Hydrogen-bonded Structure Of Water Research Articles

Lifting Hofmeister's Curse: Impact of Cations on Diffusion, Hydrogen Bonding, and Clustering of Water.

Water plays a role in the stability, reactivity, and dynamics of the solutes that it contains. The presence of ions alters this capacity by changing the dynamics and structure of water. However, our understanding of how and to what extent this occurs is still incomplete. Here, a study of the low-frequency Raman spectra of aqueous solutions of various cations by using optical Kerr-effect spectroscopy is presented. This technique allows for the measurement of the changes that ions cause in both the diffusive dynamics and the vibrations of the hydrogen-bond structure of water. It is found that when salts are added, some of the water molecules become part of the ion solvation layers, while the rest retain the same diffusional properties as those of pure water. The slowing of the dynamics of the water molecules in the solvation shell of each ion was found to depend on its charge density at infinite dilution conditions and on its position in the Hofmeister series at higher concentrations. It is also observed that all cations weaken the hydrogen-bond structure of the solution and that this weakening depends only on the size of the cation. Finally, evidence is found that ions tend to form amorphous aggregates, even at very dilute concentrations. This work provides a novel approach to water dynamics that can be used to better study the mechanisms of solute nucleation and crystallization, the structural stability of biomolecules, and the dynamic properties of complex solutions, such as water-in-salt electrolytes.

Exploring the dynamic changes in hydrogen bond structure of water and heavy water under external perturbation of DMF

The Raman spectra of DMF-water/heavy water binary solutions at different volume ratios are measured to investigate the hydrogen bond structure between N, N-dimethylformamide (DMF) and water/heavy water. It was observed that when VDMF below 40 %, DMF reinforces the hydrogen bond among water molecules through the substitution of a small amount of water molecules within the tetrahedral structure. However, a similar enhancement phenomenon is not observed in heavy water. When VDMF is less than 60 %, the hydrogen bonds among DMF and heavy water molecules affect the symmetry of OD covalent bond. Furthermore, as VDMF exceeds 40 %/60 %, the tetrahedral structures of water and heavy water are gradually replaced by DMF·3H2O/3D2O, DMF·2H2O/2D2O, and DMF·H2O/D2O clusters. The transition point of hydrogen bond structure in DMF- aqueous solution moved to VDMF = 15 % under the influence of under the influence of dynamic high pressure caused by pulsed laser beam. This study provides valuable insights into the microstructure of water/heavy water clusters.

The Molecular Ocean

We report on progress in observing the hydrogen-bonded structure of water and sea water by deep-ocean Raman spectroscopy. In the normal ocean, the abundance of single H2O species is less than 20%. The principal form is the tetrahedral pentamer, and the (H2O)[Formula: see text] nH2O equilibrium plays a dominant role in controlling physicochemical processes and the speed of sound. The enthalpy of the H-bond in water is 2.624 kcal/mol, and in sea water 2.258 kcal/mol due to the quantity of non-HB water in the solvation shell of sea salt ions. The activation energy of viscous flow is 4.28 kcal/mol at one atmosphere pressure, consistent with the need to break hydrogen bonds and overcome the van der Waals intermolecular forces. The activation energy decreases exponentially with depth/pressure and is 10% less at 4,000 m depth. We suggest this is due to the pressure-induced shift in the water equilibrium to favor the less compressible quasi-planar pentamer, tetramer, and so on forms. We address the long-standing conclusion that microbial swimming by means of rotating flagella is only 1%–2% efficient. This neglects the need for microbes to overcome the activation energy of viscous flow; [Formula: see text]95% of the mechanical energy produced by the flagella must be used to break H-bonds and overcome intermolecular forces.

