Thesis (Ph.D.)--University of Nebraska-Lincoln, 2006. / Title from title screen (site viewed May 22, 2007). PDF text: x, 87 p. : ill. ; 1.11Mb. UMI publication number: AAT 3237059. Includes bibliographical references. Also available in microfilm and microfiche formats.

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Modern theories of polymer solutions are highly successful in describing the physical properties of polymers. However, they encounter enormous difficulty when the system involves long range interactions, such as Coulomb and hydrodynamic interactions. Complexity usually arises from coupling between these interactions and the long polymer chain. In this thesis, I illustrate aspects of these complicated systems by using computer modeling techniques. For charged systems, I have been mainly interested in two physical aspects, the so-called counterion condensation and the conformational properties of polyions. Specifically, we studied the distribution of counterions around the polyions and the conformation as a function of Coulomb strength, chain length, monomer density and salt concentration. We found that condensed ions are arranged in such a way that neighboring dipoles are attractive. The counterion condensation rates are deviated from the Manning's condensation theory. The total charge fraction of polyions decrease as salt concentrations increase. We simulated polyion size and compared values to those of modern conformation theories, in particular, Muthukumar's theories. While we found, that theory can describe polyion size for most of cases, it fails when multivalent salts are added to the system. The failure of theory follows the neglect of the role of individual ions by mean field theory and a need to describe the effect of multivalent ions. We propose a simple modification of the original theory and obtain satisfactory results. For the systems with hydrodynamic interactions, we are particularly interested in the simple shear and extensional flow. We simulated in Ottinger's hydrodynamics approximation a bead-rod chain under the extensional flow and observed the possible existence of a first order transition. The critical strain rate for the transition scales as a power law in chain length with an exponent of −1.4, in good agreement with experimental results.

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A spectroscopic study of several calcium and strontium containing molecules has been completed. In total, seven electronic transitions from six different calcium or strontium containing species were observed and analyzed at high resolution. Using laser excitation spectroscopy in a laser ablation source, the high-resolution spectra of the A2Π- X2Σ+ transition of SrCCH, the B2A1- X2A1 transition of CaCH3, the A2E- X2A1 and B2A1- X2A1 transitions of SrCH3, along with the B2E- X2A1 transitions of SrBH4 and CaBH4 have been recorded and analyzed. For each molecule, a geometric structure in the ground and excited states was estimated and the fine structure constants for the excited state were investigated. A comparison of these geometries and parameters with those of other calcium and strontium containing species has yielded important information on bonding and electronic structure. For the A2Π state of SrCCH, the B2A1 state of CaCH3, and the A2E and B2A1 states of SrCH3, it was found that these states arise predominantly from pσ or pπ atomic orbitals located on Ca+ or Sr+ ions, consistent with the analogous states of CaF, SrF, CaOH and SrOH. For the B2E states of SrBH4 and CaBH4 a similar analysis showed an increased amount of d-atomic orbital character in these states. The D state of CaOH was investigated at high resolution using optical-optical double resonance spectroscopy in a Broida oven source. An analysis of the resulting molecular constants showed that the Ca-O bond length and spin-rotation parameter of the state have the smallest values of those for all the observed 2Σ+ states of CaOH. This evidence suggested that the D2Σ+ state arises from a Ca+ atomic orbital of mainly 5sσ character. This atomic orbital assignment was shown to be consistent with both previous work on CaF and recent theoretical calculations on CaOH.

