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We have implemented a cluster-continuum method using density functional theory to model water clusters and various charged species derived from water. The two aims of this study are to determine the minimal basis required for proper modeling of water autoionization and to determine the minimum number of explicit water molecules required to properly model the energetics of solvation. The thermodynamics of water autoionization converge following a modified power law to deliver chemically accurate values of the Gibbs energy change for autoionization with tractably small clusters. Convergence is slower and not exponential as assumed in previous work. We identify the n = 21 set of clusters as the first effectively bulk water like clusters that can capture the energetic influence of both the first and second solvation shells. In this cluster, a water molecule is encapsulated in the center of a closed shell of other water molecules that hydrogen bond to form five-membered rings. The total energy change for clusters with n ≥ 21 calculated using both the RPBE-D3 and ωB97X-D exchange–correlation functionals with the 6-311+G** basis set is shown to deliver good approximations to the free energy change at 298 K. This is true even though neither functional models the individual enthalpy or entropy contributions particularly well. [ABSTRACT FROM AUTHOR]

We present an efficient, open-source formulation for coupled-cluster theory through perturbative triples with domain-based local pair natural orbitals [DLPNO-CCSD(T)]. Similar to the implementation of the DLPNO-CCSD(T) method found in the ORCA package, the most expensive integral generation and contraction steps associated with the CCSD(T) method are linear-scaling. In this work, we show that the t1-transformed Hamiltonian allows for a less complex algorithm when evaluating the local CCSD(T) energy without compromising efficiency or accuracy. Our algorithm yields sub-kJ mol−1 deviations for relative energies when compared with canonical CCSD(T), with typical errors being on the order of 0.1 kcal mol−1, using our TightPNO parameters. We extensively tested and optimized our algorithm and parameters for non-covalent interactions, which have been the most difficult interaction to model for orbital (PNO)-based methods historically. To highlight the capabilities of our code, we tested it on large water clusters, as well as insulin (787 atoms). [ABSTRACT FROM AUTHOR]

We investigate the performance of time-dependent density functional theory (TDDFT) for reproducing high-level reference x-ray absorption spectra of liquid water and water clusters. For this, we apply the integrated absolute difference (IAD) metric, previously used for x-ray emission spectra of liquid water [T. Fransson and L. G. M. Pettersson, J. Chem. Theory Comput. 19, 7333–7342 (2023)], in order to investigate which exchange–correlation (xc) functionals yield TDDFT spectra in best agreement to reference, as well as to investigate the suitability of IAD for x-ray absorption spectroscopy spectrum calculations. Considering highly asymmetric and symmetric six-molecule clusters, it is seen that long-range corrected xc-functionals are required to yield good agreement with the reference coupled cluster (CC) and algebraic-diagrammatic construction spectra, with 100% asymptotic Hartree–Fock exchange resulting in the lowest IADs. The xc-functionals with best agreement to reference have been adopted for larger water clusters, yielding results in line with recently published CC theory, but which still show some discrepancies in the relative intensity of the features compared to experiment. [ABSTRACT FROM AUTHOR]

As the most important solvent, water has been at the center of interest since the advent of computer simulations. While early molecular dynamics and Monte Carlo simulations had to make use of simple model potentials to describe the atomic interactions, accurate ab initio molecular dynamics simulations relying on the first-principles calculation of the energies and forces have opened the way to predictive simulations of aqueous systems. Still, these simulations are very demanding, which prevents the study of complex systems and their properties. Modern machine learning potentials (MLPs) have now reached a mature state, allowing us to overcome these limitations by combining the high accuracy of electronic structure calculations with the efficiency of empirical force fields. In this Perspective, we give a concise overview about the progress made in the simulation of water and aqueous systems employing MLPs, starting from early work on free molecules and clusters via bulk liquid water to electrolyte solutions and solid–liquid interfaces. [ABSTRACT FROM AUTHOR]

In the interstellar medium, diols and other prebiotic molecules adsorb onto icy mantles surrounding dust grains. Water in the ice may affect the reactivity and photoionization of these diols. Ethylene glycol (EG), 1,2-propylene glycol, and 1,3-propylene glycol clusters with water clusters were used as a proxy to study these interactions. The diol–water clusters were generated in a continuous supersonic molecular beam, photoionized by synchrotron-based vacuum ultraviolet light from the Advanced Light Source, and subsequently detected by reflectron time-of-flight mass spectrometry. The appearance energies for the detected clusters were determined from the mass spectra, collected at increasing photon energy. Clusters of both diol fragments and unfragmented diols with water were detected. The lowest energy geometry optimized conformers for the observed EG–water clusters and EG fragment–water clusters have been visualized using density functional theory (DFT), providing insight into hydrogen bonding networks and how these affect fragmentation and appearance energy. As the number of water molecules clustered around EG fragments (m/z 31 and 32) increased, the appearance energy for the cluster decreased, indicating a stabilization by water. This trend was supported by DFT calculations. Fragment clusters from 1,2-propylene glycol exhibited a similar trend, but with a smaller energy decrease, and no trend was observed from 1,3-propylene glycol. We discuss and suggest that the reactivity and photoionization of diols in the presence of water depend on the size of the diol, the location of the hydroxyl group, and the number of waters clustered around the diol. [ABSTRACT FROM AUTHOR]

In this study, we use molecular dynamics simulations of liquid water to investigate how shear thinning affects the viscosity of liquid water by structural changes of the hydrogen bond network. The effect of shear on viscosity can be divided into two parts: shear-induced destruction of the hydrogen bond network and the influence of the water structure on shear viscosity. First, strong shear destroys tetrahedral structures and thus reduces the connectivity of the hydrogen bond network. It is mainly because shear deformation, characterized by compression and expansion axes, respectively, triggers the destruction and formation of hydrogen bonds, resulting in anisotropic effects on water structures. At the same time, shear destroys large clusters and enhances the formation of small ones, resulting in a decrease in average cluster sizes. Second, the change of viscosity obeys a power law relationship with the change of hydrogen bond structures, highlighting a one-to-one correspondence between structure and property. Meanwhile, in order to explain why the structure affects viscosity, we define hydrogen-bond viscosity and find that the cooperative motion of the water structures can promote momentum transfer in the form of aggregations. Hydrogen-bond viscosity accounts for 5%–50% of the total viscosity. Our results elucidate that water structures are the important structural units to explain the change of water properties. [ABSTRACT FROM AUTHOR]

Helium nanodroplets ("HNDs") are widely used for forming tailor-made clusters and molecular complexes in a cold, transparent, and weakly interacting matrix. The characterization of embedded species by mass spectrometry is often complicated by the fragmentation and trapping of ions in the HNDs. Here, we systematically study fragment ion mass spectra of HND-aggregated water and oxygen clusters following their ionization by charge transfer ionization ("CTI") and Penning ionization ("PEI"). While the efficiency of PEI of embedded clusters is lower than for CTI by about factor 10, both the mean sizes of detected water clusters and the relative yields of unprotonated cluster ions are significantly larger, making PEI a "soft ionization" scheme. However, the tendency of ions to remain bound to HNDs leads to a reduced detection efficiency for large HNDs containing > 1 0 4 helium atoms. These results are instrumental in determining optimal conditions for mass spectrometry and photoionization spectroscopy of molecular complexes and clusters aggregated in HNDs. [ABSTRACT FROM AUTHOR]

