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We study the proton conductivity properties of MOF-801. We find that MOF-801 possesses intrinsic proton carrier sites, μ3-OH groups, in clusters yielding the generation of hydrogen-bonding networks with guest water molecules at high relative humidity (RH), facilitating proton transport. Remarkably, this material has a high proton conductivity of 1.82 × 10−3 S cm−1 under 98% RH at 90 °C and maintains its performance over an extended time. Our investigations reveal that the increase in proton conductivity is correlated to numerous hydrogen bonds within the MOF structure. The activation energy of this process is low (Ea = 0.21 eV), showing that the protons hop through the membrane by the Grotthus mechanism. Interestingly, density functional theory (DFT) calculations combined with molecular dynamics (MD) simulations show that a water cluster mechanism dominates the proton conductivity in this material via the large number of hydrogen bonds formed at different temperatures and relative humilities.

The behavior of water adsorption on carbonaceous materials is distinct from the simple gases, enabling it as a complementary probe for characterization. Doing so requires a profound understanding of how water adsorbs microscopically. Experimental water isotherms for bimodal micro-mesoporous carbon exhibit a stepwise behavior with two steps for high temperatures and, surprisingly, one step for low temperatures. The two-step behavior and the unusual temperature dependence is worthy of an explanation from microscopic perspective, and to this end we carried out extensive Monte Carlo simulation for water adsorption in a pore model composed of linearly connected micropore and mesopore. Our simulation results show that water molecules could readily fill the micropore section and the prerequisite for the filling of the mesopore section is the existence of a water cluster spanning across the junction between the micropore and the mesopore at 298 K. Temperature is another important factor and stronger thermal fluctuations at higher temperatures facilitate the advancement of the interfaces of adsorbed water thus making filling in mesopore happen even without the formation of the PSC at high temperatures (e.g., 450 K). The findings in this paper offer useful insights on the characterization of bimodal porous carbon via water adsorption.

Dissipative Particle Dynamics is used to model water clustering in ion exchange membranes. We consider polymers with hydrophobic backbone alternatingly grafted with short hydrophilic ([C]) and hydrophobic linear (A6) or Y-shaped side chains (ie. Ap [As][As]; p(s) = 6(0), 4(1), 2(2), 0(3)). At 16% water volume fraction water cluster connectivity (DMC(W), water diffusivity, and inter water domain distance increase with length p and average number of bonds ( ) separating A and nearest C beads. Exchange of the pendent A and C beads for (A [C]A [A6])10 to form (A [A]A [A5C])10 decreases water cluster connectivity. This is because the lower number of bonds between nearest C beads for (A [C]A [A6])10 forces them to join the same water domain. This cooperative mechanism also explains deviations from the increase of DMC(W) with for similar ion exchange capacity (IEC). At high IEC (A [Ax+1C])10 architectures favour good connected pores which is surpassed by the H-phobic side chain (A [C]A [Ax])10 architectures at low IEC.

Emergency response to floods requires timely information on water extents, which can be produced by satellite-based remote sensing. As the synthetic aperture radar (SAR) can emit and receive signal in nighttime or cloudy conditions, it is particularly suitable to delineate water extent during flood events. Thresholding SAR imagery is one of the most widely used approaches to delineate water extent for its effectiveness and efficiency. However, most thresholding methods rely on a single threshold to separate water and land without considering the complexity and variability of different land surface types in an image. To account for the heterogeneous surface characteristics, this paper proposes a new local thresholding method to water delineation with SAR images. Specifically, our method follows four major steps. First, a global threshold is applied to the SAR imagery to delineate initial water pixels, from which non-water pixels are further clustered into several land surface types. This divides the SAR imagery into one water cluster and several land clusters. Second, local thresholds are estimated at each subset of land cluster paired with water cluster by fitting Gamma distributions to the backscatter intensities of the combined water/land pixels in each subset. Third, local water extents are delineated from each subset and then merged as the union of all subsets. The results are combined across multiple polarizations by taking an intersection operation to generate the global inundation extent. Finally, the flood water extent is further improved by imposing basic hydrologic constraints. This approach is fast and fully automated for flood detection. Our experiments using Sentinel-1 SAR imagery show that the proposed local thresholding approach could distinguish water from non-water with significantly higher accuracy (4–13% improvement in the harmonic mean of user’s and producer’s accuracy of water) than conventional global-thresholding methods.

Understanding water distribution behaviors plays an essential role in shale gas development due to the hydraulic fracturing technology. In this study, water vapor adsorption isotherms were measured for Upper Triassic Yanchang and Lower Silurian Longmaxi samples at 288.15 K, 298.15 K and 308.15 K to investigate the adsorption behaviors of water on shale. For a description of adsorption process, a Dent’s model provides an estimate of primary and secondary adsorption sites of water adsorption. The effects of temperature, shale mineralogy, and water distribution were discussed. The results show that temperature has a negative effect on water vapor adsorption. Adsorption capacities of primary and secondary sites decrease with increasing temperature. Water vapor adsorption capacity is tightly associated with clay content, whereas water vapor adsorption has no significant relationship with total organic carbon (TOC). Normalized water vapor adsorption content also has no significant relationship with TOC, which indicates no obvious correlation between water vapor adsorption and TOC content. The inter-crystal pores of clay minerals provide significant specific surface for gas adsorption in shale. At low relative pressure, a large number of water molecules adsorb on the primary sites. At high relative vapor pressure, most of the primary sites have been occupied, so that the secondary adsorption sites will be utilized. Therefore, due to relative weak binding energies in secondary adsorption sites, water cluster are formed in micro-pores of shale. As relative vapor pressure increases, capillary condensation gradually predominates over the adsorption. The study will reveal mechanism of water adsorption and distribution characteristics on shale and provide some foundation for geological reserve estimation and shale gas recovery prediction.

