Publication Date:
2009-12-08
Description:
Despite the widespread importance of aqueous bicarbonate chemistry, its conjugate acid, carbonic acid, has remained uncharacterized in solution. Here we report the generation of deuterated carbonic acid in deuterium oxide solution by ultrafast protonation of bicarbonate and its persistence for nanoseconds. We follow the reaction dynamics upon photoexcitation of a photoacid by monitoring infrared-active marker modes with femtosecond time resolution. By fitting a kinetic model to the experimental data, we directly obtain the on-contact proton-transfer rate to bicarbonate, previously inaccessible with the use of indirect methods. A Marcus free-energy correlation supports an associated pKa (Ka is the acid dissociation constant) of 3.45 +/- 0.15, which is substantially lower than the value of 6.35 that is commonly assumed on the basis of the overall carbon dioxide-to-bicarbonate equilibrium. This result should spur further exploration of acid-base reactivity in carbon dioxide-rich aqueous environments such as those anticipated under sequestration schemes.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Adamczyk, Katrin -- Premont-Schwarz, Mirabelle -- Pines, Dina -- Pines, Ehud -- Nibbering, Erik T J -- New York, N.Y. -- Science. 2009 Dec 18;326(5960):1690-4. doi: 10.1126/science.1180060. Epub 2009 Nov 12.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Max Born Institut fur Nichtlineare Optik und Kurzzeitspektroskopie, Max Born Strasse 2A, D-12489 Berlin, Germany.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19965381" target="_blank"〉PubMed〈/a〉
Print ISSN:
0036-8075
Electronic ISSN:
1095-9203
Topics:
Biology
,
Chemistry and Pharmacology
,
Computer Science
,
Medicine
,
Natural Sciences in General
,
Physics
