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This work presents a systematic assessment of QM/QM' and QM/MM models with respect to direct QM calculations for the tautomerization (neutral to zwitterion) reactions of amino acids (glycine, alanine, valine, aspartate, and neutral and protonated histidine) solvated in a 160 water cluster. The effect of varying QM region size and choice of embedding potentials, including fixed-charge and polarizable molecular mechanics force fields (TIP3P and EFP) and various semiempirical QM methods (PM7, GFN2-xTB, DFTBA, DFTB3, HF-3c, and PBEh-3c), on the accuracy of the models was examined. A surprising finding was that molecular mechanics force fields outperformed many of the semiempirical methods. Generally, the errors in the QM/QM' and QM/MM models converge slowly with respect to the QM region size, requiring 50 or more waters to be included in the QM region before the error in the model falls below 1 kcal mol-1 of its pure QM result. Different QM region selection schemes were also compared, and it was found that selection based on Natural Population Analysis (NPA) atomic charges significantly reduced the error in the QM/QM' and QM/MM models particularly if a low-quality embedding potential was used. It is envisaged that these results will be useful for the development of future hybrid QM models.

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.

Experimental data suggest that the solubility of copper in high-temperature water vapor is controlled by the formation of hydrated clusters of the form CuCl(H2O)n, where the average number of water molecules in the cluster generally increases with increasing density [Migdisov, A. A.; et al. Geochim. Cosmochim. Acta2014, 129, 33-53]. However, the precise nature of these clusters is difficult to probe experimentally. Moreover, there are some discrepancies between experimental estimates of average cluster size and prior simulation work [Mei, Y. Geofluids2018, 2018, 4279124]. We have performed first-principles Monte Carlo (MC) and molecular dynamics (MD) simulations to explore these clusters in finer detail. We find that molecular dynamics is not the most appropriate technique for studying aggregation in vapor phases, even at relatively high temperatures. Specifically, our MD simulations exhibit substantial problems in adequately sampling the equilibrium cluster size distribution. In contrast, MC simulations with specialized cluster moves are able to accurately sample the phase space of hydrogen-bonding vapors. At all densities, we find a stable, slightly distorted linear H2O-Cu-Cl structure, which is in agreement with the earlier simulations, surrounded by a variable number of water molecules. The surrounding water molecules do not form a well-defined second solvation shell but rather a loose network of hydrogen-bonded water with molecular CuCl on the outside edge of the water cluster. We also find a broad distribution of hydration numbers, especially at higher densities. In contrast to previous simulation work but in agreement with experimental data, we find that the average hydration number substantially increases with increasing density. Moreover, the value of the hydration number depends on the choice of cluster definition.

The reaction of Criegee intermediates with water vapor has been widely known as a key Criegee reaction in the troposphere. Herein, we investigated the reaction of the smallest Criegee intermediate, CH2OO, with a water cluster through fragment-based ab initio molecular dynamics simulations at the MP2/aug-cc-pVDZ level. Our results show that the CH2OO-water reaction could occur not only at the air/water interface but also inside the water cluster. Moreover, more than one reactive water molecules are required for the CH2OO-water reaction, which is always initiated from the Criegee carbon atom and ends at the terminal Criegee oxygen atom via a directional proton transfer process. The observed reaction pathways include the loop-structure-mediated and stepwise mechanisms, and the latter involves the formation of transient H3O+. The lifetime of transient H3O+ is on the order of a few picoseconds, which may impact the atmospheric budget of the other trace gases in the actual atmosphere.

Examined here are the structures of complexes of benzophenone microsolvated with up to three water molecules by using broadband rotational spectroscopy and the cold conditions of a molecular jet. The analysis shows that the water molecules dock sideways on benzophenone for the water monomer and dimer moieties, and they move above one of the aromatic rings when the water cluster grows to the trimer. The rotational spectra shows that the water trimer moiety in the complex adopts an open-loop arrangement. Ab initio calculations face a dilemma of identifying the global minimum between the open loop and the closed loop, which is only solved when zero-point vibrational energy correction is applied. An OH⋅⋅⋅π bond and a Burgi-Dunitz interaction between benzophenone and the water trimer are present in the cluster. This work shows the subtle balance between water-water and water-solute interactions when the solute molecule offers several different anchor sites for water molecules.

7,8-Dihydro-8-oxoguanine (8-oxoG) has attracted considerable attention from analysts because it is collected with GC → TA transversions in DNA replication; especially, due to the lower redox potential compared to guanine, 8-oxoG is considered to be the ultimate “positive hole” sink, where the oxidation of DNA is funneled into this direction. Thus, lots of efforts have been made on the one-electron oxidation of 8-oxoG and the ensuing deprotonation reaction. However, there still have been some inconsistent results and the deprotonation mechanism of 8-oxoG˙+ remains elusive to a larger extent in previous studies. Herein, we performed a thorough investigation on 8-oxoG˙+ deprotonation reaction by density functional theory (DFT). Our calculation results show that the pKa values of active protons in 8-oxoG˙+ are 0.23 (N7–H), 3.42 (N1–H), 5.91 (N2–Ha) and 6.43 (N2–Hb), respectively, where the deviation is about 0.32. This result rationalizes previous inconsistent experimental results. The energy barriers for N7–H transfer of 8-oxoG˙+ toward the direction of O6 and O8 are 11.7 and 13.1 kJ mol−1, respectively, and that for N1–H is 28.5 kJ mol−1, indicating that the N1–H of 8-oxoG˙+ could act as a potential deprotonation site. Then, to clearly illustrate the mechanism for 8-oxoG˙+ deprotonation of N7–H, 15 other hydration models were built by assessing systematically the effects of explicit water molecules added in the hydration model. It is found that these three water molecules placed around N7–H, O6/O8 of 8-oxoG˙+ as well as the one located in the second hydration shell are necessary for describing the process of 8-oxoG˙+ deprotonation from N7–H, where the protonated water cluster plays an important role in the process of proton release from 8-oxoG˙+ to the first hydration shell. Moreover to introduce an additional water molecule located in the negative direction of proton transfer (around O8/O6) is helpful for estimating the energy barrier of proton transfer accurately. These results would provide an in-depth perspective to understand the important role of 8-oxoG in DNA oxidative damage.

