Vinsamlegast notið þetta auðkenni þegar þið vitnið til verksins eða tengið í það: http://hdl.handle.net/1946/32021
Unmodified chitosan is a biopolymer that possesses antimicrobial, antioxidant, antitumor, hemostatic, analgesic, film-forming and mucoadhesive activities. Furthermore it is non-toxic, biodegradable and biocompatible. However, chitosan also has some limitations for medical use. Good antimicrobial activity is only achieved at pH lower than 6.5 and chitosan has poor aqueous solubility above this pH. These drawbacks limit the applications of chitosan, but chemical modification can be used to improve these properties. One example is antioxidant-chitosan conjugates. Many approaches to this modification have been reported but in general it can be challenging to obtain well-defined products.
The aim of the current work was to develop a new and efficient synthesis procedure for conjugating hydroxycinnamic acids (HCA-s) to chitosan with the degree of substitution (DS) 25 and 50%, based on the use of tertbutyldimethylsilyl (TBDMS) protection. The HCA-s used were cinnamic, p-coumaric, ferulic and caffeic acids. In order to confirm the structure and the DS, the products were characterized by 1H-NMR and ATR-IR spectroscopies. The initial experiments resulted in very low DS values (1-3%). To increase the DS, a full factorial design was carried out utilizing the Design of Experiment (DOE) method. A 5.1-fold increase in the DS was obtained with the help of the design, followed by an additional 3.9-fold increase by using excess acyl chloride, resulting in a 60.1% DS in case of the cinnamic acid-chitosan conjugate. Six published procedures were carried out following literature and only much lower DS values were obtained (0-7.6%). Since the published methods were unable to provide high DS, the newly developed method was used to synthesize the remaining conjugates with three different DS values (low, medium, high).
The minimum inhibitory concentration (MIC) of the conjugates against E. coli and S. aureus were studied. The antimicrobial activity was comparable to native chitosan when the DS was low. However, a clearly negative effect was observed when the DS was high, which contradicts several publications. Finally, the antioxidant activity was investigated by DPPH free radical scavenging assay. While chitosan did not possess antioxidant activity in the tested concentrations, the p-coumaric, caffeic and ferulic acid conjugates exhibited enhanced activities. The DPPH scavenging activity was in linear correlation with the DS, furthermore in case of the caffeic acid-chitosan conjugate, the conjugate exhibited a lower IC50 than caffeic acid itself.
|MS Thesis Vivien Nagy Final4.pdf||5.2 MB||Opinn||Heildartexti||Skoða/Opna|
|Declaration of access MS thesis.pdf||22.52 kB||Lokaður||Yfirlýsing|