A Photophysical Investigation on the Role of Complexity on Controlling the Functions of Pluronic F127 and Sodium Deoxycholate Supramolecular Hydrogels
| dc.contributor.author | Awasthi, Ankur | |
| dc.contributor.supervisor | Bohne, Cornelia | |
| dc.date.accessioned | 2023-09-29T22:06:29Z | |
| dc.date.available | 2023-09-29T22:06:29Z | |
| dc.date.copyright | 2023 | en_US |
| dc.date.issued | 2023-09-29 | |
| dc.degree.department | Department of Chemistry | |
| dc.degree.level | Doctor of Philosophy Ph.D. | en_US |
| dc.description.abstract | Colloidal states of matter, where a solid three-dimensional network entraps a liquid mobile phase are known as gels. Based on the nature of the interactions between the building blocks that constitute the solid matrix, gels can be classified into chemical or supramolecular gels. The covalent linkages involved in chemical gels make them irreversible and functionally rigid in nature. The non-covalent nature of the interactions between the building blocks in supramolecular gels makes them more reversible and susceptible to external stimuli. However, the involvement of non-covalent interactions in the formation of supramolecular gels, increases the complexity associated with such systems and makes it difficult to predict their function. The primary objective of this dissertation was to understand the essential theoretical concepts that could facilitate the prediction of function in supramolecular gels. With respect to hydrogels, function can have various meanings depending on the type of application intended. For example, the release kinetics of loaded drugs from hydrogels can be considered one kind of function for a hydrogel. Another kind of function for a hydrogel could be its mechanical strength that can impact the different kinds of application a particular gel can be employed for. An additional outcome the work done in this dissertation seeks to emphasize is the significance of increased complexity in the designing of functional systems. Complexity is defined by the interconnected relationships between the various molecules involved in functional systems. By investigating systems where the complexity is gradually increased, my aim is to show that this increased complexity can be harnessed to design better functional hydrogel systems. The first project involved using known theoretical concepts around the self-assembly of polymeric F127 hydrogels. The micellar microstructures of the hydrogel allow for guest localization in either the hydrophobic core or the hydrophilic corona. By choosing a water insoluble fluorophore like N, N′-bis(salicylidene)-(2-(3′,4′-diaminophenyl)benzothiazole (BTS), the hydrophobic effect was exploited to confine BTS to the core of the F127 micelles. This fluorophore confinement to the hydrophobic core of the micelles allowed us to generate an emissive hydrogel whose emission color was seen to be unaffected by changes in its environmental pH. This emission is seen to be a result of all three forms of BTS, i.e., the neutral, tautomer and dianionic forms, existing in the excited state. Additionally, by changing the iv concentration of BTS localized within the hydrogels, the emission color from F127 hydrogels can be modulated. The second project utilized the technique of fluorescence quenching to gain a detailed understanding of the microstructures present in sodium deoxycholate (NaDC) hydrogels. Pyrene was used as a polarity sensitive fluorophore to investigate this hydrogel system. The ratio between peak I and III (I/III) of pyrene steady-state emission spectra revealed details around the polarity of pyrene localization within the hydrogels. The accessibility of two different quenchers, an ionic quencher, iodide anion and a neutral quencher, nitromethane to excited pyrene was studied using steady-state and time-resolved fluorescence. Steady-state results indicate that pyrene in the hydrophilic parts of the gel is quenched more efficiently than in the hydrophobic parts of the gel, irrespective of the quencher used. However, time-resolved studies indicate that among the three possible microenvironments available for pyrene localization, there exists a microenvironment that allows access to nitromethane but not to iodide anions. These results indicate the availability of microstructures in the hydrogel that have a high negative charge density, which is responsible for the lack of access to iodide anions due to electrostatic repulsions. The addition of cucurbit[6]uril (CB[6]) to these hydrogels results in a relocation of pyrene from the hydrophilic region to the hydrophobic regions of the hydrogel, indicated by the lack of alteration to the I/III ratio with increasing quencher concentration as well as the decreased access of the quencher. Moreover, the time-resolved studies indicate an increased heterogeneity for pyrene, which is a result of its complexation to CB[6]. Using the information from this project and previous work in the group, a molecular image of the hydrogel is successfully created that can explain the difference in release kinetics of pyrene and rhodamine 6G from NaDC-CB[6] hydrogels. The last project was designed to investigate if the release kinetics of guests from a hydrogel system would be dependent on the binding kinetics between the building blocks of a multi component hydrogel. This involved the design and synthesis of a monourea derivative, and studying its gelation behavior and binding kinetics with CB[6]. The gelation studies involved the use of inversion vial tests to observe how the gelation behaviour of the urea is affected due to the presence of salts and CB[6]. The study of the binding kinetics showed the presence of both fast v (0–50 s) and slow kinetic processes (5-30 min). The information from the kinetic studies confirm the presence of binding interactions of the urea with NaCl and CB[6], which are possibly responsible for the changes in its gelation behaviour. Using the available information from the preliminary studies done in this work, prospective new functionalized ureas that may possess better gelation properties in aqueous solvents in presence of CB[6] are proposed. | en_US |
| dc.description.scholarlevel | Graduate | en_US |
| dc.identifier.uri | http://hdl.handle.net/1828/15473 | |
| dc.language | English | eng |
| dc.language.iso | en | en_US |
| dc.rights | Available to the World Wide Web | en_US |
| dc.subject | Surpramolecular hydrogels | en_US |
| dc.subject | fluorescence | en_US |
| dc.subject | kinetics | en_US |
| dc.subject | control over hydrogel function | en_US |
| dc.subject | comlexity | en_US |
| dc.subject | host-guest chemistry | en_US |
| dc.subject | dynamics | en_US |
| dc.subject | pluronic F127 | en_US |
| dc.subject | sodium deoxycholate | en_US |
| dc.subject | fluorescence quenching | en_US |
| dc.subject | monourea derivatives | en_US |
| dc.subject | excited state intramolecular proton transfer | en_US |
| dc.subject | physical chemistry | en_US |
| dc.subject | Hydrogels | en_US |
| dc.subject | stimuli resistant hydrogel | en_US |
| dc.subject | molecular visualization of hydrogels | en_US |
| dc.subject | cucurbit[6]uril | en_US |
| dc.subject | cucurbit[n]uril | en_US |
| dc.subject | heterogeniety | en_US |
| dc.subject | microheterogeneity | en_US |
| dc.subject | hydrogel microenvironments | en_US |
| dc.title | A Photophysical Investigation on the Role of Complexity on Controlling the Functions of Pluronic F127 and Sodium Deoxycholate Supramolecular Hydrogels | en_US |
| dc.type | Thesis | en_US |