The aim of the work is to study interaction of N-acetylneuraminic acid (NANA) with the surface of ultrafine silica (UFS) with the participation of glucose and sucrose in aqueous solution at the supramolecular level by density functional theory method (exchange-correlation functional B3LYP, basis set of 6-31G (d, p). The adsorption of N-acetylneuraminic acid, as well as individual carbohydrates (glucose and sucrose) on the hydrated surface of UFS in aqueous solution, was considered as a process of replacement of water molecules on the surface of silica by adsorbate molecules. This work considers two schemes of carbohydrate molecule influence on adsorption of N-acetylneuraminic acid. According to the first scheme the interaction of the NANA molecule occurs with the silica-monosaccharide complex, according to the second scheme, the silica cluster interacts with the NANA-monosaccharide complex, where silica binds to the complex through the carbohydrate molecule. The analysis of the calculated geometric and energy characteristics show that adsorption on the surface of silica, with hydration taken into account, is thermodynamically probable for the sucrose. The glucose molecule has a positive value (+9.8 and +2.7 kJ / mol) is an unfavorable process in terms of thermodynamics regardless of the hydrating water cluster size. The N-acetylneuraminic acid molecule has a value of -1.3 kJ / mol for the reaction with five water molecules and +0.9 kJ / mol with eight water molecules. It was found that the presence of sucrose on the silica surface in the aqueous solution weakens the hydration energy (i.e. it is easier to replace the cluster of water with the N-acetylneuraminic acid molecule from the surface of the modified adsorbent), which in turn promotes NANA adsorption on the silica surface. Therefore, scheme 1 is thermodynamically more likely than scheme 2. This indicates that there is a mutual influence of substances in a mixture of NANA with carbohydrates on the interaction with silica in comparison with the interaction of substances with silica alone.

High-order charge transfer is incorporated into the fragment molecular orbital (FMO) method using a charge transfer state with fractional charges. This state is used for a partition analysis of properties based on segments that may be different from fragments in FMO. The partition analysis is also formulated for calculations without fragmentation. All development in this work is limited to density-functional tight-binding. The analysis is applied to a water cluster, crambin (PDB: 1CBN), and two complexes of Trp-cage (1L2Y) with ligands. The contributions of functional groups in ligands are obtained, providing useful information for drug discovery.

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.

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

The structure of the title compound, 4-(dimethylamino)pyridin-1-ium-2,5-dichloro-3,6-dioxocyclohexa-1,4-diene-1,4- bis (olate) 4-dimethylaminopyridine water undeca-solvate, C 57 H 87 Cl 5 N 12 O 21 , obtained from interaction between chloranilic acid (caH 2 ), and dimethyl aminopyridine (DMAP) has been determined by single crystal X-ray diffraction. The title compound, (DMAPH) 5 (ca) 2.5 ·(DMAP)·11H 2 O, crystallized in the triclinic crystal system with space group, P (no. 2), a = 13.3824(15) A, b = 13.4515(17) A, c = 19.048(2) A, α = 86.014(4)°, β = 88.821(4)°, γ = 86.367(4)°, V = 3413.3(7) A 3 , Z = 2, T = 100(2) K, μ(MoKα) = 0.294 mm -1 , Dcalc = 1.414 g/cm 3 , 59413 reflections measured (3.76° ≤ 2Θ ≤ 56°), 16405 unique ( R int = 0.0517, R sigma = 0.0589) which were used in all calculations. The final R 1 was 0.0460 (I ≥ 2σ(I)) and wR 2 was 0.1271 (all data). Using supramolecular chemistry principles, proton donors (chloranilic acid) and acceptor (DMAP) were combined to generate a multicomponent hydrogen-bonded system. Due to the presence of protonated bases (DMAPH + ), the dominant interactions are the N + -H···O hydrogen bonds, whereas the negative charges of an acceptor from the chloranilate dianion (ca 2- ) are delocalized. Additionally, three sets of water clusters in the title compound were identified, namely a cyclic pentamer, a linear, and an acute-shaped trimer water cluster. It was further observed that strong hydrogen bond interactions occurred between the solvated aqua molecule(s) acting as a proton donor and the neutral DMAP acting as a proton acceptor. The crystal packing is further stabilized by O-H···Cl and C-H···Cl weak halogen interactions. The lattice metric strength is further held by observed π-π stacking interactions (centroid-centroid) with inter centroid distances between sets of the DMAPH rings of 3.624(3), 3.642(4), 3.739(3), 3.863(3) and 3.898(3) A, respectively.