This study examines the structures, energies, and IR vibrational spectra of the sulfur dioxide–water SO2(H2O) complexes by employing coupled cluster theory CCSD(T) with Dunning style correlation consistent type basis sets aug-cc-pV(n+d)Z (n = D, T, Q, 5). Complete basis set (CBS) extrapolations have been carried out to predict binding energies for two isomers of the SO2(H2O) complex: a stacked global minimum (1A) structure and a hydrogen-bonded local minimum (1B) structure. The CCSD(T)/CBS extrapolation predicts an intermolecular S–O distance rS⋯O = 2.827 Å for the stacked isomer, which is in excellent agreement with an experimental measurement of 2.824 Å [K. Matsumura et al., J. Chem. Phys., 91, 5887 (1989)]. The CCSD(T)/CBS binding energy for the stacked dimer 1A and hydrogen-bonded form 1B is De = −4.37 kcal/mol and De = −2.40 kcal/mol, respectively. This study also employs anharmonic VPT2 MP2/aug-cc-pV(n+d)Z level corrections to CCSD(T)/aug-cc-pV(n+d)Z vibrational frequencies in both forms of SO2(H2O). The anharmonic CCSD(T)/aug-cc-pV(Q+d)Z OH stretching frequencies in the stacked structure 1A are 3743 cm−1 (ν3) and 3647 cm−1 (ν1), and these align well with the recorded IR spectroscopic values of 3745 and 3643 cm−1, respectively [C. Wang et al., J. Phys. Chem. Lett., 13, 5654 (2022)]. If we combine CCSD(T)/aug-cc-pV(n+d)Z De values with VPT2 vibrational frequencies, we obtain a new CCSD(T)/aug-cc-pV(Q+d)Z anharmonic dissociation energy D0 = −3.48 kcal/mol for 1A and D0 = −1.74 kcal/mol for 1B. In summary, the results presented here demonstrate that the application of CCSD(T) calculations with aug-cc-pV(n+d)Z basis sets and CBS extrapolations is critical in probing the structure and IR spectroscopic properties of the sulfur dioxide–water complex. [ABSTRACT FROM AUTHOR]

We launched a combined negative ion photoelectron spectroscopy and multiscale theoretical investigation on the geometric and electronic structures of a series of acetonitrile-solvated dodecaborate clusters, i.e., B12H122−·nCH3CN (n = 1–4). The electron binding energies of B12H122−·nCH3CN are observed to increase with cluster size, suggesting their enhanced electronic stability. B3LYP-D3(BJ)/ma-def2-TZVP geometry optimizations indicate each acetonitrile molecule binds to B12H122− via a threefold dihydrogen bond (DHB) B3–H3 ⁝⁝⁝ H3C–CN unit, in which three adjacent nucleophilic H atoms in B12H122− interact with the three methyl hydrogens of acetonitrile. The structural evolution from n = 1 to 4 can be rationalized by the surface charge redistributions through the restrained electrostatic potential analysis. Notably, a super-tetrahedral cluster of B12H122− solvated by four acetonitrile molecules with 12 DHBs is observed. The post-Hartree–Fock domain-based local pair natural orbital- coupled cluster singles, doubles, and perturbative triples [DLPNO-CCSD(T)] calculated vertical detachment energies agree well with the experimental measurements, confirming the identified isomers as the most stable ones. Furthermore, the nature and strength of the intermolecular interactions between B12H122− and CH3CN are revealed by the quantum theory of atoms-in-molecules and the energy decomposition analysis. Ab initio molecular dynamics simulations are conducted at various temperatures to reveal the great kinetic and thermodynamic stabilities of the selected B12H122−·CH3CN cluster. The binding motif in B12H122−·CH3CN is largely retained for the whole halogenated series B12X122−·CH3CN (X = F–I). This study provides a molecular-level understanding of structural evolution for acetonitrile-solvated dodecaborate clusters and a fresh view by examining acetonitrile as a real hydrogen bond (HB) donor to form strong HB interactions. [ABSTRACT FROM AUTHOR]

We rely on a total of 23 (cluster size, 8 structural, and 14 connectivity) descriptors to investigate structural patterns and connectivity motifs associated with water cluster aggregation. In addition to the cluster size n (number of molecules), the 8 structural descriptors can be further categorized into (i) one-body (intramolecular): covalent OH bond length (rOH) and HOH bond angle (θHOH), (ii) two-body: OO distance (rOO), OHO angle (θOHO), and HOOX dihedral angle (ϕHOOX), where X lies on the bisector of the HOH angle, (iii) three-body: OOO angle (θOOO), and (iv) many-body: modified tetrahedral order parameter (q) to account for two-, three-, four-, five-coordinated molecules (qm, m = 2, 3, 4, 5) and radius of gyration (Rg). The 14 connectivity descriptors are all many-body in nature and consist of the AD, AAD, ADD, AADD, AAAD, AAADD adjacencies [number of hydrogen bonds accepted (A) and donated (D) by each water molecule], Wiener index, Average Shortest Path Length, hydrogen bond saturation (% HB), and number of non-short-circuited three-membered cycles, four-membered cycles, five-membered cycles, six-membered cycles, and seven-membered cycles. We mined a previously reported database of 4 948 959 water cluster minima for (H2O)n, n = 3–25 to analyze the evolution and correlation of these descriptors for the clusters within 5 kcal/mol of the putative minima. It was found that rOH and % HB correlated strongly with cluster size n, which was identified as the strongest predictor of energetic stability. Marked changes in the adjacencies and cycle count were observed, lending insight into changes in the hydrogen bond network upon aggregation. A Principal Component Analysis (PCA) was employed to identify descriptor dependencies and group clusters into specific structural patterns across different cluster sizes. The results of this study inform our understanding of how water clusters evolve in size and what appropriate descriptors of their structural and connectivity patterns are with respect to system size, stability, and similarity. The approach described in this study is general and can be easily extended to other hydrogen-bonded systems. [ABSTRACT FROM AUTHOR]

The electronic properties of SO2 at the surface of a water cluster were investigated by employing a combination of Born–Oppenheimer molecular dynamics and electron propagator theory (EPT). In our work, we utilized a revised version of the Perdew–Burke–Ernzerhof (PBE) exchange-correlation functional, which incorporates empirical corrections for dispersion interactions in line with a recent study of the air–water interface conducted by Ohto et al. [J. Phys. Chem. Lett. 10(17), 4914–4919 (2019)]. Polarization effects induce a significant broadening of the electron binding energy distribution, as predicted by EPT. This broadening can result in a substantial increase in electron affinity, impacting the chemical reactivity of SO2 at the air–water interface, a topic of significant and recent research interest. We discuss the relationship between electron binding energies (EBEs) and the specific connections of SO2 to water. The results indicate that configurations involving an OS⋯H bond tend to yield higher electron affinities compared to complex formation through S⋯OW bonds. Surprisingly, SO2 molecules not bound to water molecules according to a specific criterion may also exhibit higher electron affinities. This feature can be explained by the role played by the polarization field from water molecules. Our best estimate for the HOMO–LUMO (H–L) gap of SO2 at the surface of a water cluster is 11.6 eV. Very similar H–L gaps are predicted for isolated and micro-solvated SO2. Fukui functions for the gas phase, and the micro-solvated SO2–H2O complex supports the view that the LUMO is predominantly localized on the SO2 moiety. [ABSTRACT FROM AUTHOR]

