EXCITED-STATE PROTON-TRANSFER TO METHANOL WATER MIXTURES
EXCITED-STATE PROTON-TRANSFER TO METHANOL WATER MIXTURES
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DOI：
10.1021/j100178a030
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发表时间：
1991-12-12
影响因子：
--
通讯作者：
PINES, E
中科院分区：
文献类型：
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作者：
AGMON, N;HUPPERT, D;PINES, E
我们测量了8-羟基芘-1，3，6-三磺酸盐在水-甲醇混合溶剂中由于质子转移到溶剂中而引起的荧光衰减。数据同意定量与可逆的，扩散影响的质子转移机制在所有的解决方案。没有显着偏离短时间指数衰减或长时间幂律衰减，可以支持最近提出的水分子扩散机制。溶剂引起的去质子化速率系数的变化非常接近于相应的平衡系数。测量和文献pK数据的分析表明，组成的依赖性主要是由于本地化的反质子稳定性在富水的解决方案和质子稳定性在富甲醇的解决方案。与文献汇编的质子转移自由能的定量协议。这些观察结果挑战了流行的观点，即四个水分子的最小簇是这些溶液中所需的质子受体。
We have measured the fluorescence decay of 8-hydroxypyrene-1,3,6-trisulfonate due to proton transfer to solvent in water-methanol mixtures. The data agree quantitatively with the reversible, diffusion-influenced proton-transfer mechanism in all solutions. No significant deviations from a short-time exponential decay or a long-time power law decay were found that could support a recently suggested water molecule diffusion mechanism. Solvent-induced variations in the deprotonation rate coefficient are very close to those in the corresponding equilibrium coefficient. Analysis of measured and literature pK data indicates that the composition dependence is mainly due to localized counterion stability in water-rich solutions and to proton stability in methanol-rich solutions. Quantitative agreement with literature compilations of proton-transfer free energy is obtained. These observations challenge the prevailing idea that a minimal cluster of four water molecules is the required proton acceptor in these solutions.