Inhomogeneous dynamics in confined water nanodroplets.
Ontology highlight
ABSTRACT:
SUBMITTER: Dokter AM
PROVIDER: S-EPMC1592463 | biostudies-literature |
REPOSITORIES: biostudies-literature
Similar Datasets
Project description:Molecular dynamics simulations of water confined in two hydrophilic cylindrical pores-PH and PL-that differ in their silanol surface concentration (7.6 and 3.0 nm(-2), respectively) have been performed at 300 K. A strong interaction of interfacial water molecules with the pore was systematically found and gives rise to a layering effect, a significant distortion of both the hydrogen bond network (HBN) and the tetrahedral structure of these water molecules, and a corresponding subdiffusive mean square displacement along the main axis of the pores. By contrast, water molecules in the inner part of both pores were found to behave similarly to bulk water. The HBN and the tetrahedral configuration of water were more gradually distorted in the PL pore given the larger heterogeneity and rugosity of the surface, and the number of water-pore hydrogen bonds did not scale linearly with the silanol surface concentration of the pores, in part because of the close proximity between silanols in the PH pore. With the PL pore, the dynamic slowing down of water was found consistent with the experiment, suggesting that it provides a better model for the cylindrical MCM-41 mesopores. The structural and dynamical properties of water vary little with the silica force field.
| S-EPMC3427945 | biostudies-literature
Project description:A fundamental understanding of confined water is crucial for developing selective ion transport and water purification membranes, yet the roles of nanopore geometry and functionality on confined water dynamics remain unresolved. We report the synthesis of perdeuterated ionic alkylsulfonate amphiphiles and their water-induced self-assembly into lyotropic liquid crystal (LLC) mesophases with well-defined, convex, sulfonate-lined nanopores. Quasielastic neutron scattering (QENS) measurements demonstrate that the water self-diffusion coefficients within these sulfonate-lined convex nanopores depend on the hydration level and amphiphile counterion identity (H+, K+, NMe4+). The consistency of the observed counterion-dependent water dynamics trends with those of carboxylate LLCs is rationalized on the basis of similarities in the counterion spatial distributions in the water-filled channels, which we deduce from electron density maps derived from small-angle X-ray scattering (SAXS) analyses. These findings indicate that water diffusion is systematically faster in sulfonate-lined nanopores as compared to carboxylate-lined pores due to weaker water interactions with the softer and more hydrophobic-SO3- functionalities. These molecular-level insights into the relationships between convex pore wall chemical functionalities, hydrated counterions, and confined water diffusion may inform future development of new nanoporous media.
| S-EPMC7122394 | biostudies-literature
Project description:While polyamide (PA) membranes are widespread in water purification and desalination by reverse osmosis, a molecular-level understanding of the dynamics of both confined water and polymer matrix remains elusive. Despite the dense hierarchical structure of PA membranes formed by interfacial polymerization, previous studies suggest that water diffusion remains largely unchanged with respect to bulk water. Here, we employ neutron spectroscopy to investigate PA membranes under precise hydration conditions, and a series of isotopic contrasts, to elucidate water transport and polymer relaxation, spanning ps-ns timescales, and Å-nm lengthscales. We experimentally resolve, for the first time, the multimodal diffusive nature of water in PA membranes: in addition to (slowed down) translational jump-diffusion, we observe a long-range and a localized mode, whose geometry and timescales we quantify. The PA matrix is also found to exhibit rotational relaxations commensurate with the nanoscale confinement observed in water diffusion. This comprehensive 'diffusion map' can anchor molecular and nanoscale simulations, and enable the predictive design of PA membranes with tuneable performance.
| S-EPMC9120036 | biostudies-literature
Project description:Liquid water nanodroplets are important in earth's climate, and are valuable for studying supercooled water because they resist crystallisation well below the bulk freezing temperature. Bulk liquid water has well-known thermodynamic anomalies, such as a density maximum, and when supercooled is hypothesised to exhibit a liquid-liquid phase transition (LLPT) at elevated pressure. However, it is not known how these bulk anomalies might manifest themselves in nanodroplets. Here we show, using simulations of the TIP4P/2005 water model, that bulk anomalies occur in nanodroplets as small as 360 molecules. We also show that the Laplace pressure inside small droplets reaches 220?MPa at 180?K, conditions close to the LLPT of TIP4P/2005. While the density and pressure inside nanodroplets coincide with bulk values at moderate supercooling, we show that deviations emerge at lower temperature, as well as significant radial density gradients, which arise from and signal the approach to the LLPT.