Three novel metal-organic complexes, formulated as [Cu2(2-HBA)2(bimb)4] (1), {[Cd(CEDA)(bimb)]·H2O}n (2), and {[Ag2(bimb)2]·(1,4-CDA)·13H2O} (3) (bimb = 1,2-bis((1H-imidazole-1-yl)methyl)benzene; 2-HBA = 2-hydroxybenzoic acid; CEDA = cyclohex-4-ene-1,2-dicarboxylic acid; 1,4-CDA = cyclohexane-1,4-dicarboxylic acid), were synthesized by self-assembly of mixed ligands with Cu(II), Cd(II), and Ag(I) under hydrothermal conditions and characterized by means of single-crystal X-ray diffraction, X-ray powder diffraction, infrared spectra, thermogravimetric analysis, fluorescence spectra and UV–vis absorption spectra. 1 is shown as a 0D structure, which is formed by Cu2+, 2-HBA ligands and bimb ligands. 2 displays a 1D ladder structure, which is built by Cd2+, CEDA ligands and bimb ligands, and it is assembled into 2D structure by hydrogen bonding. 3 possesses a 0D [Ag(bimb)]2 dimer which is assembled into 3D structure by the Ag O weak interaction and hydrogen bonding. Interestingly, a rare 13-core water cluster participates in forming the network of 3. The UV–vis spectrum and luminescence properties were also studied and discussed.

Using the multiphase lattice Boltzmann method (LBM), the liquid water transport dynamics is simulated in a gas diffusion layer (GDL) of polymer electrolyte membrane fuel cells (PEMFCs). The effect of rib structure on the water invasion process in the micro-porous GDL is explored by comparing the two cases, i.e., with rib and without rib structures. The liquid water distribution and water saturation profile are presented to determine the wetting mechanism in the GDL. The results show that the liquid water transport in the GDL is strongly governed by capillary force and the rib structure plays a significant role on water distribution and water transport behavior in the GDL. Comparison of two cases confirms that the rib structure influences on the location of water breakthrough. The liquid water distribution and water saturation profile indicate that the high resistance force underneath the rib suppresses the growth of water cluster, resulting in the change of flow path. After water breakthrough, the liquid water distribution under the channel has little variation, whereas that under the rib continues to change. The predicted value of effective permeability is in good agreement with Carman-Kozeny correlation and experimental results in the literature. The results suggest that the LBM approach is an effective tool to investigate the water transport behavior in the GDL.

Poly-lactic acid (PLA) is widely used as a controlled drug release material and the diffusion property of water within the polymer matrix is closely related to the drug release profile. This paper studies the water diffusion in PLA by molecular dynamic simulations. Free volume analysis indicates that water molecules are expected to fill in the free volumes of the polymer matrix forming water clusters at low water content. Along with the increase of the water concentration, the polymer starts to swell and the density of the system starts to drop. Due to the high mobility of water within water cluster, the calculated diffusion coefficient dramatically increases along with the incensement of water content. Thus, we conclude that the diffusion of water is a self-accelerate process, with higher mobility of water in the case where more water exists.

A new series of six isostructural molecular solids of the composition [{Al(H2O)6}{Ln(pda)3}].10H2O where Ln = Sm, Eu, Gd, Tb, Dy and Yb have been synthesized and structurally characterised. All the solids are built of three major building blocks: the lanthanide dipicolinate anion, {Ln(pda)3}3−, the counter cation, {Al(H2O)6}3+ and a hexameric water cluster in chair form. The cations and the anions supramolecularly aggregate forming a 2D H-bonded sheet; the sheets are further stabilised through hexameric water clusters in chair form and water molecules. The crystals containing Sm, Eu, Tb and Dy showed characteristic emission of lanthanide ions.

The hydrothermal reaction of NiSO4·6H2O and 4,4′-bis(1-imidazolyl)bipheny (bibp) has afforded a new nickel complex, {[Ni4(µ3-OH)4(µ4-SO4)(bibp)4](OH)2·12H2O}n (1). The Ni(II) centers are bridged by µ3-OH- anions into cubic [Ni4(µ3-OH)4] units, which are connected by bibp ligands and µ4-SO42- anions into a double-walled 3D framework with channels along c direction. Unusual 1D water cages with a repeat of vase-like water cluster are trapped in the channels. Magnetic studies reveal ferromagnetic behavior for complex 1, and the thermal property of 1 was also studied.

Real time in-situ observation by small-angle neutron scattering (SANS) was performed to observe the development of microstructure in a polyelectrolyte membrane packed in a polymer electrolyte fuel cell (PEFC) during initial conditioning. By utilizing the excellent penetrability of neutrons, an operating fuel cell was studied. SANS originating from the membrane was analyzed to determine the water cluster radius (Rc) and its number density (ρc). We found that Rc increased and ρc decreased, as the load current was increased during initial conditioning. The maximum Rc achieved at high current density became larger as the conditioning cycle proceeded. In this process, two water clusters combined and the connectivity of proton conduction channels was enhanced. As a consequence, was reduced ohmic loss, which was detected by using a special segmented electrode cell covering the cell section corresponding to that observed by SANS. Keywords: Small-angle neutron scattering, Polymer electrolyte fuel cell, Aging effect, Connectivity of proton conduction channel

The application of an external electric field to a solution alters the orientational probability distribution of water molecules. Hence, the forces exerted by the solvent on the charged groups of the solute are modified. In this study, the mechanisms underlying the dependence of these forces on the external electric field are proposed. To evaluate the accuracy of these hypotheses, an external electric field is applied to a water cluster containing a solute with electric dipoles and/or charges, and the forces of the solvents acting on the dipoles and charges are calculated from the trajectories obtained in molecular dynamics simulations. The simulation results are found to be consistent with the proposed mechanisms.

