Cation Effects on Pre-Reactive CO₂ Accessibility and Interfacial Transfer in Aqueous Glycinate Solutions via...

Alkali-metal amino acid solutions are attractive liquid sorbents for carbon capture. Potassium glycinate shows more favorable CO₂ capture behavior than sodium and lithium analogues despite sharing the same reactive amine motif. However, the molecular origin of this countercation effect remains unresolved. Here, we use molecular dynamics simulations to examine how K⁺, Na⁺, and Li⁺ regulate CO₂ accessibility and transport in aqueous glycinate solutions. We treat CO₂ uptake as a multistep process in which interfacial accessibility and transport precede chemical conversion, and we isolate this pre-reactive stage. Li⁺ forms a compact coordination environment with glycinate and water, restricting molecular mobility and reducing CO₂ access to glycinate-centered regions. In contrast, K⁺ maintains a more diffuse solvation environment, supporting higher diffusivities, larger interfacial CO₂ populations, and more frequent vapor-to-liquid transfer events. Collectively, these results identify interfacial gating, defined as cation-dependent control of CO₂ population and exchange frequency at the vapor-liquid boundary, as the interfacial manifestation of a cation-controlled CO₂ accessibility mechanism around glycinate.