Hydrogen Bond Network Of Water Research Articles

Neutron scattering on an aqueous sodium chloride solution in the gigapascal pressure range

An aqueous 3 m (=mol kg−1) NaCl solution in D2O is investigated at 0.1 MPa (hereafter denoted as 0 GPa)/298 K, 1 GPa/298 K, 1 GPa/523 K, and 4 GPa/523 K by neutron scattering combined with an empirical potential structure refinement (EPSR) method. The pressure and temperature dependence of the ion solvation and association and solvent water structure is discussed in pair correlation functions, coordination number distributions, angular distributions (orientational correlation), and spatial density functions (3D structure). The Na+ solvation is characterized as nearly octahedral coordination with about five water molecules and one Cl− over a pressure range measured. The Na–Ow (water oxygen) and Na–Dw (water hydrogen) distances are 2.34–2.37 Å and 2.82–3.00 Å, respectively. The water dipole is tilted by about 31° from the Na–O bond direction and the angle distribution becomes broader with an increase in pressure and temperature. The Cl− solvation shows a change in the coordination number of a water oxygen atom from 11 at 0 GPa to 15 at 4 GPa. An increase in the coordination number of a water hydrogen atom with pressure is observed; the values fall within five to six. The first neighbor Cl–Dw and Cl–Ow distances are 2.19–2.28 Å and 3.10–3.21 Å, respectively. The hydrogen-bonded angle Cl−···Dw–Ow is almost linear over a whole pressure range, but the angle distribution becomes broader upon compression. Another interesting finding of the Cl− solvation is the formation of extended solvation shells of Cl− in the gigapascal pressure range as if they behave as a structure making ion as Na+. The extended solvation shell of Cl– is caused by the breakdown or distortion of the hydrogen-bonded network of solvent water under compression. The coordination number of water oxygen increases from 4.7 at 0 GPa to 12–13, close to a value seen in simple liquids like Ar at 1–4 GPa. Despite such a drastic increase in water oxygen coordination number, the coordination number of the water hydrogen decreases from 2.2 at 0 GPa to 1.8 at 4 GPa, with the Ow–Dw distance lengthening from 1.77 Å to 1.95 Å, i.e., the hydrogen bonds between water molecules are retained in the gigapascal pressure range. The hydrogen bond angle Ow···Dw–Ow is almost linear, but the angle distribution is broadened upon compression, suggesting the distortion of the hydrogen bonds. Thus, it is concluded that compression of an aqueous NaCl solution to the gigapascal pressure causes the distortion of the hydrogen bonds between water molecules, resulting in the formation of the second and extended shells of a structure breaking Cl−.

Importance of Hydrogen Bonding in Crowded Environments: A Physical Chemistry Perspective.

Cells are heterogeneous on every length and time scale; cytosol contains thousands of proteins, lipids, nucleic acids, and small molecules, and molecular interactions within this crowded environment determine the structure, dynamics, and stability of biomolecules. For decades, the effects of crowding at the atomistic scale have been overlooked in favor of more tractable models largely based on thermodynamics. Crowding can affect the conformations and stability of biomolecules by modulating water structure and dynamics within the cell, and these effects are nonlocal and environment dependent. Thus, characterizing water's hydrogen-bond (H-bond) networks is a critical step toward a complete microscopic crowding model. This perspective provides an overview of molecular crowding and describes recent time-resolved spectroscopy approaches investigating H-bond networks and dynamics in crowded or otherwise complex aqueous environments. Ultrafast spectroscopy combined with atomistic simulations has emerged as a powerful combination for studying H-bond structure and dynamics in heterogeneous multicomponent systems. We discuss the ongoing challenges toward developing a complete atomistic description of macromolecular crowding from an experimental as well as a theoretical perspective.

