TY - JOUR
T1 - Distance-dependent proton transfer along water wires connecting acid-base pairs
AU - Cox, M. Jocelyn
AU - Timmer, Rutger L.A.
AU - Bakker, Huib J.
AU - Park, Soohyung
AU - Agmon, Noam
PY - 2009/6/18
Y1 - 2009/6/18
N2 - We report time-resolved mid-IR kinetics for the ultrafast acid-base reaction between photoexcited 8-hydroxypyrene-l,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 the fact that k(r) shows a steeper dependence on r at higher temperatures.
AB - We report time-resolved mid-IR kinetics for the ultrafast acid-base reaction between photoexcited 8-hydroxypyrene-l,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 the fact that k(r) shows a steeper dependence on r at higher temperatures.
UR - http://www.scopus.com/inward/record.url?scp=67049114092&partnerID=8YFLogxK
U2 - 10.1021/jp9004778
DO - 10.1021/jp9004778
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AN - SCOPUS:67049114092
SN - 1089-5639
VL - 113
SP - 6599
EP - 6606
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 24
ER -