Stimuli responsive polypeptides
Kapetanakis, Antonios (2016) Stimuli responsive polypeptides. PhD thesis, Dublin City University.
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Great progress has been made over the last years on the synthesis of biodegradable and biocompatible polymers. Specifically synthetic polypeptides posses these characteristics and have been highlighted as potential candidates for a variety of applications such as drug and gene delivery or tissue engineering. Inspired by this, the aim of this PhD project was to synthesize a library of various polypeptides of linear and star-shaped architecture with combined selective binding and stimuli responsive properties. The synthesis of the polypeptides was achieved by N-carboxyanhydride ring opening polymerization (NCA-ROP) of the corresponding amino-acids.
Selective binding properties were introduced to the polypeptides by conjugation with sugar molecules, i.e. galactose. Copper catalyzed [3+2] Huisgen cycloaddition reaction was the technique applied in order to obtain glycosylated polypeptides. Their binding to biological
model systems was investigated and confirmed by highly specific lectin-binding experiments. This synthetic strategy was applied to all the synthesized polypeptides that are described in chapters 2 to 5.
More specifically, in chapter 2 and 3 the synthesis of homo and block star glycopolypeptides was attempted. In chapter 2, -propargyl L-glutamate NCA was polymerized using a second generation poly(propyleneimine) (PPI) dendrimer as initiator and conjugated with azidogalactose through Cu catalyzed ''click'' chemistry. To increase the functionality of the system a second block was added to the polymeric chain. Moreover, a simple loading experiment was conducted to study the ability of the star-glycopeptides to host guest molecules. Solubility problems and the inability to selectively deprotect each polypeptide block separately led to the synthesis of a different type of star glycopolypeptides, which is
described in chapter 3. In this case, DL-propargylglycine NCA and ε-carbobenzyloxy-Llysine NCA were polymerized using PPI dendrimer as initiator to obtain random and block star copolymers. After conjugation with galactose, enzyme linked lectin assays (ELLA) were performed to prove their bio-recognition. Moreover, the successful complexation with plasmid DNA was demonstrated for one of the glycopolypeptides due to the interaction of ngatively charged DNA molecule and the positively charged poly(lysine) on the polypeptide chain.
In chapters 4 and 5 the addition of temperature as a stimulus was attempted and its effect on the lectin binding was investigated. For that purpose, in Chapter 4, linear polypeptides were synthesized by the polymerization of -propargyl L-glutamate NCA, followed by the xi subsequent co-click of 1-azido-2-(2-methoxyethoxy) ethane (mEO2) and azido-galactose.
Varying the ratios of the two units on the polymer backbone, the hydrophilicity as well as the Cloud Point temperature (Tcp) could be modified. Moreover, it was demonstrated that lectin binding can be thermally controlled. In chapter 5, a similar study was performed for star polypeptides using again -propargyl L-glutamate NCA, which was polymerized by PPI dendritic initiator. After the co-click of (mEO2) and azido-galactose the same effect of temperature on the lectin-binding was observed. Moreover, a comparison between linear and star glycopolypeptides revealed the effect of the structure and molecular weight on cloud point and helicity.
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