两亲性聚氨基酸三嵌段共聚物构筑pH/溶剂可控多级纳米结构

pH/Solvent Tunable Hierarchical Nanostructures Assembled from an Amphiphilic Polypeptide-containing Triblock Copolymer

通过开环聚合(ROP)和原子转移自由基聚合(ATRP)合成了一种pH响应性三嵌段共聚物聚乙二醇-b-聚赖氨酸-b-聚苯乙烯(PEG-b-PLL-b-PS),在水-有机溶剂混合溶液中进行组装,并采用透射电子显微镜(TEM)、原子力显微镜(AFM)和衰减全反射红外光谱法(ATR-IR)表征.该三嵌段共聚物在四氢呋喃(THF)与水的混合溶剂(V∶V=1∶1)中可组装成疏水性聚苯乙烯为核、亲水性聚赖氨酸和聚乙二醇分别为内壳和外壳的球状胶束.采用TEM和AFM发现该球状胶束在四氢呋喃(THF)水溶液中退火7 d后可进一步转变为纤维状结构.进一步除去THF后,可恢复至粒径略小的冻结球状胶束.另外,球状胶束的粒径随着pH的增加而增加,当pH为13时,聚赖氨酸的二级结构由无规卷曲构象过渡到α-螺旋构象,聚集体由球形结构过渡到空心囊泡.溶液经透析后可使囊泡恢复至球状胶束.

Similar to natural proteins,polypeptides can form secondary structures depending on their physical properties.Many efforts have been made towards the self-assembly of triblock copolymer containing polypeptide as an important component to construct hierarchical structures by utilizing the pH-responsive conformation transformation.In this work,a pH-responsive poly(ethylene glycol)-b-poly(L-lysine)-b-poly(styrene)(PEG-b-PLL-b-PS)triblock copolymer was prepared via a combination of controlled ring opening polymerization(ROP)and atom transfer radical polymerization(ATRP).In the triblock copolymer,PLL is water-soluble in acidic solution with random coil conformation,but becomes insoluble helix in alkaline solution.PEG has excellent water solubility that can exhibit protein-resistant property.PS serves as hydrophobic part.Self-assembly of the polymer was examined by transmission electron microscopy(TEM),atomic force microscopy(AFM)and attenuated total reflection-infrared spectrometer(ATR-IR).The triblock copolymer forms spherical micelles in 1∶1 volume ratio of tetrahydrofuran-water mixed solvent,in which the hydrophobic PS segment forms a core and the two hydrophilic segments PLL and PEG serve as shell and corona,respectively.The spheres as the subunits further transform into hierarchical 1D fiber-like structure in the presence of THF after 7 d of aging,confirmed by both TEM and AFM techniques.Upon removing THF,the spherical shape was re-obtained with slightly smaller diameter,so called“frozen micelles”.Further,the diameter of the spheres increases with pH increasing.A sphere-to-vesicle transition was observed at pH 13 as the secondary conformation of PLL transforms from coil toα-helix.The dialysis of these solutions can convert the vesicles back into spherical morphology with slightly smaller diameter.