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Distance-Dependent Proton Transfer along Water Wires Connecting Acid-Base Pairs M. Jocelyn Cox,
 

Summary: Distance-Dependent Proton Transfer along Water Wires Connecting Acid-Base Pairs
M. Jocelyn Cox,
Rutger L. A. Timmer,
Huib J. Bakker,*,
Soohyung Park,
and
Noam Agmon*,
FOM-institute for Atomic and Molecular Physics, Kruislaan 407, 1098 SJ Amsterdam, The Netherlands, and
Institute of Chemistry and the Fritz Haber Research Center, The Hebrew UniVersity of Jerusalem,
Jerusalem 91904, Israel
ReceiVed: January 16, 2009; ReVised Manuscript ReceiVed: April 20, 2009
We report time-resolved mid-IR kinetics for the ultrafast acid-base reaction between photoexcited
8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS), and acetate at three concentrations (0.5, 1.0,
and 2.0 M) and three temperatures (5, 30, and 65 C) in liquid D2O. The observed proton-transfer kinetics
agree quantitatively, over all times (200 fs-500 ps), with an extended Smoluchowski model which includes
distance-dependent reactivity in the form of a Gaussian rate function, k(r). This distance dependence contrasts
with the exponential k(r) that is typically observed for electron-transfer reactions. The width of k(r) is essentially
the only parameter varied in fitting the proton-transfer kinetics at each concentration and temperature. We
find that k(r) likely represents the rate of concerted (multi)proton hopping across "proton wires" of different
length r that connect acid-base pairs in solution. The concerted nature of the proton transfer is supported by

  

Source: Agmon, Noam - Institute of Chemistry, Hebrew University of Jerusalem

 

Collections: Chemistry