Mechanistic insight toward EGFR activation induced by ATP: role of mutations and water in ATP binding patterns

The discovery of mutations within the kinase domain of the epidermal growth factor receptor (EGFR) gene has enabled a new era of targeted therapy in non-small cell lung cancer (NSCLC). Drugs belonging to the family of tyrosine kinase inhibitors (TKIs) are designed to bind ATP binding cleft, anyway, the occurrence of aminoacidic mutations decreases the effectiveness of the antitumoral treatment. Despite many efforts has been already made, the impact of the mutations on conformation and stability of EGFR-ATP complexes is still not fully understood. Therefore, we investigated the effect of mutations that leads to changes in Michaelis-Menten constant (K m) using dynamic docking simulations. We focused on six different EGFR forms in relation to different mutation states, then we found a good correlation between the calculated ATP affinities and K m values. Moreover, since dynamic switching of TK-EGFR from the inactive towards the active state is known to regulate the kinase activity, we observed that ATP induces the inwards movement of the αC-helix with the Lys745 close to Glu762 in all cases. This means that ATP binding should be the first step in promoting the conformational shift to the active state. Finally, we highlighted for the first time the key contribution of water hydrogen bond and water-bridge networks in the modulation of ATP affinity. The identified mutant-specific ATP binding patterns and conformational features could be much useful to guide cancer therapy and develop more personalized medicine. Communicated by Ramaswamy H. Sarma

Interfacial layers between ion and water detected by terahertz spectroscopy.

Dynamic fluctuations in the hydrogen-bond network of water occur from femto- to nanosecond timescales and provide insight into the structural/dynamical aspects of water at ion-water interfaces. Employing terahertz spectroscopy assisted with molecular dynamics simulations, we study aqueous chloride solutions of five monovalent cations, namely, Li, Na, K, Rb, and Cs. We show that ions modify the behavior of the surrounding water molecules and form interfacial layers of water around them with physical properties distinct from those of bulk water. Small cations with high charge densities influence the kinetics of water well beyond the first solvation shell. At terahertz frequencies, we observe an emergence of fast relaxation processes of water with their magnitude following the ionic order Cs > Rb > K > Na > Li, revealing an enhanced population density of weakly coordinated water at the ion-water interface. The results shed light on the structure breaking tendency of monovalent cations and provide insight into the properties of ionic solutions at the molecular level.

Molecular dynamics and network analysis reveal the contrasting roles of polar solutes within organic phase amphiphile aggregation

Amphiphile self-assembly in non-polar media is often enhanced by polar co-solutes. This is observed within many biphasic separations processes, where amphiphiles mediate transport of water and acid into organic solution. A myriad of competitive intermolecular interactions have thus far prevented a fundamental understanding of the individual and dual roles of these polar solutes upon amphiphile self-assembly in non-polar media. Toward this end, the current work employs classical molecular dynamics and intermolecular network analyses to deconstruct the individual affects of water and nitric acid upon the self-assembly of N,N,N’,N’-tetraoctyl-3-oxapentanediamide (TODGA), a prevalent amphiphile extractant used in metal ion separations. In the absence of acid, and at low water concentration, H2O is found to promote local dimer and trimer formation of TODGA, however as [H2O]org increases, preferential self-solvation leads to large (H2O)n clusters that cause TODGA clusters to sorb to the (H2O)n periphery and supports extended aggregation. Addition of HNO3 to the humid solutions disrupts the water hydrogen bond network and inhibits the formation of large water clusters - thus preventing extended aggregation behavior and encouraging local aggregation. Prior experimental observations of enhanced TODGA self-assembly under these conditions are attributed primarily to the role of water rather than co-extracted HNO3, thus providing valuable new insight into the means by which extractant aggregation can be tuned within separations processes. The different roles of polar co-solutes, that derive from their individual hydrogen bonding capabilities and competitive interactions in the context of preferred solvation environments, is of fundamental importance amphiphile behavior in non-polar media.

High-donor electrolyte additive enabling stable aqueous zinc-ion batteries

The performance benefits of metallic zinc, despite many promising characteristics (such as low cost and high capacity) in rechargeable batteries, are still compromised by dendritic growth and parasitic side reactions originating from reactive aqueous electrolytes, which dramatically restrain future application. In this work, a facile strategy is proposed via introducing high-donor-number organic solvent N, N-dimethyl acetamide (DMA) as electrolyte additive to achieve high Zn reversibility. Based on multiscale theoretical and experimental investigations, it is demonstrated that high-donor DMA additive with strong electron-donating ability can confine free water activity, replace the water in Zn2+ solvation sheath, and reshape hydrogen-bonding network of water. The DMA-modified electrolyte enables remarkable suppression of water-involved hydrogen evolution and severe corrosion, which contributes to preferentially uniform deposition and ultralong cycling life of 4500 h at current density of 1 mA cm−2 in symmetric cell, and high Coulombic efficiency of 99.6% in asymmetric cell. Coupling with VO2-based cathodes, the full battery can deliver high specific capacity of 261 mAh g − 1 at -18 °C and long operation stability of 500 cycles. This strategy presents a promising approach for development of high-performance aqueous metal batteries.

