Scholarship & Research
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Item A thermodynamic and optical assessment of soluble carbon particulate effects on lipid film structure and organization(Montana State University - Bozeman, College of Letters & Science, 2022) Shaikh, Nida; Chairperson, Graduate Committee: Robert Walker; This is a manuscript style paper that includes co-authored chapters.Research described in this thesis investigates the effects of carbonaceous particulate matter on model biological membrane structure, organization, and function. Although the harmful impacts of black carbon are well-documented, researchers lack the chemically-specific, mechanistic information necessary for understanding how black carbon aerosols affect lung surfactant spreading and compression. Surface specific optical spectroscopy methods together with complementary thermodynamic methods are used to measure how carbon nanoparticles, a model for black carbon aerosols that are a component of particulate matter (PM 2.5 ), change average lipid conformation, orientation, thickness, and compressibility in monolayers, and how these changes affect overall membrane organization. Addressing these questions requires a suite of independent, but complementary, experimental techniques including Langmuir trough and surface tension measurements, surface specific nonlinear optical spectroscopy measurements including both second harmonic generation and sum frequency generation, and spectroscopic ellipsometry measurements. Work presented in this thesis discusses cooperative adsorption as a possible mechanism to explain the interactions between DPPC monolayers and PHFs at biologically-relevant aqueous - air interfaces. The experiments forthcoming represent a detailed investigation of 1) the mechanism(s) responsible for accumulation of carbon particulates at the aqueous/monolayer/air interface present in the lungs, and 2) how specific thermodynamic behavior and optical properties (i.e. structure, composition, membrane integrity, orientation, thickness, and organization) at the aqueous/monolayer/air interface change with the inclusion of non-biological, nano-sized materials. Motivating this work is a need to develop a predictive understanding of black carbon - lung surfactant interactions and how non-biological, nano-sized materials impact membrane structure and function.Item Organic enrichment at aqueous interfaces studied with non-linear spectroscopy: cooperative adsorption of soluble saccharides to lipid monolayers(Montana State University - Bozeman, College of Letters & Science, 2019) Link, Katie Ann; Chairperson, Graduate Committee: Robert Walker; Chia-Yun Hsieh, Aashish Tuladhar, Zizwe Chase, Zheming Wang, Hongfei Wang and Robert A. Walker were co-authors of the article, 'Vibrational studies of saccharide-induced lipid film reorganization at aqueous/vapor interfaces' in the journal 'Chemical physics' which is contained within this thesis.; Gabrielle N. Spurzem, Aashish Tuladhar, Zizwe Chase, Zheming Wang, Hongfei Wang and Robert A. Walker were co-authors of the article, 'Organic enrichment at aqueous interfaces: cooperative adsorption of glucuronic acid to DPPC monolayers studied with vibrational sum frequency generation' submitted to the journal 'Journal of physical chemistry B' which is contained within this thesis.; Gabrielle N. Spurzem, Aashish Tuladhar, Zizwe Chase, Zheming Wang, Hongfei Wang, and Robert A. Walker were co-authors of the article, 'Cooperative adsorption of trehalose to DPPC studied with vibrational sum frequency generation' which is contained within this thesis.Field measurements of sea spray aerosols have reported high concentrations of soluble organic material that are in excess of the concentration of soluble organics in the ocean. The studies described in this dissertation investigated a possible mechanism for this increase deemed cooperative adsorption. The cooperative adsorption mechanism describes an interaction between an insoluble Langmuir monolayer at the aqueous/vapor interface and soluble organic molecules that would not normally be enriched at the surface. In this model, the soluble organics are drawn to the surface through non-covalent interactions with the lipid surfactant. This mechanism was investigated with the surface specific nonlinear optical technique, vibrational sum frequency generation spectroscopy. These optical measurements were coupled with surface tension measurements and differential scanning calorimetry measurements. To study cooperative adsorption, model systems were used; these were composed of a phosphatidylcholine lipid surfactant, DPPC, and soluble saccharides including glucosamine, glucuronic acid, and trehalose. Glucosamine, in both a positive and neutral state, induced ordering in both expanded and condensed DPPC monolayers, supporting cooperative adsorption as a mechanism. Glucuronic acid, an anion, ordered lipid monolayers in the limits that the lipid DPPC was moderately packed and there were no competing ions in solution. Trehalose, a larger, uncharged saccharide showed, through ordering the DPPC monolayer, indications of cooperative adsorption in moderately packed DPPC when the trehalose concentration was sufficiently high. These results support cooperative adsorption as a mechanism for the accumulation of soluble organics in sea spray aerosols with some limitations.