Formation of pure gaseous water cluster in the supersonic gas flow from a conical nozzle was investigated by simulation. The simulation results show that average size of water cluster indicates a different size evolution along the gas flow, i.e., the average cluster size firstly increases to a maximum size and then decreases slowly, rather than keeps increasing like other gases. By further calculations of the nucleation rate and the growth rate of water cluster, it is found that the decrease of average size results from a high nucleation rate and a low size growth rate in the downstream of gas flow far away from conical nozzle throat. Formation of pure gaseous water cluster in the supersonic gas flow from a conical nozzle was investigated by simulation. The simulation results show that average size of water cluster indicates a different size evolution along the gas flow, i.e., the average cluster size firstly increases to a maximum size and then decreases slowly, rather than keeps increasing like other gases.

Acid dissociation, and thus liberation of excess protons in small water droplets, impacts on diverse fields such as interstellar, atmospheric or environmental chemistry. At cryogenic temperatures below 1 K, it is now well established that as few as four water molecules suffice to dissociate the generic strong acid HCl, yet temperature‐driven recombination sets in simply upon heating that cluster. Here, the fundamental question is posed of how many more water molecules are required to stabilize a hydrated excess proton at room temperature. Ab initio path integral simulations disclose that not five, but six water molecules are needed at 300 K to allow for HCl dissociation independently from nuclear quantum effects. In order to provide the molecular underpinnings of these observations, the classical and quantum free energy profiles were decomposed along the dissociation coordinate in terms of the corresponding internal energy and entropy profiles. What decides in the end about acid dissociation, and thus ion pair formation, in a specific microsolvated water cluster at room temperature is found to be a fierce competition between classical configurational entropy and internal energy, where the former stabilizes the undissociated state whereas the latter favors dissociation. It is expected that these are generic findings with broad implications on acid–base chemistry depending on temperature in small water assemblies., Temperature dependent: Extensive ab initio path integral simulations disclose that the number of water molecules required to allow for acid dissociation, and thus for the generation of hydrated excess protons, in restricted aqueous environments such as finite HCl(H2O)n clusters, is temperature dependent.

Syntheses were performed at room temperature using Ni(NO3)2·6H2O, cyclam (cyclam = 1,4,8,11-tetraazacyclotetradecane) and the precursors Li8[Nb6O19]· ≈22H2O or Na7[HNb6O19]·15H2O in a DMSO-H2O mixture. Yellow crystals of the new compound {[Ni(cyclam)]2H4Nb6O19}·12H2O could be obtained after one week applying the Li+ or Na+ salt as starting materials. The crystal structure is unique in polyoxoniobate (PONb) chemistry and displays two interpenetrating three-dimensional (3D) networks. The [Nb6O19]8– anion is expanded by four Ni2+ centered complexes via Ni–O bonds to terminal O2− anions of the hexaniobate anion. The 3D networks are generated by further Ni–O bond formation between neighboring [Nb6O19]8− anions. The remaining void space is occupied by H2O molecules which form a water cluster.

Proton transfer is regarded as a fundamental process in chemical reactions of DNA molecules and continues to be an active research theme due to the connection with charge transport and oxidation da...

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.

Gas-phase near-edge X-ray-absorption fine structure (NEXAFS) action spectroscopy around the oxygen K-edge and mass spectrometry were employed to probe isolated substance P (SP) molecular ions, both bare and progressively solvated with 4 and 11 water molecules. Detailed mass spectra of bare and hydrated precursors are presented for the resonant photon energy of 532 eV that corresponds to O1s --> pi(amide)* core excitation, triggering resonant Auger decay and fragmentation from the ionized radical molecular system. The fragmentation pattern of doubly protonated SP hydrated with 4 water molecules clearly shows a series of abundant doubly charged backbone fragments, as well as triply charged precursor with small neutral losses, all preserving full water cluster. This is drastically different from the collisional induced dissociation of the hydrated peptide where the water loss is a dominant relaxation process. Moreover, the action NEXAFS obtained from several resolved small backbone fragments revealed increased fragmentation of hydrated SP relative to the bare one, due to a resonant O1s excitation of the attached water molecules. Such unexpected result inspires further experimental developments to investigate possible nonlocal energy transfer from the solvent to the biomolecules within the first solvation shell. The experiment is supported by molecular dynamics and DFT calculations to estimate the intensity of the resonant X-ray absorption of bare and hydrated SP around peptide and water O1s excitation region.

We theoretically study the size effect of water molecule clusters not only on electrostatic interaction between two charged surfaces in an aqueous electrolyte but also on electroosmotic transport in a nanofluidic channel. Applying a free energy based mean-field approach accounting for different sizes of ions and water molecule clusters, we derive a set of coupled equations to compute electrostatic and electroosmotic properties between charged surfaces. We verify that the smaller the size of a water cluster, the stronger the electroosmotic transport in nanofluidic channels. In addition, we find that an increase in size of a water cluster yields a decrease in electrostatic interaction strength between similar or oppositely charged planar surfaces.We theoretically study the size effect of water molecule clusters not only on electrostatic interaction between two charged surfaces in an aqueous electrolyte but also on electroosmotic transport in a nanofluidic channel. Applying a free energy based mean-field approach accounting for different sizes of ions and water molecule clusters, we derive a set of coupled equations to compute electrostatic and electroosmotic properties between charged surfaces. We verify that the smaller the size of a water cluster, the stronger the electroosmotic transport in nanofluidic channels. In addition, we find that an increase in size of a water cluster yields a decrease in electrostatic interaction strength between similar or oppositely charged planar surfaces.

