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The advancement of experimental methods has provided new information about the structure and structural fluctuations of water. Despite the appearance of numerous models, which aim to describe a wide range of thermodynamic and electrical characteristics of water, there is a deficit in systemic understanding of structuring in aqueous solutions. A particular challenge is the fact that even pure water is a heterogeneous, multicomponent system composed of molecular and supramolecular structures. The possibility of the existence of such structures and their nature are of fundamental importance for various fields of science. However, great difficulties arise in modeling relatively large supramolecular structures (e.g. extended hydration shells), where the bonds between molecules are characterized by low energy. Generally, such structures may be non-equilibrium but relatively long-lived. Evidently, the short times of water microstructure exchanges do not mean short lifetimes of macrostructures, just as the instability of individual parts does not mean the instability of the entire structure. To explain this paradox, we review the data from experimental and theoretical research. Today, only some of the experimental results on the lifetime of water structures have been confirmed by modeling, so there is not a complete theoretical picture of the structure of water yet. We propose a new hierarchical water macrostructure model to resolve the issue of the stability of water structures. In this model, the structure of water is presented as consisting of many hierarchically related levels (the stratification model). The stratification mechanism is associated with symmetry breaking at the formation of the next level, even with minimal changes in the properties of the previous level. Such a hierarchical relationship can determine the unique physico-chemical properties of water systems and, in the future, provide a complete description of them. [ABSTRACT FROM AUTHOR]

The article focuses on easily adjustable technological parameters controlling the effectiveness of pulsating water jet (PWJ). The first technological parameter is standoff distance; this parameter controls water cluster development and should be set optimal according to process hydraulic parameters. The second parameter is feedrate, this parameter, when considering linear trajectory, controls the impact distribution on the treated area. Four hydraulic pressure levels (30, 40, 50, and 60 MPa) were selected for the experiment. The standoff distance was during the experimental runs ranging from 26 to 68 mm with the goal of finding optimal value. The optimal standoff distance was selected based on Rz and Rv parameters. Rz and Rv values show increasing tendency with increment of standoff distance followed by culmination and then decreasing tendency. The impact distribution ranged from 8 000 to 40 000 impacts per millimeter. The decrease in water impact shows strictly decreasing tendencies in all evaluated parameters. However, the increase in pressure level shows better percentual retainment of erosion effectivity during the lowering of water impact distribution. [ABSTRACT FROM AUTHOR]

The advancement of experimental methods has provided new information about the structure and structural fluctuations of water. Despite the appearance of numerous models, which aim to describe a wide range of thermodynamic and electrical characteristics of water, there is a deficit in systemic understanding of structuring in aqueous solutions. A particular challenge is the fact that even pure water is a heterogeneous, multicomponent system composed of molecular and supramolecular structures. The possibility of the existence of such structures and their nature are of fundamental importance for various fields of science. However, great difficulties arise in modeling relatively large supramolecular structures (e.g. extended hydration shells), where the bonds between molecules are characterized by low energy. Generally, such structures may be non-equilibrium but relatively long-lived. Evidently, the short times of water microstructure exchanges do not mean short lifetimes of macrostructures, just as the instability of individual parts does not mean the instability of the entire structure. To explain this paradox, we review the data from experimental and theoretical research. Today, only some of the experimental results on the lifetime of water structures have been confirmed by modeling, so there is not a complete theoretical picture of the structure of water yet. We propose a new hierarchical water macrostructure model to resolve the issue of the stability of water structures. In this model, the structure of water is presented as consisting of many hierarchically related levels (the stratification model). The stratification mechanism is associated with symmetry breaking at the formation of the next level, even with minimal changes in the properties of the previous level. Such a hierarchical relationship can determine the unique physico-chemical properties of water systems and, in the future, provide a complete description of them.

In the crystal of the title compound, C18H14O10·2H2O, the arene rings of the biphenyl moiety are tilted at an angle of 24.3 (1)°, while the planes passing through the carboxyl groups are rotated at angles of 8.6 (1) and 7.7 (1)° out of the plane of the benzene ring to which they are attached. The crystal structure is essentially stabilized by O—H...O bonds. Here, the carboxyl groups of neighbouring host molecules are connected by cyclic R22(8) synthons, leading to the formation of a three-dimensional network. The water molecules in turn form helical supramolecular strands running in the direction of the crystallographic c-axis (chain-like water clusters). The second H atom of each water molecule provides a link to a methoxy O atom of the host molecule. A Hirshfeld surface analysis was performed to quantify the contributions of the different intermolecular interactions, indicating that the most important contributions to the crystal packing are from H...O/O...H (37.0%), H...H (26.3%), H...C/C...H (18.5%) and C...O/O...C (9.5%) interactions.

In the crystal of the title compound, C18H14O10⋅2H2O, the arene rings of the biphenyl moiety are tilted at an angle of 24.3 (1)°, while the planes passing through the carboxyl groups are rotated at angles of 8.6 (1) and 7.7 (1)° out of the plane of the benzene ring to which they are attached. The crystal structure is essentially stabilized by O--H⋯O bonds. Here, the carboxyl groups of neighbouring host molecules are connected by cyclic R2²(8) synthons, leading to the formation of a three-dimensional network. The water molecules in turn form helical supramolecular strands running in the direction of the crystallographic caxis (chain-like water clusters). The second H atom of each water molecule provides a link to a methoxy O atom of the host molecule. A Hirshfeld surface analysis was performed to quantify the contributions of the different intermolecular interactions, indicating that the most important contributions to the crystal packing are from H⋯O/O⋯H (37.0%), H⋯H (26.3%), H⋯C/C⋯H (18.5%) and C⋯O/O⋯C (9.5%) interactions. [ABSTRACT FROM AUTHOR]