We report threshold collision induced dissociation experiments on protonated water clusters thermalized at low temperature for sizes n = 19–23. Fragmentation cross sections are recorded as a function of the collision energy and analyzed with a statistical model. This model allows us to account for dissociation cascades and provides values for the dissociation energies of each cluster. These values, averaging around 0.47 eV, are in good agreement with theoretical predictions at various levels of theory. Furthermore, the dissociation energies show a trend for the n = 21 magic and n = 22 anti-magic numbers relative to their neighbours, which is also in agreement with theory. These results provide further evidence to resolve the disagreement between previously published experimental values. A careful quantitative treatment of cascade dissociation in this model introduces interdependence between the dissociation energies of neighboring sizes, which reduces the number of free fitting parameters and improves both reliability and uncertainties on absolute dissociation energies deduced from experiments. [ABSTRACT FROM AUTHOR]

This work reports the development of an algorithm for rapid and efficient evaluation of energy gradients for large molecular clusters employing correlated methods viz. second-order Møller–Plesset perturbation theory (MP2) theory and couple cluster singles and doubles (CCSD). The procedure segregates the estimation of Hartree–Fock (HF) and correlation components. The HF energy and gradients are obtained by performing a full calculation. The correlation energy is approximated as the corresponding two-body interaction energy. Correlation gradients for each monomer are approximated from the respective monomer-centric fragments comprising its immediate neighbours. The programmed algorithm is explored for the geometry optimization of large molecular clusters using the BERNY optimizer as implemented in the Gaussian suite of software. The accuracy and efficacy of the method are critically probed for a variety of large molecular clusters containing up to 3000 basis functions, in particular large water clusters. The CCSD level geometry optimization of molecular clusters containing ∼800 basis functions employing a modest hardware is also reported. [ABSTRACT FROM AUTHOR]

We investigate small tantalum clusters Tan+, n = 2–4, for their capability to cleave N2 adsorption spontaneously. We utilize infrared photon dissociation (IR-PD) spectroscopy of isolated and size selected clusters under cryogenic conditions within a buffer gas filled ion trap, and we augment our experiments by quantum chemical simulations (at DFT level). All Tan+ clusters, n = 2–4, seem to cleave N2 efficiently. We confirm and extend a previous study under ambient conditions on Ta2+ cluster [Geng et al., Proc. Natl. Acad. Sci. U. S. A. 115, 11680–11687 (2018)]. Our cryo studies and the concomitant DFT simulations of the tantalum trimer Ta3+ suggest cleavage of the first and activation of the second and third N2 molecule across surmountable barriers and along much-involved multidimensional reaction paths. We unravel the underlying reaction processes and the intermediates involved. The study of the N2 adsorbate complexes of Ta4+ presented here extends our earlier study and previously published spectra from (4,m), m = 1–5 [Fries et al., Phys. Chem. Chem. Phys. 23(19), 11345–11354 (2021)], up to m = 12. We confirm the priory published double activation and nitride formation, succeeded by single side-on N2 coordination. Significant red shifts of IR-PD bands from these side-on coordinated μ2-κN:κN,N N2 ligands correlate with the degree of tilting towards the second coordinating Ta center. All subsequently attaching N2 adsorbates onto Ta4+ coordinate in an end-on fashion, and we find clear evidence for co-existence of end-on coordination isomers. The study of stepwise N2 adsorption revealed adsorption limits m(max) of [Tan(N2)m]+ which increase with n, and kinetic fits revealed significant N2 desorption rates upon higher N2 loads. The enhanced absolute rate constants of the very first adsorbate steps kabs(n,0) of the small Ta3+ and Ta4+ clusters independently suggest dissociative N2 adsorption and likely N2 cleavage into Ta nitrides. [ABSTRACT FROM AUTHOR]

Using adiabatic molecular dynamics coupled with the fluid dynamics equations, we model nucleation in an expanding beam of water vapor and argon on a microsecond scale. The size distribution of clusters, their temperature, and pickup cross sections in dependence on velocity are investigated and compared to the geometric cross sections and the experiment. The clusters are warmer than the expanding gas because of the time scale of relaxation processes. We also suggest that their translational and rotational kinetic energies are modified due to evaporative cooling. The pickup cross sections determined for the final clusters using molecules of the same kind increase with decreasing velocity, still obeying the (a + b N 1 / 3 ) 2 law. [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. [ABSTRACT FROM AUTHOR]

Catalysts based on Pt single atom (SA) on metal oxides have shown tremendous potentials for alkaline hydrogen evolution reaction (HER), but they are severely limited by insufficient electron interactions of Pt sites and supports. Herein, a new methodology is developed to precisely locate Pt SAs and Pt clusters into NiCo layered double oxide (LDO) nanosheets, achieved using a dual‐ion etching process with subsequent phase transformation method. Uniquely, the Pt SAs are inserted into LDO layers to form Pt─Co bonds by occupying partial Ni positions, significantly strengthening electron interactions with NiCo LDO and promoting activity of HER. Results from density functional theory calculations indicate that the H* species are preferentially absorbed onto O sites on top of these Pt SAs, which are coupled with their adjacent Pt clusters to accelerate water dissociation in the Volmer step. As‐obtained Pt─NiCo LDO exhibits a low overpotential of 92 mV at 10 mA cm−2 and a Tafel slope of 73 mV dec−1, an excellent stability over 105 hours at 60 mA cm−2, and its mass activity is 6 times higher than commercial 20% Pt/C. This study highlights essential functions of coupling interactions between Pt SAs/clusters and LDOs to boost HER for hydrogen energy production. [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. [ABSTRACT FROM AUTHOR]

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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]

Aliphatic diols such as ethylene and propylene glycol are the key products in the chemical industry for manufacturing polymers. The synthesis of these molecules usually implies sequential processes, including epoxidation of olefins using hydrogen peroxide or oxygen with subsequent hydrolysis to glycols. Direct hydroxylation of olefins by cheap and green oxidants is an economically attractive and environmentally friendly route for the synthesis of diols. Here, we report a photocatalytic reaction for the dihydroxylation of ethylene and propylene to their glycols at room temperature using water as the oxidant. The photocatalyst contains Pd clusters stabilized by sub-nanometric polyoxometalate with TiO2 as the host material. Under light irradiation, it results in production rates of ethylene glycol and propylene glycols of 146.8 mmol·gPd−1·h−1 and 28.6 mmol·gPd−1·h−1 with liquid-phase selectivities of 63.3 % and 80.0 %, respectively. Meanwhile, green hydrogen derived from water is produced as another valuable product. Combined spectroscopy investigation suggests that the reaction proceeds via π-bonded adsorption of olefins over Pd clusters with hydroxylation by hydroxyl radicals formed by photocatalytic dissociation of water. A direct, selective photocatalytic method for synthesizing glycols from olefins at room temperature uses water as the oxidizing agent and H2 as byproduct. The hydroxylation proceeds by hydroxyl radicals formed by photocatalytic dissociation of water. [ABSTRACT FROM AUTHOR]

