Solvent Water Molecules Research Articles

Inhibiting zinc dendrites and side reactions enabled by solvation structure regulation and facile de-solvation process

Rechargeable aqueous zinc-ion batteries show great promise as next-generation energy storage devices given their advantages of low cost and high safety. However, dendrite growth and detrimental side reactions result in poor reversibility of Zn anodes. Here, TEG molecules were introduced as additives to regulate the solvation structure through occupying the position of water molecules in the solvation shell, which also further decreasing the de-solvation energy barrier. The lower de-solvation energy barrier is beneficial for the dissociation of solvation water molecules and help to restrain the water decomposition and the related by-products. Theoretical studies also reveal that TEG is more easily adsorbed on the surface of zinc than water molecules, electrons are more easily transferred from the TEG molecule to the zinc foil, thus promoting the uniform deposition of zinc atoms. Benefiting from the solvation structure regulation and facile de-solvation process of Zn2+, Zn/Zn symmetric cell achieve a long cycling life of 2000 h at the current density and capacity of 1 mA cm−2 and 1mAh cm−2, and a MnO2-Zn full cell reach a superior stability of 3000 cycles at the current density of 1000 mA g−1.

The stability of oxygen-centered radicals and its response to hydrogen bonding interactions.

The stability of various alkoxy/aryloxy/peroxy radicals, as well as TEMPO and triplet dioxygen (3 O2 ) has been explored at a variety of theoretical levels. Good correlations between RSEtheor and RSEexp are found for hybrid DFT methods, for compound schemes such as G3B3-D3, and also for DLPNO-CCSD(T) calculations. The effects of hydrogen bonding interactions on the stability of oxygen-centered radicals have been probed by addition of a single solvating water molecule. While this water molecule always acts as a H-bond donor to the oxygen-centered radical itself, it can act as a H-bond donor or acceptor to the respective closed-shell parent.

Why Dissolving Salt in Water Decreases Its Dielectric Permittivity.

The dielectric permittivity of salt water decreases on dissolving more salt. For nearly a century, this phenomenon has been explained by invoking saturation in the dielectric response of the solvent water molecules. Herein, we employ an advanced deep neural network (DNN), built using data from density functional theory, to study the dielectric permittivity of sodium chloride solutions. Notably, the decrease in the dielectric permittivity as a function of concentration, computed using the DNN approach, agrees well with experiments. Detailed analysis of the computations reveals that the dominant effect, caused by the intrusion of ionic hydration shells into the solvent hydrogen-bond network, is the disruption of dipolar correlations among water molecules. Accordingly, the observed decrease in the dielectric permittivity is mostly due to increasing suppression of the collective response of solvent waters.

Examining the Hydration Behavior of Aqueous Calcium Chloride (CaCl2) Solution via Atomistic Simulations

Equilibrium molecular dynamics simulations are performed to examine the hydration behavior of Ca2+ and Cl− across a wide range of salt concentrations (from 1 wt.% to 60 wt.% CaCl2) in an aqueous solution. The predicted radial distribution functions (RDFs) and coordination numbers (CNs) of Ca2+–water, Cl−–water, and Ca2+–Cl− agree with the previous studies conducted at concentrations below the solubility limit at room temperature. The hydration limit of aqueous calcium chloride solution is identified at 10 wt.% CaCl2 as the CNs remain constant below it. Beyond the bulk solubility limit ~44.7 wt.% CaCl2, a noticeable decrease in the CN of Cl− and water is recorded, implying the saturation of the solution. The solvating water molecules decrease with increasing salt concentration, which can be attributed to the growth in the number of ion pairs.

Effect of Explicit Water Molecules on the Electrochemical Hydrogenation of CO2 on Sn(112)

Water is typically treated as an implicit solvent in modeling electrochemical reactions in an aqueous environment. Such treatment may not be adequate, as a series of concerted or sequential proton-electron transfer steps that explicitly involve water molecules are likely to play important roles in a reaction, such as the electrochemical hydrogenation of CO2. Herein, we use the electrochemical hydrogenation of CO2 on the Sn(112) surface as a model, and employ the density functional theory (DFT) method to examine the effect of up to 12 explicit water molecules on the stability of the hydrogenation intermediates. Our results show that six water molecules are needed to account for the local interaction between an intermediate and the water solvent. Furthermore, the hydrogen bonding interaction between the explicit water molecules and intermediates causes a significant stabilization to the O-containing intermediates, such as the HCOO* and CHO* + OH* species. The inclusion of explicit water molecules also altered the prediction of the potential-limiting step from the formation of H* atoms without the explicit water molecules to the formation of H2COO* in the presence of water molecules and increased selectivity towards methane. This work provides useful insights into the electrocatalytic hydrogenation of CO2, emphasizing the importance of including explicit water molecules to account for the hydrogen bonding interaction between solvent water molecules and the reaction intermediates.

Relation between the Hydrated Electron Solvation Structure and Its Partial Molar Volume.

It is now generally accepted that the hydrated electron occupies a cavity in water, but the size of the cavity and the arrangements of the solvating water molecules have not been fully characterized. Here, we use the Kirkwood-Buff (KB) approach to examine how the partial molar volume (VM) provides insight into these issues. The KB method relates VM to an integral of the electron-water radial distribution function, a key measure of the hydrated electron structure. We have applied it to three widely used pseudopotentials, and the results show that VM is a sensitive measure of the fidelity of hydrated electron descriptions. Thus, the measured VM places constraints on the hydrated electron structure that are important in developing and evaluating the model descriptions. Importantly, we find that VM does not reflect only the cavity size (and thus should not be used to infer the cavity radius) but is strongly dependent on the extended solvation structure.