Electrolytic hydrogen production from water at neutral pH was achieved by using novel proton (H+) conduction system assisted by zeolite. Experimental and computational insights demonstrated that defective silanol nest generated by dealumination played an important role in the formation of water clusters and the H+ conduction over the zeolites proceeded via exchange of H‐bonding between water molecules in the cluster. In addition, a proper balance between hydrophilicity and hydrophobicity is required for effective H+ conduction and silanol nest afford the balance. Furthermore, the contribution of hydrophilicity of the zeolite for the adsorption of water molecules became more drastic at high temperatures. Water electrolysis efficiency was strongly dependent on the H+ conductivity over the beta‐type zeolite. The electrolytic cell containing the zeolite has the potential to be applied to the new hydrogen production system. [ABSTRACT FROM AUTHOR]

Using a solvothermal method, we have synthesized two coordination polymers of Cu(II). One is a 1D polymer {[Cu(bpy)(NDC)(H2O)]·2H2O}n (1, 1D) formed with 1,8-naphthalene dicarboxylic acid (H2NDC) and 2,2′-bipyridine (bpy) as an auxiliary ligand, while the other is a 2D polymer {[Cu3(TMA) (Imd)3]·5H2O·2DMF}n (2, 2D) formed with trimellitic acid (H3TMA) and imidazole (Imd) as an auxiliary ligand. Both coordination polymers 1 and 2 were formed through an in situ hydrolytic ring opening reaction of 1,8-naphthalic anhydride and trimelitic anhydride with bipyridine and imidazole ligands, respectively. The asymmetric unit of polymer 1 contains asymmetric η1 binding mode (one of the carboxylate) linking distorted square-pyramidal [Cu(NDC)(bpy)(H2O)]2+ coordination units. The syn-syn-η1:η1 linear polymeric conformation exist in the 1D coordination polymer with adjacent Cu...Cu distance is 6.849 Å. A chain of cyclic tetrameric water clusters is present between the stacked layers of the 3D supramolecular structure. The formation of the 3D supramolecular structure is guided by various weak interactions such as O–H...O, C–H...O, C–H...π and π...π interactions. The coordination polymer 2 forms 3D supramolecular architecture guided by various weak interactions such as O–H...O, C–H...O and N–H...O interactions. The crystal structures of both coordination polymers have been determined using single crystal X-ray diffraction and their structural features are described. [ABSTRACT FROM AUTHOR]

The title compound, C20H32N82+·2Br−·3H2O, was obtained by the reaction of 1,3,5,7-triazatricyclo[3.3.1.13,7]decane with 1,3-bis(bromomethyl)benzene in acetonitrile. The asymmetric unit contains a unique 1,1′-(benzene-1,3-diyldimethanediyl)bis(3,5,7-triaza-1-azoniatricyclo[3.3.1.13,7]decane)dication, two bromide anions and three water molecules. The 3,5,7-triaza-1-azoniatricyclo[3.3.1.13,7]decane (C6N4H12)+ moieties lie on the same side of the molecule, and the pseudo torsion angle (H12N4C6)CH2⋯CH2(C6N4H12) is −5.25 (18)°. The molecular dication C20H32N8+ is charge-balanced by a pair of crystallographically independent halide hydrate clusters, and the cation and clusters are interlinked by CH⋯O and CH⋯Br hydrogen bonds. The Hirshfeld surface analysis and fingerprint plots reveal that the packing in compound 2 is directed mainly by H⋯H (56.7%) and H⋯Br/Br⋯H (21.3%) contacts. The thermal analysis showed between 30 and 180 °C the gradual loss of three water molecules, which represents the loss of one and two crystalline water molecules from the two types of clusters, respectively. A second noticeable weight loss between 180 and 230 °C is observed, depictive of the thermal decomposition of the dication of the title compound.

Context: We investigated the interaction between glycine and Li+ in water environment based on the Gly·Li+(H2O)n (n = 0–8) cluster. Our study shows that for Gly·Li+, Li+ binds to both carbonyl oxygen and amino nitrogen to form a bidentate structure, and the first three water molecules preferentially interact with Li+. For n = 0–5, the complexes of Gly·Li+(H2O)n exist in neutral form, and when the water number reached 6, the complex can coexist in neutral and zwitterionic form, then zwitterionic structures are dominant for n = 7, 8. The analyses by RDG, AIM, and ESP in conjunction with the calculated interaction energies show that the interaction between Li+ and Gly decreases gradually with the water molecules involved successively from n = 1 to 6 and then increases for n = 7–8. Additionally, the infrared spectra of Gly·Li+(H2O)n (n = 0–8) are also calculated. Methods: The initial structures were optimized using Gaussian 09 program package in B3LYP-D3 (BJ)/6-311G(d, p) method, and the frequency was calculated with 6–311 + G(2d, p) basis set. GaussView5.0.9 was used to view simulation infrared spectra. The noncovalent interaction method (NCl), energy decomposition (EDA), atoms in molecules (AIM) analysis, and electrostatic potential (ESP) analyses were conducted using Multiwfn software to gain a deeper understanding of the interaction properties of Gly, Li+, and water. [ABSTRACT FROM AUTHOR]

The article describes the procedure for generating solutions to the Schrödinger equation by the Monte Carlo method. Hexamer 6(H2O), dodecamer 12(H2O), and tetradecamer 14(H2O) water clusters act as a demonstration quantum system illustrating this generator. The generator of solutions to the Schrödinger equations is derived from the algorithm proposed by the author earlier, based on the intersection of the finite-difference and Monte Carlo approaches, as well as methods of the spatial convergence of the scattering centers of the particles' nuclei and scattering centers of electrons of an arbitrary quantum system, tested on water clusters. As a result of this information, it turned out to be possible to construct an algorithm for generating an unlimited number of different spatial structures of the scattering clouds of the particles' nuclei and electrons at the same dissociation energy of a quantum system. [ABSTRACT FROM AUTHOR]

