Dokument: Thermosensitive Display of Carbohydrate Ligands on Microgel Scaffolds to facilitate switchable Bioadhesion
| Titel: | Thermosensitive Display of Carbohydrate Ligands on Microgel Scaffolds to facilitate switchable Bioadhesion | |||||||
| URL für Lesezeichen: | https://docserv.uni-duesseldorf.de/servlets/DocumentServlet?id=55089 | |||||||
| URN (NBN): | urn:nbn:de:hbz:061-20210104-114119-7 | |||||||
| Kollektion: | Dissertationen | |||||||
| Sprache: | Englisch | |||||||
| Dokumententyp: | Wissenschaftliche Abschlussarbeiten » Dissertation | |||||||
| Medientyp: | Text | |||||||
| Autor: | Paul, Tanja Janine [Autor] | |||||||
| Dateien: |
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| Beitragende: | Jun. Prof. Dr. Schmidt, Stephan [Betreuer/Doktorvater] Prof. Dr. Janiak, Christoph [Gutachter] | |||||||
| Dewey Dezimal-Klassifikation: | 500 Naturwissenschaften und Mathematik » 540 Chemie | |||||||
| Beschreibung: | Interactions between carbohydrates and lectins at the surface of cells control numerous biological processes such as fertilization, cell-cell communication, signaling, and bacterial as well as viral infections. The interactions of lectins and carbohydrates are usually weak, thus multivalency is a hallmark of carbohydrate-binding, which is of key importance to increase the affinity and specificity and to control downstream biological functions. These multivalent effects on the cell surface are highly complex and not completely understood. A valuable strategy to decipher these mechanisms are well-controlled glycomimetic structures and studying their interaction with biological targets. These glycomimetics represent simplified analogues of the complex oligosaccharide structures found on the cell surface, e.g. by only presenting the terminal carbohydrate unit on the polymer scaffold. Glycomimetic polymer scaffolds can have various shapes like linear or branched polymers, 2D polymer arrays or microgels. Furthermore, polymer scaffolds allow the control over the elastic modulus and the hydrophobicity of the overall structure, which will, in turn, affect the interaction and adhesion properties to cells. Using so-called responsive polymers, these parameters can be controlled by remotely “switching” the temperature, pH or other parameters. Importantly, the multivalent presentation of carbohydrate ligands on polymer scaffolds and thus the specific adhesion cells could be controlled by such switchable scaffolds as well. This thesis thus aims at synthesizing thermoresponsive glycopolymer mimetics and investigating their binding properties upon temperature stimulus.
In the first part of this thesis, thermoresponsive microgels based on poly(N-isopropylacrylamide) (P(NIPAM)) are functionalized with carbohydrate ligands. By varying the glycomonomer concentration, it is possible to synthesize a set of microgels with different carbohydrate densities in a single reaction step below 1 mol%. The microgels show a decrease in the lower critical solution temperature (LCST) and an increase in size when the carbohydrate concentration increases. These microgels are able to undergo a 10-fold change in volume when crossing the LCST, which allows for a drastic change in the ligand density on the surface of the microgels. To test this effect, binding studies towards the lectin Concanavalin A (ConA) are carried out indicating that the binding affinity is increased with temperature and the collapse of the microgels. Additionally, binding studies with Escherichia coli (E.coli) showed stronger specific binding when the temperature is raised above the LCST. Further studies with fluorescence microscopy and shorter incubation times showed that it is possible to catch and release E. coli upon temperature switch. In the second part of this thesis, carbohydrate-bearing thermoresponsive polymers are synthesized via a two-step approach. In the first step, a poly(active ester) is synthesized. In the second step, amine-functionalized carbohydrates and isopropylamine are grafted onto the polymer. Using this technique, a set of ten glyco-functionalized thermoresponsive polymers is produced, and the effect of different carbohydrate linkers, as well as the ratio of the carbohydrate to the thermoresponsive N-isopropylacrylamide (NIPAM) units, is investigated. In the binding studies, the polymers serve as temperature-dependent adhesion inhibitors for ConA and E. coli and a change in the adhesion inhibition can be observed in dependence of the carbohydrate concentration within the polymer. Interestingly, for polymers with low amounts of carbohydrate (below 2 mol%), the binding affinity can be switched by temperature stimulus, and the inhibition of ConA decreases with elevated temperature while the inhibition of E. coli is enhanced. The coil-to-globule transition of the polymers leads to a different accessibility of the ligands and causing a different inhibition towards the different sized receptors. Based on the encouraging results of the first parts, selected carbohydrate-functionalized microgels are used to prepare thin films on solid surfaces. An inhibition and direct binding assay are carried out, and it is found out that ConA binding is time-dependent, where for short incubation times (30 min) the binding above the LCST is favored and at long incubation times (24 h) the binding towards the swollen microgel surface is stronger due to diffusion of the receptor into the microgel network. The ability of the surfaces to bind bacteria is tested with E. coli. As seen before, contradicting results compared to ConA binding are obtained. For an incubation time of 30 min, no differences in binding above or below the LCST can be observed, while for 24 h the affinity towards the collapsed microgel surface is enhanced. Overall, these results show, that diffusion times and the size of the receptor are parameters that lead to diverging binding affinities above or below the LCST of the glycopolymer scaffolds. To summarize, in this thesis, the effects of ligand density on different thermoresponsive scaffolds as well as their temperature-dependent binding towards different sized receptors in solution and on surfaces are demonstrated. The results shed new light on contradicting results in the literature on the specific binding of glycopolymer scaffolds above or below the LCST. New insights are provided, not only in carbohydrate-lectin based interactions but also for the development of catch and release devices for pathogens. | |||||||
| Lizenz: |  Urheberrechtsschutz | |||||||
| Fachbereich / Einrichtung: | Mathematisch- Naturwissenschaftliche Fakultät » WE Chemie » Organische Chemie und Makromolekulare Chemie | |||||||
| Dokument erstellt am: | 04.01.2021 | |||||||
| Dateien geändert am: | 04.01.2021 | |||||||
| Promotionsantrag am: | 20.10.2020 | |||||||
| Datum der Promotion: | 11.12.2020 |