Unified view of the hydrogen-bond structure of water in the hydration shell of metal ions (Li+, Mg2+, La3+, Dy3+) as observed in the entire 100–3800 cm−1 regions

Hydrogen-bond (H-bond) structure of water in the hydration shell of an anion is fairly well understood, but the corresponding knowledge for cation hydration shell is sparse, mainly because of the overwhelming effect of anion on water that easily masks the subtle effect of cation. Moreover, most of the hydration shell investigations are confined to the OH stretch band of water. Using Raman difference spectroscopy with simultaneous curve fitting (Raman-DS-SCF), we have retrieved the spectrum of water pertaining to the hydration shell of different metal ions (Li+, Mg2+, La3+, Dy3+) in the entire spectral region of 100–3800 cm−1, encompassing the intermolecular H-bond stretch (HOH---OH2; 200 cm−1), librational (300–1000 cm−1), HOH bend (1640 cm−1), bend-librational combination (2120 cm−1) and intramolecular O–H stretch (3000–3700 cm−1) of water. The hydration shell spectra and their polarization dependence (Polarized Raman) are compared for different metal ions and with the hydration shell of Cl− anion and also the high temperature water component (80 °C; extracted by Raman-DS-SCF). These results reveal that the hydration shells of high charge density metal ions have “enhanced” as well as “reduced” H-bond structure. The intermolecular H-bonds become stiffer and the librational freedom of the water gets restricted in the hydration shell. The bend-librational combination band blue-shifts to a large extent and appears toward the tail of the OH stretch, which is expected to facilitate the ultrafast energy dissipation of higher vibrational modes of water.

Atomic insights into the heterogeneity and the interface interactions of nanoconfined aqueous electrolyte solution

The structure and properties of nanoconfined electrolyte (nano electrolyte) solutions are important subjects in biochemistry, electrochemistry, separation science, etc. In the present work, neutron scattering and data driven reverse Monte Carlo were employed to quantitatively reveal the microstructure of aqueous CaCl2 solution in mesoporous silica MCM-41 at the atomic level. The electrolyte solution distributes in-homogeneously in the pores of mesoporous silica along the radial direction, which can be divided into the core, the transition, and the interface regions. The hydrogen bond structure of water in nano electrolytes is strengthened in the core region, analogous to that of nano water confined in nanochannels, and the ion association was enhanced in the transition region. The structure of the solution in the interface region was analogous to the bulk electrolyte solution under high pressure because of the confinement and interface effects. When the package ratio of nano electrolyte solution is insufficient, small amount of solution quasi-monolayer adsorb on the internal surface of mesoporous silica, the majority solution preferentially forms clusters with different sizes to adhere to the wetted interface. The anomalous hydrogen-bonding structure and ion association found in the present work improve our understanding of nanoconfined electrolyte solutions.

Vibrational Coupling and Hydrogen-Bond Structure of Water in the Extended Hydration Shell of Metal Ions.

Intra- and intermolecular vibrational coupling (VC) and hydrogen bonding (H-bonding) of water are sparsely understood in the hydration shell (HS) of a metal ion, though the corresponding knowledge for an anion is quite extensive. This is primarily due to the overwhelming effect of anions on water, which masks the subtle perturbing influence of most of the cations. Using Raman difference spectroscopy with simultaneous curve fitting (Raman-DS-SCF) in combination with isotopic dilution and polarized Raman spectroscopy, we have elucidated the VC and H-bonding of water in the HS of bi- and trivalent metal ions─Mg2+, Ca2+, La3+, Gd3+, Dy3+. Polarized Raman measurement of the HS water with VC "turned on" and "turned off" (using isotopically diluted water, HOD) reveals that water retains the intra- and intermolecular vibrational coupling in the HS of high-charge-density metal ions, which is in stark contrast to that of an anion. Hydration shell spectroscopy in HOD unambiguously shows that the average H-bonding of water becomes stronger in the HS than that of bulk water. The first HS water strongly donates two H-bonds to the second HS water (ν̅max ≈ 3200 cm-1) but weakly accepts a H-bond from the second HS water (ν̅max ≈ 3590 cm-1), which makes the HS water heterogeneous in terms of its H-bond structure. The weakly interacting OH (ν̅max 3585 cm-1 in HOD) red-shifts by ∼ 15 cm-1 while the VC is "turned on" (ν̅max ≈ 3600 cm-1 in H2O), revealing the intramolecular coupling of water in the HS of metal ions.

