导　　师： 张阿方

学科专业： 070305

授予学位： 硕士

作　　者： ;

机构地区： 上海大学

摘　　要： 温度敏感型多肽聚合物的合成研究近年来受到广泛关注。它们不仅具有常规温敏聚合物的智能响应行为，同时还具有多肽二次有序构象、生物相容性和生物可降解性等的结构及特征，因而在药物可控释放、基因载体、组织工程、蛋白质纯化和智能界面等方面有重要的研究价值和应用前景。弹性蛋白肽（ELP）是迄今为止研究最受关注的一类温敏多肽，已被应用于制备包括线形或梳形等不同结构的温敏多肽聚合物，但其温敏行为普遍存在相变过程缓慢、相变温度范围宽等问题。 本论文首次合成了每个重复单元侧基带有两个弹性蛋白肽基元（VPGVG）的高密度梳形多肽聚合物。通过液相合成法有效制备了序列为VPGVG的弹性蛋白五肽。在其端基通过赖氨酸基元引入聚合单元，采用大单体路线经自由基聚合反应制得了不同分子量的多肽聚合物。对所得聚合物及其对应的脱保护产物进行了结构分析。发现两种脱保护聚合物在一定pH值的缓冲溶液中具有温敏行为。采用UV//Vis进行了浊度测试以对其温敏特性深入研究，发现这类高密度梳形聚合物表现出优异的温敏行为，其相转变温度（LCST）范围比文献报道的要明显窄。进一步分析发现脱保护聚合物的LCST随分子量、浓度、pH、盐浓度的增加而降低。采用圆二色谱（CD）对保护和脱保护的不同聚合物进行二次有序结构表征发现，它们都呈现部分β-turnⅡ型二级结构。 在此工作基础上，进一步利用醛基与氨基可以在一定条件下形成希夫碱动态键的反应，将核点为醛基、具有潜在温敏特性的烷氧醚树枝化基元G1与脱保护的弹性蛋白肽梳形聚合物侧链端氨基进行反应，制备了具有希夫碱动态键链构造的一类新型温敏多肽聚合物。通过调整溶液pH值变化实现了对聚合物动态键链的形成与断链的控制。采用UV//Vis对所得动态键链梳形聚合物的温敏特性进行了分析，有趣地发现该聚合物的温敏性可以通过温度及时间来调控：加热聚集促进了动态键链的形成，从而提高侧链接枝率，使得聚合物的相变温度从弹性蛋白肽的50oC以上降低到烷氧醚树枝基元的40oC以下。而聚集促使的动态键链在降温后会发生解离，这使得聚合物的相变温度可以通过溶液存放数日而得到回复。另外动态聚合物的LCST还可以通过调整动态键链形成组分之间的比例和溶液pH来调节。 采用动态光散射（DLS）对脱保护的高密度梳形多肽聚合物及其对应的动态聚合物温敏过程中的聚集行为进行了表征。发现动态聚合物形成的聚集体尺寸要比相应脱保护聚合物的要大，说明前者的聚集驱动力（疏水性）要远大于后者。 Thermoresponsive polypeptides combine the characteristics of stimuli-responsiveness from thermoresponsive polymers and ordered structures frompolypeptides, which have received much attention recently. Elastin-like peptides/(ELPs/) are one intriguing type of peptides which show thermoresponsive behavior atcertain conditions. Polymers of various architectures carrying ELPs have beenreported, which are bio-compatible and biodegradable, and have shown promisingapplications in drug control release, gene delivery, tissue engineering, proteinpurification and smart interface. However, the main drawback of these reportedpolymer systems are significant: they normally possess thermoresponsive behaviorwith very broad phase transition temperature range. In present thesis, we report for the first time the synthesis of comb-likepolymers which carry two ELP side chains with a sequence of VPGVG. The ELPwas synthesized through solution phase peptide synthesis methodology. By cappingthe peptide chain end with polymerizable unit, comb-like polymers of differentmolar masses were prepared via macromonomer route through free radicalpolymerization. These polymers, together with their deprotected counterparts, werecharacterized. The deprotected polymers show thermoresponsive behavior in buffer,thus their thermoresponsiveness was characterized with UV//Vis spectroscopy, whichreveals deprotected polymers show sharp phase transitions /(~3oC/) at proper pH.Further analysis show that LCST of deprotected polymers varied with molecularweight, polymer concentration, pH and inorganic salt. Secondary structure analysisof the peptidic polymers indicated that they adopted partially type Ⅱ β-turnconformation. Based on these findings, dynamic covalent chemistry was also applied to thisthermoresponsive system. The chemistry is based on the dynamic covalent Schiff’sbase linkage formed from aldehydes and amino groups. Mixing of deprotected comb-like polymers with amino terminated ELP side chains with oligo/(ethyleneglycol/)-based dendron G1produced the corresponding dynamic covalent polymers.Their thermoresponsiveness was characterized with UV//Vis spectroscopy. It wasinterestingly found the dynamic linkage was enhanced by heating, whichconsequently reduced the phase transition temperatures. This phenomenon isreversible upon cooling. The LCSTs of dynamic polymers can also be tuned bychange of pH and ratios between the dynamic components. The thermally-induced aggregation processes of the comb-like peptidicpolymers and the corresponding covalent polymers were followed with DLS, andfound particle size from the deprotected polymers were much smaller than theseformed from the dynamic polymers.

关 键 词： 弹性蛋白肽 温敏 梳形聚合物 动态键联

分 类 号： [O631]

领　　域： [理学] [理学]