From Networked to Isolated: Observing Water Hydrogen Bonds in Concentrated Electrolytes with Two-Dimensional Infrared Spectroscopy.

Superconcentrated electrolytes have emerged as a promising class of materials for energy storage devices, with evidence that high voltage performance is possible even with water as the solvent. Here, we study the changes in the water hydrogen bonding network induced by the dissolution of lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) in concentrations ranging from the dilute to the superconcentrated regimes. Using time-resolved two-dimensional infrared spectroscopy, we observe the progressive disruption of the water-water hydrogen bond network and the appearance of isolated water molecules interacting only with ions, which can be identified and spectroscopically isolated through the intermolecular cross-peaks between the water and the TFSI- ions. Analyzing the vibrational relaxation of excitations of the H2O stretching mode, we observe a transition in the dominant relaxation path as the bulk-like water vanishes and is replaced by ion-solvation water with the rapid single-step relaxation of delocalized stretching vibrations into the low frequency modes being replaced by multistep relaxation through the intramolecular H2O bend and into the TFSI- high frequency modes prior to relaxing to the low frequency structural degrees of freedom. These results definitively demonstrate the absence of vibrationally bulk-like water in the presence of high concentrations of LiTFSI and especially in the superconcentrated regime, while additionally revealing aspects of the water hydrogen bond network that have been difficult to discern from the vibrational spectroscopy of the neat liquid.

Correlated Local Fluctuations in the Hydrogen Bond Network of Liquid Water.

The hypothesis that liquid water can separate into two phases in the supercooled state has been supported by recent experimental and theoretical studies. However, whether such structural inhomogeneity extends to ambient conditions is under intense debate. Due to the dynamic nature of the hydrogen bond network of liquid water, exploring its structure requires detailed insight into the collective motion of neighboring water molecules, a missing link that has not been examined so far. Here, highly sensitive quantum mechanical calculations detect that the time evolution of nearby hydrogen bonds is strongly correlated, revealing a direct mechanism for the appearance of short-range structural fluctuations in the hydrogen bond network of liquid water for the first time. This correlated dynamics is found to be closely connected to the static structural picture. The distortions from the tetrahedral structure do not occur independently but are correlated due to the preference of nearby donors and acceptors to be in similar environments. The existence of such cooperative fluctuations is further supported by the temperature dependence of the local structural evolution and explained by conventional analysis of localized orbitals. It was found that such correlated structural fluctuations are only observed on a short length scale in simulations at ambient conditions. The correlations of the nearby hydrogen bond pairs of liquid water unveiled here are expected to offer a new insight into connecting the dynamics of individual water molecules and the local structure of the hydrogen bond network.

Steady-like topology of the dynamical hydrogen bond network in supercooled water.

We investigate the link between topology of the hydrogen bond network (HBN) and large-scale density fluctuations in water from ambient conditions to the glassy state. We observe a transition from a temperature-dependent topology at high temperatures, to a steady-like topology below the Widom temperature TW ∼ 220K signaling the fragile-to-strong crossover and the maximum in structural fluctuations. As a consequence of the steady topology, the network suppresses large-scale density fluctuations much more efficiently than at higher temperatures. Below TW , the contribution of coordination defects of the kind A 2 D 1 (two acceptors and one donor) to the kinetics of the HBN becomes progressively more pronounced, suggesting that A 2 D 1 configurations may represent the main source of dynamical heterogeneities. Below the vitrification temperature, the freezing of rotational and translational degrees of freedom allow for an enhanced suppression of large-scale density fluctuations and the sample reaches the edges of nearly hyperuniformity. The formed network still hosts coordination defects, hence implying that nearly hyperuniformity goes beyond the classical continuous random network paradigm of tetrahedral networks and can emerge in scenarios much more complex than previously assumed. Our results unveil a hitherto undisclosed link between network topology and properties of water essential for better understanding water's rich and complex nature. Beyond implications for water, our findings pave the way to a better understanding of the physics of supercooled liquids and disordered hyperuniform networks at large.

