含鏻聚多肽的合成与温敏性质研究

Synthesis and Thermoresponsive Properties of Polypeptides Bearing Phosphonium Pendants

通过亲核取代反应合成了一系列含鏻和氯反离子的聚多肽(P1-Cl^P5-Cl).利用核磁共振氢谱和傅里叶变换红外光谱验证了聚合物的分子结构.在核磁共振氢谱图中,通过特征氢峰的积分面积计算了三丁基鏻和三苯基鏻侧基的含量和接枝度.通过离子交换反应合成了一系列含鏻和碘或氟硼酸根反离子的聚多肽(P1-I^P5-I和P1-BF4~P5-BF4).三丁基鏻含量为x=0.89的P2-I和P2-BF4样品在水溶液中具有可逆的高临界溶解温度(UCST)类型的温敏性质.变温紫外-可见光谱的结果表明,UCST类型的相转变温度(Tpt)具有显著的聚合物浓度、盐浓度和种类的依赖性.Tpt随聚合物浓度、碘化钠或氟硼酸钠浓度的增加而升高,随氯化钠浓度的增加而降低.

A series of polypeptides bearing phosphonium pendants and chloride counter anions（P1-Cl-P5-Cl） were synthesized by nucleophilic substitution between poly（γ-3-chloropropyl-L-glutamate）（PCPLG） and tributyl phosphine and/or triphenyl phosphine. Their molecular structures were verified by 1 H nuclear magnetic resonance（1 H-NMR） and Fourier transform infrared（FTIR）. From 1 H-NMR spectra, the molar content and grafting efficiency of tributyl phosphonium and/or triphenyl phosphonium moieties were calculated by integration of the characteristic proton peaks. All resulting polypeptides showed high grafting efficiency（≥ 87%）. Polypeptides bearing phosphonium pendants and iodide（P1-I-P5-I） or tetrafluoroborate counter anions（P1-BF_4-P5-BF_4） were synthesized by ion exchange. All polypeptides with chloride counter-anions were readily soluble in water. Nevertheless, P1-X（X = I, BF_4） with exclusive tributyl phosphonium and P5-X（X = I, BF_4） with exclusive triphenyl phosphonium showed poor solubility in water. It is interesting to observe that P2-I and P2-BF_4 samples with appropriate molar content of tributyl phosphonium moieties（x = 0.89） showed reversible thermoresponsiveness of UCST（upper critical solution temperature）. This phenomenon suggested that co-grafting or copolymerization of the two non-thermoresponsive ionic liquid moieties led to UCST type thermoresponsivenes. To the best of our knowledge, this is the first example of thermoresponsive polypeptides bearing phosphonium pendants. Variable temperature UV-Vis spectroscopy was used to study the UCST type solution phase transition behaviors of P2-I and P2-BF_4. In a cooling/heating cycle, UV-Vis spectra revealed good reversibility of the UCST type phase transitions. Yet, a noticeable hysteresis was also observed. The UCST type phase transition temperature（Tpt） was also determined by UV-Vis spectroscopy at different temperatures. In DI water, the values of Tpt of P2-I and P2-BF_4 were in the temperature range of 11.5-60.2 ℃ and 45.5-71.0 ℃, respectively, and highly dependent on counter anions, polymer concentration, nature of salts and salt concentration. Under the same experimental condition, P2-BF_4 with more hydrophobic tetrafluoroborate counter anions showed higher Tpt than P2-I with iodide counter anions. Furthermore, Tpt increased with increased polymer concentration, sodium iodide or sodium tetrafluoroborate concentration. Yet, it decreased with increased sodium chloride concentration.