The transition zone (TZ) in an oil reservoir has traditionally been a volume of lesser interest compared to the oil-saturated zone. Researchers have suggested that it can contain commercial hydrocarbon volumes. Therefore, this paper seeks to summarize the characterization methods of TZs for the assessment of oil production opportunities. Another goal is to summarize the potential methods of oil production from TZs. It is conceivable that TZs will produce both water and oil together. However, some surprising instances of dry oil (i.e., 100% oil, with no associated connate water) production, due to the formation of water clusters, have also been observed earlier. Also, oil can possibly be found below the current free water level. Characterizing TZs is more complicated compared to the oil-saturated (irreducible water saturation) zone. TZs can show variable wettability and permeability characteristics due to several complex phenomena related to buoyancy, capillarity, diagenesis, cementation, and reservoir tilting. Careful TZ core characterization followed by reservoir simulation and oil production can increase the overall reserves. Methods for TZ characterization include petrophysical logs (resistivity and NMR), geophysical analysis (AVO and P-wave absorption), and reservoir modeling (saturation height functions and wettability). Analysis of core obtained from TZs using the centrifuge method can reveal the residual oil saturation and relative permeabilities, which can aid the prediction of future oil production. More complicated analyses include structure and stratigraphic geological models and basin modeling for hydrocarbon migration history. Possible oil production methods from TZs include CO2 injection, surfactant flooding, combined carbonated water and surfactant flooding, and smart well placement. We recommend including TZs that span several meters in depth as part of reserves calculation. [ABSTRACT FROM AUTHOR]

A procedure is discussed for obtaining various solutions to the Schrödinger equation by the Monte Carlo method. Water clusters, namely, the hexamer 6(H2O), dodecamer 12(H2O), and tetradecamer 14(H2O) are used as quantum systems to illustrate the procedure. Various solutions to the Schrödinger equation are derived from the algorithm earlier proposed by the author, which is based on the intersection of the finite-difference and Monte Carlo approaches and on the water-cluster-tested methods for spatially reducing scattering centers of particle nuclei and scattering centers of electrons of an arbitrary quantum system. Ultimately, it has become possible to construct an algorithm for generating an unlimited number of various spatial structures of scattering clouds of particle nuclei and electrons at a given dissociation energy of a quantum system. [ABSTRACT FROM AUTHOR]

The structure and electronic properties of the molybdenum disulfide (MoS2) monolayer upon water cluster adsorption are studied using density functional theory and the optical properties are further analyzed with the Bethe–Salpeter equation (BSE). Our results reveal that the water clusters are electron acceptors, and the acceptor tendency tends to increase with the size of the water cluster. The electronic band gap of both pristine and defective MoS2 is rather insensitive to water cluster adsorbates, as all the clusters are weakly bound to the MoS2 surface. However, our calculations on the BSE level show that the adsorption of the water cluster can dramatically redshift the optical absorption for both pristine and defective MoS2 monolayers. The binding energy of the excitons of MoS2 is greatly enhanced with the increasing size of the water cluster and finally converges to a value of approximately 1.16 eV and 1.09 eV for the pristine and defective MoS2 monolayers, respectively. This illustrates that the presence of the water cluster could localize the excitons of MoS2, thereby greatly enhance the excitonic binding energy. [ABSTRACT FROM AUTHOR]

The results of modeling the spatial positions of hydrogen and oxygen nuclei in a water cluster are presented as a direct computational experiment. The method for the numerical solution of the Schrödinger equation, which was previously developed by the author and is based on the Monte Carlo method, is used. This method has proven to be very efficient in terms of computer time. The input data of this method are the average positions of the particles included in the quantum system, for the calculation of which another method is developed. In the method of constructing the average positions of quantum particles, several energy isomers of water clusters are constructed. It is this multiplicity that is of primary theoretical interest. For the purpose of testing the technique, a model of an individual water molecule with the generally accepted geometry of particle arrangement, as well as the so-called geometry of an unfolded water molecule, is built. The energy isomers of the dimer, trimer, and hexamer of water presented in this study are considered as possible geometric structures of water clusters and serve as an illustration of the use of the proposed method for calculating quantum systems. The water dimer model is constructed in the form of three geometric structures of the arrangement of hydrogen and oxygen nuclei, conventionally called quasi-two-dimensional, octahedral, and quasi-one-dimensional. The water trimer model is reduced to a discussion of two geometries: three-dimensional and quasi-two-dimensional. Finally, the geometry of the water hexamer in the form of an octahedron, at the vertices of which there are oxygen nuclei, and all twelve protons are located in the center, is considered. Water cluster models are understood as the construction of scattering clouds of all quantum particles included in the cluster. [ABSTRACT FROM AUTHOR]

