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Enhanced Acidity of Acetic and Pyruvic Acids on the Surface of Water
Version 2 2021-05-18, 12:04
Version 1 2018-07-23, 19:48
online resource
posted on 2021-05-18, 12:04 authored by Alexis
J. Eugene, Elizabeth A. Pillar-Little, Agustín
J. Colussi, Marcelo I. GuzmanUnderstanding the acid–base behavior of carboxylic acids
on aqueous interfaces is a fundamental issue in nature. Surface processes
involving carboxylic acids such as acetic and pyruvic acids play roles
in (1) the transport of nutrients through cell membranes, (2) the
cycling of metabolites relevant to the origin of life, and (3) the
photooxidative processing of biogenic and anthropogenic emissions
in aerosols and atmospheric waters. Here, we report that 50% of gaseous
acetic acid and pyruvic acid molecules transfer a proton to the surface
of water at pH 2.8 and 1.8 units lower than their respective acidity
constants pKa = 4.6 and 2.4 in bulk water.
These findings provide key insights into the relative Bronsted acidities
of common carboxylic acids versus interfacial water. In addition,
the work estimates the reactive uptake coefficient of gaseous pyruvic
acid by water to be γPA = 0.06. This work is useful
to interpret the interfacial behavior of pyruvic acid under low water
activity conditions, typically found in haze aerosols, clouds, and
fog waters.