Probing the Gold/Water Interface with Surface-Specific Spectroscopy.

Water is an integral component in electrochemistry, in the generation of the electric double layer, and in the propagation of the interfacial electric fields into the solution; however, probing the molecular-level structure of interfacial water near functioning electrode surfaces remains challenging. Due to the surface-specificity, sum-frequency-generation (SFG) spectroscopy offers an opportunity to investigate the structure of water near working electrochemical interfaces but probing the hydrogen-bonded structure of water at this buried electrode-electrolyte interface was thought to be impossible. Propagating the laser beams through the solvent leads to a large attenuation of the infrared light due to the absorption of water, and interrogating the interface by sending the laser beams through the electrode normally obscures the SFG spectra due to the large nonlinear response of conduction band electrons. Here, we show that the latter limitation is removed when the gold layer is thin. To demonstrate this, we prepared Au gradient films on CaF2 with a thickness between 0 and 8 nm. SFG spectra of the Au gradient films in contact with H2O and D2O demonstrate that resonant water SFG spectra can be obtained using Au films with a thickness of ∼2 nm or less. The measured spectra are distinctively different from the frequency-dependent Fresnel factors of the interface, suggesting that the features we observe in the OH stretching region indeed do not arise from the nonresonant response of the Au films. With the newfound ability to probe interfacial solvent structure at electrode/aqueous interfaces, we hope to provide insights into more efficient electrolyte composition and electrode design.

Whether the Research on Ethanol–Water Microstructure in Traditional Baijiu Should Be Strengthened?

Baijiu is a unique and traditional distilled liquor in China. Flavor plays a crucial rule in baijiu. Up to now, the research on the flavor of baijiu has progressed from the identification of volatile compounds to the research on key aroma compounds, but the release mechanism of these characteristic compounds is still unclear. Meanwhile, volatile compounds account for only a tiny fraction, whereas ethanol and water account for more than 98% of the content in baijiu. By summarizing the ethanol-water hydrogen bond structure in different alcoholic beverages, it was found that flavor compounds can affect the association strength of the ethanol-water hydrogen bond, and ethanol-water can also affect the interface distribution of flavor compounds. Therefore, the research on ethanol-water microstructure in baijiu is helpful to realize the simple visualization of adulteration detection, aging determination and flavor release mechanism analysis of baijiu, and further uncover the mystery of baijiu.

Improvement in growth of plants under the effect of magnetized water

<abstract> <p>The magnetic field can change the polarity characteristics and hydrogen-bond structure of water; therefore, magnetized water can affect plant growth and development. Magnetized water is hexagonal water created by passing water through a specific magnet that can activate and ionize water molecules to change its structure. This review highlights the use of magnetized water in the agricultural sector to enhance plant growth and food productivity. We discussed the impact of magnetized water on seed germination, vegetative growth, fruit production, soil and pigments of treated plants. Plant growth and development can be improved both qualitatively and quantitatively via irrigation with magnetized water. It can promote seed germination, seedling early vegetative development, improvement of the mineral content of fruits and seeds, the enzyme activity of the soil, improved water use efficiency, higher nutrient content, and better transformation and consumption efficiency of nutrients; it can also mitigate soil salinity. Furthermore, magnetized water had a substantial good influence on the mobility and uptake of micronutrient concentrations, as well as promoted better growth criteria, all of which increased biomass and total yield. Also, irrigating plants with magnetized water resulted in a considerable increase in chloroplast pigments (carotenoids, chlorophyll a, and b) and photosynthetic activity. Magnetizing low-quality water (brackish water, saline water or water contaminated with metals) can be considered as an alternative tool to overcome the problem of scarcity and shortage of water resources. As a result, magnetic treatment of irrigation water could be a promising technique to boost agricultural production while also being environmentally beneficial in the future. The major challenge in using magnetized water in agriculture is creating pumps that are compatible with the technical and practical needs of magnetic systems while also effectively integrating irrigation components.</p> </abstract>

Temperature-Induced Change of Water Structure in Aqueous Solutions of Some Kosmotropic and Chaotropic Salts.