[Display omitted] • Adsorption configurations of water clusters were predicted using DFT calculations. • Water clusters tend to form quadrilateral and cubic shapes on –COOH and –OH. • Cubic water clusters on –OH exhibit a more regular shape than those on –COOH. • Synergistic effect of neighboring OFGs enhances adsorption of water clusters. The water in coal causes many negative effects on the processing and utilization of coal. Oxygen-containing functional groups (OFGs) are primary adsorption sites for water molecules on coal surfaces. However, little is known about the adsorption configuration of water clusters on OFGs. In this study, density functional theory (DFT) calculations were used to predict the adsorption configurations of water clusters on –COOH and –OH. The results indicated that water clusters tend to form quadrilateral and cubic shapes on both –COOH and –OH, with quadrilateral water clusters being more stable than cubic water clusters. The cubic water cluster is adsorbed on –COOH through two water molecules that directly form hydrogen bonds with –COOH. In contrast, the cubic water cluster is adsorbed on –OH through a water molecule at one of its vertices. The strong attraction of –COOH to water molecules introduces a minor defect in the cubic water cluster. Because of the synergistic effect of neighboring OFGs on the adsorption of water molecules, the average adsorption energy of water molecules is greater than that of water clusters on a single OFG. These results provide valuable microstructural insights into the adsorption of water on coal. [ABSTRACT FROM AUTHOR]

Water dominates the wood cell wall in the hygroscopic range. The state and amount of cell wall water influence the physical and mechanical properties of wood. 2D time-domain nuclear magnetic resonance (2D TD-NMR) is capable of resolving cell wall water. To identify the relaxation property of cell wall water, 2D TD-NMR with saturation recovery Carr-Purcell-Meiboom-Gill pulse sequence was applied on Fagus sylvatica and Pinus taeda L. at equilibrium state under 12, 34, 47, 65, 84, and 97% relative humidity (RH), as well as during adsorption process from dry to 84% RH. The result showed that two pools of cell wall water were identified, the water molecules in disordered surface of cellulose microfibrils and their surrounding hemicellulose (Peak B), and the water molecules in the domain of matrix including lignin and surrounding hemicellulose (Peak C). B-water and C-water exhibited different relaxation properties with different moisture contents. With increasing RH, B-water gained more mobility than C-water. Through the calculation based on cluster theory, it was hypothesized that the formation of water clusters in high RH region may exist in the reservoir of B-water. During the sorption process from a dry state to equilibrium at 84% RH, the amount of B- and C-water gradually increased, whereas B-water appeared earlier than C-water but took a longer time to equilibrate. When the sub-equilibrium state was attained, the T1/T2 ratio stayed stable. [ABSTRACT FROM AUTHOR]

Path-Integral Molecular Dynamics (PIMD) method is key to include nuclear quantum effects (NQEs) in molecular dynamics simulations which can influence a variety of properties. As a first application of the interface between the i-PI code and the deMon2k electronic structure code, we apply it to evaluate NQEs on the 13 C isotropic nuclear shielding/chemical shift of a set of linear carboxylate ions solvated by a water cluster. A quantum mechanics / molecular mechanics treatment of the electronic structure in conjunction with relevant combination of thermostat and number of replicas in the PIMD algorithm allows for a good convergence of the 13 C isotropic nuclear shielding values regardless of the considered carboxylate. The simulations demonstrate that regardless of the considered carboxylate ion and carbon atom, inclusion of NQEs always improves agreement with the experimental data when looking at relative 13 C isotropic chemical shifts in a given compound. The present study thus paves the ways to new applications of the deMon2k code, whether it be for pure quantum mechanics or quantum mechanics / molecular mechanics simulations, for simulations taking into account NQEs. [ABSTRACT FROM AUTHOR]

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The work presents algorithms and results of the direct computational experiment on mathematical modeling of water clusters treated as quantum systems numerically described using the corresponding Schrödinger equation. The method earlier developed by the author for Monte Carlo numerical solution of the Schrödinger equation is used. This method has proved itself to be quite time-efficient. Its input data are average positions of particles in a quantum system, for description of which a second method is developed. Several energy isomers of water clusters are found by the method for construction of average positions of quantum-system particles. The energy isomers of the water dimer, trimer, and hexamer given in the work are regarded as possible geometrical structures of water clusters and illustrate the use of the proposed methods for calculation of quantum systems. [ABSTRACT FROM AUTHOR]

Fuel cells are expected to play an important role in global carbon neutralization and future social development with high conversion efficiency and zero emissions. The core of the fuel cell is the proton exchange membrane (PEM). However, the unclear of the proton transport mechanism in PEMs limits the development of membranes with improved performance. Perfluorosulfonic acid (PFSA) membranes are currently the most widely used type of PEM, and exhibit varying proton transport capabilities with various chemical structures. In this study, the hydration morphology of several PFSA membranes was studied using dissipative particle dynamics. The result shows that under low water content the hydrophilic and hydrophobic phases separated and the water clusters are relatively isolated. The increased water content formed hydrophilic channels, while the increase in equivalent weight decreases the water cluster size and improves water dispersion. Aciplex 1128 shows great variation owing to the presence of a long sulfonic acid terminated side chain in water cluster size and dispersion compared with Nafion. The average diffusivity and mean square displacement results showed similar results. These results will promote the development of high performance PEM for fuel cells. [ABSTRACT FROM AUTHOR]

The hydrogen bond interactions between methyl-imidazolium cation (MIM+) and fatty acid anions (CmHnCOO–, where m = 1–6; n-3–13) of ionic liquids are studied in both gas phase and water phase using density functional theory. The structural properties show that the presence of N–H···O and C–H···O hydrogen bonds between [MIM]+ and [CmHnCOO]– (m = 1–6; n-3–13) ionic liquids. From the vibrational frequency analysis, it was found that the hydrogen bond interaction between [MIM]+ and [CmHnCOO]– (m = 1–6; n-3–13) ionic liquids are red-shifted in frequency. The natural bond orbital analysis show that the N–H···O hydrogen bond associated with the large charge transfer which has the higher stabilization energy (i.e. E(2) ~ 38 kcal/mol). Further, the cation/anion–water cluster (H2O)1–3 interactions show that the water molecules are preferred to interact with anions. In the case of ionic liquid–water cluster interaction, the water molecules occupies the interstitial space between cation and anion of ionic liquids which results in weakening the cation–anion interaction. [ABSTRACT FROM AUTHOR]