Surface wettability effect on heat transfer across solid-water interfaces

• Mechanisms of surface wettability effect on interfacial heat transfer are unraveled. • Hydrophilic surface promotes heat transfer through enhanced hydrogen-bonded network. • Molecular roughness with high biphasic contact area is beneficial to heat transfer. • Multiple and shallow vacancies are better than the deep but fewer ones on substrate. Although it has been found that the heat transfer across solid–liquid interface can be affected by the surface wettability, the underlying mechanism remains ambiguous. Herein non-equilibrium molecular dynamics simulations are conducted to unravel the microscopic mechanisms of heat transfer across solid-water interfaces. Specifically, two aspects of the solid surface wettability are investigated including modifying surface chemistry and introducing molecular roughness. We find that enlarging the solid-water interaction strength facilitates the formation of hydrogen-bonded network of water, hence enhancing the interfacial heat transfer. In addition, introducing molecular roughness can promote heat transfer by increasing the solid-water contact area. When the contact area remains the same, the substrates with multiple and shallow vacancies are more beneficial to heat transfer than those with deep but fewer vacancies. This work sheds insights into the mechanistic understanding of the heat transfer process and provides theoretical guidance for the development of efficient heat transfer devices.

Water Diffusion Proceeds via a Hydrogen-Bond Jump Exchange Mechanism.

The self-diffusion of water molecules plays a key part in a broad range of essential processes in biochemistry, medical imaging, material science, and engineering. However, its molecular mechanism and the role played by the water hydrogen-bond network rearrangements are not known. Here we combine molecular dynamics simulations and analytic modeling to determine the molecular mechanism of water diffusion. We establish a quantitative connection between the water diffusion coefficient and hydrogen-bond jump exchanges, and identify the features that determine the underlying energetic barrier. We thus provide a unified framework to understand the coupling between translational, rotational, and hydrogen-bond dynamics in liquid water. It explains why these different dynamics do not necessarily exhibit identical temperature dependences although they all result from the same hydrogen-bond exchange events. The consequences for the understanding of water diffusion in supercooled conditions and for water transport in complex aqueous systems, including ionic, biological, and confined solutions, are discussed.

High-Dimensional Fluctuations in Liquid Water: Combining Chemical Intuition with Unsupervised Learning

The microscopic description of the local structure of water remains an open challenge. Here, we adopt an agnostic approach to understanding water's hydrogen bond network using data harvested from molecular dynamics simulations of an empirical water model. A battery of state-of-the-art unsupervised data-science techniques are used to characterize the free-energy landscape of water starting from encoding the water environment using local atomic descriptors, through dimensionality reduction and finally the use of advanced clustering techniques. Analysis of the free energy under ambient conditions was found to be consistent with a rough single basin and independent of the choice of the water model. We find that the fluctuations of the water network occur in a high-dimensional space, which we characterize using a combination of both atomic descriptors and chemical-intuition-based coordinates. We demonstrate that a combination of both types of variables is needed in order to adequately capture the complexity of the fluctuations in the hydrogen bond network at different length scales both at room temperature and also close to the critical point of water. Our results provide a general framework for examining fluctuations in water under different conditions.

Water Structure at the Hydrophobic Nanodroplet Surface Revealed by Vibrational Sum Frequency Scattering Using Isotopic Dilution.

The water structure at the hydrophobic/water interface is key toward understanding hydrophobicity at the molecular level. Herein, we characterize the hydrogen-bonding network of interfacial water next to sub-micron-sized hydrophobic oil droplets dispersed in water using isotopic dilution vibrational sum frequency scattering (SFS) spectroscopy. The relative intensity of different modes, the frequency shift of the uncoupled O–D spectrum, and a low-frequency shoulder (2395 cm–1) reveal that water forms an overall stronger hydrogen-bonding network next to hydrophobic droplets compared to bulk water and the air/water interface. Half of the spectral width of the oil droplet SFS spectrum is determined by inter- and intramolecular coupling of water molecules. Isotopic dilution also confirms the presence of a broad distribution (ca. 2640–2745 cm–1) of non-water-hydrogen-bonded O–D modes that are red-shifted and broadened compared to similar species at the air/water interface. This band corroborates the presence of charge transfer between water and oil.

