Amphiphilic carbohydrate-containing compounds for multifunctional nano/macro structures
by Shuang Wang
Date of Examination:2020-09-29
Date of issue:2020-11-18
Advisor:Prof. Dr. Kai Zhang
Referee:Prof. Dr. Kai Zhang
Referee:Prof. Dr. Michael P. Schön
Referee:Prof. Dr. Thomas Heinze
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Description:Doctoral dissertation
Abstract
English
In living organisms, carbohydrate-containing compounds, such as glycoproteins, glycopeptides, and glycolipids, play key roles in numerous physiological and pathological events via carbohydrate-protein interactions amplified by “glycol-cluster effect”. Inspired by the multifunctional natural glycoconjugates, huge synthetical carbohydrate-containing compounds in the form of polymers and surfactants have been produced and applied in our daily life. In this study, renewable and biodegradable cellulose had been chosen as the biopolymer backbone during the synthesis of carbohydrate-containing polymers. Novel cellulose derivatives with regioselective distributions of pendant glucose moieties were successfully synthesized via a series of essential reactions: nucleophilic reaction to introduce primary hydroxyl groups with the longer chain at C6 position; further sequential TEMPO/[bis(acetoxy)iodo]benzene (BAIB)-mediated oxidation of primary hydroxy groups, Schiff base formation and reduction reactions in one-pot to introduce free thiol groups; thiol-ene click reaction to introduce glucose moieties. The glycosylated cellulose derivatives with a degree of substitution ascribed to glucose moieties of 0.6 could reversibly bind with 1,4-benzenediboronic acid (BDBA) in DMSO with the assistance of NaOH and form nanoparticles via nanoprecipitation. Besides, novel fluorescence cellulose derivatives bearing mannose moieties were synthesized via photo- and thermal- initiated thiol-ene click reactions by sequentially conjugating hydrophilic mannose-oxyethoxylpropane-thiol (Mann-SH) and fluorescent coumarin-oxyhexyl-thiol (Coum-SH) and rhodamine B-ethyl-thiol (RhB-SH) to cellulose backbone with terminal double bonds. The amphiphilic fluorescence cellulose derivatives formed uniform nanoparticles with average sizes ranging from 240-554 nm in low ionic strength solutions (<0.085 M). The thermal-stable uniform nanoparticles bearing mannose moieties exhibited excellent dispersion stability in NaOH solution even at elevated temperature via binding to BDBA. Moreover, carbohydrate-containing bolaamphiphiles (CHO-Bolas) were synthesized and exhibited interesting reversible temperature- and pH-responsive micelle-to-vesicle transition (MVT). Micelles of 20-55 nm turned into vesicles of up to 1.5 μm reaching the MVT transition temperatures (TMVT) in acidic or neutral aqueous solutions. In alkaline aqueous solution, CHO-Bolas coassembled with BDBA into microsized helix structures upon cooling. In general, the carbohydrate-containing compounds in the form of polymer and surfactants displayed boronic acid-sensitivity due to the clustered carbohydrate moieties and formed nano/macro structures. This thesis is a cumulative work including 3 publications. All papers were prepared to submit/published in peer-reviewed journals, one was already published and two of them are in manuscripts and prepared to submit. The background, the objective of the study, results and discussion of the three publications and the conclusion are presented in Section 1-4.
Keywords: carbohydrate compounds; self-assembly