Dokument: Studies on coacervation phase behavior of sequence-controlled polyelectrolytes
| Titel: | Studies on coacervation phase behavior of sequence-controlled polyelectrolytes | |||||||
| URL für Lesezeichen: | https://docserv.uni-duesseldorf.de/servlets/DocumentServlet?id=69117 | |||||||
| URN (NBN): | urn:nbn:de:hbz:061-20250325-112139-8 | |||||||
| Kollektion: | Dissertationen | |||||||
| Sprache: | Englisch | |||||||
| Dokumententyp: | Wissenschaftliche Abschlussarbeiten » Dissertation | |||||||
| Medientyp: | Text | |||||||
| Autor: | Illmann, Michele Denise [Autor] | |||||||
| Dateien: |
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| Beitragende: | Prof. Dr. Hartmann, Laura [Gutachter] PD Dr. Schaper, Klaus [Gutachter] | |||||||
| Dewey Dezimal-Klassifikation: | 500 Naturwissenschaften und Mathematik » 540 Chemie | |||||||
| Beschreibung: | Many biologically relevant molecules are polyelectrolytes e.g., DNA or proteins, but also synthetic polyelectrolytes are of great importance in our everyday life e.g., as superabsorbers or adhesives. When two polyelectrolytes are mixed together, a polyelectrolyte complex is formed, which can occur in the form of coacervates. Coacervation describes a liquid-liquid phase separation, in which most of both polymers are deposited in one of the two phases – the polymer-rich phase or coacervate. This process is based on the electrostatic interaction between the charged groups of the polymers and is induced at a certain polymer and salt concentration. Coacervate formation is again relevant both for natural and synthetic polyelectrolytes. An example from nature is the velvet worm: coacervate formation of its hunting slime enables its unique hunting skill by forming stiff fibers through mechanical shear forces out of this slime. Another example is a cell, where phase separation of intrinsically disordered proteins (IDPs) leads to the formation of membraneless organelles and can thus protect internal cell processes from the cytoplasm without an additional solid cell membrane. Despite the wide relevance, the formation of coacervates is not yet fully understood, as not only polymer-related parameters such as chain length, charge sequence and -density are key indicators. Many external influences such as salt concentration, temperature or the pH value can have an impact on the phase separation process by affecting the net charge of the polymer complex. To gain deeper insights, the tailor-made synthesis of polyelectrolytes with controllably variable structures supports the research of coacervation formation. In the present work, the aim was to synthesize sequence-controlled polyelectrolytes in order to investigate the impact of placing the same charged groups at different positions within the overall polyelectrolyte structure on the coacervate formation and to explore new possible applications in the field of biomimetic systems.
The first part of the thesis focuses on the synthesis of such sequence-controlled polyelectrolytes. Previous studies of coacervation behavior focused on the synthesis of sequence-controlled polyelectrolytes using solid-phase synthesis, a well-known approach for the sequential assembly of building blocks towards peptide structures. However, this type of synthesis is limited in its number of repeating units. Solid-phase synthesis was used in this work in combination with polymer analogous reactions to access brush-shaped polyelectrolytes and polyampholytes. For this purpose, oligo-electrolytes and oligo-ampholytes were sequentially synthesized using Fmoc-based solid-phase synthesis, which were subsequently coupled onto active ester polymers using the “grafting to” method. The method benefits from using the same polymer backbone for the conversion to the polyelectrolyte and polyampholyte structures, which contributed to greater comparability in the further process. The challenge during oligomer synthesis was to find a suitable protection group to keep the amino acids side chains inactive during the overall synthesis to prevent crosslinking during polymer analogous reaction. Alloc and Allyl protection groups were used to protect lysine and glutamic acid side chains, because of their good stability in both acidic and alkaline conditions as well as their general applicability on oligo-electrolyte and oligo-ampholyte synthesis. Active ester polymers were produced by polymerizing pentafluoro phenyl monomers via RAFT polymerization. The obtained polyactive ester derivatives were used as a polymer backbone for the subsequent substitution of the pentafluoro phenyl side chains with terminal primary amine groups of the oligomers. Comparable linear structures were obtained by conjugating active ester polymers with glycine and ethanolamine. The targeted functionalization degree of the oligomers into the polymer was chosen to compare with the linear charged polyelectrolytes. Final cleavage of the amino acid side chain Alloc and Allyl protection groups after polymer conversion was challenging, as currently existing cleavage protocols were optimized on solid-phase synthesis systems