Quantum effects and the excess proton in water

Abstract

The influence of nuclear quantum effects on the excess proton in water is examined through quantum dynamical computer simulations. Results are presented for the isotope effects on both the proton exchange process and the infrared absorption spectrum. A critical assessment of the accuracy of density-functional-theory-based molecular dynamics simulation methods for addressing this problem is also given.

Labile supramolecular structures and their dynamics in associated liquids based on NMR data

“…Proton hydrates are linked to the environment by H bonds, whose characteristics are similar to those in pure water. 4. Changes in the proton chemical shifts depending on the composition correlate with the changes in the density.…”

“…Dependences of the chemical shifts (δ) and the linewidth (∆) of the average 14 N NMR signals (1, 2) at 25 °C and 17 O NMR signals(3,4) at 20 °C on the composition of the N 2 O 5 -HNO 3 system ( 14 N chemical shifts are given relative to MeNO 2 as the external standard, and the 17 O chemical shifts are given relative to H 2 O as the external standard). The correlation coefficients for the approximating straight lines are 0.963 and 0.974 for δ and 0.465 and 0.825 for ∆ for the regions q N < 0.06 and q N > 0.For concentrations L > 1, the proton chemical shifts increase by several Hertzs during measurements; the observed chemical shifts were extrapolated to the instant of mixing.…”

Reactions in complex biologically relevant systems: challenges for computational approaches

“…Therefore, the use of classical dynamics is a well-defined approximation for our purposes (calculation of infrared spectra [28,30,49]). Previous studies on protonated water dimer (H 5 O 2 + ) have also investigated the influence of describing the dynamics of the transferring proton with quantum mechanical methods [37,45]. Some of the investigations used empirical valence bond potential energy surfaces (EVB), while others were based on evaluating energies and forces at the density functional level.…”

Conformational analysis, tautomerization, IR, Raman, and NMR studies of 3-phenylazo-2,4-pentanedione

“…The chosen reaction coordinate is the N-H distance. Although several authors have shown that DFT methods provide very low energy barriers for proton transfer processes for adiabatic approach [15,18,20] the applied level of theory is a compromise between the computational costs and the reliability of the results. The different local topology of the energy curve can be attributed to the stronger hydrogen bond and the higher electron charge delocalization in the HA1 tautomer which makes the potential well steeper than in the less stable AE4 configuration.…”