This title appears in the Scientific Report :
2023
Please use the identifier:
http://dx.doi.org/10.18154/RWTH-2023-08845 in citations.
Please use the identifier: http://dx.doi.org/10.34734/FZJ-2024-00769 in citations.
Alternating amphiphilic polymers : from gels and micelles to translocation through lipid membranes
Alternating amphiphilic polymers : from gels and micelles to translocation through lipid membranes
Amphiphilic polymers possess both hydrophobic and hydrophilic properties, which make them able to self-assemble in aqueous solutions, be surface active and have simultaneous solubility in polar and non-polar solvents. Therefore, they find various applications, also in industry, in different areas li...
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Personal Name(s): | Kostyurina, Ekaterina (Corresponding author) |
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Förster, Stephan Friedrich (Supervisor) / Richtering, Walter (Supervisor) | |
Contributing Institute: |
Neutronenstreuung; JCNS-1 JCNS-FRM-II; JCNS-FRM-II |
Imprint: |
Aachen
RWTH Aachen University
2023
|
Physical Description: |
161 pages |
Dissertation Note: |
Dissertation, RWTH Aachen, 2023 |
DOI: |
10.18154/RWTH-2023-08845 |
DOI: |
10.34734/FZJ-2024-00769 |
Document Type: |
Dissertation / PhD Thesis |
Research Program: |
Jülich Centre for Neutron Research (JCNS) (FZJ) |
Subject (ZB): | |
Link: |
OpenAccess |
Publikationsportal JuSER |
Please use the identifier: http://dx.doi.org/10.34734/FZJ-2024-00769 in citations.
Amphiphilic polymers possess both hydrophobic and hydrophilic properties, which make them able to self-assemble in aqueous solutions, be surface active and have simultaneous solubility in polar and non-polar solvents. Therefore, they find various applications, also in industry, in different areas like detergency, agriculture, food, material engineering or pharmaceutics. In experimental studies, statistical copolymer or block copolymer architectures are usually investigated, because of their ease of synthesis or their structural analogy to surfactants. A copolymer structure that links the two architectures is an alternating copolymer, which is easily accessible by polycondensation reactions. Using alternating hydrophilic and hydrophobic building blocks with varying lengths allows a systematic variation between statistical and multi-block architectures. In this project, the alternating amphiphilic polymers (AAP) were broadly and systematically studied with respect to their thermodynamic characteristics and structure formation in water and in an application to translocation through lipid membranes. Most of the AAPs used in this work were synthesized as polyesters from hydrophobic dicarboxylic acids and hydrophilic polyethylene glycol (PEG) units. These polymers possess a lower critical solution temperature (LCST) behavior in water, where the critical temperature can be varied in the range from 0 to 100oC by adjusting the lengths of hydrophobic and hydrophilic units. Moreover, the same LCST, which can be used as a measure for the overall polymer polarity, can be achieved by different combinations of unit lengths. In this way, the polarity profile along the polymer chain can be changed from a more homogeneous to a more alternating one. Depending on the overall polarity and on the polarity profile the AAPs can be dissolved in water as free chains, form micelles, gels, or ordered crystalline phases. These structures were investigated by small angle x-ray and neutron scattering and a qualitative phase diagram which represents the structures as a function of the hydrophobic and hydrophilic unit lengths was constructed. The micelles formed by the AAP have a pronounced core constructed by the hydrophobic domains embedded in a PEG rich and water poor matrix, whereas the micellar shell consists of a smaller number of PEG end groups or internal PEG units forming loops. Such micelles differ structurally from micelles formed by block copolymers or surfactants, where the core is formed exclusively by the hydrophobic units. The AAP gels are formed by interconnected micellar structures, which make the gel mechanically stable and can arrange in a crystalline order at high concentrations. The ability to tune the AAP polarity allows achieving polymers which are simultaneously soluble in water and non-polar environments as, for example, the interior of lipid membranes. Water soluble AAPs having such a balanced polarity can passively translocate lipid membranes, which was extensively studied in this thesis. The translocation properties were systematically studied by time-resolved Pulsed Field Gradient (PFG) NMR using large unilamellar vesicles (LUV) as model membranes. The restricted LUV inner volume allows to access independently adsorption and desorption rates, as well as the concentration of the translocating species in the membrane. It was found that the translocation process consists of a relatively fast membrane saturation with the polymers and a slow desorption process. The translocation time varies from minutes to hours depending on polymer and lipid composition, polymer molecular weight, and temperature. On the basis of these measurements a basic thermodynamic model of the translocation process was developed. Neutron reflectometry (NR) measurements proved that the AAP having short hydrophobic/hydrophilic units are located mainly in the hydrophobic interior of the membrane. The concentration in the membrane calculated from the NR study was similar to the one obtained by PFG NMR. Using fluorescent microscopy on giant unilamellar vesicles the ability of transferring a hydrophobic molecule through lipid membranes was proved. The ability of the AAPs to translocate and transfer molecules through lipid membranes can be important for biomedical applications. Therefore, potential cell toxicity properties of the AAPs were tested with living HeLa cells. The AAPs synthesized as polyesters showed no visible effect on the viability of these cells. Therefore, as the next step, in vivo translocation studies were performed using a fluorescently labeled AAP. The translocation through the plasma membrane of four different cell types was proved in a series of fluorescence microscopy measurements. The ability to tune the AAP composition in a wide range by still maintaining the translocation properties makes these polymers very interesting for biomedical applications. |