Ueki Takeshi, Matsukawa Ko, Masuda Tsukuru, Yoshida Ryo
National Institute for Materials Science (NIMS) , 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
Department of Materials Engineering, School of Engineering, The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
J Phys Chem B. 2017 May 4;121(17):4592-4599. doi: 10.1021/acs.jpcb.7b01309. Epub 2017 Apr 25.
Herein, we describe the physicochemical aspects of the Belousov-Zhabotinsky (BZ) reaction in hydrated protic ionic liquids (PILs) combined with different cations with a hydrogen sulfate ([HSO]) anion. PILs were prepared from the neutralization reactions of sulfuric acid with 13 different aliphatic amines. The amine structure was selected to investigate the effect of the number of active protons, alkyl chain length (hydrophilicity), and cationic linearity on the mechanism of the BZ reaction. The pK values of PILs were significantly higher (pK = 1.0-2.5) than those of inorganic acids (HSO = -3.0; HNO = -1.4), the conventional proton source in a BZ reaction. A periodic redox oscillation was observed in Ru(bpy) when appropriate amounts of BZ reaction substrates (NaBrO oxidant; malonic acid reductant) were added to the hydrated PILs. A long-lasting BZ oscillation was realized when hydrophilic cations (ammonium, ethylammonium, and dimethylethylammonium) were employed. Interestingly, a large ΔA (oscillation amplitude of absorbance for the scale of the oscillation stability observed after 5000 s from the initiation of the BZ reaction) was achieved for PILs possessing less than four carbon atoms in their cationic structure. The apparent BZ oscillation activation energy (E) in the hydrated PILs was estimated to be ∼40 kJ mol, which is 30 kJ mol less than that observed in a conventional system. The catalytic reaction in the BZ reaction subprocess suppresses the total activation energy of the reaction. To realize long-lasting self-oscillating polymeric materials acting under milder condition, we demonstrated an autonomous coil-globule polymer chain transition (BZ-driven) that directly converts chemical energy to mechanical motion in hydrated PILs without freely diffusing Ru(bpy) metal catalyst. Ethylammonium hydrogen sulfate ([ea-H][HSO]) is selected as the suitable proton source for the BZ reaction. A well-defined self-oscillating polymer that incorporated Ru(bpy) metal catalyst into the polymer backbone accompanied by good compatibility in hydrated [ea-H][HSO] is successfully prepared by ATRP, followed by postmodification of the metal catalyst. The rhythmic solubility changes of the polymer under milder conditions, realized by combination with PILs, will expand the potential applications of PILs to novel functional materials.
在此，我们描述了水合质子离子液体（PILs）中Belousov-Zhabotinsky（BZ）反应的物理化学方面，该离子液体结合了不同的阳离子与硫酸氢根（[HSO₄⁻]）阴离子。PILs由硫酸与13种不同脂肪胺的中和反应制备。选择胺结构以研究活性质子数、烷基链长度（亲水性）和阳离子线性对BZ反应机理的影响。PILs的pK值显著高于（pK = 1.0 - 2.5）BZ反应中传统质子源无机酸（H₂SO₄ = -3.0；HNO₃ = -1.4）的pK值。当向水合PILs中加入适量的BZ反应底物（NaBrO₃氧化剂；丙二酸还原剂）时，在Ru(bpy)₃²⁺中观察到周期性的氧化还原振荡。当使用亲水性阳离子（铵、乙铵和二甲基乙铵）时，实现了持久的BZ振荡。有趣的是，对于阳离子结构中碳原子数少于四个的PILs，实现了较大的ΔA（从BZ反应开始5000 s后观察到的振荡稳定性尺度下吸光度的振荡幅度）。水合PILs中表观BZ振荡活化能（Ea）估计约为40 kJ/mol，比传统体系中观察到的低30 kJ/mol。BZ反应子过程中的催化反应降低了反应的总活化能。为了实现能在更温和条件下起作用的持久自振荡聚合物材料，我们展示了一种自主的线圈-球状体聚合物链转变（由BZ驱动），其在水合PILs中直接将化学能转化为机械运动，无需自由扩散的Ru(bpy)₃²⁺金属催化剂。硫酸乙铵（[ea-H][HSO₄]）被选为BZ反应的合适质子源。通过原子转移自由基聚合（ATRP）成功制备了一种定义明确的自振荡聚合物，该聚合物将Ru(bpy)₃²⁺金属催化剂掺入聚合物主链，并在水合[ea-H][HSO₄]中具有良好的相容性，随后对金属催化剂进行后修饰。通过与PILs结合在更温和条件下实现的聚合物有节奏的溶解度变化，将扩大PILs在新型功能材料方面的潜在应用。