The interaction between two ligated nanoparticles depends on whether they are isolated or immersed in a liquid solvent. However, very little is known about the influence of solvent vapor on the interaction between two ligated nanoparticles. Recent experiments yield the surprising result that the cyclic exposure of solvent free suspended monolayers of dodecane thiol ligated gold nanoparticles (AuNPs) to water vapor and dry nitrogen generates reversible cyclic decreases and increases in Young’s modulus of the monolayer, implying corresponding cyclic changes in the AuNP–AuNP interaction. We examine how water vapor interacts with an isolated dodecane thiol dressed AuNP and how water vapor affects the interaction between a pair of nanoparticles, using all-atom molecular-dynamics simulations. We find that there is condensation of water molecules onto the ligand shell of an AuNP in the form of clusters of 100–2000 molecules that partially cover the shell, with most of the water in a few large clusters. A water cluster bridges the AuNPs, with a sensibly constant number of water molecules for AuNP–AuNP separations from the edge-to-edge contact up to center-to-center separations of 100 A. The wet AuNP–AuNP interaction has a slightly deeper and wider asymmetric well than does the dry interaction, a change that is qualitatively consistent with that implied by the observed water vapor induced change in Young’s modulus of a monolayer of these AuNPs. We find that macroscopic analyses of water drop–deformable surface interactions and dynamics provide both guidance to understanding and qualitatively correct predictions of the phenomena observed in our simulations.

Although small water clusters (SWCs) are important in many research fields, efficient methods of preparing SWCs are still rarely reported, which is mainly due to the lack of related materials and understanding of the molecular interaction mechanisms. In this study, a series of functional molecules were added in water to obtain small water cluster systems. The decreasing rate of the half-peak width in a sodium dodecyl sulfate (SDS)–water system reaches ≈20% at 0.05 mM from 17O nuclear magnetic resonance (NMR) results. Based on density functional theory (DFT) and molecular dynamics (MD) simulation calculation, it can be concluded that functional molecules with stronger negative electrostatic potential (ESP) and higher hydrophilicity have a stronger ability to destroy big water clusters. Notably, the concentrations of our selected molecule systems are one to two magnitudes lower than that of previous reports. This study provides a promising way to optimize aqueous systems in various fields such as oilfield development, protein stability, and metal anti-corrosion.

Theoretical descriptions of excited state proton transfer (ESPT) have had various degrees of success. This work presents a theoretical description of the photodissociation of the 7-hydroxyflavylium cation (7-HF), the fundamental chromophoric moiety of anthocyanin natural plant pigments. ESPT of 7-HF is promoted by a significant shift of charge away from the OH group in the first singlet excited state, leading smoothly to the excited conjugate base and a protonated water cluster. Several factors contribute to the consistency of the results of the present study: (1) the theoretical approach (TD-DFT with the B3-LYP functional and def2-TZVP basis set utilizing Grimme's D3 dispersion correction); (2) the modeling of the solvent effect combining hydrogen bonding of the photoacid to a cluster of discrete water molecules in a water-like continuum solvent (COSMO); (3) the large S1 -S2 energy gap of flavylium cations; and (4) the electrostatics of the ESPT in which a proton is transferred from a cationic photoacid to water without Coulombic interaction between the proton and the conjugate base.

Producción Científica, The structure of butyl carbamate and of its complex with water generated in a supersonic expansion has been characterized by Fourier transform microwave spectroscopy. Up to 13 low-energy conformations of the monomer have been predicted which differ in the relative orientation of the butyl chain and the amide group. However, only three conformations have been observed experimentally. The remaining low energy conformers are expected to interconvert into the observed rotamers through collisional relaxation processes in the supersonic jet. The values of the C-O-Cα-Cβ dihedral angle observed for the two most stable conformers of butyl carbamate, with extended configurations, can be directly correlated with the values of this angle in the two experimentally observed conformers of the shorter-chain molecule, ethyl carbamate. The less stable form shows a weak C-H...O=C intramolecular hydrogen bond from the terminal methyl group to the carbamate C=O group, stabilizing a folded configuration. For the most stable butyl carbamate monomer the complex with one molecule of water has been observed. In that complex the water molecule attaches to the amide group in a cyclic arrangement using two hydrogen bonds. The results indicate that water does not substantially alter the conformational behavior of butyl carbamate., Ministerio de economia, industria y competitividad CTQ2016-75253-P

Given the piecewise approach to modeling intermolecular interactions for force fields, they can be difficult to parameterize since they are fit to data like total energies that only indirectly connect to their separable functional forms. Furthermore, by neglecting certain types of molecular interactions such as charge penetration and charge transfer, most classical force fields must rely on, but do not always demonstrate, how cancellation of errors occurs among the remaining molecular interactions accounted for such as exchange repulsion, electrostatics, and polarization. In this work we present the first generation of the (many-body) MB-UCB force field that explicitly accounts for the decomposed molecular interactions commensurate with a variational energy decomposition analysis, including charge transfer, with force field design choices that reduce the computational expense of the MB-UCB potential while remaining accurate. We optimize parameters using only single water molecule and water cluster data up through pentamers, with no fitting to condensed phase data, and we demonstrate that high accuracy is maintained when the force field is subsequently validated against conformational energies of larger water cluster data sets, radial distribution functions of the liquid phase, and the temperature dependence of thermodynamic and transport water properties. We conclude that MB-UCB is comparable in performance to MB-Pol, but is less expensive and more transferable by eliminating the need to represent short-ranged interactions through large parameter fits to high order polynomials.

