Investigating interfacial systems with solid-state nuclear magnetic resonance: characterization of lipids and materials
Creators: name: Bernstein, Ashley Dorothy
Publisher: name: No Publisher Supplied
Year: 2024

description: Solid-state NMR (ssNMR) is a powerful and versatile technique for characterizing a wide range of samples from biomolecules to materials. Solid-state NMR can provide atomic resolution insight into the structure and dynamics of complex systems. This work utilizes solid-state NMR to study lipids and materials.Lipid bilayers are investigated in chapters 2 and 3. Chapter 2 lays out the ground work for how ssNMR can be used to probe lipids at natural abundance using 31P and 1H. Liposome preparation optimization is also discussed, with sonication being chosen due to the resultant liposome size and longevity. Various lipid compositions are characterized, including liposomes containing phosphatidylserine (PS), which were studied in the presence of calcium. The longevity of the liposomes being studied is shown to be over two years. Studies of the lipid phosphatidylinositol triphosphate (PIP3) are presented, including with 2 mM [Ca2+] present. As intracellular calcium levels are significantly lower, PIP3-containing liposomes at a range of calcium concentrations were prepared and characterized in chapter 3. This calcium titration of PIP3-containing liposomes with and without PS is the focus of chapter 3. A full assignment of PIP3 by 1H, 31P, and 13C ssNMR is shown. The addition of calcium to PIP3-containing liposomes decreases head group rotational motion for the PIP3 head group phosphates both with and without PS. The formation of PIP3 clusters excludes the lipid phosphatidylcholine, which has increases in head group mobility with an increase in calcium concentration for the highest concentrations. Lateral diffusion decreases are observed via cross polarization kinetics with an increase in calcium concentration for PS and PIP3, with and without PS. The lateral diffusion of phosphatidylcholine only decreases with increased calcium concentration with both PIP3 and PS present, as the anionic lipid clusters are significantly larger.Solid-state NMR studies of materials are discussed in chapter 4. Drug-loaded polymers were studied due to their different drug release rates. 13C, 1H, and 19F NMR spectra did not show any changes upon drug loading for either polymer, indicating that no chemical interaction was occurring. NMR cryoporometry showed that the pore diameter of the slower releasing polymer was significantly smaller than the faster releasing polymer, making the pores more tortuous and difficult for the drug to leave the pores. Two different metal organic frameworks (MOFs) were also studied. The first, Zn-adtb, separates the linear C6 isomer nHex from other C6 isomers. The C6 isomers were found to reside within the 1D pore system of the MOF and to be highly mobile, indicating that the MOF is acting like a molecular sieve. The second MOF, Zr-tcbpe, was studied for its potential hydrolysis of CS2. A peak corresponding to CO2 was observed growing as the CS2 peak shrunk in intensity. Lead acetate tape tests were performed for proof of hydrolysis, leading to the discovery that the solvent Zr-tcbpe was synthesized in could hydrolyze the CS2 without the MOF present. A search for a set of suitable conditions to test Zr-tcbpe’s CS2 hydrolysis was carried out but was unsuccessful. Other parameters such as crushing the MOF were found to enhance the hydrolysis of CS2.