Structure from Dynamics: Vibrational Dynamics of Interfacial Water as a Probe of Aqueous Heterogeneity

Abstract

The structural heterogeneity of water at various interfaces can be revealed by time-resolved sum-frequency generation spectroscopy. The vibrational dynamics of the O–H stretch vibration of interfacial water can reflect structural variations. Specifically, the vibrational lifetime is typically found to increase with increasing frequency of the O–H stretch vibration, which can report on the hydrogen-bonding heterogeneity of water. We compare and contrast vibrational dynamics of water in contact with various surfaces, including vapor, biomolecules, and solid interfaces. The results reveal that variations in the vibrational lifetime with vibrational frequency are very typical, and can frequently be accounted for by the bulk-like heterogeneous response of interfacial water. Specific interfaces exist, however, for which the behavior is less straightforward. These insights into the heterogeneity of interfacial water thus obtained contribute to a better understanding of complex phenomena taking place at aqueous interfaces, such as photocatalytic reactions and protein folding.

Simulations of Nanoseparated Charged Surfaces Reveal Charge-Induced Water Reorientation and Nonadditivity of Hydration and Mean-Field Electrostatic Repulsion

“…5 (a). For elevated surfaces charges σ = −0.38 and −0.77 e/nm 2 the water orientation changes profoundly and water hydrogens point to the surface due to the negative surface charge, in agreement with previous experiments and simulations [29][30][31]61,62 .…”

“…However, already for a moderate surface charge density σ = −0.77e/nm 2 this additivity breaks down, which we rationalize by a modification of the hydration repulsion due to the surface-charge induced re-orientation of interfacial water. That water reacts sensitively to the presence of surface charges is known from simulations and experiments [29][30][31]61,62 , we show that this restructuring modifies the hydration repulsion and thus the effective surface interaction pressure significantly. Corrections to PB theory due to ion correlation effects, which have been extensively discussed 37 , are relatively unimportant for moderate surface charge densities and monovalent couterions.…”

Time-dependent vibrational sum-frequency generation spectroscopy of the air-water interface

“…In this paper, we demonstrate a simple computational scheme to determine the time-dependent frequency-resolved vSFG spectrum of the air-water interface. Our computational scheme complements the recently reported experimental time-resolved vSFG/2D-SFG techniques [20][21][22][23][24][25][26] . In particular, we note that the here presented computational method directly implements a pulse sequence proposed by Bonn and coworkers 28 .…”

“…Ron Shen and coworkers experimentally demonstrated for the first time the applicability of vSFG spectroscopy to study the air-water interface [11][12][13] . This technique has been further extended to more complex experimental setups like phase-sensitive vSFG, timeresolved vSFG, two-dimensional vSFG (2D-vSFG) to name just a few [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] .…”

Hidden Isolated OH at the Charged Hydrophobic Interface Revealed by Two‐Dimensional Heterodyne‐Detected VSFG Spectroscopy

“…Fori nvestigating interfacial water, vibrational sum-frequencyg eneration (VSFG) spectroscopy is av ery powerful tool because of its inherent interface selectivity,a nd VSFG has been extensively utilized to study the structure and dynamics at interfaces. [12] In particular,phase-sensitive heterodyne-detected vibrational sum-frequencyg eneration (HD-VSFG) spectroscopy enables direct measurements of the imaginary part of the second-order nonlinear susceptibility (Imc (2) ), which can be interpreted in the same way as bulk IR absorption spectra that correspond to Imc (1) (c (1) :l inear susceptibility). [12c] Furthermore,t he sign of the Imc (2) signal provides direct information about the up/down orientation of molecules at the interface, [12c,d] which is crucial information to understand the interfacial structure at the molecular level.…”