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.

Previous studies have shown that the use of a 20 keV water cluster beam as a primary beam for the analysis of organic and bio-organic systems resulted in a 10-100 times increase in positive molecular ion yield for a range of typical analytes compared to C60 and argon cluster beams. This resulted in increased sensitivity to important lipid molecules in the bioimaging of rat brain. Building on these studies, the present work compares 40 and 70 keV water cluster beams with cluster beams composed of pure argon, argon and 10%CO2, and pure CO2. First, as previously, we show that for E/nucleon about 0.3 eV/nucleon water and nonwater containing cluster beams generate very similar ion yields, but below this value, the water beams yields of BOTH negative and positive "molecular" ions increase, in many cases reaching a maximum in the

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.

Electron attachment onto water clusters to form water cluster anions is studied by varying the point of electron attachment along a molecular beam axis and probing the produced cluster anions using photoelectron spectroscopy. The results show that the point of electron attachment has a clear effect on the final distribution of isomers for a cluster containing 78 water molecules, with isomer I formed preferentially near the start of the expansion and isomer II formed preferentially once the molecular beam has progressed for several millimetres. These changes can be accounted for by the cluster growth rate along the beam. Near the start of the expansion, cluster growth is proceeding rapidly with condensing water molecules solvating the electron, while further along the expansion, the growth has terminated and electrons are attached to large and cold preformed clusters, leading to the isomer associated with a loosely bound surface state.

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.

We investigate water desorption from hydrophobic surfaces using two curved Ag single crystals centered at (111) and (001) apices. On these types of crystals the step density gradually increases along the curvature, allowing us to probe large ranges of surface structures in between the (001), (111) and (110) planes. Subtle differences in desorption of submonolayer water coverages point toward structure dependencies in water cluster nucleation. The B-type step on hydrophobic Ag binds water structures more strongly than adjacent (111) planes, leading to preferred desorption from steps. This driving force is smaller for A-type steps on (111) terraces. The A′-type step flanked by (001) terraces shows no indication of preferred desorption from steps. Extrapolation to the (311) surface, not contained within either curved surface, demonstrates that both A- and A′-type steps can be regarded chemically identical for water desorption. The different trends in desorption temperature on the two crystals can thus be attributed to stronger water adsorption at (001) planes than at (111) planes and identical to adsorption at the step. These results show that our approach to studying the structure dependence of water desorption is sensitive to variations in desorption energy smaller than ‘chemical accuracy’, i.e. 1 kcal mol−1.

The common understanding of zeolite acidity is based on Lowenstein's rule, which states that Al-O-Al aluminium pairs are forbidden in zeolites. This rule is generally accepted to be inviolate in zeolites. However, recent computational research using a 0 K DFT model has suggested that the rule is violated for the acid form of several zeolites under anhydrous conditions [Fletcher et al., Chem. Sci., 8, (2017), 7483]. The effect of water loading on the preferred aluminium distribution in zeolites, however, has so far not been taken into account. In this article, we show by way of ab initio molecular dynamics simulations that Lowenstein's rule is obeyed under high water solvation for acid chabazite (H-CHA) but disobeyed under anhydrous conditions. We find that varying the water loading in the pores leads to dramatic effects on the structure of the active sites and the dynamics of solvation. The solvation of Bronsted protons in the surrounding water was found to be the energetic driving force for the preferred Lowenstein Al distribution and this driving force is absent in non-Lowenstein (Al-O(H)-Al) moieties. The preference for solvated protons further implies that the catalytically active species in zeolites is a protonated water cluster, rather than a framework Bronsted site. Hence, an accurate treatment of the solvation conditions is crucial to capture the behaviour of zeolites and to properly connect simulations to experiments. This work should lead to a change in modelling paradigm for zeolites, from single molecules towards high solvation models where appropriate.

15‐crown‐5 ether (15C5) and its complexes with water (w) have been studied using broadband Fourier transform microwave spectroscopy in a supersonic jet. A new conformer of 15C5 has been observed and established as the new global minimum out of a total of nine isolated structures. In addition, two 15C5‐w and two 15C5‐w2 clusters have been observed. The cluster structures have been unambiguously identified through the observation of water 18O isotopologue spectra. In all the clusters, at least one water molecule, located close to the axis of the 15C5 ring, interacts through two simultaneous hydrogen bonds to the endocyclic oxygen atoms. This interaction reshapes the 15C5 ring to reduce its rich conformational landscape to only two open structures, related to those found in complexes with Li+ or Na+ ions. In the most abundant 15C5‐w2 form, the two water molecules repeat the same interaction scheme while binding to opposite sides of the ring. In the second most abundant dihydrated form the two water molecules lie on the same side of the ring. This finding is exceptionally rare because water‐water interactions typically prevail over the formation of additional solutewater contacts, and it showcases the particular binding features of crown ethers., Ministerio de economia, industria y competitividad CTQ2016-75253-P

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.