Quantum chemical simulation of the adsorption of N acetylneuraminic acid (NANA) on the surface of silica with the participation of the fructose molecule by the method of density functional theory B3LYP, 6-31G (d, p) was done. The influence of the solvent was taken into account in the supermolecular and continuum approximations, and a cluster approach was used for the adsorption complexes. NANA adsorption of the hydrated silica surface was considered as a process of replacement of water molecules on the silica surface by adsorbate molecules. Two schemes of influence of fructose molecule on NANA adsorption are considered. According to the first scheme, the hydrated NANA molecule interacts with the hydrated silicon-fructose adsorption complex. According to the second scheme, the cluster of hydrated silica interacts with the hydrated NANA-fructose complex. The energy of intermolecular interaction according to the scheme 1 is -9.2 kJ / mol, which is significantly lower compared to the same value with the participation of glucose or sucrose (-20.5 and -86.2 kJ / mol). Scheme 2 proved to be a thermodynamically unfavorable process, as its energy effect is +6.9 kJ / mol, in contrast to similar processes for glucose (-21.8) and sucrose (-87.7 kJ / mol). This confirms the experimental fact of the interaction of substances in a mixture of NANA with carbohydrates in relation to the interaction with silica in comparison with the interaction of substances with silica separately.

Summary: As a key species in understanding the hydrogen-bonding network transitions between liquid water and ice, the neutral water heptamer is a challenging experimental target, owing to the richness of low-lying isomers. Here, we report the size-specific infrared spectra of confinement-free, neutral water heptamer (H2O)7 based on threshold photoionization using a tunable vacuum ultraviolet free electron laser. The complexity of the observed spectra indicates that many nearly isoenergetic isomers are present at finite temperatures. Two classes of prism- and cage-like structures are identified in a high-pressure pulsed supersonic expansion of water heptamer, in which the former is favored energetically at low temperatures and serves as a major contributor to the experimental spectrum. These findings provide key information for filling the gap between well-studied water hexamer and octamer.

The structure and electronic properties of the molybdenum disulfide (MoS2) monolayer upon water cluster adsorption are studied using density functional theory and the optical properties are further analyzed with the Bethe–Salpeter equation (BSE). Our results reveal that the water clusters are electron acceptors, and the acceptor tendency tends to increase with the size of the water cluster. The electronic band gap of both pristine and defective MoS2 is rather insensitive to water cluster adsorbates, as all the clusters are weakly bound to the MoS2 surface. However, our calculations on the BSE level show that the adsorption of the water cluster can dramatically redshift the optical absorption for both pristine and defective MoS2 monolayers. The binding energy of the excitons of MoS2 is greatly enhanced with the increasing size of the water cluster and finally converges to a value of approximately 1.16 eV and 1.09 eV for the pristine and defective MoS2 monolayers, respectively. This illustrates that the presence of the water cluster could localize the excitons of MoS2, thereby greatly enhance the excitonic binding energy.

The hydrogen bonding characteristics of water clusters (H2O)n (n=14-17) are investigated by using Quantum Theory of Atoms in Molecules (QTAIM). The stabilities of the water clusters are related to the strength and number of hydrogen bonding. The strength of hydrogen bonding is primarily concerned with the characteristic of the donor molecule. The electron densities of bonding critical points of hydrogen bonding formed by DAA, DDAA and DDA molecule as hydrogen-donor (H-donor) are about 0.045 a.u., 0.035 a.u. and 0.025 a.u. respectively. The strength of hydrogen bonding formed by DAA as H-donor is the strongest, and that formed by DDA as H-donor is the weakest. The strength of hydrogen bonding in pentagonal rings is stronger than that in the cubes. [ABSTRACT FROM AUTHOR]

The parallel-tempering molecular dynamics (PTMD) method is a key computational tool to explore complex potential energy surfaces. As a result of its computational cost, it has mainly been coupled to force-field approaches despite the interest it could also represent for ab initio studies. In this article, we present the native implementation of the PTMD algorithm in the deMon2k code which is the first implementation of this approach in a DFT code based on localized basis set. To take advantage of the intrinsic parallel nature of the PTMD algorithm without modifying the Message Passing Interface (MPI) scheme dedicated to the calculation of the electronic structure, a two-layer MPI architecture was implemented. Both synchronous and asynchronous communications between processes for configuration exchanges were implemented in order to test the parallel efficiency of the code. This article presents the implementation details and their application to describe phase changes in the water hexamer (H 2 O) 6 at the DFT level. [ABSTRACT FROM AUTHOR]

[Display omitted] • Magnetization pretreatment can prevent scale formation in RO process to some extent. • In magnetization process, flow rate has more influence on the characteristics of carbonate precipitation than the time. • Magnetization breaks the hydrogen bond of water molecules, forming smaller water clusters, causing scaling less likely to occur and slower to settle. • After magnetization, the decay of water flux tends to slow down during RO and the flux recovery increases after cleaning. In this study, magnetization pretreatment was applied to the reverse osmosis process. The scale inhibition effect and the mechanism of magnetization treatment were analyzed. The results show that after magnetization, the decay of water flux tended to slow down during RO and the flux recovery increased after cleaning. The Ryznar stability index of the solutions was calculated, which showed that magnetization could increase the solubility of carbonate solution and reduce the trend of carbonate scaling to a certain extent. The infrared spectra of the solutions showed that the hydrogen bonds of water molecules in the solution decreased after magnetization, indicating that the magnetization made the hydrogen bonds of water molecules break to form smaller clusters of water molecules, which might make the water molecules pass through the membrane more easily. After magnetization, the crystal size of the carbonate precipitated decreased and the sedimentation rate slowed down. Different flow rates and magnetization times were selected during the magnetization process. The results showed that when the flow velocity was greater than 0.24 m/s, the RSI, scale size and precipitation rate of the magnetized solution changed significantly compared with that of the unmagnetized solution. At the flow velocity of 0.48 m/s, the optimal magnetization time is 5 min. Moreover, the SEM characterization of the fouled membrane after filtration showed that after magnetization, the calcium carbonate deposited on the membrane surface appeared aragonite crystal, and the fouling was more loose, so it was easier to wash away during the membrane cleaning process. [ABSTRACT FROM AUTHOR]