Graphitic carbon nitride (g-C3N4) is a novel two-dimensional, nitrogen-doped carbon material with various applications in many fields. Recently, g-C3N4 has exhibited excellent ability in separations. In this work, mechanisms of water and ion permeation across nanoporous g-C3N4 membranes with different pore diameters were studied using non-equilibrium molecular dynamics simulations. The water conduction rates derived from our simulations are in good agreement with previous experimental data. Due to the nanoscale confinement, we observe a stacked water cluster structure within the narrowest nanochannel. Similar structures are obscure as the increase of the nanochannel sizes. For desalination purposes, we find that the nanoporous g-C3N4 membrane with the desired opening may completely reject calcium and chloride ions, whereas sieve out monovalent cations with acceptable rejection rates (over 70%). This work provides molecular insight into the mechanism of water and ion transport through nanoporous g-C3N4, which strongly supports that this novel material is a promising candidate for developing selective membrane for water desalination.

Water clusters are hydrogen bonded molecular assembly of water molecules. They have been extensively studied using experiments, ab initio calculations and molecular simulations. The molecular arrangement of water in water cluster provide significant insights into behavior of water in bulk, confinement and close to surfaces. Here molecular dynamics simulations of TIP4P/2005 water clusters are performed in weak electrid fields. These fields introduce additional forces of varying magnitude 0.1–25 % of forces existing in without-field water clusters. Autocorrelation functions of distance, energy and velocities are analysed. Molecular arrangements in water clusters does not disintegrate under additional forces.

Nanodiamond particles, basically those produced by detonation method, are acquiring progressive attraction in different fields such as material, biomedical, and environmental engineering. Aqueous environments are usually dealt with at different stages of preparation, preservation, and application of these particles. The aim of this article is to perform a systematic first-principles density functional theory analysis on the interaction of C35 ultrasmall octahedral nanodiamond and its full homogeneous carboxylated and aminated forms, with water derived specie, namely, neutral, protonated, and deprotonated water and (H2O)20 water cluster. The effect of solvent media on the interactions has been considered through conductor like screening model. Through the calculations, C35 showed a hydrophobic nature, and C35(COOH)36 and C35(NH2)36 demonstrated hydrophilic characteristics. The interactions of all the water derived specie with the non-functionalized C35 were more intense compared with the functionalized C35(COOH)36 and C35(NH2)36 nanodiamonds, either in the gas phase or water media. Interestingly, in water media, the interaction energies of H3O+ and OH− with C35(NH2)36 were almost zero; only the interaction of H3O+ with C35(COOH)36 was zero, testifying to its Bronsted-Lowry acidic nature. To understand the nature of the interactions the electron density differences were utilized.

Due to their preferential cation transport, dense cation exchange membranes like Nafion membranes are unsuitable for Zn/Br redox flow batteries which require bi-ionic transport of Zn2+ and Br- ions. This work shows that scaling the water cluster size of Nafion membranes by a pre-hydration treatment can achieve not only a high ionic conductivity but also a bi-ionic transport property. Small angle X-Ray scattering, diffusion cell, and electrochemical analysis verify that by increasing the pre-hydration temperature, the water clusters are expanded, resulting in an increase of water uptake, ionic conductivity and the anion transference number. The bi-ionic transport and low area specific resistance induced by the pretreatment enable the successful operation of a Zn/Br redox flow battery with a NRE-212 membrane. Compared with a conventional porous membrane, the properly treated Nafion membrane has an 11.3% higher energy efficiency indicating that the dense structured ion exchange membrane can be used for Zn/Br flow batteries by scaling the water cluster size.

The present letter reports unusual high fluorescence anisotropy of excited state intramolecular proton transfer (ESIPT) prone 2-(2′-hydroxyphenyl)benzoxazole (HBO) in water followed by its imidazole (HBI) and thiazole (HBT) analogues. The low fluorescence anisotropy of the acetate compound of HBO in water reveals the key role of the hydrogen bonded cage-like probe-water cluster for the findings in water. Formation of the aquated cluster is controlled possibly by the combined effect of the electronegativity and mesomeric effect of the heteroatom away from the ESIPT site. The work invites further explorations, preferably from computational perspective, for a proper explanation.

A coordination polymer with ordered and non-acidic water-cluster guest molecules, [Zn(cis-chdc)(bpp)]·6H2O (denoted as Zn2-(H2O)12, H2chdc = 1,4-cyclohexanedicarboxylic acid; bpp = 1,3-bis(4-pyridyl)propane), which captures a kind of (H2O)12 cluster inside the cavity, is found to be an efficient proton conducting solid electrolyte. Zn2-(H2O)12 has a high conductivity of 0.241 mS·cm−1 at 318 K and 95% RH (relative humidity), which is higher than the other kinds of water-only guested coordination polymers (CPs). The configuration of the water clusters has been described and the role it plays in the process of proton transportation has been investigated preliminarily.

Far-infrared vibration–rotation-tunneling (VRT) spectra of gas-phase water reported previously have been interpreted in terms of polaronic exciton coupled model. An increase of the energy gap (Δν) between the neighboring absorption lines, which is observed in the spectrum within a pattern responsible for water cluster absorption, correlates with spin–orbit coupling parameter (β). Namely, experimental ratio (Δνi+1/Δνi) = 1.188996 ± 0.051361 has been found in fair agreement with β= 1.19100654 that implies the accumulation of difference between the absorption and emission energies. This correlation means the electrons coupled with protons establishing hydrogen bonds accumulate the energy difference. Relation deduced earlier for Boson peak frequency admitted to estimate fast Debye relaxation time for water that is found to be 0.183704 ps.

