Qu Chen, Shi Yi, Jing Benxin, Gao Haifeng, Zhu Yingxi
Department of Chemical Engineering and Materials Science, Wayne State University, Detroit, Michigan 48202, United States.
ACS Macro Lett. 2016 Mar 15;5(3):402-406. doi: 10.1021/acsmacrolett.6b00111. Epub 2016 Mar 4.
The conformational structure of a polyelectrolyte chain in dilute aqueous solution is strongly coupled with its surrounding electrostatic environment. With the introduction of branched topology, the distribution of counterions in the vicinity of a polyelectrolyte chain becomes highly inhomogeneous, giving rise to complex structures of branched polyelectrolytes in dilute aqueous solution. To directly probe the local electrostatic conditions near a branched polyelectrolyte in aqueous solutions, star-shaped poly(2-vinylpyridine) (P2VP) polymers with precise labeling of one single fluorophore at different locations, for example, the star center or the terminal group of one arm, were synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization of vinyl-terminated P2VP macromonomers. Using fluorescence correlation spectroscopy (FCS) combined with photon counting histogram (PCH) analysis, the conformational structures and local electric potential of P2VP star polyelectrolytes were investigated in dilute aqueous solutions of varied pH at a single molecule level. Despite the same hydrodynamic radius of P2VP stars, pH-sensitive fluorophores labeled at different locations sensitively differentiated the higher electric potential at the star center from the lower electric potential at the periphery in dilute aqueous solutions.
在稀水溶液中，聚电解质链的构象结构与其周围的静电环境紧密相关。随着支化拓扑结构的引入，聚电解质链附近抗衡离子的分布变得高度不均匀，导致稀水溶液中支化聚电解质形成复杂结构。为了直接探测水溶液中支化聚电解质附近的局部静电条件，通过乙烯基封端的P2VP大分子单体的可逆加成-断裂链转移（RAFT）聚合，合成了在不同位置（例如星型中心或一条臂的末端基团）精确标记单个荧光团的星型聚（2-乙烯基吡啶）（P2VP）聚合物。利用荧光相关光谱（FCS）结合光子计数直方图（PCH）分析，在单分子水平上研究了不同pH值稀水溶液中P2VP星型聚电解质的构象结构和局部电势。尽管P2VP星型聚合物具有相同的流体力学半径，但在不同位置标记的pH敏感荧光团能够灵敏地区分稀水溶液中星型中心较高的电势和外围较低的电势。