This work is dedicated to the theoretical investigation of the influence of water clusters’ organisation and size on the electronic spectrum of an interacting benzene (Bz) molecule using both TD-DFT and CASPT2 approaches. Two series of geometries, namely $$Geo_{IEI}$$ and $$Geo_{IED}$$ were extracted from two Bz-hexagonal ice configurations leading to maximum and minimum ionization energies respectively. An appropriate basis set containing atomic diffuse and polarisation orbitals and describing the Rydberg states of Bz was determined. The TD-DFT approach was carefully benchmarked against CASPT2 results for the smallest systems. Despite some discrepancies, the trends were found to be similar at both levels of theory: the positions and intensities of the main $$\pi \rightarrow \pi ^{\star }$$ transitions were found slightly split due to symmetry breaking. For the smallest systems, our results clearly show the dependence of the electronic transitions on the clusters’ structures. Of particular interest, low energy transitions of non negligible oscillator strength from a Bz $$\pi$$ orbital to a virtual orbital of Rydberg character, also involving atomic diffuse functions and partially expanded on the water cluster, were found for the $$Geo_{IED}$$ series. The energies of such transitions were determined to be more than 2 eV below the ionization potential of Bz. When the cluster’s size increases, similar transitions were found for all structures, the virtual orbitals becoming mainly developed on the H atoms of the water molecules at the edge of the cluster. Given their nature and energy, such transitions could play a role in the photochemistry of aromatic species in interaction with water clusters or ice, such processes being of astrophysical interest.

Chemical reactivity and sorption in zeolites are coupled to confinement and-to a lesser extent-to the acid strength of Brønsted acid sites (BAS). In presence of water the zeolite Brønsted acid sites eventually convert into hydronium ions. The gradual transition from zeolite Brønsted acid sites to hydronium ions in zeolites of varying pore size is examined by ab initio molecular dynamics combined with enhanced sampling based on Well-Tempered Metadynamics and a recently developed set of collective variables. While at low water content (1-2 water/BAS) the acidic protons prefer to be shared between zeolites and water, higher water contents (n > 2) invariably lead to solvation of the protons within a localized water cluster adjacent to the BAS. At low water loadings the standard free energy of the formed complexes is dominated by enthalpy and is associated with the acid strength of the BAS and the space around the site. Conversely, the entropy increases linearly with the concentration of waters in the pores, favors proton solvation and is independent of the pore size/shape., Nature Communications, 12 (1), ISSN:2041-1723

Since molecular cluster ion beams are expected to have various chemical effects, they are promising candidates for improving the secondary ion yield of Tof-SIMS. However, in order to clarify the effect and its mechanism, it is necessary to generate molecular cluster ion beams with various chemical properties and systematically examine it. In this study, we have established a method to stably form various molecular cluster ion beams from relatively small amounts of liquid materials for a long time by the bubbling method. Furthermore, we applied the cluster ion beams of water, methanol, methane, and benzene to the primary beam of SIMS and compared the molecular ion yields of aspartic acid. The effect of enhancing the yields of [M+H]+ ion of aspartic acid was found to be the largest for the water cluster and small for the methane and benzene clusters. These results indicate that the chemical effect contributes to the desorption/ionization process of organic molecules by the molecular cluster ion beam.

We analyzed the interactions present in complexes that acetone, azomethane, dimethylamine, dimethyl ether, methyl acetate, and oxirane form with 39 different (H2O)n clusters (n = 1-10). A random generation of configurations and a subsequent screening procedure were employed to sample representative interactions. Using quantum chemical computations, we calculated the associated binding energies, which range from -0.19 to -10.76 kcal/mol at the DLPNO-CCSD(T)/CBS level. It was found that the binding energies can be understood in terms of various factors, including the water cluster size, the nature of the organic molecule, and the type of hydrogen bond donor. We find that the most stable complexes often arise from a combination of a strong hydrogen bond plus a secondary interaction between the organic molecule and the water cluster.

Microbial drinking water quality in premise plumbing systems (PPSs) strongly affects public health. Bacterial community structure is the essential aspect of microbial water quality. Studies have elucidated the microbial community structure in cold tap water, while the microbial community structures in hot tap and shower water are poorly understood. We sampled cold tap, hot tap, and shower water from a simulated PPS monthly for 16 consecutive months and assessed the bacterial community structures in those samples via high-throughput sequencing of bacterial 16S rRNA genes. The total relative abundance of the top five most abundant phyla (Proteobacteria, Actinobacteria, Bacteroidetes, Cyanobacteria, and Firmicutes) was greater than 90% among the 24 identified phyla. The most abundant families were Burkholderiaceae, Sphingomonadaceae, unclassified Alphaproteobacteria, unclassified Corynebacteriales, and Mycobacteriaceae. A multiple linear regression suggests that the bacterial community diversity increased with water temperature and the age of the simulated PPS, decreased with total chlorine residual concentration, and had a limited seasonal variation. The bacterial community in hot tap water had significantly lower Shannon and Inverse Simpson diversity indices (p < 0.05) and thus a much lower diversity than those in cold tap and shower water. The paradoxical results (i.e., diversity increased with water temperature, but hot tap water bacterial community was less diverse) were presumably because (1) other environmental factors made hot tap water bacterial community less diverse, (2) the diversity of bacterial communities in all types of water samples increased with water temperature, and (3) the first draw samples of hot tap water could have a comparable or even lower temperature than shower water samples and the second draw samples of cold tap water. In both a three-dimensional Non-metric multidimensional scaling ordination plot and a phylogenetic dendrogram, the samples of cold tap and shower water cluster and are separate from hot tap water samples (p < 0.05). In summary, the bacterial community in hot tap water in the simulated PPS had a distinct structure from and a much lower diversity than those in cold tap and shower water.