Effects of ion adsorption on graphene oxide films and interfacial water structure: A molecular-scale description

Graphene oxide is a promising, emerging separation material, as it is durable, dispersible in water, and has naturally forming functional groups. Bulk studies using graphene oxide flakes have demonstrated impressive metal adsorption. However, little interfacial information about water and metal organization near graphene oxide is available. A mechanistic understanding of water and ions interactions with graphene oxide films is critical toward advanced separations, including improved sorption efficiency and membrane regeneration. We study metal ion and local water organization near graphene oxide thin films formed at the air/water interface. These films are not typical membranes and allow us to determine nanoscale information about the graphene oxide-water interface. We accomplish this with x-ray reflectivity (XR), x-ray fluorescence near total reflection (XFNTR), and vibrational sum frequency generation spectroscopy (SFG). These interface-specific techniques provide the electron density profile normal to the interface, number of adsorbed ions, and information about the orientational ordering and hydrogen-bonding network of interfacial water, respectively. Via XFNTR and SFG, we find that trivalent yttrium ions preferentially adsorb to graphene oxide and affect its structure, compared to divalent strontium and monovalent cesium ions. Two different interfacial water populations can be described, based on their hydrogen bonding strength, and the adsorbed ions affect these populations differently. These results provide fundamental information about ion and water organization at the interface and help address the large computational-experimental agreement gap for graphene oxide systems. Additionally, they are relevant for improved soft-scaffold graphene oxide membranes and downstream applications.

Fluorescence of KCl Aqueous Solution: A Possible Spectroscopic Signature of Nucleation.

Ion pairing in water solutions alters both the water hydrogen-bond network and ion solvation, modifying the dynamics and properties of electrolyte water solutions. Here, we report an anomalous intrinsic fluorescence of KCl aqueous solution at room temperature and show that its intensity increases with the salt concentration. From the ab initio density functional theory (DFT) and time-dependent DFT modeling, we propose that the fluorescence emission could originate from the stiffening of the hydrogen bond network in the hydration shell of solvated ion-pairs that suppresses the fast nonradiative decay and allows the slower radiative channel to become a possible decay pathway. Because computations suggest that the fluorophores are the local ion-water structures present in the prenucleation phase, this band could be the signature of the incoming salt precipitation.

NaCl salt effect on water structure: a Monte Carlo simulation study

ABSTRACT Monte Carlo simulations and the nearest neighbour approach have been employed in the present study to investigate the effect of NaCl salt on the local structure of water at ambient conditions. The calculations are performed at increasing concentration of NaCl starting from C = 0.5 m up to 6 m. We investigate the influence of ions on the tetrahedral structure and the hydrogen-bonded network of water. The analysis shows that increasing salt concentration results in a reduction of the tetrahedral arrangement of water in favour of a non-tetrahedral arrangement. The use of the nearest neighbour approach allows us to determinate the origin and angular characteristics of this non-tetrahedral structure. Moreover it is demonstrated that compared to Na+, Cl− ion has a larger effect on the tetrahedral structure of water.

Water in Sugar Electrolytes and Application to Electrodeposition of Superconducting Rhenium

A systematic electrochemical study is carried out on electrolytes with superhigh concentrations of fructose. The effect of fructose concentration on the viscosity and conductivity of electrolyte are determined and analyzed using Walden rule and the theory of rate process. The diffusion rates of proton and cupric cation are calculated from the peak current in cyclic voltammogram on stationary electrode and the limiting current on rotating electrodes. Raman spectroscopy is used to characterize the hydrogen bond network in water and the effect of fructose concentration on such network. Rhenium deposition with different fructose concentrations is studied on rotating disc electrodes. X-ray fluorescence, X-ray diffraction, and four point probe measurements at cryogenic temperature are used to study the deposition rate, crystallographic structure, and superconductivity of film, respectively.

