Study of structure and dynamics of monolayers containing proteins and lipids at the air-water interface using two dimensional infrared spectroscopy methods
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Chapters 3 – 8 of this dissertation are composed of individual manuscripts which have either been published or submitted to scholarly journals. In Chapter 3, 2D IR correlation analyses are performed on IRRAS spectra of surfactant proteins B and C containing lipid monolayers at the air-water interface. Based on the correlation plots, it was concluded that the secondary structures of SP-B and SP-C are heterogenous and change with increase in surface pressure. Chapter 4 describes an investigation using infrared spectroscopy into the change in the secondary structure of deacylated SP-C with pH. In Chapter 5, a new model-based 2D IR method is introduced and described using simulated spectral models. This method, k correlation, makes use of a set of simulated exponential curves that are mathematically cross-correlated against a set of experimental curves and the resulting correlation plot between spectral frequency and rate constant reveals temporal relationships in terms of a numerical parameter. In Chapter 6, the k correlation method is used to study the interaction between a phospholipid (DPPA) monolayer and the antibiotic Tetracycline by collecting PM-IRRAS spectra at the air-water interface. A synthetic peptide, mSP-B1-25, is characterized using PM-IRRAS at the air-water interface and k correlation to determine if it can be used as an effective replacement for the native SP-B protein in lung surfactant. This study, presented in Chapter 7, revealed the changes in secondary structure of the peptide present in different concentrations in a lipid matrix of deuterated DPPC and DOPG on subphases containing sodium and calcium ions. In Chapter 8, Ag nanorod substrates, that are prepared by vapor deposition on the substrate at an oblique angle, are characterized for their SERS activity. Nanorod samples of different lengths were characterized at 785nm using 1,2-trans(bi-pyridyl)-ethene as a probe molecule. Surface 8Enhancement factors of 10 were observed and the enhancement factor was found to increase with increase in the length of the nanorods.