West Chester University of Pennsylvania, 700 South High Street, West Chester, PA 19383, United States.
Millersville University of Pennsylvania, 50 East Frederick Street, Millersville, PA 17551, United States.
Spectrochim Acta A Mol Biomol Spectrosc. 2022 Dec 5;282:121702. doi: 10.1016/j.saa.2022.121702. Epub 2022 Aug 1.
The conformational change of poly (methacrylic acid) (PMAA) at various pH values is well studied; however, the application of PMAA in the field of analytical chemistry has been very limited. This investigation takes advantage of the conformational change of PMAA at various pH levels and the conformational change induced by metal ions. By adjusting the pH, thiophene-phenylanilide-acridinium molecules can serve as turn-on sensors for Hg ions. In pH 7.4 buffer with PMAA molecules, the sensor is selectively turned on by Hg ions to display strong charge shift state (CSH) emission at 560 nm. The intensity shows linear response to the concentration of Hg ions between 0.020 mM and 0.151 mM with a detection limit in nanomolar range. The photophysical properties of sensor molecules in PMAA/mercury (II) mixture at near neutral pH are comparable to those in PMAA solution in acidic condition without mercury (II) ions. The effect of pH, temperature, polymer size, and polymer concentration on emission intensity were investigated. The sensor showed excellent percent recovery (98.4 % to 103 %) of spiked mercury (II) ions in real water samples. The sensing mechanism is likely through intrachain and interchain coordination of mercury (II) ions with the carboxyl groups on the side chain of PMAA to induce an extended coil conformation of PMAA. Calculations support the conclusion that the size and geometry of the binding sites formed inside PMAA are suitable to incorporate sensor molecules and enhance the charge shift state emission of sensor molecules.
聚（甲基丙烯酸）（PMAA）在不同 pH 值下的构象变化得到了很好的研究；然而，PMAA 在分析化学领域的应用却非常有限。本研究利用 PMAA 在不同 pH 值下的构象变化和金属离子诱导的构象变化。通过调节 pH 值，噻吩-苯甲酰苯胺-吖啶分子可以作为汞离子的开启型传感器。在含有 PMAA 分子的 pH 7.4 缓冲液中，传感器被汞离子选择性地打开，在 560nm 处显示出强电荷转移态（CSH）发射。强度对 0.020mM 至 0.151mM 之间的汞离子浓度呈线性响应，检测限在纳摩尔范围内。在近中性 pH 下 PMAA/汞（II）混合物中传感器分子的光物理性质与无汞（II）离子时 PMAA 溶液中的光物理性质相当。研究了 pH 值、温度、聚合物尺寸和聚合物浓度对发射强度的影响。该传感器在实际水样中对加标汞（II）离子的回收率高达 98.4%至 103%。传感机制可能是通过汞（II）离子与 PMAA 侧链上的羧基之间的链内和链间配位，诱导 PMAA 呈现伸展的螺旋构象。计算支持这样的结论，即 PMAA 内形成的结合位点的大小和几何形状适合容纳传感器分子，并增强传感器分子的电荷转移态发射。
