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The vibrational lifetime of solute molecules is predicted to be slower at interfaces; however, ultrafast measurements show that this behavior can vary dramatically depending on interfacial structure and vibrational coupling pathways. Surprisingly, the nitrile stretch of SCN− exhibits unexpectedly rapid vibrational energy relaxation at aqueous (D2O) alumina interfaces, while there is no appreciable difference in relaxation in bulk and interfacial H2O. For interfacial D2O, the CN stretch lifetime is nearly three times shorter than in bulk D2O (T1 ∼ 22 ps). Ab initio simulations reveal an increased vibrational density of states (VDOS) at the low frequency OD stretch region compared to bulk D2O, enhancing overlap between SCN− and D2O vibrational modes. Additional factors—including stronger transition dipole–transition dipole coupling arising from reduced dielectric screening and increased orientational ordering of interfacial molecules—further accelerate vibrational relaxation at the interface. To directly probe how interfacial VDOS varies with surface structure, we employed the CN stretch lifetime of SCN− as a reporter of the O–D VDOS at two model alumina surfaces: Al2O3(0001)/D2O and Al2O3(112¯0)/D2O. IR pump–vibrational sum frequency generation (vSFG) probe measurements show a shorter vibrational lifetime at the Al2O3(0001)/D2O interface (7.1 ps) compared to the Al2O3(112¯0)/D2O interface (8.7 ps). Molecular dynamics simulations support these findings, showing that the low-frequency O–D stretch VDOS at the Al2O3(0001)/D2O interface is approximately ∼1.2 times higher than at the Al2O3(112¯0)/D2O surface. The higher VDOS provides more available accepting states for vibrational energy transfer, thus shortening the vibrational lifetime. Together, these results demonstrate that vibrational lifetimes of interfacial solutes provide a powerful experimental probe of interfacial VDOS and solute–solvent coupling. This approach offers new insight into vibrational relaxation pathways and the microscopic origins of energy dissipation in the bulk and at interfaces. 

We investigate the hypothesis that mineral/water interfaces played a crucial catalytic role in peptide formation by promoting the self-assembly of amino acids. Using classical molecular dynamics simulations, we demonstrate that the α-alumina(0001) surface exhibits an affinity of 4k_BTfor individual glycine or GG dipeptide molecules due to hydrogen bonds. In simulations with multiple glycine molecules, surface-bound glycine enhances further adsorption, leading to the formation of long chains connected by hydrogen bonds between the carboxyl and amine groups of glycine molecules. We find that the likelihood of observing chains longer than 10 glycine units increases by at least five orders of magnitude at the surface compared to the bulk. This surface-driven assembly is primarily due to local high density and alignment with the alumina surface pattern. Together, these results propose a model for how mineral surfaces can induce configuration-specific assembly of amino acids, thereby promoting condensation reactions. 

The dielectric permittivity of salt water decreases on dissolving more salt. For nearly a century, this phenomenon has been explained by invoking saturation in the dielectric response of the solvent water molecules. Herein, we employ an advanced deep neural network (DNN), built using data from density functional theory, to study the dielectric permittivity of sodium chloride solutions. Notably, the decrease in the dielectric permittivity as a function of concentration, computed using the DNN approach, agrees well with experiments. Detailed analysis of the computations reveals that the dom- inant effect, caused by the intrusion of ionic hydration shells into the solvent hydrogen-bond network, is the disruption of dipolar correlations among water molecules. Accordingly, the observed decrease in the dielectric permittivity is mostly due to increasing suppression of the collective response of solvent waters. 

Abstract Salt water is ubiquitous, playing crucial roles in geological and physiological processes. Despite centuries of investigations, whether or not water’s structure is drastically changed by dissolved ions is still debated. Based on density functional theory, we employ machine learning based molecular dynamics to model sodium chloride, potassium chloride, and sodium bromide solutions at different concentrations. The resulting reciprocal-space structure factors agree quantitatively with neutron diffraction data. Here we provide clear evidence that the ions in salt water do not distort the structure of water in the same way as neat water responds to elevated pressure. Rather, the computed structural changes are restricted to the ionic first solvation shells intruding into the hydrogen bond network, beyond which the oxygen radial-distribution function does not undergo major change relative to neat water. Our findings suggest that the widely cited pressure-like effect on the solvent in Hofmeister series ionic solutions should be carefully revisited. 

The role of geometric frustration of water molecules in the rate of water oxidation in the nanoconfined interlayer of manganese-oxide layered materials (birnessite, buserite) is examined in a well-controlled experiment. Calcium buserite is prepared, and used in a split-batch synthetic protocol to prepare calcium birnessite, sodium buserite, and sodium birnessite, and partially dehydrated sodium birnessite. Thus, four samples are prepared in which features effecting catalytic efficiency (defect density, average manganese oxidation state) are controlled, and the main difference is the degree of hydration of the interlayer (two layers of water in buserites vs. one layer of water in birnessite). Molecular dynamics simulations predict birnessite samples to exhibit geometric water frustration, which facilitates redox catalysis by lowering the Marcus reorganization energy of electron transfer, while buserite samples exhibit traditional intermolecular hydrogen bonding among the two-layer aqeuous region, leading to slower catalytic behavior akin to redox reactions in bulk water. Water oxdiation activity is investigated using chemical and electrochemical techniques, demonstrating and quantifying the role of water frustration in enhancing catalysis. Calculation and experiment demonstrate dehydrated sodium birnessite to be most effective, and calcium buserite the least effective, with a difference in electrocatlytic overpotential of ∼750 mV and a ∼20-fold difference in turnover number.