| S-EPMC6008328 | biostudies-literature
Project description:Reverse micelles are attractive nanoscale systems used for the confinement of molecules in studies of structure and chemical reactions, including protein folding, and aggregation. The simulation of reverse micelles, in which a water "pool" is separated from a nonpolar bulk phase by a surfactant layer, poses significant challenges to empirical force fields due to the diversity of interactions between nonpolar, polar, and charged groups. We have explored the dependence of system density, reverse micelle structure, and water configurational relaxation times as a function of reverse micelle composition, including water:surfactant ratio, absolute number of water molecules, and force field using molecular dynamics simulations. The resulting structures and dynamics are found to depend more on the force field used than on varying interpretations of the water:surfactant ratio in terms of absolute size of the reverse micelle. Substantial deviations from spherical reverse micelle geometries are observed in all unrestrained simulations. Rotational anisotropy decay times and water residence times show a strong dependence on force field and water model used, but power-law relaxation in time is observed independent of the force field. Our results suggest the need for further experimental study of reverse micelles that can provide insight into the distribution and dynamics of shape fluctuations in these complex systems.
| S-EPMC3709849 | biostudies-literature
Project description:Over the years, numerous experimental and theoretical efforts have been dedicated to investigating the mysteries of water and determining its new unexplored physical properties. Despite this, high-pressure studies of water and aqueous mixtures close to the glass transition still represent an unknown area of research. Herein, we address a fundamental issue: the validity of the density scaling concept for fast water dynamics. For this purpose, we performed ambient and high-pressure dielectric measurements of a supercooled equimolar aqueous mixture of an acidic ionic liquid. All isothermal and isobaric relaxation data describing the time scale of charge transport (τσ) and fast dynamics within the water clusters (τν) reveal visual evidence of a liquid-glass transition. Furthermore, both relaxation processes satisfy the ργ/T scaling concept with a single exponent γ = 0.58. Thus, the scaling exponent is a state-point-independent parameter for the dynamics of water clusters confined in ionic liquid investigated in the pressure range up to 300 MPa.
| S-EPMC10983063 | biostudies-literature
Project description:Small-angle X-ray scattering (SAXS) is used to demonstrate the presence of density fluctuations in ambient water on a physical length-scale of approximately 1 nm; this is retained with decreasing temperature while the magnitude is enhanced. In contrast, the magnitude of fluctuations in a normal liquid, such as CCl(4), exhibits no enhancement with decreasing temperature, as is also the case for water from molecular dynamics simulations under ambient conditions. Based on X-ray emission spectroscopy and X-ray Raman scattering data we propose that the density difference contrast in SAXS is due to fluctuations between tetrahedral-like and hydrogen-bond distorted structures related to, respectively, low and high density water. We combine our experimental observations to propose a model of water as a temperature-dependent, fluctuating equilibrium between the two types of local structures driven by incommensurate requirements for minimizing enthalpy (strong near-tetrahedral hydrogen-bonds) and maximizing entropy (nondirectional H-bonds and disorder). The present results provide experimental evidence that the extreme differences anticipated in the hydrogen-bonding environment in the deeply supercooled regime surprisingly remain in bulk water even at conditions ranging from ambient up to close to the boiling point.
| S-EPMC2741230 | biostudies-literature
Project description:Ubiquitin confined within nanodroplets was irradiated with a variable-power CO2 laser. Mass spectrometry analysis shows evidence for a protein "melting"-like transition within droplets prior to solvent evaporation and ion formation. Ion mobility spectrometry reveals that structures associated with early steps of denaturation are trapped because of short droplet lifetimes.
| S-EPMC5871606 | biostudies-literature
Project description:Confined and interstitial water has a key role in several chemical, physical and biological processes. It is remarkable that many aspects of water behavior in this regime (e.g., chemical reactivity) remain obscure and unaddressed. In particular for gold surfaces, results from simulations indicated that the first wetting layer would present hydrophilic behavior in contrast to the overall hydrophobic character of the bulk water on this surface. In the present work we investigate the properties of confined water on Au 〈111〉 nanochannels. Our findings, based on a large set of morphological, structural and spectroscopic experimental data and ab initio computer simulations, strongly support the hypothesis of hydrophilicity of the first wetting layer of the Au 〈111〉 surface. A unique oxidation process was also observed in the nanochannels driven by confined water. Our findings indicated that the oxidation product is Au(OH)3. Therefore, the Au surface reactivity against confined water needs to be considered for nanoscopic applications such as, e.g., catalysis in fine chemicals, pharmaceuticals, and the food industry green processes.
| S-EPMC9057077 | biostudies-literature
Project description:The manipulation of the transition states of a chemical process is essential to achieve the desired selectivity. In particular, transition states of chemical reactions can be significantly modified in a confined environment. We report a catalytic reaction with remarkable amplification of stereochemical information in a confined water cage. Surprisingly, this amplification is significantly dependent on droplet size. This water-induced chirality amplification stems from the hydrophobic hydration effects, which ensures high proximity of the catalyst and substrates presumably at the transition state, leading to higher enantioselectivity. Flow and batch reactors were evaluated to confirm the generality of this water-induced chirality amplification. Our observation on efficient chiral induction in confined water cages might lead to an understanding of the chirality amplification in the prebiotic era, which is a key feature for the chemical evolution of homochirality.
| S-EPMC6382825 | biostudies-literature