FTIR spectra of a dehydrofluorinated poly(vinylidene fluoride) film were registered at different stages of its aging. A number of spectral features were noticed to grow with the sample aging. Three of them were assigned to the stretching vibrations of triple carbon-carbon bonds. Other bands were assigned to the libration, stretching, and combination vibrations of embedded water clusters consisting of 4, 5, or 6 molecules. The mechanism explaining synchronous formation of triple carbon-carbon bonds and small water clusters in the sample during its aging is proposed. SEM data on the surface morphology of the sample confirm the proposed mechanism.

A new Mg(II)−Sm(III) heterometallic coordination polymer (Cp) with the formula [Sm2(pydc)6Mg3(H2O)6] ⋅ 11H2O (1) (H2pydc=pyridine‐2,6‐dicarbolylic acid) has been solvothermal synthesized by reacting pyridine‐2,6‐dicarbolylic acid, Sm(NO3)3 ⋅ 6H2O, MgCl2 ⋅ 6H2O and imidazole at 393 K for 48 h. It was characterized by single‐crystal X‐ray diffraction, elemental analysis, IR and TGA. The results show that coordination polymer 1 exhibits a three‐dimensional network structure and crystallizes in hexagonal crystal system, space group P6/mcc, with crystallographic data of a=15.4203(6) Å, b=15.4203(6) Å, c=15.2563(6) Å, α=β=90°, γ=120°, V=3141.7(3) Å3, and Z=2. The twenty‐member water cluster structure and topological structure of compound 1 were analyzed, and its luminescent properties were studied. It presents the characteristic emission spectra of Sm(III) ions. [ABSTRACT FROM AUTHOR]

A recent paper (Phys. Chem. Chem. Phys. 2020, 22:22,459) shows that the energy components of the extended transition state energy decomposition analysis (ETS-EDA) are path functions, and therefore, they are not uniquely defined. In this work, we apply the ETS-EDA to analyse all possible dissociation paths of the water tetramer to four free water molecules. Our results confirm that the energy components of the ETS-EDA are path functions. However, they also show that differences among energy components obtained for the different paths are relatively small, and therefore, we conclude that the information obtained from an ETS-EDA can be used to discuss the nature of chemical bonds and analyse the origin of isomerization energies and energy barriers. However, if a given process can be attained by means of different and chemically reasonable paths, we recommend to perform the ETS-EDA of a given reaction for all different paths to confirm that energy components of the ETS-EDA do not differ very much from one path to another. [ABSTRACT FROM AUTHOR]

Gas-phase molecular adsorption was investigated as a model for molecular cloud formation. Molecular adsorption on cold gas-phase hydrogen-bonded clusters containing protonated tryptophan (Trp) enantiomers and monosaccharides such as methyl-α-d-glucoside, d-ribose, and d-arabinose was detected using a tandem mass spectrometer equipped with an electrospray ionization source and cold ion trap. The adsorption sites on the surface of cold gas-phase hydrogen-bonded cluster ions were quantified using gas-phase N2 adsorption-mass spectrometry. The gas-phase N2 adsorption experiments indicated that the number of adsorption sites on the surface of the hydrogen-bonded heterochiral clusters containing l-Trp and d-monosaccharides exceeded the number of adsorption sites on the homochiral clusters containing d-Trp and d-monosaccharides. H2O molecules were preferentially adsorbed on the heterochiral clusters, and larger water clusters were formed in the gas phase. Physical and chemical properties of cold gas-phase hydrogen-bonded clusters containing biological molecules were useful for investigating enantiomer selectivity and chemical evolution in interstellar molecular clouds. [ABSTRACT FROM AUTHOR]

For chemical warfare agent removal, the humidity emerges as an unavoidable challenge that significantly affects the performance of metal–organic frameworks. In this work, via density functional theory calculations, ab initio molecular dynamics and classical molecular dynamics simulations, we investigate the structural and diffusion properties of water in the pristine defect‐free UiO‐66, one Zr‐based metal–organic framework. Through the detailed analyses of the distribution probability of water in two different cages of UiO‐66, the binding interaction between water and UiO‐66, the hydrogen bonding networks and resulted localized water clusters, we gain a fundamental understanding of structural and dynamics properties as well as the concentration dependence of water in UiO‐66. We anticipate those theoretical results could provide insight to the competitive adsorption of water and chemical warfare agents, which eventually shows the utmost importance for the design and development of the next generation porous materials with appropriate water properties in real‐life applications. [ABSTRACT FROM AUTHOR]

An extended computational approach has been utilized to explore the reactions of acids with carbonyl oxide, also known as Criegee intermediate (CI). The reactions were explored inside a water cluster containing 50 water molecules. All possibilities of product formation were considered. Among the considered acids, the rate of 1,4‐insertion follows the order HCOO < HCl < HNO3. The most stable products of the reactions between the considered acids and CI have been identified. [ABSTRACT FROM AUTHOR]

