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.