Accurate Determination of Isotope Effects on the Dynamics of H-Bond Breaking and Making in Liquid Water
Ravi Malik, Nore Stolte, Harald Forbert, Amalendu Chandra, Dominik Marx
Abstract
Isotopic substitution of light hydrogen atoms with heavier deuterium atoms in liquid water renders the resulting liquid, heavy water (D 2 O), poisonous to most organisms when it replaces a critical fraction of water in living organisms. The mechanisms through which heavy water disrupts biological function are challenging to disentangle experimentally. Isotopic substitution has long been known to affect the H-bond dynamics of liquid water, but experiments have yet to quantify the extent of the differences in the time scales of H-bond breaking and making processes between H 2 O and D 2 O. In this work, we analyze H-bond dynamics through extensive coupled cluster-quality path integral simulations of H 2 O and D 2 O under ambient conditions that grant access to unambiguous molecular analyses. We find substantial isotope substitution effects on the rates of H-bond formation and breaking, and H-bond lifetimes, with dynamics in D 2 O ∼25% slower than in H 2 O. The toxicity of D 2 O can thus be ascribed, at least in part, to the effect of slowed H-bond dynamics on biochemical reactions.