Photo-reversible and selective Cu2+ complexation of a spiropyran-carrying sulfobetaine copolymer in saline solution
作者:Takayuki Suzuki、Yuki Hirahara、Kaori Bunya、Hiraku Shinozaki
DOI:10.1039/b921169a
日期:——
A sulfobetaine copolymer (1) carrying a photochromic spiropyran residue was synthesized, which reversibly isomerized between the closed and open forms in pure water and in saline by irradiation with visible light. The thermodynamic stability of the open form of the spiropyran methacrylate (SPMA) units of compound 1 was reduced upon increasing NaCl concentration. In addition, photo-reversible and selective Cu2+ complexation in saline solution ([NaCl] = 1.0 wt%) was achieved using compound 1 with metal ions (Cu2+, Zn2+, Ni2+, or Co2+). Covalently cross-linked compound 1 showed selective Cu2+ adsorption in pure water. In contrast, the other metal ions were increasingly adsorbed as NaCl concentration increased, resulting in lower selectivity of Cu2+ ion adsorption with 1, e.g., the ratios of adsorption of Cu2+, Zn2+, Ni2+, and Co2+ with 1 in 10 wt% saline were 73, 20, 10, and 3%, respectively, while only Cu2+ adsorption was observed in a solution of 1.0 wt% NaCl. Because the stability of the open form of the SPMA units and the metal complexation of 1 were influenced by NaCl concentration, the electrostatically cross-linked networks of the zwitterionic sulfobetaine units of 1 may be loosened by NaCl addition, resulting in easy entry of metal ions into the network. The order of metal complexation among the four metals corresponded to the Irving–Williams series. Hydrogen-bonded networks of water molecules also may contribute to the relatively ineffective selective adsorption of Cu2+ ions by 1 compared to the electrically neutral spiropyran-carrying copolymer of N-isopropylacrylamide, 2.
合成了带有光致变色螺吡喃残基的磺基甜菜碱共聚物(1),该共聚物在纯水和盐水中通过可见光照射在闭合和开放形式之间可逆地异构化。化合物 1 的螺吡喃甲基丙烯酸酯 (SPMA) 单元的开放形式的热力学稳定性随着 NaCl 浓度的增加而降低。此外,使用化合物 1 与金属离子(Cu2+、Zn2+、Ni2+ 或 Co2+)在盐水溶液([NaCl] = 1.0 wt%)中实现了光可逆和选择性 Cu2+ 络合。共价交联的化合物 1 在纯水中表现出选择性吸附 Cu2+。相反,随着 NaCl 浓度的增加,其他金属离子的吸附量增加,导致 Cu2+ 离子对 1 的吸附选择性较低,例如,10 wt% 盐水中 Cu2+、Zn2+、Ni2+ 和 Co2+ 对 1 的吸附比例为 73分别为 20%、10% 和 3%,而在 1.0 wt% NaCl 溶液中仅观察到 Cu2+ 吸附。由于SPMA单元开放形式的稳定性和1的金属络合受到NaCl浓度的影响,1的两性离子磺基甜菜碱单元的静电交联网络可能会因NaCl的添加而松弛,导致金属离子容易进入进入网络。四种金属之间的金属络合顺序对应于欧文-威廉姆斯系列。与电中性的带有螺吡喃的 N-异丙基丙烯酰胺共聚物 2 相比,水分子的氢键网络也可能导致 Cu2+ 离子 1 的选择性吸附相对无效。