A recently proposed local self-interaction correction (LSIC) method [Zope \textit{et al.} J. Chem. Phys., 2019,{\bf 151}, 214108] when applied to the simplest local density approximation provides significant improvement over standard Perdew-Zunger SIC (PZSIC) for both equilibrium properties such as total or atomization energies as well as properties involving stretched bond such as barrier heights. The method uses an iso-orbital indicator to identify the single-electron regions. To demonstrate the LSIC method, Zope \textit{et al.} used the ratio $z_\sigma$ of von Weizs\"acker $\tau_\sigma^W$ and total kinetic energy densities $\tau_\sigma$, ($z_\sigma = \tau_\sigma^W/\tau_\sigma$) as a scaling factor to scale the self-interaction correction. The present work further explores the LSIC method using a simpler scaling factor as a ratio of orbital and spin densities in place of the ratio of kinetic energy densities. We compute a wide array of both, equilibrium and non-equilibrium properties using the LSIC and orbital scaling methods using this simple scaling factor and compare them with previously reported results. Our study shows that the present results with simple scaling factor are comparable to those obtained by LSIC($z_\sigma$) for most properties but have slightly larger errors. We furthermore study the binding energies of small water clusters using both the scaling factors. Our results show that LSIC with $z_{\sigma}$ has limitation in predicting the binding energies of weakly bonded system due to the inability of $z_{\sigma}$ to distinguish weakly bonded region from slowly varying density region. LSIC when used with density ratio as a scaling factor, on the other hand, provides good description of water cluster binding energies, thus highlighting the appropriate choice of iso-orbital indicator., Comment: 31 pages, 7 figures, 8 tables

In cold galactic molecular clouds, dust grains are coated by icy mantles and are prevalently charged negatively, because of the capture of the electrons in the gas. The interaction of the charged grains with gaseous cations is known to neutralize them. In this work, we focus on the chemical consequences of the neutralization process of HCO+, often the most abundant cation in molecular clouds. More specifically, by means of electronic structure calculations, we have characterized the energy and the structure of all possible product species once the HCO+ ion adsorbs on water clusters holding an extra electron. Two processes are possible: (i) electron transfer from the negative water cluster to the HCO+ ion or (ii) a proton transfer from HCO+ to the negative water cluster. Energetic considerations favor electron transfer. Assuming this scenario, two limiting cases have been considered in astrochemical models: (a) all the neutralized HCO+ is retained as neutral HCO adsorbed on the ice and (b) all the neutralized HCO+ gets desorbed to the gas phase as HCO. None of the two limiting cases appreciably contribute to the HCO abundance on the grain surfaces or in the gas.

Proton transport inside metal organics frameworks (MOFs) plays an important role to understand and develop a new type of material for a high conductivity application. One of the possible pathways of this process is via water cluster which is confined inside the MOFs structure. In this work, the mechanism of proton transport is investigated within the Density Functional Theory (DFT) calculations. Different water clusters from dimer to pentamer and octamer, which are equivalent to water structures inside the tetrahedral and cubic cavities of MOF-801, respectively, were systematically considered. The results show that proton transfer inside the pentamer cluster has the lowest barrier around 16 kJ/mol. Moreover, the presence of electric fields has a strong effect on the mechanism and energy profile of the proton transfer in both pentamer and octamer cluster. Our DFT prediction of proton migration energies is supported by experimental data of high conducting MOFs such as MOF-801.

International audience; Artificial water channels (AWCs) are known to selectively transport water, with ion exclusion. Similarly to natural porins, AWCs encapsulate water wires or clusters, offering continuous and iterative H-bonding that plays a vital role in their stabilization. Herein, we report octyl-ureido-polyol AWCs capable of self-assembly into hydrophilic hydroxy channels. Variants of ethanol, propanediol, and trimethanol are used as head groups to modulate the water transport permeabilities, with rejection of ions. The hydroxy channels achieve a single-channel permeability of 2.33 × 108 water molecules per second, which is within the same order of magnitude as the transport rates for aquaporins. Depending on their concentration in the membrane, adaptive channels are observed in the membrane. Over increased concentrations, a significant shift occurs, initiating unexpected higher water permeation. Molecular simulations probe that spongelike or cylindrical aggregates can form to generate transient cluster water pathways through the bilayer. Altogether, the adaptive self-assembly is a key feature influencing channel efficiency. The adaptive channels described here may be considered an important milestone contributing to the systematic discovery of artificial water channels for water desalination.

We review computational methods to locate energy transport networks in proteins that are based on the calculation of local energy diffusion in nanoscale systems. As an illustrative example, we discuss energy transport networks computed for the homodimeric hemoglobin from Scapharca inaequivalvis, where channels for facile energy transport, which include the cluster of water molecules at the interface of the globules, have been found to lie along pathways that experiments reveal are important in allosteric processes. We also review recent work on master equation simulations to model energy transport dynamics, including efforts to relate rate constants in the master equation to protein structural dynamics. Results for apomyoglobin involving relations between fluctuations in the length of hydrogen bonds and the energy flux between them are presented.

Kaolinite is widely distributed in shale formations. Kaolinite has two surface types, Si–O and Al–OH, and the two surfaces have different chemical properties. The surface wettability of kaolinite minerals is closely related to the occurrence of crude oil, the migration process of crude oil, and the filling process of crude oil. In this paper, we focus on the oil-water rock wettability of different alkane hydrocarbons on the different surfaces of kaolinite and construct a model of oil and water with variation of the alkane components on the surface of tetrahedral and octahedral kaolinite. Molecular dynamics methods were used to study the morphological changes in water clusters in different alkanes on different surfaces of kaolinite and to calculate the wetting angles. Studies have shown that the octahedral kaolinite surface is strongly hydrophilic, and the water clusters become monolayers adsorbed on the surface. Water easily displaces the oil on the surface and preferentially drives low carbon number alkanes. The tetrahedral siloxane kaolinite surface is oleophilic, the water molecules in C6H14–C18H38 are clustered on the surface, and the wetting angle of the water cluster in the alkane increases with increasing carbon number. Water has difficulty displacing oil on this surface.