which required an adaption to a reaction in solution. A result of this work is the successful synthesis of sequence-controlled polyelectrolytes and polyampholytes as well as their characterization by 1H-, 19F-NMR and GPC. In the second part of this work, the synthesized polyelectrolytes and polyampholytes were investigated for their coacervation behavior. For the linear charged polyelectrolytes, a phase diagram was obtained in dependance of the salt- and polymer-concentration in order to define the liquid-liquid phase separation range. The influence of polymer chain length confirmed coacervation behavior of longer polyelectrolytes, which lead to a higher salt resistance and thus to an enhanced phase separation area. However, this increase could only be observed up to a certain polymer concentration, beyond this concentration salt resistance of longer polymer backbone dropped drastically and the polyelectrolytes were present in a precipitated form and no longer in a liquid phase. When comparing linear polyelectrolytes with the brush-shaped polyelectrolytes, the salt resistance of the coacervate phase decreases significantly. Also, solubilities of the polymers were strongly impaired by this polymer structure and were therefore only analyzed at lower polymer concentrations. The investigation of linear, ampholytic polymers, on the other hand, did not lead to any phase separation, which could be due to an insufficient accumulation of charges. Coacervation was found to be favored by high charge densities of equally charged groups, which could not be guaranteed with this purely randomly constructed polyampholytes. When synthesizing polyampholytes from sequence-defined oligo-ampholytes, a system with an increased charge density was obtained to exhibit liquid-liquid phase separation at low salt concentrations. The first coacervate droplets were already observed from polymer with oligo-ampholytes with two consecutive, identical charges, even though these systems exhibited significantly lower salt resistance compared to the linear polyelectrolytes. Nevertheless, a successful initial investigation of the coacervation behavior was carried out and the first comparisons of brush-shaped polyelectrolytes and polyampholytes were made regarding their polymer length, charge distribution and charge density. In the final part of this work, glycan presenting polyelectrolytes were synthesized and investigated for their phase behavior as well as their biomolecular interactions with lectins and bacteria. For this purpose, mannose and galactose functionalized oligomers were prepared by solid-phase synthesis and converted to polyelectrolytes via polymer analogous reaction, using the same method as described before. First coacervation tests in solution showed that coacervate droplets can also be formed with these glycan presenting polyelectrolytes, which, however, show significantly slower phase separation. This may be due to a lower charge density caused by the carbohydrate units present. Furthermore, these coacervate droplets were analyzed in biological assays for their specific interactions with lectins and bacteria. It was found that the coacervates bearing mannose units were able to capture significantly more of the lectin Concanavalin A, a mannose-specific binding protein, than galactose-containing or non-glycan presenting coacervate droplets. Furthermore, in first studies with E. coli bacteria it was observed that both, the mannose-bearing and the unfunctionalized coacervates showed interaction with the bacteria. This suggests that also non-glycan interactions, most likely from the charges of the polyelectrolytes, have an influence on the capture of the bacteria within the coacervate phase. Indeed, E. coli presents a surface charge as well which was investigated by Zeta potential measurements. If, however, the mannose functionality is blocked by an access of methyl α-D-mannopyranosid or coacervates containing galactose are used, an almost shielding effect can be observed, which not only leads to "non-capture" of the E. coli bacteria but actually repelled them. To summarize this, the introduction of specific binding units into liquid condensates opens up new possibilities for the investigation of lectin-carbohydrate interactions and the design of new functional materials. Overall, this work provides an extended synthesis route that allows access to sequence-controlled polyelectrolytes and polyampholytes. In addition, initial investigations not only allowed further conclusions to be drawn about the phase behavior of coacervates, but also revealed potential for application in the field of biomimetics. | |||||||
| Lizenz: |  Dieses Werk ist lizenziert unter einer Creative Commons Namensnennung 4.0 International Lizenz | |||||||
| Fachbereich / Einrichtung: | Mathematisch- Naturwissenschaftliche Fakultät » WE Chemie » Organische Chemie und Makromolekulare Chemie | |||||||
| Dokument erstellt am: | 25.03.2025 | |||||||
| Dateien geändert am: | 25.03.2025 | |||||||
| Promotionsantrag am: | 06.08.2024 | |||||||
| Datum der Promotion: | 05.12.2024 |
