Open AccessSpeed Limits for Acid–Base Chemistry in Aqueous Solutions
Author(s) -
Mateusz L. Donten,
Joost VandeVondele,
Peter Hamm
Publication year - 2012
Publication title -
chimia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.387
H-Index - 55
eISSN - 2673-2424
pISSN - 0009-4293
DOI - 10.2533/chimia.2012.182
Subject(s) - protonation , microsecond , chemistry , aqueous solution , ion , base (topology) , proton , acid–base reaction , photochemistry , relaxation (psychology) , conjugate acid , inorganic chemistry , organic chemistry , physics , mathematical analysis , social psychology , psychology , mathematics , astronomy , quantum mechanics
Proton transfer reactions, including acid–base recombination, are commonly considered to occur 'nearly instantaneously'. However, their actual time scales may stretch far into the microsecond range, as acid–base reactions are diffusion controlled and the concentrations are low near neutral pH. The interplay of competing bases in the pH relaxation is illustrated using a model acid–base system consisting of o-nitrobenzaldehyde (oNBA) as a proton cage and acetate ions and hydroxyl ions as bases. The kinetically controlled behavior leads to highly counterintuitive states, i.e. acetate ions are transiently protonated for hundreds of nanoseconds despite the presence of a much stronger base OH–.