Resonance Raman spectra of protonated meso-tetraphenylporphine (TPP) dimers measured earlier in aqueous solutions have been interpreted in terms of polaronic exciton theory. Consideration of the incident photon interaction with H3O+ producing polaronic exciton shows up spin-orbit interaction depending (βq = 3.741657387) and almost non-depending (β = 1.19100654) on quaternary molecule coordination in the water clusters. Both β parameters that take into consideration proton and electron spin orientations have been involved in major relations derived under the development of polaronic exciton theory. Theoretically estimated energy gap between the levels with different proton spin orientations, i.e. e↓↑p↑e and e↓↓p↑e in the O Hδ+...O moiety is found to be 40.766 cm−1. Experimental energy gap 25.5 ± 1.3 cm−1 averaged for several doublets in the Raman spectrum with λex = 441.6 nm is consistent with the theoretical 25.19 cm−1 obtained using golden section as a denominator. It appears that golden section governs the fine structure under the proton sharing in the O H+...O moiety of the water cluster embedded between TPP units of the dimers.

The dynamics of water in sodium alginate film-forming solutions during drying were investigated by low-field nuclear magnetic resonance. At the beginning of drying, three transverse relaxation times at around 1.74, 28.48 and 305.38 ms were assigned to the tightly bound, moderately bound, and free water, respectively. Moreover, the free water was evaporated, followed by the formation of water cluster in the entangled alginate chains network as the drying process continued (beyond 840 min of drying time). Towards the third stage of drying process, water clusters in alginate samples was disappeared, resulting that loosely bonded waters were constrained within the weak-gel network. The observed three relaxation times revealed the multi-exponential relaxation behavior of water in alginate, which indicated that this polymer exhibited spatial heterogeneity during drying. On the basis of diffusive exchange theory, the dimension range of alginate network decreased from 1.94–23.99 to 1.83–6.62 µm as the alginate films solidified.

There is an increasing need to develop an alternative to Nafion membrane in order to reduce the cost of vanadium redox flow batteries. Pore-filled composite membranes based on Nafion is one way to reduce the amount of costly material, however its chronic problem is low conductivity and water uptake ability. We suggest a novel approach to enhance the conductivity and water uptake by incorporating propylene carbonate to modulate water channel morphologies in Nafion directly. We present a pore-filled type Nafion composite membrane to prove the effect of PC addition. Small-angle X-ray scattering and simulation results are suggested for further understanding.

A new chiral inorganic-organic hybrid with the formula (L-His)2(H7CoMo6O24)·6H2O (1), based on natural amino acid and Anderson type polyoxomolybdate was synthesized through mild condition. The chiral l -histidine molecules induced chirality to the whole structure through various types of strong and unconventional hydrogen bond (HB) interactions (CH⋯O, NH⋯O and CH···π interactions), as well as bifurcated hydrogen bonds (BHBs) between l -histidine amino acid, hexamer water cluster molecules, and H7CoMo6O24·xH2O. Following, important non-covalent CH⋯O interactions is investigated in another chiral inorganic-organic hybrid structure, (L-Pro)3(PMo12O40).4.5H2O (2), in detail. The CH⋯O hydrogen bonds lead to a chiral network similar to the DNA strands affording a promising candidate to bio-inorganic studies.

In this letter, a possible reason behind selective host-guest organization in the initial stage of sI methane hydrate nucleation is provided, through density functional theory based calculations. In doing so, we have connected earlier experimental and theoretical observations on the structure and energetics of sI methane hydrate to our findings. Geometry and relative stability of small (H 2 O) 5 and (H 2 O) 6 clusters, presence of CH 4 guest, integrity and cavity radius of (H 2 O) 20 and (H 2 O) 24 , as well as the weak van der Waals type of forces, particularly dispersion interaction, are major factors responsible for initial formation of methane encapsulated dodecahedron cavity over tetrakaidecahedron.

Polymer materials with low water uptake exhibit a highly heterogeneous interior, characterized by water clusters in the form of nanodroplets and nanochannels. Here, based on our recent insights from computer simulations, we argue that water cluster structure has large implications for ionic transport and selective permeability in polymer membranes. Importantly, we demonstrate that the two key quantities for transport, the ion diffusion and the solvation free energy inside the polymer, are extremely sensitive to molecular details of the water clusters. In particular, we highlight the significance of water droplet interface potentials and the nature of hopping diffusion through transient water channels. These mechanisms can be harvested and fine-tuned to optimize selectivity in ionic transport in a wide range of applications., Comment: 12 pages, 7 figures

Laser induced fluorescence and fluorescence emission spectra of 2-cyanoindole and the binary 2-cyanoindole-(H2O)1 cluster in a molecular beam were analyzed using a combination of Franck-Condon (FC) fits of the emission spectra and ab initio calculations. The structural changes upon electronic excitation to the lowest excited singlet state have been elucidated by a combined rotational constants/vibronic intensities fit. The experimentally determined geometry changes and the ab initio calculations point to an Lb-like excited state for the monomer. FC fits of emission spectra of the binary water cluster and quantum chemical calculations show that the emission of the water cluster also takes place from an Lb-like excited state structure. However, for 2-cyanoindole-(H2O)1 the second highest occupied molecular orbital mixes strongly with the highest one. Therefore, the difference between La and Lb characteristics are smaller than for other substituted indoles, including the other positional conformers of the n-cyanoindoles.

Herein, the mechanisms of tourmaline powder activating water were discussed via the performance of water cluster. The result suggested that the performance of water were improved by tourmaline powder. The surface tension 72.19 mN/m, dissolved oxygen 9.57 mg/L, and conductivity 0.53 us/cm of activated water were obtained at D50 of tourmaline powder 0.79 μm, dosage of tourmaline powder 20 g/L, processing time 10 min, and processing temperature 17 °C. Besides, assisted by the tourmaline powder, the full width at half maxima (FWHM) of 17O in the nuclear magnetic resonance (NMR) of water diminished from 1485 Hz to 533 Hz. The polarization electric field of tourmaline improved the water temperature to weaken and break the hydrogen bond. Based on the various infrared active vibrational bonds of tourmaline, the molecules resonate of water were promoted by the far-infrared radiation to cut off the hydrogen bonds and improve the activity of water.

