Opposing Electronic and Nuclear Quantum Effects on Hydrogen Bonds in H₂O and D₂O

Abstract

The effect of extending the OÀ H bond length(s) in water on the hydrogen-bonding strength has been investigated using static ab initio molecular orbital calculations. The "polar flattening" effect that causes a slight σ-hole to form on hydrogen atoms is strengthened when the bond is stretched, so that the σ-hole becomes more positive and hydrogen bonding stronger. In opposition to this electronic effect, path-integral ab initio molecular-dynamics simulations show that the nuclear quantum effect weakens the hydrogen bond in the water dimer. Thus, static electronic effects strengthen the hydrogen bond in H 2 O relative to D 2 O, whereas nuclear quantum effects weaken it. These quantum fluctuations are stronger for the water dimer than in bulk water.

Sweet taste of heavy water

“…Molecular dynamics simulations show, in agreement with experiment (38), that proteins in general are slightly more rigid and compact in D2O than in H2O. At a molecular level, this general behavior may be traced back to the slightly stronger hydrogen bonding in D2O vs H2O, which is due to a nuclear quantum effect, namely difference in zero-point energy (3,4). Biologically relevant situations where one may expect strong nuclear quantum effects as implications of H/D substitution directly involve proton or deuteron transfer (9).…”

“…The most notable difference in physical properties between D2O and H2O is the roughly 10% higher density of the former liquid, which is mostly a trivial consequence of deuterium being about twice as heavy as hydrogen. A more subtle effect of deuteration is the formation of slightly stronger hydrogen (or deuterium) bonds in D2O as compared to H2O (3,4). This results in a small increase of the freezing and boiling points by 3.8°C and 1.4°C, respectively, and in a slight increase of 0.44 in pH (or pD) of pure water upon deuteration (5).…”

Pure non-local machine-learned density functional theory for electron correlation

“…Of comparable computational cost as conventional low-rung functionals, the transferable KDFA approach provides access to quantitative CCSD(T) simulations for systems that before were on the brink of largest-scale supercomputing studies or simply not tractable at all. We demonstrate this for the shared proton in a protonated water dimer, as an intensely studied testbed for the role of electron correlation and nuclear quantum effects in hydrated excess protons [40][41][42][43][44][45][46][47][48][49] . An ensemble of 100,000 uncorrelated configurations of the protonated water dimer was drawn from a 5 ns MD trajectory generated at the semiempirical GFN2-XTB level of theory 50 .…”

Universal quenching of common fluorescent probes by water and alcohols

“…36,40 Furthermore, D 2 O is believed to form slightly weaker H-bonds than H 2 O. 50 In order to increase the hydrogen-bond strength between the probe and the solvent, we used hexafluoroisopropanol (HFIP) as one of the very few solvents with a higher hydrogen-bond donating capability (Kamlet-Taft acidity parameter  = 1.96) than water ( = 1.17). 51,52 We found the fluorescence quantum yield and the excited-state lifetime of ATTO655 in HFIP (Figure 3c, Table S4) to be very similar to the values of these parameters in other alcohols, including in 2-propanol, the non-perfluorinated analogue of HFIP.…”