Bicarbonate-mediated proton transfer requires cations

Area of Science:

• Environmental Chemistry
• Biogeochemistry
• Physical Chemistry

Background:

• Near-neutral bicarbonate (HCO3-) solutions are vital in biological and chemical systems.
• The mechanisms of interconversion between hydrated CO2, bicarbonate (HCO3-), and carbonate (CO32-) under proton-deficient conditions are not fully understood.
• Proton transfer dynamics in these systems remain an area of active research.

Purpose of the Study:

• To elucidate the role of cations in the dissociation of bicarbonate (HCO3-) in near-neutral aqueous solutions.
• To investigate the associated proton transfer and oxygen isotope exchange mechanisms.
• To understand the interplay between cations, bicarbonate, and water molecules.

Main Methods:

• Oxygen isotope-labeled Raman spectroscopy to track oxygen isotope exchange between bicarbonate (HCO3-) and water (H2O).
• Use of crown ether to isolate bicarbonate (HCO3-) from cations, studying the effect on dissociation.
• Molecular dynamics simulations to investigate the interactions between hydrated cations and bicarbonate (HCO3-).

Main Results:

• Cations facilitate pH-independent self-dissociation of bicarbonate (HCO3-) into hydroxide (OH-) and carbon dioxide (CO2).
• CO2 hydration and subsequent proton transfer drive oxygen isotope exchange between bicarbonate (HCO3-) and water (H2O).
• Isolation of bicarbonate (HCO3-) from cations using crown ether inhibits dissociation and subsequent reactions, confirming the cation's role.

Conclusions:

• The study reveals a novel mechanism where cations enable bicarbonate (HCO3-) dissociation and subsequent reactions in near-neutral solutions.
• This cation-bicarbonate interplay acts as a natural proton channel, crucial for understanding various chemical and biological processes.
• Findings provide insights into the fundamental chemistry of carbonate species in aqueous environments.