Most nonconventional luminogens enjoy good water solubility and biocompatibility, showing unique application prospects in fields like biological imaging. Although clustering‐triggered emission (CTE) mechanisms have been proposed to explain such emissions, it has not been thoroughly elucidated, which limits their development and application. Herein, the photoluminescence properties of polyacrylamide prepared by reversible addition‐fragmentation chain transfer (RAFT) polymerization aqueous solution are utilized to further investigate the effects of changes in concentration, in order to elucidate the emission mechanism through transmission electron microscopy (TEM), small angle X‐ray scattering (SAXS) and theoretical calculation. The results showed that the size distribution, morphology, and distance between the polymer clusters formed in the water solution are successfully correlated with the cluster emission centers. The emission mechanism of nonconventional luminogens solutions is more clearly and intuitively elucidated, which has a promoting effect on the emission and application of this field. It provides a strategy a strategy to clarify the CTE mechanism of nonconventional luminogens solution more clearly. [ABSTRACT FROM AUTHOR]

The aim of the present work is to draw the attention to an unusual object of study, namely, heat transfer in short-term superheated hydrocarbons with micro-additives of moisture. We discuss the reasons for effect of the increase in the heat transfer coefficient to samples of saturated hydrocarbons having a moisture content of 15 mg⋅kg−1 to 35 mg⋅kg−1, which is unexpectedly strong (up to 10 %) with respect to pure hydrocarbons. This effect was discovered in experiments on pulse heating of a wire probe in a substance with characteristic times of 1 ms to 10 ms. We have developed a model based on the assumption of the role of dissolved water clusters in initiating fluid motion in the course of short-term superheating of the base fluid with respect to the liquid–vapor equilibrium temperature. Depending on the degree of superheating and pressure, the values predicted by the model for the increment of the heat transfer coefficient due to micro-additives of moisture are qualitatively consistent with the data obtained from the pulse experiments. The results of this study clarify the specific features of the superheated states of composite fluids, as well as contribute to developing methods for controlling the heat flux by micro-additives of a partially soluble component to the heat carrier. [ABSTRACT FROM AUTHOR]

In order to accurately estimate the distribution of Trachinotus ovatus in marine cages, a novel method was developed using omnidirectional scanning sonar and deep-learning techniques. This method involved differentiating water layers and clustering data layer by layer to achieve precise location estimation. The approach comprised two main components: fish identification and fish clustering. Firstly, omnidirectional scanning sonar was employed to perform spiral detection within marine cages, capturing fish image data. These images were then labeled to construct a training dataset for an enhanced CS-YOLOv8s model. After training, the CS-YOLOv8s model was used to identify and locate fish within the images. Secondly, the cages were divided into water layers with depth intervals of 40 cm. The identification coordinate data for each water layer were clustered using the DBSCAN method to generate location coordinates for the fish in each layer. Finally, the coordinate data from all water layers were consolidated to determine the overall distribution of fish within the cage. This method was shown, through multiple experimental results, to effectively estimate the distribution of Trachinotus ovatus in marine cages, closely matching the distributions detected manually. [ABSTRACT FROM AUTHOR]

Freezing storage is the most common method of food preservation and the formation of ice crystals during freezing has an important impact on food quality. The water molecular structure, mechanism of ice crystal formation, and ice crystal structure are elaborated in the present review. Meanwhile the methods of ice crystal characterization are outlined. It is concluded that the distribution of the water molecule cluster structure during the crystallization process directly affects the formed ice crystals' structure, but the intrinsic relationship needs to be further investigated. The morphology and distribution of ice crystals can be observed by experimental methods while simulation methods provide the possibility to study the molecular structure changes in water and ice crystals. It is hoped that this review will provide more information about ice crystallization and promote the control of ice crystals in frozen foods. [ABSTRACT FROM AUTHOR]

With relevant chemical space growing larger and larger by the day, the ability to extend computational tractability over that larger space is of paramount importance in virtually all fields of science. The solution we aim to provide here for this issue is in the form of the generalized many-body expansion for building density matrices (GMBE-DM) based on the set-theoretical derivation with overlapping fragments, through which the energy can be obtained by a single Fock build. In combination with the purification scheme and the truncation at the one-body level, the DM-based GMBE(1)-DM-P approach shows both highly accurate absolute and relative energies for medium-to-large size water clusters with about an order of magnitude better than the corresponding energy-based GMBE(1) scheme. Simultaneously, GMBE(1)-DM-P is about an order of magnitude faster than the previously proposed MBE-DM scheme [F. Ballesteros and K. U. Lao, J. Chem. Theory Comput. 18, 179 (2022)] and is even faster than a supersystem calculation without significant parallelization to rescue the fragmentation method. For even more challenging systems including ion–water and ion–pair clusters, GMBE(1)-DM-P also performs about 3 and 30 times better than the energy-based GMBE(1) approach, respectively. In addition, this work provides the first overlapping fragmentation algorithm with a robust and effective binning scheme implemented internally in a popular quantum chemistry software package. Thus, GMBE(1)-DM-P opens a new door to accurately and efficiently describe noncovalent clusters using quantum mechanics. [ABSTRACT FROM AUTHOR]

Intermolecular Coulombic decay or electron transfer-mediated decay are the autoionization processes through which a molecule can relax. This relaxation is only possible if the inner valence's ionization potential (IP) exceeds the system's double ionization potential (DIP). To study the effects of charge and solvation shell, we have calculated the IP, DIP values, and lifetime of Na-2s and Mg-2s temporary bound states in various optimized structures of Na+-(H2O)n and Mg2+-(H2O)n (n = 1–5) micro-solvated clusters, where n water molecules are distributed in a way that some are directly bound to the metal ion and the rest to the water molecules. The first and second solvation shells are the names for the former and the latter water-binding positions, respectively. For a given n, the lifetime of decaying states is longer when water molecules are in the second solvation shell. We found that the Mg-2p state can decay for all n values in Mg2+-(H2O)n clusters, whereas the Na-2p state's decay is possible for n ≥ 2 in Na+-(H2O)n clusters. Our findings highlight the influence of metal ions' charge, different solvation shell structures, and the number of water molecules on the decay rate. These systems are relevant to the human body, which makes this study significant. [ABSTRACT FROM AUTHOR]

We present a novel framework for spin-adapted coupled cluster theory. The approach exploits the entanglement of an open-shell molecule with electrons in a non-interacting bath. Together, the molecule and the bath form a closed-shell system, and electron correlation can be included using the standard spin-adapted closed-shell coupled cluster formalism. A projection operator, which enforces conditions on the electrons in the bath, is used to obtain the desired state of the molecule. This entanglement coupled cluster theory is outlined, and proof-of-concept calculations for doublet states are reported. The approach is further extendable to open-shell systems with other values of the total spin. [ABSTRACT FROM AUTHOR]