Water clusters are ubiquitously formed in aqueous solutions by hydrogen bonding, which is quite sensitive to various environment factors such as temperature, pressure, electrolytes, and pH. Investigation of how the environment has impact on water structure is important for further understanding of the nature of water and the interactions between water and solutes. In this work, pH-dependent water structure changes were studied by monitoring the changes for the size distribution of protonated water clusters by in-situ liquid ToF-SIMS. In combination with a light illumination system, in-situ liquid ToF-SIMS was used to real-time measure the changes of a light-activated organic photoacid under different light illumination conditions. Thus, the proton transfer and pH-mediated water cluster changes were analyzed in real-time. It was found that higher concentration of free protons could lead to a strengthened local hydrogen bonding network as well as relatively larger protonated water clusters in both organic acid and inorganic acid. Besides, the accumulation of protons at the liquid-vacuum interface under light illumination was observed owing to the affinity of organic molecules to the low-pressure gas phase. The application of in-situ liquid ToF-SIMS analysis in combination with in-situ light illumination system opened up an avenue to real-time investigate light-activated reactions. Besides, the results regarding water structure changes in acidic solutions showed important insights in related atmospheric and physiochemical processes.

To investigate the effect of hydration behavior on the fluorapatite structure, single H2O molecule and three-layer water cluster adsorptions on the fluorapatite (001) surface were performed by means of density functional theory. The results show that a single H2O molecule can form stable chemisorption structures with the fluorapatite (001) surface in the form of single-site, two-site, and three-site adsorption and that the corresponding adsorption energies are 64.817, 98.712, and 139.620 kJ/mol, respectively. The interacting length of the Ca atom and the O atom of the H2O molecule is close to the length of the Ca–O bond in the bulk, and their overlap is mainly contributed by the O 2p and Ca 4s states. The fluorapatite (001) surface shows serious hydration reconstruction after adsorbing three layers of water molecules; these atoms in the surface layer are highly distorted, and the Ca and the PO4 are shifted in opposite directions along the z-axis direction. Further analysis shows that these surface Ca atoms are critical to the hydration behaviors of the transition area, as they can bind strongly to the H2O molecules, with the newly formed Ca–O bonds being between 2.164 and 2.486 Å.

In this work, the relative yields of aqueous secondary organic aerosols (aqSOAs) at the air–liquid (a–l) interface are investigated between photochemical and dark aging using in situ time-of-flight secondary ion mass spectrometry (ToF-SIMS). Our results show that dark aging is an important source of aqSOAs despite a lack of photochemical drivers. Photochemical reactions of glyoxal and hydroxyl radicals (•OH) produce oligomers and cluster ions at the aqueous surface. Interestingly, different oligomers and cluster ions form intensely in the dark at the a–l interface, contrary to the notion that oligomer formation mainly depends on light irradiation. Furthermore, cluster ions form readily during dark aging and have a higher water molecule adsorption ability. This finding is supported by the observation of more frequent organic water cluster ion formation. The relative yields of water clusters in the form of protonated and hydroxide ions are presented using van Krevelen diagrams to explore the underlying formation mechanisms of aqSOAs. Large protonated and hydroxide water clusters (e.g., (H2O)nH+, 17 < n ≤ 44) have reasonable yields during UV aging. In contrast, small protonated and hydroxide water clusters (e.g., (H2O)nH+, 1 ≤ n ≤ 17) form after several hours of dark aging. Moreover, cluster ions have higher yields in dark aging, indicating the overlooked influence of dark aging interfacial products on aerosol optical properties. Molecular dynamic simulation shows that cluster ions form stably in UV and dark aging. AqSOAs molecules produced from dark and photochemical aging can enhance UV absorption of the aqueous surface, promote cloud condensation nuclei (CCN) activities, and affect radiative forcing.

Two new CdII MOFs, namely, two‐dimensional (2D) poly[[[μ2‐1,4‐bis(1H‐benzimidazol‐1‐yl)butane](μ2‐heptanedioato)cadmium(II)] tetrahydrate], {[Cd(C7H10O4)(C18H18N4)]·4H2O}n or {[Cd(Pim)(bbimb)]·4H2O}n (1), and 2D poly[diaqua[μ2‐1,4‐bis(1H‐benzimidazol‐1‐yl)butane](μ4‐decanedioato)(μ2‐decanedioato)dicadmium(II)], [Cd2(C10H16O4)2(C18H18N4)(H2O)2]n or [Cd(Seb)(bbimb)0.5(H2O)]n (2), have been synthesized hydrothermally based on the 1,4‐bis(1H‐benzimidazol‐1‐yl)butane (bbimb) and pimelate (Pim2−, heptanedioate) or sebacate (Seb2−, decanedioate) ligands. Both MOFs were structurally characterized by single‐crystal X‐ray diffraction. In 1, the CdII centres are connected by bbimb and Pim2− ligands to generate a 2D sql layer structure with an octameric (H2O)8 water cluster. The 2D layers are further connected by O—H...O hydrogen bonds, resulting in a three‐dimensional (3D) supramolecular structure. In 2, the CdII centres are coordinated by Seb2− ligands to form binuclear Cd2 units which are linked by bbimb and Seb2− ligands into a 2D hxl layer. The 2D layers are further connected by O—H...O hydrogen bonds, leading to an 8‐connected 3D hex supramolecular network. IR and UV–Vis spectroscopy, thermogravimetric analysis and solid‐state photoluminescence analysis were carried out on both MOFs. Luminescence sensing experiments reveal that both MOFs have good selective sensing towards Fe3+ in aqueous solution. [ABSTRACT FROM AUTHOR]

