Bicarbonate-mediated proton transfer requires cations

Near-neutral HCO₃^– aqueous solution plays an essential role in respiratory, mineralization and catalysis, yet the interconversion between hydrated CO₂, HCO₃^– and CO₃^2– and the associated proton transfer under such proton-deficient conditions remain uncovered. Here we reveal that cation enables HCO₃^– to self-dissociate into OH^– and CO₂ through a pH-independent process, where CO₂ hydration and subsequent proton transfer in acid-base reactions lead to the overall exchange of oxygen isotopes between HCO₃^– and H₂O tracked by oxygen isotope-labeled Raman spectroscopy. Isolating HCO₃^– from cations with crown ether impedes HCO₃^– dissociation and the following reactions. Further molecular dynamics simulations demonstrate that the interplay between HCO₃^– and hydrated cations drives HCO₃^– dissociation. This study suggests a natural proton channel upon coupling HCO₃^– with cations.