Denaturation of Water in Alkaline Melts

Extremely high base concentrations (c_B) in ultra-alkaline liquids, also known as hydroflux, alter the thermodynamic and structural properties of water. Mixtures of water and alkali (AOH, A = Na, K) with molar base ratios of q(A) = n(H₂O):n(AOH) ≤ 2:1 (c_B ≥ 25 mol L^-1) show an overproportionally reduced vapor pressure compared to more diluted systems. The vapor pressure of a melt with q(A) = 0.8 (c_B = 70 mol L^-1) at 200°C is negligible. Ab initio molecular dynamics simulations revealed substantial structural reorganization of the hydrogen bonding network in the equimolar mixture of KOH and water. Distinctive molecular features included altered coordination geometries, shortened hydrogen bonds, and frequent proton transfer events, including Grotthuss diffusion, indicative of an altered hydrogen-bond network and increased proton mobility. Cluster population analysis shows that a significant number of H₃O₂ ^- anions are present, which exhibit a near symmetrical hydrogen bond with O···H distances <1.28 Å. The hydroflux can be seen as an intermediate between an alkaline solution and a molten salt {K⁺·H⁺·2OH-}, in which the water has a vanishing chemical activity.