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

Electrochemical activation of carbon dioxide in aqueous solution is a promising way to use carbon dioxide as a C1 building block. Mechanistic studies in the gas phase play an important role to understand the inherent chemical reactivity of the carbon dioxide radical anion. Here, the reactivity of CO2 −(H2O)n with 3-butyn-1-ol is investigated by Fourier transform ion cyclotron (FT-ICR) mass spectrometry and quantum chemical calculations. Carbon-carbon bond formation takes places, but is associated with a barrier. Therefore, bond formation may require uptake of several butynol molecules. The water molecules slowly evaporate from the cluster due to the absorption of room temperature black-body radiation. When all water molecules are lost, butynol evaporation sets in. In this late stage of the reaction, side reactions occur including H atom transfer and elimination of HOCO .

Two new Strandberg-type cluster-based phosphomolybdates {H-2a3mp}5[{PO3(OH)}{PO4}Mo5O15], 1 and {H-2a4mp}5[{PO3(OH)}{PO4}Mo5O15]·6H2O, 2 have been crystallized via solvent evaporation technique using 2-amino-3-methylpyridine (2a3mp) and 2-amino-4-methylpyridine (2a4mp) respectively. The solids were characterized using single-crystal X-ray diffraction, powder X-ray diffraction, fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy and cyclic voltammetry. The solid 1 crystallized in monoclinic system with space group P21/c, a = 8.394(1), b = 27.398(6), c = 21.521(4) A, β = 97.68(3)°, Z = 4. The solid 2 crystallized in triclinic system with space group P-1, a = 11.728(1), b = 14.234(1), c = 19.589(1) A, α = 68.906(3), β = 89.454(3), γ = 66.559(3)°, Z = 2. The solids 1 and 2 formed a supramolecular framework stabilized by hydrogen bonding interaction between cluster anions and organic moieties. CH…π interactions between the organic moieties reinforced the crystal packing in 1 and 2. While crystal packing effects resulted in the formation of solvent-accessible voids in 1; aggregation of lattice water molecules in 2 facilitated the formation of pentameric water cluster. In addition, electrochemical behavior of 1 and 2 has also been investigated. Two new Strandberg-type cluster based phosphomolybdates, 1 and 2 have been crystallized via solvent evaporation technique using 2-amino-3-methylpyridine and 2-amino-4-methylpyridine. Detailed structural analysis revealed the role of supramolecular interactions in the crystal packing of these solids. In addition, electrochemical behavior of 1 and 2 has also been investigated.

One believed path to Interstellar Complexes Organic Molecules (iCOMs) formation inside the Interstellar Medium (ISM) is through chemical recombination at the surface of amorphous solid water (ASW) mantle covering the silicate-based core of the interstellar grains. The study of these iCOMs formation and their binding energy to the ASW, using computational chemistry, depends strongly on the ASW models used, as different models may exhibit sites with different adsorbing features. ASW extended models are rare in the literature because large sizes require very large computational resources when quantum mechanical methods based on DFT are used. To circumvent this problem, we propose to use the newly developed GFN-xTB Semi-empirical Quantum Mechanical (SQM) methods from the Grimme's group. These methods are, at least, two orders of magnitude faster than conventional DFT, only require modest central memory, and in this paper we aim to benchmark their accuracy against rigorous and resource hungry quantum mechanical methods. We focused on 38 water structures studied by MP2 and CCSD(T) approaches comparing energetic and structures with three levels of GFN-xTB parametrization (GFN0, GFN1, GFN2) methods. The extremely good results obtained at the very cheap GFN-xTB level for both water cluster structures and energetic paved the way towards the modeling of very large AWS models of astrochemical interest., 9 pages, 4 figures, Submitted to LNCS (Springer) ICCSA2020

In High Kinetic Energy Ion Mobility Spectrometry (HiKE-IMS), ions are formed in a reaction region and separated in a drift region, which is similar to classical drift tube ion mobility spectrometers (IMS) operated at ambient pressure. However, in contrast to the latter, the HiKE-IMS is operated at a decreased background pressure of 10–40 mbar and achieves high reduced electric field strengths of up to 120 Td in both the reaction and the drift region. Thus, the HiKE-IMS allows insights into the chemical kinetics of ion-bound water cluster systems at effective ion temperatures exceeding 1000 K, although it is operated at the low absolute temperature of 45 °C. In this work, a HiKE-IMS with a high resolving power of RP = 140 is used to study the dependence of reduced ion mobilities on the drift gas humidity and the effective ion temperature for the positive reactant ions H3O+(H2O)n, O2+(H2O)n, NO+(H2O)n, NO2+(H2O)n, and NH4+(H2O)n, as well as the negative reactant ions O2–(H2O)n, O3–(H2O)n, CO3–(H2O)n, HCO3–(H2O)n, and NO2–(H2O)n. By varying the reduced electric field strength in the drift region, cluster transitions are observed in the ion mobility spectra. This is demonstrated for the cluster systems H3O+(H2O)n and NO+(H2O)n.

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