The adsorption of ofloxacin (OFL) on oxidized activated carbon (AC) and carbon nanotube (CNT) are compared, focusing on the differences in carbon structures. Chemical oxidation of carbonaceous materials inhibited OFL adsorption to AC, but enhanced their adsorption to CNT. The higher number of oxygen-containing functional groups facilitated the interaction of the material with water molecules, causing the blockage of AC inner pore. However, the dispersion of oxidized CNT enhanced due to its increased hydrophilicity, resulting in the exposure of some new adsorption sites, as identified by the 1H NMR relaxometry measurement. The adsorption kinetics of OFL on AC indicated that the contributions of slow adsorption and equilibrium time increased after AC oxidation. However, the equilibrium time of the fast adsorption of OFL on CNT shortened after CNT oxidation. These results indicated that the pore of AC was blocked by water cluster and the accessibility of adsorption sites on oxidized CNT was enhanced due to dispersion. This study emphasizes that the structural differences among carbonaceous materials control the oxidation effects on their adsorption characteristics for OFL.

The 16 lowest energy isomers of cationic water cluster (H 2 O) 9 + have been comprehensively searched by the particle swarm optimization algorithm combined with quantum chemistry calculations. Geometric optimization and vibration analysis of the interesting isomers were made in the MP2/aug-cc-pVDZ level. Our results show that cage structure is the most stable at low temperatures. The relative Gibbs free energy below 400 K was calculated, which indicates that the stability of the cage structure decreases as the temperature increases while the energy of ring is relatively slow. We also illustrate the computationally simulated IR spectra obtained at six different calculated levels and individual IR spectroscopy for seven isomers. The obtained molecular orbits of six representative isomers show good agreement with experiment. Finally, through the topological analysis and density gradient analysis, we compared the interaction between the H 3 O + core and H 2 O as well as the OH radicals.

We present fluorescence emission spectra of the 2-tolunitrile dimer and the 2-tolunitrile water cluster through various vibronic bands in the electronically excited state. From the transition dipole moments in the individual monomers, the 2-TN dimer has shown to form J-aggregates, which is why the one-photon allowed transition is the S1 state in this cluster in contrast to other symmetric dimers, which tend to form H-aggregates. The changes of the molecular structures upon electronic excitation have been determined from a fit of the intensities in various fluorescence emission spectra. The excited state structure of the 2-TN dimer has been found to be asymmetric, in contrast to the ground state structure. Thus, emission takes place from one of the locally excited monomer moieties in the 2-tolunitrile dimer.

Reactions between benzene and the zeolite HZSM-5, carried out at low pressure and room temperature, revealed that controlled addition of sub-stoichiometric amounts of water increases the rate of isotopic 1 H/ 2 H exchange between benzene-d 6 and the surface acid site by almost an order of magnitude relative to the control case in which no water is added. Single-ring aromatics like benzene have been identified as an active form of the hydrocarbon pool in methanol-to-hydrocarbon chemistries, but their role as reactive centers for alkylation and dealkylation chemistry is general to all of solid-acid catalysis. Maximum reaction rates were observed for water loadings of ca. 0.1 equivalents for catalysts with Si/Al equal to 15. No beneficial water effect was observed in benzene/zeolite reactions using a much lower acid-density catalyst HZSM-5 with Si/Al equal to 40. In-situ experiments strongly suggest that the origin of the water enhancement effect for the high-acid density catalyst arises from an increase in the “vehicle hopping” proton-transfer mechanism, which cannot occur when acid sites are sufficiently far apart as in the Si/Al equal to 40 catalyst. When the water loading is too high, water’s competitive adsorption and excluded volume reduces the benzene adsorption probability due to the increased proton affinity of a water cluster.

Gas phase reactions of O2 −(H2O)m and CO2 −(H2O)m with HCl as well as HNO3 are studied by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. HCl and HNO3 are efficiently taken up by the clusters. In the reactions of O2 −(H2O)m, a characteristic mass change is observed which is consistent with the evaporation of a hydroperoxyl radical HO2 , most likely formed via proton transfer to O2 −. Using CO2 −(H2O)m as the ionic reactant, products indicating the formation of HOCO are hardly observed in the HCl reaction. With HNO3, however, evidence is found for elimination of HOCO , resulting from proton transfer to CO2 −, when the clusters have lost almost all water molecules. Thermochemical cycles using literature thermochemistry show that the reactions are exothermic.

Understanding the thermal stability of the proteins in human serum is essential since human serum is the important source of pharmaceutical proteins. Near-infrared (NIR) spectroscopy was applied to the investigation of thermal changes in secondary structure and hydration of human serum proteins. However, as a multicomponent system, the overlap of the broad NIR bands makes the structural analysis very difficult directly using the spectra of serum samples. Therefore, continuous wavelet transform (CWT) was used to improve the resolution of NIR spectra, and Monte Carlo-uninformative variable elimination (MC-UVE) method was applied to the selection of the variables associated with the proteins for the structural analysis. The variables (5956, 5867, 5815, 5747, 4525, 4401, 4359 and 4328 cm −1 ) related to protein secondary structures and those (7074, 6951, 6827 and 6700 cm −1 ) connected with water species were selected. Then, the thermal stability was analyzed through the intensity variations of the selected variables with temperature from 30 °C to 80 °C. It was found that the variation of the spectral variables related to both α -helix and β -sheet changes apparently around 60 °C, indicating the beginning of the thermal denaturation and the transition from α -helix to β -sheet. Moreover, an obvious change was found around 60 °C for the content of the water specie S 3 , i.e. , the water cluster containing three hydrogen bonds. The result demonstrates that MC-UVE can identify the protein-related NIR spectral variables, and the water species may be a marker for investigation of the structural change of proteins in biochemical systems.

