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Synthesis of pH-sensitive cholesterol polymers and in vitro investigation of interactions with cell membrane
The aim of this thesis is to synthesize pH-sensitive, cholesterol containing polymers via reversible addition fragmentation chain transfer (RAFT) polymerization, as potential membrane-destabilizing agents for intracellular drug delivery applications and investigate interaction of these polymers with cell membrane. For this purpose, cholesteryl methacrylate (CMA) and 2-((tert-butoxycarbony)(2-((tert-butoxycarbonyl) amino) ethyl) amino)ethyl methacrylate (Boc-AEAEMA) were first synthesized. CMA was copolymerized with t-butyl methacrylate (t-BMA) or Boc-AEAEMA via RAFT polymerization to produce cholesterol containing copolymers having varying molecular weights and compositions. Copolymers were characterized using 1H-NMR spectroscopy and gel permeation chromatography (GPC). Linear increase in ln [M]0/[M] with polymerization time, and Mn with monomer conversion indicated the RAFT-controlled copolymerizations under the conditions tested. P(t-BMA-co-CMA) and P(Boc-AEAEMA-co-CMA) copolymers were hydrolyzed to methacrylic acid-co-CMA (p(MAA-co-CMA) and p(AEAEMA-co-CMA) copolymers, respectively, to obtain water soluble, pH-sensitive copolymers. The pH-responsive behavior of copolymers was demonstrated via UV−visible spectroscopy and dynamic light scattering measurements. These measurements revealed that (p(MAA-co-CMA) copolymers having 2 and 4 mol% CMA form nanoparticles at pH 5.5 while they exist as unimers at pH 7.4. Copolymers having 8% CMA form aggregates at both pH values. Hemolysis assays revealed that p(MAA-co-CMA) having a molecular weight above 20,000 g/mol did not show pH-dependent hemolytic activity regardless of CMA content. The cell viability results (obtained by MTT assay) indicated that p(MAA-co-CMA) at 250 μg/ml concentration is not cytotoxic to NIH3T3 cell line.