Department of Chemistry , Korea University , Seoul 02841 , Korea.
J Phys Chem B. 2018 May 17;122(19):5087-5093. doi: 10.1021/acs.jpcb.8b00588. Epub 2018 May 7.
Dissolved ions have a significant effect on the chemical equilibria and kinetics in aqueous solutions by changing the physical properties and hydrogen bond network of water. In this work, the ionic effects on the excited-state proton transfer (ESPT) reactions of Coumarin 183 (C183) in aqueous ionic solutions are comprehensively studied in terms of p K, p K, activation energies, and kinetic isotope effect (KIE). The acid dissociation constants (p K and p K) of C183 on the ground and excited states are determined by UV-visible absorption and steady-state fluorescence spectroscopy. The activation energies ( E) and KIE for the ESPT reaction of C183 are directly obtained by time-resolved fluorescence spectroscopy. The changes in p K, p K, E, and KIE values of C183 are found to be dependent on the charge density of cations. The secondary KIE is more substantially influenced by the dissolved ions than the primary KIE. Furthermore, the ionic effects on the equilibrium (p K and p K) and kinetic ( E and KIE) parameters of C183 are found to be well-explained by the free-energy reactivity relation. Our current results are very important in understanding the ionic effects on the equilibria and ESPT kinetics of photoacids in aqueous ionic solutions.
溶解的离子通过改变水的物理性质和氢键网络，对水溶液中的化学平衡和动力学有显著影响。在这项工作中，从 p K a 和 p K a 、活化能和动力学同位素效应（KIE）的角度，综合研究了离子对香豆素 183（C183）在水合离子溶液中激发态质子转移（ESPT）反应的离子效应。通过紫外-可见吸收和稳态荧光光谱法测定了 C183 在基态和激发态的酸离解常数（p K a 和 p K a ）。通过时间分辨荧光光谱法直接获得 C183 的 ESPT 反应的活化能（ E ）和 KIE。发现 C183 的 p K a 、p K a 、 E 和 KIE 值的变化取决于阳离子的电荷密度。次级 KIE 比初级 KIE 受溶解离子的影响更大。此外，通过自由能反应性关系很好地解释了离子对 C183 的平衡（p K a 和 p K a ）和动力学（ E 和 KIE）参数的影响。我们目前的结果对于理解水合离子溶液中光酸的平衡和 ESPT 动力学中的离子效应非常重要。
