关于聚电解质单链抗衡离子浓度径向分布的研究  

Radial Profile of Counterion Concentration of a Single Polyelectrolyte

作　　者：罗双江[1] 高培源[1] 郭洪霞[1] 杨京法[1] 赵江[1] 

机构地区：[1]中国科学院化学研究所

出　　处：《高分子学报》2017年第9期1479-1487,共9页Acta Polymerica Sinica

基　　金：国家自然科学基金(基金号51173197;21674121)资助项目

摘　　要：采用单分子荧光显微统计光谱技术,通过将pH响应型荧光探针分子精确标记于聚苯乙烯磺酸钠分子链末端,并通过不同长度的多肽链调节分子链与探针分子间的距离,有效测量了聚苯乙烯磺酸钠单分子链的抗衡离子浓度的空间分布.实验结果清晰展示了聚电解质分子链的抗衡离子云结构,并确定了抗衡离子浓度随着距离分子链末端长度的不同而发生变化的规律,为描述聚电解质抗衡离子浓度的径向分布特征提供了实验信息.The distribution of counterions around the charged chain of polyelectrolyte is the key aspect of itsphysical and chemical properties. In the current study, the spatial profile of counterion concentration along theradial direction of the molecular chain of sodium polystyrene sulfonate （NaPSS） is investigated by singlemolecule fluorescence technique, fluorescence correlation spectroscopy （FCS） and photon counting histogram（PCH） technique. FCS measures the diffusion coefficient （therefore the hydrodynamic radius） of a single PSS-chain while PCH measures the molecular brightness of a single fluorophore attached to the chain end. Bychemical reactions, a pH responsive fluorophore （Oregon Green 488, OG488） is precisely positioned at differentdistances to the end of PSS- chain, using hydrophilic polypeptide chains of different length as spacers. Theconcentration distribution of hydronium ions at the vicinity of the PSS- chain is measured by examining themolecular brightness of OG488, by numerical fitting the PCH data using super-Poisson distribution function. Theresults demonstrate that the concentration of hydronium in the vicinity of the PSS- chain is 2 - 3 orders ofmagnitude higher than that in the bulk solution （at the infinite distance to the chain）, evidencing the existence ofcounterion cloud around the charged chain. By varying the position of the probe with the adjustment of chainlength ofpolypeptide, the local pH value at different distances to the PSS- chain end is measured and therefore thespatial profile of counterion concentration around the direction towards away from the chain is probed. The resultsshow that the counterion concentration decreases very sharply with the increase of the distance （within 2.0 nm） tothe PSS- chain. It is further discovered that the concentration gradient decreases with the increase of the bulk pH,demonstrating the expansion of the counterion cloud as the result of the entropy effect by dilution of hydroniumions. The results clearly prove that the coun

关 键 词：聚电解质 抗衡离子 单分子荧光 

分 类 号：O631.11[理学—高分子化学]