We introduce the orbital-resolved electron density projected integral (EDPI) along the H-bond in the real space to quantitatively investigate the specific contribution from the molecular orbitals (MOs) aspect in (H 2 O) 2 . Calculation results show that, the electronic occupied orbital (HOMO-4) of (H 2 O) 2 accounts for about surprisingly 40% of the electron density at the bond critical point. Moreover, the electronic density difference analysis visualizes the electron accumulating effect of the orbital interaction within the H-bond between water molecules, supporting its covalent-like character. Our work expands the understanding of H-bond with specific contributions from certain MOs.

For investigating the effects of different azacyclo-assisting ligands and O-donor bridging ligands on the structural construction, three different structural complexes, namely, {Zn(DBTA)(phen)(H2O)}n (1) (DBTA = 2, 5-Dibromo-terephthalic acid, phen = 1,10-Phenanthroline), [Zn(DBTA)(bimb)]n (2) (bimb (1,4-bis(imidazole-1-ylmethyl)benzene) and {[Zn2(bmimb)(PO4)2]·(H2O)2}n (3) (bmimb = 1,2-bis(methylimidazole-1-ylmethyl) benzene) have been constructed by different mixed-ligands and Zn atoms. Their structures have been characterized by single-crystal X-ray diffraction analysis, elemental analysis, and Infrared spectroscopy. Complex 1 exhibits a common 2D layer with 4,4-connected topology. Complex 2 features an interesting 2-fold interpenetrating net with the aid of long-chain flexible azacyclo-assisting ligands. Complex 3 shows 3D supramolecular architecture with tetranuclear water cluster filling in the pores. Their fluorescence properties were also measured.

Effect of carbon nanotube (CNT) shape on desalination efficiency was investigated by computer simulation. Three shapes of CNT including tubular, cone, and hetero-junction (a combination of two different diameter CNTs which connected by a diverged CNT) shaped were simulated at high pressure (> 50 MPa). For the first time, we placed neutral charge CNT between two inert walls to illustrate support of CNT that is an inert polymer. Cone shaped CNT conducted water ~ 4 times faster than (6,6) CNT and rejected the ions similar to (6,6) CNT. Actually, cone-shaped CNT possesses the shorter residence time and higher number of water in the tube. This is because of the higher capacity and lower energy barrier against water to pass through it. However, hetero-junction CNT showed a slower water conductance because of the formation of water cluster at the large end of CNT that implies a high-energy barrier against water. In addition, H-bond number is also responsible for energy barrier. H-bond number in bulk of water is 4 and should be decreased to 2 to penetrate in the tubular and hetero-junction shaped CNT. Nevertheless, in a cone shaped CNT H-bond number falls down to 3 only at the entrance of the tube.

Molecular dynamics (MD) is applied to research the wettability behaviors of different scale of water clusters absorbed on organic-polluted fused quartz (FQ) surface and different surface structures. The wettability of water clusters is studied under the effect of organic pollutant. With the combined influence of pillar height and interval, the stair-step Wenzel-Cassie transition critical line is obtained by analyzing stable state of water clusters on different surface structures. The results also show that when interval of pillars and the height of pillars keep constant respectively, the changing rules are exactly the opposite and these are termed as the “waterfall” rules. The substrate models of water clusters at Cassie-Baxter state which are at the vicinity of critical line are chosen to analyze the relationship of HI (refers to the pillar height/interval) ratio and scale of water cluster. The study has found that there is a critical changing threshold in the wettability changing process. When the HI ratio keeps constant, the wettability decreases first and then increase as the size of cluster increases; on the contrary, when the size of cluster keeps constant, the wettability decreases and then increase with the decrease of HI ratio, but when the size of water cluster is close to the threshold the HI ratio has little effect on the wettability.

The structures of the ionized water cluster (H2O)7+ are investigated through the particle swarm optimization method combined with ab initio method. Some new lower energy structures are found after geometric optimization at the MP2/aug-cc-pVDZ level when compared with previous report. We studied the effect of the zero point vibrational energies on the relative energy order of these isomers, the relationship between their schemes and their relative energies, and the composition of their foremost molecular orbitals. The relative free energies of (H2O)7+ isomers below 350 K, the infrared spectra of five lowest energy isomers, and their electronic characteristics were discussed in detail, respectively. Based on topological analysis and reduced density gradient analysis, we find that the interaction between H3O+ core and water molecules is stronger than the interaction between OH radical and water molecules by comparing the structural and the bonding strengths within these cationic water clusters.

Degradation is the key factor to determine the efficiency and stability of the silicon solar cells, which highly affects their cost and practical performance. Humidity has been well recognized to accelerate the degradation process of the silicon solar cells, but the microscopic mechanism of light-induced degradation in hydrogenated silicon devices at water vapor environment is still elusive. In this paper, combining time-dependent density functional theory with ab initio molecular dynamics (AIMD), we show the water cluster adsorption slightly more elongates the Si-Si bond under illumination compared to the vacuum, which induces electron localization to further greatly facilitate the oxygen molecule absorption and dissociation. This external degradation process is different from the intrinsic degradation mechanisms in hydrogenated silicon devices under light irradiation caused by formation of metastable hydrogen complexes. The transition-state calculations of degradation pathway show the oxidation reaction energy barrier of Si cluster in water vapor environment is lower than that in vacuum, which confirms AIMD observations. Our results not only shed new insight for understanding the microscopic mechanism of light-induced degradation under water vapor, but would also be beneficial for controlling the light-induced silicon degradation of solar cell in real application.