Two new CdII MOFs, namely, two‐dimensional (2D) poly[[[μ2‐1,4‐bis(1H‐benzimidazol‐1‐yl)butane](μ2‐heptanedioato)cadmium(II)] tetrahydrate], {[Cd(C7H10O4)(C18H18N4)]·4H2O}n or {[Cd(Pim)(bbimb)]·4H2O}n (1), and 2D poly[diaqua[μ2‐1,4‐bis(1H‐benzimidazol‐1‐yl)butane](μ4‐decanedioato)(μ2‐decanedioato)dicadmium(II)], [Cd2(C10H16O4)2(C18H18N4)(H2O)2]n or [Cd(Seb)(bbimb)0.5(H2O)]n (2), have been synthesized hydrothermally based on the 1,4‐bis(1H‐benzimidazol‐1‐yl)butane (bbimb) and pimelate (Pim2−, heptanedioate) or sebacate (Seb2−, decanedioate) ligands. Both MOFs were structurally characterized by single‐crystal X‐ray diffraction. In 1, the CdII centres are connected by bbimb and Pim2− ligands to generate a 2D sql layer structure with an octameric (H2O)8 water cluster. The 2D layers are further connected by O—H...O hydrogen bonds, resulting in a three‐dimensional (3D) supramolecular structure. In 2, the CdII centres are coordinated by Seb2− ligands to form binuclear Cd2 units which are linked by bbimb and Seb2− ligands into a 2D hxl layer. The 2D layers are further connected by O—H...O hydrogen bonds, leading to an 8‐connected 3D hex supramolecular network. IR and UV–Vis spectroscopy, thermogravimetric analysis and solid‐state photoluminescence analysis were carried out on both MOFs. Luminescence sensing experiments reveal that both MOFs have good selective sensing towards Fe3+ in aqueous solution. [ABSTRACT FROM AUTHOR]

We explore the kinetic processes that sustain equilibrium in a microscopic, finite system. This is accomplished by monitoring the spontaneous, time-dependent frequency evolution (the frequency autocorrelation) of a single OH oscillator, embedded in a water cluster held in a temperature-controlled ion trap. The measurements are carried out by applying two-color, infrared-infrared photodissociation mass spectrometry to the D3O+·(HDO)(D2O)19 isotopologue of the “magic number” protonated water cluster, H+·(H2O)21. The OH group can occupy any one of the five spectroscopically distinct sites in the distorted pentagonal dodecahedron cage structure. The OH frequency is observed to evolve over tens of milliseconds in the temperature range (90 to 120 K). Starting at 100 K, large “jumps” are observed between two OH frequencies separated by ∼300 cm−1, indicating migration of the OH group from the bound OH site at 3,350 cm−1 to the free position at 3,686 cm−1. Increasing the temperature to 110 K leads to partial interconversion among many sites. All sites are observed to interconvert at 120 K such that the distribution of the unique OH group among them adopts the form one would expect for a canonical ensemble. The spectral dynamics displayed by the clusters thus offer an unprecedented view in to the molecular-level processes that drive spectral diffusion in an extended network of water molecules. [ABSTRACT FROM AUTHOR]

We seek to explain why the hydrogen bond possesses unusual strength in small water clusters that account for many of the complex behaviors of water. We have investigated and visualized the donation of covalent character from covalent (sigma) to hydrogen bonds by calculating the eigenvector coupling properties of quantum theory of atoms in molecules (QTAIM), stress tensor σ(r), and Ehrenfest Force F(r) on the F(r) molecular graph. The next‐generation three‐dimensional (3‐D) bond‐path framework sets are presented, and only the F(r) bond‐path framework sets reproduce the earlier finding on the coupling between covalent (sigma) and hydrogen bonds that possess a degree of covalent character. Exploration of the bond‐path between the covalent (sigma) and hydrogen bond's critical points provides an explanation for the previously obtained coupling results. The directional character of the covalent (sigma) and hydrogen bonds' 3‐D bond‐path framework sets for the F(r) explains differences found in the earlier results from QTAIM and the stress tensor σ(r). [ABSTRACT FROM AUTHOR]

Intermolecular interactions in bulk water are dominated by pairwise and non‐pairwise cooperative interactions. While accurate descriptions of the pairwise interactions are available and can be tested by precise low‐frequency spectra of the water dimer up to 550 cm−1, the same does not hold for the three‐body interactions. Here, we report the first comprehensive spectrum of the water trimer in the frequency region from 70 to 620 cm−1 using helium‐nanodroplet isolation and free‐electron lasers. By comparison to accompanying high‐level quantum calculations, the experimentally observed intermolecular bands can be assigned. The transition frequencies of the degenerate translation, the degenerate in‐plane and the non‐degenerate out‐of‐plane libration, as well as additional bands of the out‐of‐plane librational mode are reported for the first time. These provide a benchmark for state‐of‐the‐art water potentials and dipole‐moment surfaces, especially with respect to three‐body interactions. [ABSTRACT FROM AUTHOR]

Infrared spectroscopic study of neutral water clusters is crucial to understanding of the hydrogen-bonding networks in liquid water and ice. Here we report infrared spectra of size-selected neutral water clusters, (H2O)n (n = 3−6), in the OH stretching vibration region, based on threshold photoionization using a tunable vacuum ultraviolet free-electron laser. Distinct OH stretch vibrational fundamentals observed in the 3,500−3,600-cm−1 region of (H2O)5 provide unique spectral signatures for the formation of a noncyclic pentamer, which coexists with the global-minimum cyclic structure previously identified in the gas phase. The main features of infrared spectra of the pentamer and hexamer, (H2O)n (n = 5 and 6), span the entire OH stretching band of liquid water, suggesting that they start to exhibit the richness and diversity of hydrogen-bonding networks in bulk water. [ABSTRACT FROM AUTHOR]