Tunneling splittings observed in molecular rovibrational spectra are significant evidence for tunneling motion of hydrogen nuclei in water clusters. Accurate calculations of the splitting sizes from first principles require a combination of high-quality inter-atomic interactions and rigorous methods to treat the nuclei with quantum mechanics. Many theoretical efforts have been made in recent decades. This Perspective focuses on two path-integral based tunneling splitting methods whose computational cost scales well with the system size, namely, the ring-polymer instanton method and the path-integral molecular dynamics (PIMD) method. From a simple derivation, we show that the former is a semiclassical approximation to the latter, despite that the two methods are derived very differently. Currently, the PIMD method is considered to be an ideal route to rigorously compute the ground-state tunneling splitting, while the instanton method sacrifices some accuracy for a significantly smaller computational cost. An application scenario of such a quantitatively rigorous calculation is to test and calibrate the potential energy surfaces of molecular systems by spectroscopic accuracy. Recent progress in water clusters is reviewed, and the current challenges are discussed. [ABSTRACT FROM AUTHOR]

At present, the proton exchange membrane fuel cell (PEMFC) is one of the most promising new energy solutions. The structure and material properties of the gas diffusion layer (GDL) are important factors that restrict the efficient water management and structural stability of PEMFCs. The complex mesoscopic fibrous porous structure of the GDL results in complex multiphase flow dynamics problems that have highly nonlinear characteristics. It is difficult to describe the details of mesoscopic multiphase coupled transport dynamics and numerically solve problems in which there is a two-phase flow with a high-density ratio. To solve these problems, a mesoscopic multiphase coupled transport model based on a lattice Boltzmann method and volume-of-fluid (LBM-VOF) model is proposed. Moreover, we also discuss the mechanism of the interaction between the fibrous porous structure and internal multiphase flow. The results obtained illustrate that the proposed method can obtain dynamic details of the flow field for fibrous porous media. The surface wettability of fibres strongly influences both the distribution and stability of liquid water clusters within porous materials. Concurrently, the fibre diameter assumes a pivotal role in governing lateral water diffusion and exclusion efficiency. This work lays a foundation for efficient water and thermal management of PEMFCs. [ABSTRACT FROM AUTHOR]

VV10 is a powerful nonlocal density functional for long-range correlation that is used to include dispersion effects in many modern density functionals, such as the meta-generalized gradient approximation (mGGA), B97M-V, the hybrid GGA, ωB97X-V, and the hybrid mGGA, ωB97M-V. While energies and analytical gradients for VV10 are already widely available, this study reports the first derivation and efficient implementation of the analytical second derivatives of the VV10 energy. The additional compute cost of the VV10 contributions to analytical frequencies is shown to be small in all but the smallest basis sets for recommended grid sizes. This study also reports the assessment of VV10-containing functionals for predicting harmonic frequencies using the analytical second derivative code. The contribution of VV10 to simulating harmonic frequencies is shown to be small for small molecules but important for systems where weak interactions are important, such as water clusters. In the latter cases, B97M-V, ωB97M-V, and ωB97X-V perform very well. The convergence of frequencies with respect to the grid size and atomic orbital basis set size is studied, and recommendations are reported. Finally, scaling factors to allow comparison of scaled harmonic frequencies with experimental fundamental frequencies and to predict zero-point vibrational energy are presented for some recently developed functionals (including r2SCAN, B97M-V, ωB97X-V, M06-SX, and ωB97M-V). [ABSTRACT FROM AUTHOR]

The structures of magnesium chloride dimer-water clusters, (MgCl2)2(H2O)n−/0, were investigated with size-selected anion photoelectron spectroscopy and theoretical calculations to understand the dissolution of magnesium chloride in water. The most stable structures were confirmed by comparing vertical detachment energies (VDEs) with the experimental measurements. A dramatic drop of VDE at n = 3 has been observed in the experiment, which is in accordance with the structural change of (MgCl2)2(H2O)n−. Compared to the neutral clusters, the excess electron induces two significant phenomena in (MgCl2)2(H2O)n−. First, the planar D2h geometry can be converted into a C3v structure at n = 0, making the Mg–Cl bonds easier to be broken by water molecules. More importantly, a negative charge-transfer-to-solvent process occurs after adding three water molecules (i.e., at n = 3), which leads to an obvious deviation in the evolution of the clusters. Such electron transfer behavior was noticed at n = 1 in monomer MgCl2(H2O)n−, indicating that the dimerization between two MgCl2 molecules can make the cluster more capable of binding electron. In neutral (MgCl2)2(H2O)n, this dimerization provides more sites for the added water molecules, which can stabilize the entire cluster and maintain its initial structure. Specifically, filling the coordination number to be 6 for Mg atoms can be seen as a link between structural preferences in the dissolution of the monomers, dimers, and extended bulk-state of MgCl2. This work represents an important step forward into fully understanding the solvation of MgCl2 crystals and other multivalent salt oligomers. [ABSTRACT FROM AUTHOR]

The practical description of disordered chemical reactions, where the reactions involve multiple species at multiple sites, is presently a challenge using correlated electronic structure methods due to their high computational cost and steep scaling. Here, we describe the gradient theory of multi-fragment density matrix embedding theory, which potentially provides a minimal computational framework to model such processes at the correlated electron level. We present the derivation and implementation of the gradient theory, its validation on model systems and chemical reactions using density matrix embedding, and its application to a molecular dynamics simulation of proton transport in a small water cluster, a simple example of multi-site reaction dynamics. [ABSTRACT FROM AUTHOR]

Although clusters made of polycyclic aromatic hydrocarbon and water monomers are relevant objects in both atmospheric and astrophysical science, little is known about their energetic and structural properties. In this work, we perform global explorations of the potential energy landscapes of neutral clusters made of two pyrene units and one to ten water molecules using a density-functional-based tight-binding (DFTB) potential followed by local optimizations at the density-functional theory level. We discuss the binding energies with respect to various dissociation channels. It shows that cohesion energies of the water clusters interacting with a pyrene dimer are larger than those of the pure water clusters, reaching for the largest clusters an asymptotic limit similar to that of pure water clusters and that, although the hexamer and octamer can be considered magic numbers for isolated water clusters, it is not the case anymore when they are interacting with a pyrene dimer. Ionization potentials are also computed by making use of the configuration interaction extension of DFTB, and we show that in cations, the charge is mostly carried by the pyrene molecules. [ABSTRACT FROM AUTHOR]

The interactions between molecules and electrode surfaces play a key role in electrochemical processes and are a subject of extensive research, both experimental and theoretical. In this paper, we address the water dissociation reaction on a Pd(111) electrode surface, modeled as a slab embedded in an external electric field. We aim at unraveling the relationship between surface charge and zero-point energy in aiding or hindering this reaction. We calculate the energy barriers with dispersion-corrected density-functional theory and an efficient parallel implementation of the nudged-elastic-band method. We show that the lowest dissociation barrier and consequently the highest reaction rate take place when the field reaches a strength where two different geometries of the water molecule in the reactant state are equally stable. The zero-point energy contributions to this reaction, on the other hand, remain nearly constant across a wide range of electric field strengths, despite significant changes in the reactant state. Interestingly, we show that the application of electric fields that induce a negative charge on the surface can make nuclear tunneling more significant for these reactions. [ABSTRACT FROM AUTHOR]

