19,5° em relação a normal com um comprimento de ligação de 2,08 A. As superfícies Si (111)-(2x1) e Si (111)-(4x2) utilizando o modelo de cadeias ? forneceram os mesmos resultados para a geometria atômica e energia total. Os átomos de Cl posicionam-se com ângulos de 24,2° e 25,2° em relação a normal e comprimento de ligação de 2,09 A. Um efeito de blindagem e observado para a superfície livre Si (111)-(1x1) originado pela presença de ligações ? entre orbitais pz dos átomos das duas primeiras camadas. Estes estados são mais ligados do que os estados de mesma natureza para os átomos da terceira e da quarta camada. Esta blindagem e removida após a deposição de CI ocorrendo uma troca em nível de energia entre estes estados. Para a superfície Si (111)- (1x1)CI os átomos de Cl posicionam-se normalmente à superfície com comprimento de ligação de 2,08 A. A geometria relaxada dos átomos de Si aproxima-se da geometria ideal. Em todos os casos, os estados apresentados na região do gap fundamental são temem removidos após a deposição de átomos de Cl. Estados puros de CI e estados ressonantes apresentam-se especialmente nas regiões dos gaps estômagos. Uma técnica para a separação de estados eletrônicos originários de uma determinada região do cristal é introduzida. Esta técnica mostrou-se eficiente num processo de identificação de estados eletrônicos, contribuindo como uma ferramenta importante na investigação rigorosa sobre a ocorrência de estados da mesma natureza na estrutura eletrônica do cristal. / We have done within the ab-initio density-functional formalism and norm-conserved pseudo-potential, detailed studies for the atomic geometry and electronic structure of Si(001) covered with atomic chlorine on tlle (2x1) and (4x2) reconstructions, and molecular chlorine adsorption on the (2x1) reconstruction. The surface Si(111) with atomic chlorine adsorption on the (1x1), (2x1) and (4x2) reconstructions were performed as well. The Si(001)-(2x1) with molecular de-position have shown evidences of non-desorption of the SiCl2 compound. The results for ato-mic deposition of Cl on Si(001)-(2x1) and Si(001)-(4x2) surfaces were the same for the atomic geometry and total energy per surface atom. The CI atoms stay at 19.5° off normal and Si-CI bond-length is 2.08 A for the relaxed surface. The Si(111)-(2x1) and Si(111)-(4x2) surfaces with the 11\" model chain have shown the same results for atomic geometry and total energy. The CI atoms atop the Si atoms with 24.2° and 25.2° off normal each one and the bond-length is 2.09 A for both. We have found screening effects on the clean Si(111)-(1x1) surface. These effects are origina-ted by 11\" bonds of pz orbitals between the first and the second atom layer that are more energetically bonded than the similar states observed between the third and the fourth atom layer. The screening is removed after CI deposition observing the swap of energy levels betwe-en that states. For Si(111)-(1x1)Cl surface, the Cl atoms atop surface normally with bond-length 2.08 A. The relaxed geometry for the Si atoms approaches to the ideal geometry. The states that have been found in the gap region for all clean surfaces are completely remo-ved after Cl deposition. Pure Cl states and resonant states were found specially in the intern stomach gaps. We have introduced a technique to collect electronic states originated from one specific crys-tal region. This technique has shown to be very efficient for electronic state identification pro-cess, contributing as an important tool for rigorous analyses, conceming about electronic sta-tes of the same nature in the electronic structure.

In this research, the interfacial behavior of Trichoderma reesei CBHI and Thermomonospora fusca E��� cellulases were studied at synthetic surfaces. For this purpose, colloidal silica and polystyrene particles were used to prepare cellulase-particle suspensions that were analyzed by several solution-phase techniques. These included circular dichroism spectroscopy, size exclusion chromatography and filtration, and a spectrophotometric assay for cellulase activity. All techniques were performed in the presence and absence of particles. Circular dichroism spectroscopy (CD) and size exclusion chromatography showed, however, that binding did not occur between either cellulase and silica, presumably because silica is hydrophilic and negatively charged. Binding did occur between each cellulase and polystyrene, most likely mediated through hydrophobic associations. Cellulase-polystyrene complexes were not analyzed using CD because of high light absorption by the polystyrene nanoparticles. Upon adsorption to polystyrene, the activity of the E��� dropped about 95% relative to that of the free enzyme. While this substantial loss in activity may have been the result of binding being mediated through the catalytic domain, strong evidence supporting the thought that adsorption occurs through hydrophobic associations, mediated through the binding domain, suggests that structural or steric factors were partly responsible for the loss. / Graduation date: 1999

Graduation date: 1996

No description available.

No description available.

Graduation date: 1993

Thesis (M.S.)--University of Michigan, 1979.

Thesis (doctoral)--Göteborg University, 1997. / Added t.p. with thesis statement inserted.

Thesis (M.S.)--University of Michigan, 1979.

Thesis (doctoral)--Göteborg University, 1997. / Added t.p. with thesis statement inserted.