The hydroxyl radical reactions are of extremely significant in combustion chemistry. Direct dynamics simulations are used to study the atomic-level mechanisms of OH(H2O)n + CH4 (n = 0,1,2) reactions starting from the [(H2O)nOH---H---CH3] central barrier, which is the important step in the combustion of CH4 in an O2/H2O environment. The simulation results show the propensity for the solvated products due to the thermodynamic preference and the stability of water cluster in products. Although there is a deep minimum (H2O)nH2O---CH3 complex in the product exit channel on potential energy surface, the majority of the trajectories avoided this well and instead directly dissociated to products, showing a non-IRC behavior. Significantly, with the addition of two water molecules, the reaction probability, and thus the reaction rate constant increases compared to the one hydrated reaction. This study provides an understanding of CH4 combustion in O2/H2O atmosphere.

Chemical denaturation of protein represents a secondary/tertiary structural change, which has been measured by absorption and CD spectra in the liquid phase. In this study, we used gas-phase photoelectron detachment yield (PDY) spectra for elucidating isolated structures of bovine serum albumin (BSA) ions and their conjugated ions with cetyltrimethylammonium bromide (CTAB), whose conjugation causes a significant chemical denaturation in the protein structure. The obtained PDY spectrum of BSA ions shows a broad peak near 208 nm, which significantly disappears in that of CTAB-denatured BSA. This result indicates the CTAB-denatured BSA has a stable unfolding structure in the isolated water cluster.

The paper is focused on a deep analysis of transport properties of natural hemp fibers (HF) functionalized through a mechano-chemical treatment assisted by high energy ball milling. The effect of milling time on fibers’ morphology was investigated by means of the scanning electron microscopy and FTIR spectroscopy. The results show that the mechanical effect induced a reduction of the mean diameter of hemp fibers and, simultaneously, the achievement of a close packing of cellulose chains. The barrier properties appeared to be dependent either on the packing of cellulose or the water cluster formation. Fick’s law solution in cylindrical coordinates was used to simulate experimental sorption kinetics and to extrapolate the diffusion parameters. The change of diffusion with equilibrium moisture content was described through an empirical relationship. Sorption isotherms were explained on the basis of Park model which accounts for a dual mode sorption at low activities as well as the water clustering phenomenon occurring at high activities. The mean cluster size (MCS) of water molecules was estimated through the application of Zimm Lundberg theory. Finally, the spreading pressure calculation allowed to estimate the driving force of diffusion inside the systems.

Water sorption provides a great approach to understand water-shale interaction. In this research, water sorption isotherms of fourteen Wufeng-Longmaxi shale samples collected from the eastern Sichuan Basin of China were generated and then interpreted by classical sorption models. The sorption behavior of water and its relationship with pore structure, organic/inorganic composition, and temperature (278–333 K) were explored using organic geochemistry, mineralogy, and gas physical sorption. Brunauer-Emmett-Teller theory functions well for these isotherms but generates ambiguous model parameters, suggesting that multilayer sorption concept is not suitable for water sorption. Dent model distinguishes between primary and secondary sorption, and the resulting specific surface area (ADent(H2O)) is not comparable to the nitrogen-determined specific surface area (ABET(N2)). However, ADent(H2O)/ABET(N2) linearly decreases with increasing ABET(N2), and water saturation is negatively correlated with total pore volume. These observations collectively support the surface-chemistry-controlled clustering mechanism for water sorption. Clay minerals dominate water sorption at low relative pressure because they provide more hydrophilic sorption sites for water cluster formation and growth. Nevertheless, organic matter becomes increasingly important with increasing relative pressure, primarily because a specific-sized organic pore has higher filling pressure than the same-sized clay pore resulting in more pronounced condensation in organic pores at high relative pressure. The water desorption branch shifts to higher relative pressure with increasing temperature and thus, the hysteresis loop shrinks, indicating a mechanism of capillary evaporation similar to wetting fluid nitrogen. The water adsorption branch is insensitive to temperature change, reflecting a temperature-independent clustering mechanism between 278 K and 333 K. The enthalpy of adsorption of collected shale samples is smaller than that of lower-maturity shales but close to that of condensation of bulk water. Based on this finding, we argue that higher-maturity shales have weaker interaction with water, which gives rise to lower temperature sensitivity of water sorption. Therefore, in the future, detailed investigations should revolve around water sorption behavior and its response to temperature in shales with different thermal maturities.

A new dinuclear vanadium(V) complex, [(µ-O)2V2O2L2]·4H2O, [where HL = 2-((2-(ethylamino)ethylimino)methyl)-5-(diethylamino)phenol] has been synthesized and subsequently characterized by elemental and spectral studies. Structure of the complex has been confirmed by single crystal X-ray diffraction study. The four lattice water molecules in the crystal structure are assembled to form a tetrameric water cluster (W4), stabilized via hydrogen bonding interactions. These clusters further interconnect with the complex moiety to generate a 1D supramolecular chain of the complex in the solid state. The interaction energies and the possible cooperativity effects have been studied using DFT calculations and the MEP surface analysis.