Manipulation of confined water dynamics by voltage keeps great importance for diverse applications. However, limitations on the membrane functions, voltage-control range, and unclear dynamics need to be addressed. Herein, we report an anomalous electrically controlled gating phenomenon on cation-intercalated multi-layer Ti3C2 membranes and reveal the confined water dynamics. The water permeation rate was improved rapidly following the application and rise of voltage and finally reached a maximum rate at 0.9 V. The permeation rate starts to decrease from 0.9 V. Below 0.9 V, the electric field affects the charge and polarity of water molecules and then leads to ordered and denser rearrangement in the two-dimensional (2D) channel to accelerate the permeation rate. Above 0.9 V, with the assistance of metal cations, the surge in current induced aggregation of water molecules into clusters, thereby limiting the water mobility. Based on these findings, a high-performance humidity sensor was developed by simultaneously optimizing the response and recovery speeds through electric manipulation. This work provides flexible strategies in intelligent membrane design and nanofluidic sensing. Nanoconfined water has unique properties, often leading to the discovery of unexpected phenomena, which play key roles in applications such as sensing, filtration, and catalysis. Here authors report electrically controlled gating in cation (K+/Li+) intercalated multilayer Ti3C2 and describe anomalous water dynamics in electrical angstrom-scale channels. [ABSTRACT FROM AUTHOR]

This research addresses the presence of substances of very high concern (SVHCs) confronting the drinking water sector. Responding adequately to the potential hazards by SVHCs, knowledge of emission pathways, toxicity, presence in drinking water sources, and removability during water production is crucial. As this information cannot be received for each compound individually, we employed a detailed clustering approach based on chemical properties and structures of SVHCs from lists with over 1,000 compounds. Through this process, 915 substances were divided into 51 clusters. We tested this clustering in risk assessment. To assess the risks, we developed toxicity prediction models utilizing random forests and multiple linear regression. These models were applied to make toxicity predictions for the list of compounds. This study shows that clustering is a viable approach to reducing sample size. In addition, the toxicity models provide insights into the potential human health risks. This research contributes to more informed decision-making and improved risk assessment in the drinking water sector, aiding in the protection of human health and the environment. This principle is generally applicable. If in a group a suitable representative is found, data from experiments with this compound can be used to gauge the behaviour of chemicals in this group. [ABSTRACT FROM AUTHOR]

Atomically precise low‐nuclearity (n<10) silver nanoclusters (AgNCs) have garnered significant interest due to their size‐dependent optical properties and diverse applications. However, their synthesis has remained challenging, primarily due to their inherent instability. The present study introduces a new feasible approach for clustering silver ions utilizing highly negative and redox‐inert polyoxoniobates (PONbs) as all‐inorganic ligands. This strategy not only enables the creation of novel Ag‐PONb composite nanoclusters but also facilitates the synthesis of stable low‐nuclearity AgNCs. Using this method, we have successfully synthesized a small octanuclear rhombic [Ag8]6+ AgNC stabilized by six highly negative [LiNb27O75]14− polyoxoanions. This marks the first PONb‐protected superatomic AgNC, designated as {Ag8@(LiNb27O75)6} (Ag8@Nb162), with an aesthetically spherical core–shell structure. The crystalline Ag8@Nb162 is stable under ambient conditions, What's more, it is water‐soluble and able to maintain its molecular cluster structure intact in water. Further, the stable small [Ag8]6+ AgNC has interesting temperature‐ and pH‐dependent reversible fluorescence response, based on which a multiple optical encryption mode for anti‐counterfeit technology was demonstrated. This work offers a promising avenue for the synthesis of fascinating and stable PONb‐protected AgNCs and sheds light on the development of new‐type optical functional materials. [ABSTRACT FROM AUTHOR]

Water interactions with cellulose, hemicellulose, and lignin in cell walls significantly influence their dimensional properties and thus the many applications of wood and other cellulosic materials. The sustainable development and application of wood and cellulosic materials require a better understanding of the mechanisms involved in the deformation with moisture changes. The dimensional changes of multiscale structures of Masson pine were studied during moisture desorption, and the differences at different scales were compared. The confocal laser scanning microscopy (CLSM) was used to observe the deformation of cells. The detail of wood nanostructure was characterized by small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). The molecular interaction between moisture and cell wall was studied using Fourier-transform infrared (FTIR). The results revealed that weakly hydrogen-bonded water molecules and water molecule clusters desorbed from the wood cell walls during moisture loss. The loss of water molecules altered the wood nanostructure, resulting in 12% and 7% reductions in the distances between the elementary fibrils in the latewood (LW) and earlywood (EW) cell walls, respectively. The dimensions of the cellulose crystallites in LW and EW decreased by 5% and 2%, respectively. At the cellular level, the tangential shrinkage of LW and EW were 9% and 6%, respectively. The reduction of the shrinkage at the larger scale can be attributed to the mutual inhibition and fine-tuning of the multi-scale hierarchical structures in wood. These findings provide insight into the instability of wood or natural cellulosic materials during moisture desorption and contribute to developing of more targeted wood-based materials. [ABSTRACT FROM AUTHOR]

Structural changes induced by water play a pivotal role in chemistry and biology but remain challenging to predict, measure, and control at molecular level. Here we explore size‐governed gas‐phase water aggregation in the flexible molecule 4‐hydroxy‐2‐butanone, modeling the conformational adaptability of flexible substrates to host water scaffolds and the preference for sequential droplet growth. The experiment was conducted using broadband rotational spectroscopy, rationalized with quantum chemical calculations. Two different isomers were observed experimentally from the di‐ to the pentahydrates (4‐hydroxy‐2‐butanone‐(H2O)n=2–5), including the 18O isotopologues for the di‐ and trihydrates. Interestingly, to accommodate water molecules effectively, the heavy atom skeleton of 4‐hydroxy‐2‐butanone reshapes in every observed isomer and does not correspond to the stable conformer of the free monomer. All solvates initiate from the alcohol group (proton donor) but retain the carbonyl group as secondary binding point. The water scaffolds closely resemble those found in the pure water clusters, balancing between the capability of 4‐hydroxy‐2‐butanone for steering the orientation and position of the water molecules and the ability of water to modulate the monomer's conformation. The present work thus provides an accurate molecular description on how torsionally flexible molecules dynamically adapt to water along progressing solvation. [ABSTRACT FROM AUTHOR]

