Direct observation of the dynamics of carbonic acid/bicarbonate buffer in aqueous environment

The bicarbonate/carbonic-acid buffer is spontaneously generated when atmospheric CO₂ react with water according to CO₂ + H₂O = HCO₃- + H + = H₂CO₃ and is the main pH-stabilizing agent in nature controlling the pH of the oceans and of large fresh-water reservoirs as well as the pH of blood. We have recently demonstrated that H₂CO₃ may be generated within a few hundreds of ps and that it has remained completely stable during our time-window of observation which was about 1 ns [1]. The carbonic acid, for a long time a species of elusive nature in aqueous solution, was generated by the rapid protonation of HCO₃- ions utilizing optically excited photoacids [2], a technique we developed to investigate ultrafast acid-base reactions in aqueous solutions [3,4]. We have also demonstrated using Marcus correlation that the Brønsted acidity of carbonic acid is slightly larger than that of formic acid. Considering its now proven ns-stability in aqueous solutions and its considerable acid-strength, intact carbonic acid should be regarded a highly reactive molecule by its own merit.

Our experimental results suggest new insights concerning the reactivity of the bicarbonate/carbonic acid buffer under conditions relevant for ecology, biophysiology, marine biology and planning for large scale CO₂ sequestration projects aiming to reduce the green-house effect of CO₂ by reducing its partial pressure in the atmosphere.

References
1. Adamczyk, K., Prémont-Schwarz, M., Pines, D., Pines E., Nibbering E. T. J., Science 326 (2009) 1690.
2. Tolbert, L. M.; Solntsev, K. M., Acc. Chem. Res., 35 (2002) 19.
3. Rini, M., Magnes, B.-Z., Pines, E., Nibbering, E. T. J., Science 301 (2003) 349.
4. Mohammed, O. F., Pines, D., Dreyer, J., Pines. E., and Nibbering, E. T. J., Science 310 (2005( 83.

For more information contact Prof. Laren Tolbert (404-894-4093).