The knowledge of the binding energy of molecules on astrophysically relevant ices can help to obtain an estimate of the desorption rate, i.e. the molecules residence time on the surface. This represents an important parameter for astrochemical models, crucial to determine the chemical fate of complex organic molecules formed on dust grains and observed in the densest regions of the interstellar medium. In this work, we propose a new robust procedure to study the interaction of atoms and molecules with interstellar ices, based on \textit{ab initio} molecular dynamics and density functional theory, validated by high-level \textit{ab initio} methods at a CCSD(T)/CBS level. We have applied this procedure to hydrogen fluoride (HF), a promising tracer of the molecular content of galaxies. In total we found 13 unique equilibrium structures of HF binding to small water clusters of up to 4 molecules, with binding energies ranging from 1208 to 7162 K. We computed a 22-molecules model of amorphous solid water (ASW) surface using \textit{ab initio} molecular dynamics simulations and carried out a systematic analysis of the binding sites of HF, in terms of binding modes and binding energies. Considering 10 different water clusters, we found a binding energy distribution with an average value of $5313\pm74$ K, and a dispersion of $921\pm115$ K. Finally, the effect of the electrostatic field of the 22 water molecules on the binding energies was investigated incrementally by symmetry adapted perturbation theory, in order to gauge the effect of the water environment. The results indicate that the extent of the electrostatic interaction of HF with ASW depends strongly on the properties of the binding site. We expect that this work will provide a solid foundation for a systematic development of a binding energy distribution database of molecules on interstellar surfaces., Comment: 12 pages, 9 figures, 6 tables, accepted to Mol. Astrophys

The methods most frequently used in the aldehyde detection were based on derivatization reactions with disadvantage of time-consuming. In this study, a method was developed to rapidly detect acrolein and crotonaldehyde by a water-assisted atmospheric pressure chemical ionization tandem mass spectrometry (APCI-MS/MS). With the addition of water, solvent ion signal was suppressed due to the formation of protonated water cluster, which benefited for the analysis of spectra. Two orders of linear range were obtained in the concentration from 0.01 to 1 μg/L with the addition of water. Finally, this method was successfully applied to detect acrolein and crotonaldehyde in tobacco smoke with analytical period less than four minutes. The experimental results indicate that the developed method has the potential application in environmental monitoring of acrolein and crotonaldehyde.

Enceladus has a dynamic plume that is emitting gas, including water vapor, and dust. The gas is ionized by solar EUV radiation, charge exchange, and electron impact and extends throughout the inner magnetosphere of Saturn. The charge exchange collisions alter the plasma composition. Ice grains (dust) escape from the vicinity of Enceladus and form the E ring, including a portion that is negatively charged by the local plasma. The inner magnetosphere within 10 R S (Saturn radii) contains a complex mixture of plasma, neutral gas, and dust that links back to Enceladus. In this paper we investigate the energy distributions, ion species and densities of water group ions in the plume of Enceladus using test particle and Monte Carlo methods that include collisional processes such as charge exchange and ion-neutral chemical reactions. Ion observations from the Cassini Ion and Neutral Mass Spectrometer (INMS) for E07 are presented for the first time. We use the modeling results to interpret observations made by the Cassini Plasma Spectrometer (CAPS) and the INMS. The low energy ions, as observed by CAPS, appear to be affected by a vertical electric field ( E Z =−10 µV/m) in the plume. The E Z field may be associated with the charged dust and/or the pressure gradient of plasma. The model results, along with the results of earlier models, show that H 3 O + ions created by chemistry are predominant in the plume, which agrees with INMS and CAPS data, but the INMS count rate in the plume for the model is several times greater than the data, which we do not fully understand. This composition and the total ion count found in the plume agree with INMS and CAPS data. On the other hand, the Cassini Langmuir Probe measured a maximum plume ion density more than 30,000 cm −3 , which is far larger than the maximum ion density from our model, 900 cm −3 . The model results also demonstrate that most of the ions in the plume are from the external magnetospheric flow and are not generated by local ionization. The origin of the ions in the plume was investigated using two different velocity models. Most ions were created by the interaction with background magnetospheric plasma and by photoionization. INMS and CAPS also detected water cluster ions. We will interpret these observations as a result of ion collisions with neutral water clusters, (H 2 O) n , originating in the tiger stripe vents as suggested by Tokar et al. (2009). We also estimated the process of generating cluster ions based on the INMS observations. We suggest that the most likely source is reaction of H 3 O + with neutral water clusters or dimers such as (H 2 O) 2 formed in the plume vents.

The isomerization processes of 3-hydroxy-2(1H)-pyridinethione with water or water cluster in the aqueous solution were explored at B3LYP-D3/6-311++G(3df,3pd) level of theory. The results suggest that the formation of P2 dominates over that of P1 in the isolated reaction, whereas the barrier difference of transition states between them will decrease gradually with increasing of water number from one to three and the production of P1 will be competitive to that of P2 with water dimer or water trimer. Furthermore, the location of water or water cluster between N and S is more suitable for the formation of active component P1.

The state of water in hydrated powders of KCl and KCl/AM1/H2O composite system before and after addition of hydrophobic organic substances was investigated using 1H NMR spectroscopy with layer-by-layer freezing-out of bulk and interfacial waters. It is found that water retention in the nanocomposite consisting of hydrated powder of KCl and hydrophobic silica AM1-300 (model of stimulating protective composition “ECOSTIM”) is significantly higher than in the powders of mineral fertilizers. When KCl/AM1/H2O composite system is in contact with a hydrophobic substance, imitating the hydrophobic sites of the seed surface, the additional growth of interfacial water binding is observed. This takes place probably due to the gain of free energy as a result of water cluster defragmentation in nanoscale systems containing hydrophobic and hydrophilic constituents. The state of water in hydrated powders of KCl and KCl/AM1/H2O composite system was studied. It is found that water retention in the nanocomposite is significantly higher than in the powders of KCl. When a composite system is in contact with a CDCl3, the growth of water binding is observed. The growth of free energy as a result of water cluster defragmentation in nanoscale systems.

A nitrate-water cluster [(NO 3 ) 2 (H 2 O) 8 ] 2− confined in the hydrophobic cavity of a cucurbit[8]uril complex with Sr 2+ has been observed. It represents the first example of inorganic anion-water cluster formation inside the cucurbit[ n ]uril hydrophobic cavity.