A spectroscopic study of several calcium and strontium containing molecules has been completed. In total, seven electronic transitions from six different calcium or strontium containing species were observed and analyzed at high resolution. Using laser excitation spectroscopy in a laser ablation source, the high-resolution spectra of the A2Π- X2Σ+ transition of SrCCH, the B2A1- X2A1 transition of CaCH3, the A2E- X2A1 and B2A1- X2A1 transitions of SrCH3, along with the B2E- X2A1 transitions of SrBH4 and CaBH4 have been recorded and analyzed. For each molecule, a geometric structure in the ground and excited states was estimated and the fine structure constants for the excited state were investigated. A comparison of these geometries and parameters with those of other calcium and strontium containing species has yielded important information on bonding and electronic structure. For the A2Π state of SrCCH, the B2A1 state of CaCH3, and the A2E and B2A1 states of SrCH3, it was found that these states arise predominantly from pσ or pπ atomic orbitals located on Ca+ or Sr+ ions, consistent with the analogous states of CaF, SrF, CaOH and SrOH. For the B2E states of SrBH4 and CaBH4 a similar analysis showed an increased amount of d-atomic orbital character in these states. The D state of CaOH was investigated at high resolution using optical-optical double resonance spectroscopy in a Broida oven source. An analysis of the resulting molecular constants showed that the Ca-O bond length and spin-rotation parameter of the state have the smallest values of those for all the observed 2Σ+ states of CaOH. This evidence suggested that the D2Σ+ state arises from a Ca+ atomic orbital of mainly 5sσ character. This atomic orbital assignment was shown to be consistent with both previous work on CaF and recent theoretical calculations on CaOH.

In order to gain an understanding of the interaction of probe molecules with NaCh aggregates, steady-state and time-resolved photophysical methods were used. By employing several probe molecules, an understanding of how the structure of the probe affected binding to the two distinct sites in the aggregates was investigated. The first half of the thesis examined the reactivity of benzophenone (Bp) and 4,4-dimethylbenzophenone (DMBp) with NaCh aggregates by studying the kinetics of both the ketone triplet excited states and the ketone ketyl radicals. There were three species of triplet excited states observed in the presence of primary aggregates. One of the ketone triplet excited state species was located within the primary aggregate, and it reacted to form ketyl radicals. Other triplet states included in the primary aggregate were found to be long-lived, while a third species of triplet states was present in the aqueous phase. At higher bile salt concentrations, and in the presence of secondary aggregates, a layer of complexity was added. The binding dynamics for the triplet excited state with the secondary binding sites were much faster than those observed for the primary binding site. Hydrogen abstraction did not compete with other deactivation pathways in the presence of secondary aggregates, and thus only self-quenching and exit of the excited state probe from the secondary site were observed. Ketyl radical recombination took place in water and in the secondary sites. The second half of the research focused on the study a series of naphthalene (Np) derivatives in order to look at the effects of shape and hydrophobicity of probe molecules on the interactions between these probes and the host NaCh aggregates. 1-Ethylnaphthalene, 2-ethylnaphthalene, 1-acetonaphthone, 2-acetonaphthone, 1-naphthyl-1-ethanol and 2-naphthyl-1-ethanol were studied. 1-Ethylnaphthalene and 2-ethylnaphthalene were Ethylnaphthalene, 2-ethylnaphthalene, 1-acetonaphihone, 2-acetonaphthone, 1-naphthyl- 1-ethanol and 2-naphthyl-1-ethanol were studied. I-Ethylnaphthalene and 2- ethylnaphthalene were contained within the primary binding site, while 1-naphthyl-1-ethanol, 2-naphthyl-1-ethanol, 1-acetonaphthone and 2-acetonaphthone were contained within the secondary binding site. The effect of the position of the substituent was only noticed when the probe molecules formed weak interactions with the outside of the primary aggregate, and not when the probe was complexed to one of the binding sites present in the NaCh system. The naphthalene probe molecules were also used to study the effect of ionic strength on NaCh aggregate formation. It was found that primary aggregation occurred at lower NaCh concentration as the ionic strength was increased. No effect of ionic strength was observed on the formation of secondary aggregates. All the findings in this study are consistent with an aggregation model in which two distinct binding sites are present. The shape of the probe as well as its hydrophobicity are critical to its interaction with the NaCh aggregates. From these dynamic studies it was found that only a small number of NaCh monomers (6-13) are needed to define both the primary and secondary binding sites. / Graduate

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