D/H control of chemical kinetics in water solutions under low deuterium concentrations

Abstract

Variations in the isotopic composition drastically changes properties of molecules. This also applies to H2O, one of the most indispensable substances on Earth. Here we investigated physical, chemical and biological characteristics of deuterium depleted water (0.5 mM HDO) compared to water with natural deuterium content (16 mM HDO) and heavy water D2O. Reaction systems of different organization levels were probed: molecular (galactose mutarotation), supramolecular (destabilase-lysozyme activity), two-phase heterogenic (suspension of slightly water-soluble active pharmaceutical ingredients), and living cells (unicellular biosensor S. ambigua lifespan). We have shown that the mutarotation rate constant for the l-galactose was 2-fold less than that for the D-isomer over the whole temperature range without dependence on HDO concentration in low values, whereas the first-order mutarotation kinetics was not observed for l-galactose in heavy water. Interestingly, the initial rate of lysozyme activity of destabilase-lysozyme increased two-fold in deuterium-depleted water whereas there was no activity change in heavy water. In suspension system, the dissolution kinetics of active pharmaceutical ingredients conformed with the normal kinetic isotope effect when kH/kD > 1. This confirms the important role of variations in the solvent (water) isotopic composition in the dissolution process acceleration. However, the most important isotope effect was observed in the living cells, where the rate constant for the processes of irreversible S. ambigua cell transition (from an active state to an immobilized state) increased up to 800 times under deuterium depletion.