Entropic Effects and Slow Kinetics Revealed in Titrations of D₂O−H₂O Solutions with Different D/H Ratios

Abstract

There is much renewed interest in the arrangement and kinetic of hydrogen bonds in water and heavy water. D 2 O forms a higher average number of hydrogen bonds per molecule (10% more) compared to the case for H 2 O, which cause a larger entropic cost for solvating molecules in D 2 O. Here we used isothermal titration calorimetry (ITC) to investigate the enthalpy of titration of D 2 O-H 2 O solutions with different D/H isotope ratios. We found significant enthalpy deviations (exothermic contributions) relative to the computed enthalpy for the limit of ideal mixing both for dilution titration and for concentration titration (injection of solutions with lower D/H ratios into solutions with higher ratios and vice versa). We propose that the observed exothermic deviations might be connected to entropic effects associated with differences in the H and D arrangements that depend on the D/H ratio of the solutions. This ratio varies during the titration processes, leading to the entropy production beyond that of ideal mixing. We also used the ITC in the nonstirring mode to measure the titration kinetics and found long relaxation times of up to tens of minutes for the concentration titrations (but not for the dilution titrations). These observations are consistent with slow propagation of the reaction H 2 O + D 2 O T 2HDO that involves hopping of deuterium and rearrangements of the H and D bonding.

Decimal Solvent-Based High-Entropy Electrolyte Enabling the Extended Survival Temperature of Lithium-Ion Batteries to −130 °C

“…The enthalpy contribution was calculated from the measured heat of ideal mixing in the stirring mode from Redlich-Kister polynomial equations (Figure 4b), while the entropy change could be computed based on the deviations of heat production in the nonstirring mode from ideal mixing (Figure 4c and Supporting Information Figure S7). 76 These results demonstrated that the introduction of more kinds of miscible solvents increased the system entropy, which is the underlying reason for the greatly depressed freezing point of multicomponent electrolytes. Based on these observations, we can get a comprehensive picture of the whole process (Figure 4d and Supporting Information Figure S8).…”

Phase Diagram and Tie-Line Determination for the Ternary Mixture DOPC/eSM/Cholesterol

“…However, all of these methods have some shortcomings. Some of them involve the use of deuterated samples, which affects the hydrogen bonding in the system (53). Others are based on the use of bilayer stacks or multilamellar vesicles, and thus the bilayer hydration, interbilayer interactions, and/or interactions with the substrate can influence the results.…”

Calcium Ion-Induced Structural Changes in Carboxymethylcellulose Solutions and Their Effects on Adsorption on Cellulose Surfaces

“… 48 D 2 O forms a stronger and higher average number of hydrogen bonds (10% more) compared to water. 49 − 51 Thus, it is a more structured liquid than H 2 O. 52 Therefore, when CMC is adsorbed from D 2 O, the entropy gain due to the release of structured D 2 O molecules from the cellulose surface would be more significant and result in high adsorption than CMC adsorbed from H 2 O, as is seen in Figure 11 .…”