Atomically precise low‐nuclearity (n<10) silver nanoclusters (AgNCs) have garnered significant interest due to their size‐dependent optical properties and diverse applications. However, their synthesis has remained challenging, primarily due to their inherent instability. The present study introduces a new feasible approach for clustering silver ions utilizing highly negative and redox‐inert polyoxoniobates (PONbs) as all‐inorganic ligands. This strategy not only enables the creation of novel Ag‐PONb composite nanoclusters but also facilitates the synthesis of stable low‐nuclearity AgNCs. Using this method, we have successfully synthesized a small octanuclear rhombic [Ag8]6+ AgNC stabilized by six highly negative [LiNb27O75]14− polyoxoanions. This marks the first PONb‐protected superatomic AgNC, designated as {Ag8@(LiNb27O75)6} (Ag8@Nb162), with an aesthetically spherical core–shell structure. The crystalline Ag8@Nb162 is stable under ambient conditions, What's more, it is water‐soluble and able to maintain its molecular cluster structure intact in water. Further, the stable small [Ag8]6+ AgNC has interesting temperature‐ and pH‐dependent reversible fluorescence response, based on which a multiple optical encryption mode for anti‐counterfeit technology was demonstrated. This work offers a promising avenue for the synthesis of fascinating and stable PONb‐protected AgNCs and sheds light on the development of new‐type optical functional materials. [ABSTRACT FROM AUTHOR]

Solar‐driven CO2 reduction and water oxidation to liquid fuels represents a promising solution to alleviate energy crisis and climate issue, but it remains a great challenge for generating CH3OH and CH3CH2OH dominated by multi‐electron transfer. Single‐cluster catalysts with super electron acceptance, accurate molecular structure, customizable electronic structure and multiple adsorption sites, have led to greater potential in catalyzing various challenging reactions. However, accurately controlling the number and arrangement of clusters on functional supports still faces great challenge. Herein, we develop a facile electrosynthesis method to uniformly disperse Wells‐Dawson‐ and Keggin‐type polyoxometalates on TiO2 nanotube arrays, resulting in a series of single‐cluster functionalized catalysts P2M18O62@TiO2 and PM12O40@TiO2 (M=Mo or W). The single polyoxometalate cluster can be distinctly identified and serves as electronic sponge to accept electrons from excited TiO2 for enhancing surface‐hole concentration and promote water oxidation. Among these samples, P2Mo18O62@TiO2‐1 exhibits the highest electron consumption rate of 1260 μmol g−1 for CO2‐to‐CH3OH conversion with H2O as the electron source, which is 11 times higher than that of isolated TiO2 nanotube arrays. This work supplied a simple synthesis method to realize the single‐dispersion of molecular cluster to enrich surface‐reaching holes on TiO2, thereby facilitating water oxidation and CO2 reduction. [ABSTRACT FROM AUTHOR]

Solar‐driven CO2 reduction and water oxidation to liquid fuels represents a promising solution to alleviate energy crisis and climate issue, but it remains a great challenge for generating CH3OH and CH3CH2OH dominated by multi‐electron transfer. Single‐cluster catalysts with super electron acceptance, accurate molecular structure, customizable electronic structure and multiple adsorption sites, have led to greater potential in catalyzing various challenging reactions. However, accurately controlling the number and arrangement of clusters on functional supports still faces great challenge. Herein, we develop a facile electrosynthesis method to uniformly disperse Wells‐Dawson‐ and Keggin‐type polyoxometalates on TiO2 nanotube arrays, resulting in a series of single‐cluster functionalized catalysts P2M18O62@TiO2 and PM12O40@TiO2 (M=Mo or W). The single polyoxometalate cluster can be distinctly identified and serves as electronic sponge to accept electrons from excited TiO2 for enhancing surface‐hole concentration and promote water oxidation. Among these samples, P2Mo18O62@TiO2‐1 exhibits the highest electron consumption rate of 1260 μmol g−1 for CO2‐to‐CH3OH conversion with H2O as the electron source, which is 11 times higher than that of isolated TiO2 nanotube arrays. This work supplied a simple synthesis method to realize the single‐dispersion of molecular cluster to enrich surface‐reaching holes on TiO2, thereby facilitating water oxidation and CO2 reduction. [ABSTRACT FROM AUTHOR]

The strengths of various types of individual hydrogen bonds (HBs) present in microhydrated clusters of HNO and HONO, i.e., HNO(H2O)n and HONO(H2O)n (n = 1–4), were examined using a molecular tailoring approach-based (MTA-based) method at the MP2/aug-cc-pVTZ//MP2/6-311++G(d,p) level of theory. The calculated binding energies (EBE) fall in a broader range for the HONO(H2O)n complexes (from −2.32 to −38.52 kcal mol−1) than for the HNO(H2O)n complexes (from −2.93 to −34.49 kcal mol−1). The HBs involving HONO as the proton donor (HB energy falls between 7.88 and 15.08 kcal mol−1) are stronger than that involving HNO as the proton donor (HB energy falls between 3.11 and 7.24 kcal mol−1). This may be attributed to the stronger acidity of the proton present in HONO. Among various HNO(H2O)n and HONO(H2O)n complexes, the strongest HB (energy = 15.08 kcal mol−1) was found in one of the isomers of HONO(H2O)4. The most distinctive feature of HBs of HONO compared to that of HNO is their greater energy and cooperativity contribution when it interacts with water as the HB donor. On the other hand, the –N＝O moiety of HNO is a stronger HB acceptor than that of HONO in their monohydrate complexes, but this trend is not observed in the larger clusters because of the greater cooperative contribution found in HONO. Furthermore, in HNO(H2O)n complexes, the self-associative interaction between water molecules is preferred in larger clusters (n = 4), whereas cross-associative interactions between HONO and water are dominant along with the water⋯water interactions for all HONO(H2O)n=1–4 complexes, leading to the formation of the most stable cyclic cluster. [ABSTRACT FROM AUTHOR]

Controlling blood loss is crucial for saving lives during trauma. Based on the current application of solid waste in hemostatic materials, this study reports the synthesis of a hydroxyapatite/tourmaline composite material (referred to as ST) and a hemostatic sponge (referred to as STS). These materials were synthesized through hydrothermal processes and lyophilization techniques using seashells, tourmaline, and chitosan as precursors. The phase analysis and microstructure characterization were performed using XRD, SEM, TEM, and HRTEM. Owing to the spontaneous polarization of tourmaline attracting free ions in the system, the shells were deposited on the surface of tourmaline particles in the form of hydroxyapatite (HA) through dissolution and recrystallization during the hydrothermal process. HA can release free Ca2+, an important component in the coagulation system, while tourmaline can enhance cell metabolism by reducing water molecular clusters, thereby altering the permeability of cell membranes. ST particles were incorporated into the chitosan sponge matrix to prevent particle shedding. Through orthogonal design experiments on the preparation process of ST, the optimal preparation conditions were determined as follows: a hydrothermal temperature of 180 °C, a hydrothermal time of 12 h, a pH value of 8, and a shell-to-tourmaline ratio of 8 : 1. The composite materials were evaluated for their adsorption capacity, clotting time, hemolysis rate, antibacterial rate, and cytotoxicity. The results demonstrated a higher liquid adsorption rate, significantly reduced clotting time, a hemolysis rate of <5.0%, an antibacterial capacity of 88.5%, and lower cytotoxicity. These findings suggest that STS has the potential to be a safe, effective, and cost-efficient hemostatic agent. [ABSTRACT FROM AUTHOR]

