Author ORCID Identifier

https://orcid.org/0000-0001-5077-8556

Year of Publication

2020

Degree Name

Master of Science in Chemical Engineering (MSChE)

Document Type

Master's Thesis

College

Engineering

Department

Chemical and Materials Engineering

First Advisor

Dr. Barbara L. Knutson

Second Advisor

Dr. Stephen E. Rankin

Abstract

In this work, we incorporated 4-(N-Boc-aminometyl) phenylboronic acid (BA), at different concentrations, into 1,2-dipalmitoyl-sn-glycero-3- phosphocholine (DPPC) bilayers confined within nanopores of two different mean pore diameters of 7.4 nm and 11.7 nm of micron sized silica particles. The confinement of DPPC into nanopores resulted in the depression in the main phase transition temperatures compared to the liposomal system. The addition of BA was found to induce disruptions in the acyl chains of the lipid molecules at all concentrations of the solute. The lipid bilayer cooperativity was found to be higher in the confined systems compared to the liposomal systems despite the presence of higher disorder in the hydrophobic acyl chains in the former as suggested by lower main phase transition temperatures. The partition coefficient of BA within the bilayers of DPPC was found to be higher in liposomal systems in comparison to the confined systems. The differences in mean pore sizes of the micron sized silica did not result in any significant differences in the partitioning behaviour of BA within DPPC. The results helped us understand the partitioning of BA in systems in which DPPC was confined into silica nanopores relative to DPPC liposomes. The knowledge of the behaviour of boronic acid in confined systems can help us in designing biomimetic systems, with optimum concentrations of the embedded molecule, to serve the purpose of separation of compounds from dilute aqueous solutions.

Subsequently, the method of evaporation deposition was used to fill the pores of silica nanoparticles with 1,2-dipalmitoyl-sn-glycero-3- phosphocholine (DPPC) and assess the effect of increasing the mass ratio of lipid to silica nanoparticles on the zeta potential and colloidal stability of the nanoparticles. An increase in the mass ratio resulted in observable reductions in magnitudes of zeta potential of the resulting nanoparticles compared to bare silica nanoparticles. Lipid enveloping of pore filled silica nanoparticles results in zeta potentials comparable to that of DPPC liposomes. The reductions in zeta potentials of the lipid filled silica nanoparticles were hypothesized to be the result of several isolated lipid bilayers covering the exterior surface of the nanoparticles, besides filling the nanopores. The complete assessment of colloidal stability of the system necessitates obtaining of information regarding the changes in hydrodynamic diameters and the settling behaviour, with extended time periods, of the lipid filled particles in conjunction with the obtained values of zeta potential of the system. The determination of the optimal amount of lipids that can be deposited into the silica nanopores would enable the designing of systems involving extraction and sensing of highly lipophilic molecules from dilute solutions.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.165

Funding Information

National Science Foundation Kentucky EPSCoR program (NSF Award No: 1355438). The funding was received from 2017-2019.

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