EXCITED-STATE PROTON-TRANSFER TO METHANOL WATER MIXTURES

被引:131
作者
AGMON, N
HUPPERT, D
MASAD, A
PINES, E
机构
[1] HEBREW UNIV JERUSALEM,FRITZ HABER RES CTR,IL-91904 JERUSALEM,ISRAEL
[2] TEL AVIV UNIV,RAYMOND & BEVERLY SACKLER FAC EXACT SCI,SCH CHEM,IL-69978 TEL AVIV,ISRAEL
[3] UNIV CHICAGO,DEPT CHEM,CHICAGO,IL 60637
关键词
D O I
10.1021/j100178a030
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
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.
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页码:10407 / 10413
页数:7
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