Water Dynamics and Structure of Highly Concentrated LiCl Solutions Investigated Using Ultrafast Infrared Spectroscopy.

In highly concentrated salt solutions, the water hydrogen bond (H-bond) network is completely disrupted by the presence of ions. Water is forced to restructure as dictated by the water-ion and ion-ion interactions. Using ultrafast polarization-selective pump-probe (PSPP) spectroscopy measurements of the OD stretch of dilute HOD, we demonstrate that the limited water-water H-bonding present in concentrated lithium chloride solutions (up to four waters per ion pair) is, on average, stronger than that occurring in bulk water. Furthermore, information on the orientational dynamics and the angular restriction of water H-bonded to both water oxygens and chloride anions was obtained through analysis of the frequency-dependent anisotropy decays. It was found that, when the salt concentration increased, the water showed increasing restriction and slowing at frequencies correlated with strong H-bonding. The angular restriction of the water molecules and strengthening of water-water H-bonds are due to the formation of a water-ion network not present in bulk water and dilute salt solutions. The structural evolution of the ionic medium was also observed through spectral diffusion of the OD stretch using 2D IR spectroscopy. Compared to bulk water, there is significant slowing of the biexponential spectral diffusion dynamics. The slowest component of the spectral diffusion (13 ps) is virtually identical to the time for complete reorientation of HOD measured with the PSPP experiments. This result suggests that the slowest component of the spectral diffusion reflects rearrangement of water molecules in the water-ion network.

A Universal Additive Strategy to Reshape Electrolyte Solvation Structure toward Reversible Zn Storage

AbstractThe benefits of Zn, despite many of its performance advantages (e.g., high theoretical capacity and low redox potential), are compromised by severe side reactions and Zn dendrite growth in aqueous electrolytes, due to the coordinated H2O within the Zn2+‐solvation sheath and reactive free water in the bulk electrolyte. Unlike most efforts focused on costly super‐concentrated electrolytes and single additive species, a universal strategy is proposed to boost Zn reversibility in dilute electrolytes via adding carbonyl‐containing organic solvents. Based on experimental investigations and multiscale simulations, the representative electrolyte with a N‐methyl‐2‐pyrrolidone polar additive is proved to assist in structural reshaping of Zn2+‐solvation and stabilizing the hydrogen bond network of water. This synergy is instrumental in contributing to suppressed water‐induced parasitic reactions and dendrite formation, which enables high average coulombic efficiency of 99.7% over 1000 cycles in an Zn/Cu asymmetric cell, and an ultralong cycling lifespan of 2000 cycles with 99.4% capacity retention in a Zn/VS2@SS full cell. Even with an elevated cathodic mass loading (up to 9.5 mg cm‐2), the cycling stability is still maintained. The proposed strategy provides new insight into electrolyte additive design and sheds light on high‐performance Zn‐ion batteries.

Reshaping the electrolyte structure and interface chemistry for stable aqueous zinc batteries

Metallic zinc (Zn) with high safety and low cost is an ideal anode for aqueous batteries, but suffers from water-induced side reactions and dendrite growth. Herein, we significantly stabilize the Zn anode in a non-concentrated aqueous zinc trifluoromethanesulfonate (Zn(OTF)2) electrolyte when 1,2-dimethoxyethane (DME) additive is used to simultaneously regulate the electrolyte structure and Zn interface chemistry. We find that the introduction of DME not only interrupts the original hydrogen-bond network of water but also creates a unique Zn2+-solvation structure with the co-participation of DME and OTF−, which restrains the water-induced parasitic reactions. The in-situ formation of an organic-inorganic hybrid ZnF2-ZnS-rich interphase on Zn derived by the decomposition of DME and OTF− can suppress water penetration onto Zn and homogenize Zn2+ plating. In addition, DME molecules preferentially adsorb on the Zn surface, preventing the random growth of Zn dendrites. This novel H2O+DME electrolyte enables Zn anodes to achieve unprecedented cycling stability (over 5000 h at 2.0 mA cm−2) and high reversibility (99.7% Coulombic efficiency over 800 cycles). The efficacy of DME additives is further demonstrated in Zn//V2O5•nH2O full batteries with both coin- and pouch-type configurations. This work will inspire the design of efficient electrolytes for stable aqueous batteries.