Identifying Eigen-like hydrated protons at negatively charged interfaces

Abstract

Despite the importance of the hydrogen ion in a wide range of biological, chemical, and physical processes, its molecular structure in solution remains lively debated. Progress has been primarily hampered by the extreme diffuse nature of the vibrational signatures of hydrated protons in bulk solution. Using the inherently surface-specific vibrational sum frequency spectroscopy technique, we show that at selected negatively charged interfaces, a resolved spectral feature directly linked to the H 3 O + core in an Eigen-like species can be readily identified in a biologically compatible pH range. Centered at~2540 cm −1 , the band is seen to shift to~1875 cm −1 when forming D 3 O + upon isotopic substitution. The results offer the possibility of tracking and understanding from a molecular perspective the behavior of hydrated protons at charged interfaces.

Proton Traffic Jam: Effect of Nanoconfinement and Acid Concentration on Proton Hopping Mechanism

“…This effect arises from the strong co‐adsorption of hydronium to the interface with its chloride counter ion with increasing acid concentration, which creates a minimal amount of water solvation in a 2D interfacial network with a reduced hydrogen‐bonding capacity [69] . In fact only recently has evidence of the hydration structure of protons at an interface been observed, where Eigen‐like hydrated protons (H 9 O 4 + ) were identified near negatively charged monolayers at biologically relevant pH, [70] similar to the observations made here.…”

First-Principles Study of C–C Coupling Pathways for CO2 Electrochemical Reduction Catalyzed by Cu(110)

“…All energetics reported in this study were calculated under U = −1.0 V SHE and pH = 6.8 conditions. The Eigen complex, where a proton is solvated by four explicit water molecules, was used as the proton source to locate the transition state of hydrogenation by a proton–electron pair . A previous theoretical study demonstrated that the results obtained from this Eigen model are similar to those obtained by using a water bilayer model .…”

Direct Evidence for a Surface and Bulk Specific Response in the Sum-Frequency Generation Spectrum of the Water Bend Vibration

“…The structure and dynamics of aqueous interfaces is of high relevance for many different scientific fields. [1][2][3][4][5][6][7][8][9] Many important chemical and biological processes take place at aqueous interfaces, like for instance molecular recognition at bio-membranes, protein folding, and energy conversion and storage. [10][11][12][13][14][15] The structural properties of the neat water/air interface 16,17 and charged aqueous interfaces have been extensively studied with vibrational sum-frequency generation spectroscopy (VSFG) in the frequency region of the water OH stretch vibrations.…”