Study On Synthesis And Responsiveness Of UCST Polypeptides With Different Side Chain Structures

Stimulus-responsive polymer can change its structure to respond to external stimuli（such as temperature,light intensity,p H,electromagnetic field,etc.）,it is a"smart"material,and has a wide range of applications in many fields,including drug delivery,Antibacterial treatment and tissue engineering.Depending on the nature of the groups in the main chain or side chain of the stimuli-responsive polymer,stimuli-responsive polymers can be roughly divided into two categories:ionic stimuli-responsive polymers and non-ionic stimuli-responsive polymers.In this paper,a series of ionic and no-nionic stimuli-responsive polypeptides with different molecular weights were synthesized.The structures of intermediates and target products were characterized by GPC,FTIR and ¹H NMR,and the stimulus response behavior of the target products was explored by means of UV-vis and DLS,Focusing on the effects of non-ionic side group structure on polymer solution properties,and the influence of different side chain sequence structures on the properties of ionic polymers,while enriching the types of stimuli-responsive polypeptides,and providing guidance for temperature-responsive polymer molecular design The specific work of this article is as follows:In the second chapter,we synthesized a series of poly（γ-propargyl-L-glutamic acid）（PPLG）with different molecular weights.On the basis of it,we synthesized the UCST temperature with pendant formamide groups by click chemistry.Responsive properties of homopolypeptide PPLG-Am and polypeptide PPLG-Amx were discussed with regard to the structure and properties of the target polymer.The study found that the target polymer was in deionized water and PBS buffer solution with p H=7.1-7.4 With the UCST type temperature response property,the UCST type solution phase transition mechanism is attributed to the hydrogen bonding interaction of the polymer in water.As the molecular weight increases,the UCST type phase transition temperature of the polymer in water continuously increases.With the introduction of the hydrophobic group n-hexyl,the UCST properties of the polymer in water gradually disappeared,and the solubility in PBS buffer solution also continued to decrease.In Chapter 3,we synthesized side chains with different OEG（oligoethylene glycol）composition through multiple esterification reactions,ester bond hydrolysis reactions,and acid chloride esterification reactions.Based on the known polymer PCPLG（polyγ-3chloropropyl-L-glutamic acid）,the first case of UCST-type polypeptide ion with different OEG sequence structure was synthesized by azide reaction,click chemistry,etc.Liquid,namely PPLG-OEGx-OEGx’-Im BF₄（x=2,3;x’=2,3;）.The study found that the UCST phase transition of the polymer is concentration-dependent,and as the OEG chain length increases,the UCST phase transition temperature of the polymer increases,and then we 2,3;x’=2,3;)blood compatibility and antibacterial properties were explored,and the polymer PPLG-OEGx-OEGx’-Im BF₄（x=2,3;x’=2,3;）The hemolysis rate in 2%red blood cells is less than 5%,showing good blood compatibility.In the in vitro antibacterial experiment,it was found that the polymers PPLG-OEG₂-OEG₃-Im BF₄and PPLG-OEG₃-OEG₃-Im BF₄had good bacteriostatic ability within 12 hours,and had the characteristics of bacteriostatic at 37℃and 25℃.