Low-temperature ¹H NMR spectroscopy was used to study the pig spinal and brain tissues of the original samples at different temperatures, in chloroform, including that with the addition of hydrochloric acid, and in a mixture of chloroform and trifluoroacetic acid (TFAА) in a ratio of 6:1. It has been found that water in the tissues of the pig's brain and spinal cord is bound and is part of polyassociates, the radius of which is in the range R = 1–100 nm. During the freezing-thawing process, only the signal of bound water is observed in the ¹H NMR spectra, while the protons of biopolymers and phospholipid membranes are not detected in the spectra, which indicates their low molecular mobility. Chloroform dissolves in the substance of cell membranes, increasing the mobility of aliphatic groups, and the membrane material passes from an ordered to a partially disordered state. This effect is much stronger for spinal cord tissue, which is due to the lower content of interstitial water. The characteristics of interstitial water layers were calculated: the concentration of strongly and weakly bound water, the maximum decrease in the Gibbs free energy in the layer of strongly bound water and interfacial energies. It has been found that for spinal cord tissue, the introduction of chloroform into the system is accompanied by a decrease in the binding of water in the nervous tissue (the amount of highly bound water decreases from 180 to 250 mg/g), and the value of interfacial energy decreases from 24 to 19.6 J/g. However, these changes have little effect on the radius distributions of interstitial water clusters. The main maximum of the distribution does not change and is observed at R = 20 nm. In the presence of TFAА, the amount of strongly bound water increases to 1400 mg/g, and the value of interfacial energy increases to 77.6 J/g. For brain tissue, their value turned out to be significantly less. Thus, chloroform had virtually no effect on the binding energy of water in the tissue, and the effect of TFAА also turned out to be half that for spinal cord tissue. [ABSTRACT FROM AUTHOR]

As one of the most important and basic magnetic materials, Fe3O4 nanoparticles have wide applications in water treatment. In this paper, the Fe3O4 nanoparticles were synthesized by solvothermal method. The magnetic Fe3O4 nanoparticles were obtained with sizes ranging from about 10 to 150 nm, with a distinct anti-spinel structure and an abundance of hydroxyl groups on the surface. Moreover, the saturated magnetization and the coercivity of the Fe3O4 nanoparticles are 84.08 emu g−1 and 89.52 Oe, respectively. This confirms that it has a good magnetic property compared with the commercial Fe3O4 nanoparticles. And then, the magnetic Fe3O4 nanoparticles were cultured biochemically with activated sludge to form the magnetic flocculent clusters for water treatment. The results show that the settling performance is excellent, and the sludge activity is well maintained, with microorganisms still abundant. Besides, the recovery rate of the magnetic flocculants was 95%. [ABSTRACT FROM AUTHOR]

The use of solid-oxide materials in electrocatalysis applications, especially in hydrogen-evolution reactions, is promising. However, further improvements are warranted to overcome the fundamental bottlenecks to enhancing the performance of solid-oxide electrolysis cells (SOECs), which is directly linked to the more-refined fundamental understanding of complex physical and chemical phenomena and mass exchanges that take place at the surfaces and in the bulk of electrocatalysis materials. Here, we developed an eReaxFF force field for barium zirconate doped with 20 mol% of yttrium, BaZr0.8Y0.2O3-δ (BZY20) to enable a systematic, large-length-scale, and longer-timescale atomistic simulation of solid-oxide electrocatalysis for hydrogen generation. All parameters for the eReaxFF were optimized to reproduce quantum-mechanical (QM) calculations on relevant condensed phase and cluster systems describing oxygen vacancies, vacancy migrations, electron localization, water adsorption, water splitting, and hydrogen generation on the surfaces of the BZY20 solid oxide. Using the developed force field, we performed both zero-voltage (excess electrons absent) and non-zero-voltage (excess electrons present) molecular dynamics simulations to observe water adsorption, water splitting, proton migration, oxygen-vacancy migrations, and eventual hydrogen-production reactions. Based on investigations offered in the present study, we conclude that the eReaxFF force field-based approach can enable computationally efficient simulations for electron conductivity, electron leakage, and other non-zero-voltage effects on the solid oxide materials using the explicit-electron concept. Moreover, we demonstrate how the eReaxFF force field-based atomistic-simulation approach can enhance our understanding of processes in SOEC applications and potentially other renewable-energy applications. [ABSTRACT FROM AUTHOR]

Nafion, a widely used proton exchange membrane in fuel cells, is a representative perfluorosulfonic acid membrane consisting of a hydrophobic Teflon backbone and hydrophilic sulfonic acid side chains. Its thermal conductivity (k) is critical to fuel cell's thermal management. During fuel cell operation, water molecules inevitably enter Nafion and could strongly affect its k. In this work, we measure the k of Nafion of different water content (λ). Findings reveal that k is significantly low in a vacuum environment characterized as 0.110 W m−1 K−1, but at λ ∼1, a notable increase is observed, reaching 0.162 W m−1 K−1. Moreover, k at λ ≈ 6 is 60% higher than that of λ ∼1. This exceptional k increase is far beyond the theoretical prediction by the effective medium theory that only considers simply physical mixing. Rather this k increase is attributed to the formation of water clusters and channels with increased λ, creating thermal pathways through hydrogen bonding, thereby improving chemical connections within the Nafion structure and augmenting its k. Furthermore, it is observed that Nafion's k reaches the maximum value of 0.256 W m−1 K−1 at λ ≈ 6, with no further increase up to λ ≈ 10.5. This phenomenon is explained by the coalescence of water clusters at λ ≈ 6, forming channels that optimize heat transfer pathways and connections within the Nafion structure. Moreover, the free movement of water molecules within water channels (λ > 6) shows physical alterations in Nafion structure (significant volume increase), which have a lesser impact on k. [ABSTRACT FROM AUTHOR]

Highlights : A clear negative correlation between the size of water clusters and the concentration of dissolved oxygen was observed. This implied that smaller clusters water exhibits higher concentrations of dissolved oxygen. Oxygen molecules are primarily existed at the surfaces or interfaces of water clusters and can rapidly traverse the gas liquid interface. A semi empirical formula relating the average number of water molecules in a cluster to 17O NMR half peak width was derived, demonstrating an approximate lin ear relationship. The structure of liquid water is primarily composed of three-dimensional networks of water clusters formed by hydrogen bonds, and dissolved oxygen is one of the most important indicators for assessing water quality. In this work, distilled water with different concentration of dissolved oxygen were prepared, and a clear negative correlation between the size of water clusters and dissolved oxygen concentration was observed. Besides, a phenomenon of rapid absorption and release of oxygen at the water interfaces was unveiled, suggesting that oxygen molecules predominantly exist at the interfaces of water clusters. Oxygen molecules can move rapidly through the interfaces among water clusters, allowing dissolved oxygen to quickly reach a saturation level at certain partial pressure of oxygen and temperature. Further exploration into the mechanism by molecular dynamics simulations of oxygen and water clusters found that oxygen molecules can only exist stably at the interfaces among water clusters. A semi-empirical formula relating the average number of water molecules in a cluster (n) to 17O NMR half-peak width (W) was summarized: n = 0.1 W + 0.85. These findings provide a foundation for exploring the structure and properties of water. [ABSTRACT FROM AUTHOR]