The hydrogen bond structure of water was examined by comparing the temperature dependent OH-stretching bands of water and aqueous NaClO4, KClO4, Na2SO4, and K2SO4 solutions. Results called attention to the role of cations on top of the importance of anions determining the emerging structure of a multi-layered system consisting single water rings or multi-ring water-clusters.

Structure of an aqueous RbCl solution in the gigapascal pressure range by neutron diffraction combined with empirical potential structure refinement modeling

An aqueous 3 m (=mol/kg) RbCl solution in D2O is measured at 298 K/0.1 MPa, 298 K/1 GPa, 523 K/1 GPa, and 523 K/4 GPa by neutron diffraction. The interference functions are analyzed by an empirical potential structure refinement (EPSR) modeling. The ion hydration and association and hydrogen-bonded water structure as a function of temperature and pressure are revealed in the pair correlation function, coordination number, triangular distribution, and spatial density function (3D structure). The results show that structure parameters are temperature and pressure-dependent. The second hydration layer of Rb+ and Cl− becomes evident under elevated pressure and temperature conditions. The average oxygen coordination number of Rb+ in the first hydration layer increases from 6.3 ± 1.7 at ambient pressure to 8.9 ± 2.3 at 4 GPa with decreasing coordination distance of 0.290 nm to 0.288 nm. The average oxygen coordination number of Cl− in the first hydration shell increases from 5.9 ± 1.5 at ambient pressure to 9.1 ± 2.1 at 4 GPa, and the corresponding coordination distance decreases from 0.322 nm to 0.314 nm with increasing pressure. The orientation of the water dipole in the first solvation shell of Rb+ and a central water molecule is sensitive to pressure, but that in the first solvation shell of Cl- does not change very much regardless of the thermodynamic condition. The number of contact-ion pairs Rb+-Cl− decreases with elevated temperature and increases with elevated pressure. Water molecules are closely packed, and the tetrahedral hydrogen-bonded network of water molecules no longer exists in extreme conditions.

Hydrogen-Bonded Structure of Water in the Loop of Anchored Polyrotaxane Chain Controlled by Anchoring Density.

Hydrogen-bonded network of water surrounding polymers is expected to be one of the most relevant factors affecting biocompatibility, while the specific hydrogen-bonded structure of water responsible for biocompatibility is still under debate. Here we study the hydrogen-bonded structure of water in a loop-shaped poly(ethylene glycol) chain in a polyrotaxane using synchrotron soft X-ray emission spectroscopy. By changing the density of anchoring molecules, hydrogen-bonded structure of water confined in the poly(ethylene glycol) loop was identified. The XES profile of the confined water indicates the absence of the low energy lone-pair peak, probably because the limited space of the polymer loop entropically inhibits the formation of tetrahedrally coordinated water. The volume of the confined water can be changed by the anchoring density, which implies the ability to control the biocompatibility of loop-shaped polymers.

Local structure in lithium chloride solution: a Monte-Carlo simulation study

ABSTRACT Monte-Carlo simulations and the nearest neighbour approach have been employed in the present study to investigate the structural properties of aqueous solutions of LiCl salt at ambient conditions. The calculations are performed at increasing concentration of LiCl starting from c = 0.1 m up to 10 m. The analysis shows that increasing salt concentration results in a reduction of the tetrahedral arrangement of water in favour of a non-tetrahedral arrangement characterised by an O–O–O angle between the reference oxygen and two of its four closest oxygen neighbours at 60°. Moreover, the LiCl concentration has a considerable effect on the hydrogen-bonding structure of water. By correctly choosing the nearest neighbours, it is found that the deviation in water structure is due to the presence of chloride ion, not lithium ion, in the first solvation shell of water. It is also demonstrated that in concentrated LiCl solution Cl− ions can substitute the fourth water neighbour which leads to a tetrahedral network formed by water molecules and Cl− ions around a central water molecule. The analysis of the effect of concentration increase on the arrangement of the four closest water molecules neighbours from a reference lithium cation allows us to elucidate a structural maker role of Lithium ion.

Wettability of graphene and interfacial water structure

<h2>Summary</h2> Understanding the wettability of graphene is important for various applications, such as water desalination, energy storage, and catalysis. However, the detailed water hydrogen-bonding structure at the water-graphene interface is not yet fully understood. Using vibrational sum-frequency-generation (VSFG) spectroscopy, we elucidate the water structure at a water-graphene interface. As the number of graphene layers increases, water molecules with dangling OH groups become more populated, indicating the transition from transparency to translucency. We compare the water contact angles on the graphene surfaces with VSFG results, showing an excellent correlation between the water adhesion energy of graphene and the fraction of dangling OH groups estimated from the VSFG spectrum. This observation suggests that the VSFG could be an incisive technique for measuring water's adhesion energy on any spatially confined interface where the water contact angle cannot be measured. We anticipate that the VSFG results will help to elucidate the wettability of low-dimensional materials. <h3>Video Abstract</h3>

Role of Ions on the Surface-Bound Water Structure at the Silica/Water Interface: Identifying the Spectral Signature of Stability.

Isolating the hydrogen-bonding structure of water immediately at the surface is challenging, even with surface-specific techniques like sum-frequency generation (SFG), because of the presence of aligned water further away in the diffuse layer. Here, we combine zeta potential and SFG intensity measurements with the maximum entropy method referenced to reported phase-sensitive SFG and second-harmonic generation results to deconvolute the SFG spectral contributions of the surface waters from those in the diffuse layer. Deconvolution reveals that at very low ionic strength, the surface water structure is similar to that of a neutral silica surface near the point-of-zero-charge with waters in different hydrogen-bonding environments oriented in opposite directions. This similarity suggests that the known metastability of silica colloids against aggregation under both conditions could arise from this distinct surface water structure. Upon the addition of salt, significant restructuring of water is observed, leading to a net decrease in order at the surface.

Water hydrogen-bonding structure and dynamics near lipid multibilayer surface: Molecular dynamics simulation study with direct experimental comparison.

Lipid multibilayers are excellent model systems for studying water structures and dynamics near biological membrane surfaces. In particular, the orientational distribution and rotational dynamics of water molecules near hydrophilic lipid groups are found to be sensitive to the chemical nature and charge distributions of the amphiphilic lipids. To elucidate how different parts of these lipids affect the water hydrogen-bonding structure and dynamics and to directly compare with recent experimental results, we carried out molecular dynamics (MD) simulations of lipid multibilayer systems. We found that the water molecules close to positively charged choline groups have a broad distribution of orientations due to the clathratelike shell formation around the choline groups but that those associated with phosphate groups, even in the second hydration shell, are orientationally restricted due to their strong hydrogen bonding with the phosphate group. These MD simulation results are in excellent agreement with our time-resolved infrared pump-probe anisotropy measurements, and we believe that they provide valuable insights into the role of water molecules in maintaining lipid bilayer integrity.

A resummed thermodynamic perturbation theory for positive and negative hydrogen bond cooperativity in water

In this paper a resummed thermodynamic perturbation theory is developed which accounts for both positive and negative hydrogen bond cooperativity in water. The theory is developed in Wertheim’s multi-density statistical mechanics. We demonstrate that the hydrogen bonded structure of water is controlled by positive hydrogen bond cooperativity in homodromic hydrogen bonded clusters. Inclusion of negative anti-cooperativity in antidromic hydrogen bonded structures has little effect on the underlying hydrogen bond structure of liquid water. The resummed perturbation theory is shown to give hydrogen bond statistics consistent with first principles ab initio molecular dynamics simulations. In addition, the theory is shown to be in good agreement with experiment in the prediction of the average number of hydrogen bonds per water molecule in a liquid at ambient conditions. Finally, we develop a full thermodynamic model for water by including contributions to the free energy for isotropic square well attractions. We demonstrate that the model gives good representation of saturated liquid density, hydrogen bonding and vapor pressure. In addition, we show the full model predicts the anomalous minima in isothermal compressibility and isobaric heat capacity.

Bulk Contributions Modulate the Sum-Frequency Generation Spectra of Water on Model Sea-Spray Aerosols

Summary Vibrational sum-frequency generation (vSFG) spectroscopy is used to determine the molecular structure of water at a model sea-spray aerosol surface. Both measured and calculated spectra display specific features as a result of third-order contributions to the vSFG response, and these are associated with finite interfacial electric potentials. We demonstrate that theoretical modeling enables separation of the third-order contributions, thus allowing for a systematic analysis of the strictly surface-sensitive, second-order component of the vSFG response. This study provides fundamental insights into the interfacial molecular organization and hydrogen-bonding structure of water, which mediate heterogeneous processes on sea-spray aerosols. Our results emphasize the key role that computer simulations can play in interpreting vSFG spectra and revealing microscopic details at complex aqueous interfaces, which can be difficult to extract from experiments because of the mixing of second-order, surface-sensitive, and third-order bulk-dependent contributions to the vSFG response.

Coexistence of Kosmotropic and Chaotropic Impacts of Urea on Water As Revealed by Terahertz Spectroscopy.

Whether urea can serve as a kosmotrope or chaotrope has long been a topic of debate. In this study, broad-band THz spectroscopy (0.2-12 THz) of aqueous solutions of urea was used to characterize the hydration state and the hydrogen bond structure of water around urea. Three low-frequency vibration modes of urea were found around 2, 4, and above 12 THz. After eliminating the contribution of these modes, the "urea-vibration-free" complex dielectric constant was decomposed into the relaxation modes of bulk water and the oscillation modes of water. When hydration water is defined to be reorientationally retarded relative to bulk, our analysis revealed that the hydration number is 1.9 independent of urea concentrations up to 5 M, and this number is in close agreement with that of water constrained by strong acceptor hydrogen bonds of urea oxygen. Regarding the hydrogen bond structure, it was found that the tetrahedral-like water structure is mostly preserved (though the hydrogen bond lifetime is significantly shortened) but the population of non-hydrogen-bonded water molecules fragmented from the network is markedly increased, presumably due to urea's NH2 inversion. These experimental results point to the coexistence of apparently two contradictory aspects of urea: dynamical retardation (the kosmotropic aspect) by the -CO group and slight structural disturbance (the chaotropic aspect) by the -NH2 group.

Weakly perturbative imaging of interfacial water with submolecular resolution by atomic force microscopy.

Scanning probe microscopy has been extensively applied to probe interfacial water in many interdisciplinary fields but the disturbance of the probes on the hydrogen-bonding structure of water has remained an intractable problem. Here, we report submolecular-resolution imaging of the water clusters on a NaCl(001) surface within the nearly noninvasive region by a qPlus-based noncontact atomic force microscopy. Comparison with theoretical simulations reveals that the key lies in probing the weak high-order electrostatic force between the quadrupole-like CO-terminated tip and the polar water molecules at large tip–water distances. This interaction allows the imaging and structural determination of the weakly bonded water clusters and even of their metastable states with negligible disturbance. This work may open an avenue for studying the intrinsic structure and dynamics of ice or water on surfaces, ion hydration, and biological water with atomic precision.