Cocrystallization-Driven Double-Optimized Stratagem toward Directional Self-Assembly for the First Ternary Salt Cocrystal of Cardiotonic Drug Milrinone with Different Phenolic Acids Exhibits Optimal In Vitro/Vivo Biopharmaceutical Peculiarities.

The current research leverages the structural features and property superiorities along with benefits in protecting cardiovascular system of gallic acid (GLC) and gentisic acid (HGA) to optimize in vitro/vivo peculiarities of cardiotonic drug milrinone (MIL) through developing a stratagem of cocrystallization-driven double-optimized ternary salt cocrystal. This strategy assembles MIL ternary salt cocrystal by shaping a cocrystallization moiety relying on noncovalent interplays with GLC to obtain permeability advancement and molding a salt segment via the salification of proton transfer between HGA and MIL molecules to facilitate solubility enhancement. While the ameliorative in vitro properties further modulate the in vivo pharmacokinetic behaviors, thus fulfilling a dual optimization of MIL's biopharmaceutical characteristics on both in vitro and in vivo aspects. Along this line, the first MIL ternary salt cocrystal, viz., [HMIL+-GA-]-MIL-GLC-H2O (denoted as MTSC hereinafter), has been satisfactorily constructed and precisely structurally identified by diversified techniques. The single-crystal X-ray diffraction experiment validates that a molecular salt [HMIL+-GA-] species cocrystallizes with one neutral MIL, two GLC, and five solvent water molecules, among which the organic constituents compose laminated hydrogen bond networks, and then are self-assembled by water molecules to a 3D supramolecular structure. The unique structural feature and stacking pattern of MTSC make both the permeability and solubility be respectively enhanced by 9.69 times and 5.17- to 6.03-fold compared with the parent drug per se. The experimental outcomes are powerfully supported by associated calculations based on density functional theory. Intriguingly, these optimal in vitro physicochemical natures of MTSC have been potently converted into strengths of in vivo pharmacokinetics, showcasing the elevated drug plasma concentration, elongated half-life, alongside advanced bioavailability. Consequently, this presentation not just contributes a brand-new crystalline form with utility values, but ushers in a new dimension of ternary salt cocrystals for improving in vitro/vivo limitations of poor drug bioavailability.

Twisted Intramolecular Charge Transfer‐Based Fluorometric Detection of D‐fructose by Boronic Acid‐Containing BF2‐β‐Diketonate Complexes

AbstractNovel BF2‐β‐diketonate complexes 1–4 bearing phenylboronic acid moieties and methoxyphenyl or dimethylaminophenyl groups were synthesized and their photophysical properties, pH response, and reactivity to D‐fructose were evaluated. Complexes 1 and 2 bearing a methoxyphenyl group luminesced with high intensity in a range of non‐polar to polar solvents, except in DMSO, whereas complexes 3 and 4 containing a dimethylaminophenyl group with twisted intramolecular charge transfer (TICT) properties showed a dramatic decrease in luminescence intensity with increasing solvent polarity. The luminescence intensity of complexes 1 and 2 decreased with increasing pH due to intermolecular vibration which associated with hydrogen bonding between the complexes and solvent water molecules, whereas it increased when they reacted with D‐fructose due to the suppression of the intermolecular vibration. In contrast, the luminescence intensity of complexes 3 and 4 increased with increasing pH and upon reaction with D‐fructose due to the loss of its TICT properties. The photophysical properties of complexes 1–4 and the TICT properties of complexes 3 and 4 were supported by density functional theory calculations.

Interfacial binding rope theory of ion transport in sub-nanochannels and its application for osmotic energy conversion

Osmotic energy conversion is a promising method of sustainable electricity generation using seawater and river water. Artificial pure NaCl solutions are commonly used, whereas the effects of multivalent-ion ingredients present in natural seawater on osmotic power generation remain unclear. In this study, the impacts of coexisting ions in multicomponent seawater (MS) are experimentally assessed using graphene oxide membrane (GOM). Divalent cation in MS shows inferior transport to monovalent cation, thereby presenting a lower power density than when using pure NaCl solutions. Inspired by experimental results, an interfacial binding rope theory is proposed to clarify ion-wall interactions and cation transport in sub-nanochannels with hydrophilic functional groups. The binding rope networks include direct cation-wall connections mediated by composition-changed hydration shells, indirect connections by H-bonds linking solvated water molecules and functional groups, and electrostatic attractions between cations and negatively charged surfaces. The theory feasibility is confirmed by first-principles calculations focusing on the charge distribution, binding site and length, surface electrification, and cation diffusivity and selectivity in GOM sub-nanochannels. Divalent cation diffuses slower than monovalent cation in both pure solutions and confined channels. For the mixed solution in channels, both monovalent and divalent cations show worse diffusivities due to additional monovalent-divalent electrostatic repulsions, as well as inferior cation selectivity due to weakened deprotonation reactions. Bridged by environment-controlled interfacial potential distribution, ion diffusivity, and ion selectivity, this theory guides the improvement of MS-based osmotic performance under regulations of concentration gradient, pH, and temperature. A power density of 8.52 W m–2 and stable output within 27 days are achieved. The interfacial binding rope theory could be popularized to refine the transport mechanisms of various cations in diverse hydrophilic sub-nanochannel materials, promoting the application of osmotic power generation and other nanoscale technologies.

Study of the Magnesium Comenate Structure, Its Neuroprotective and Stress-Protective Activity.

The crystal structure and the biological activity of a new coordination compound of magnesium ions with comenic acid, magnesium comenate, was characterized and studied. Quantitative and qualitative analysis of the compound was investigated in detail using elemental X-ray fluorescent analysis, thermal analysis, IR-Fourier spectrometry, UV spectroscopy, NMR spectroscopy, and X-ray diffraction analysis. Based on experimental analytical data, the empirical formula of magnesium comenate [Mg(HCom)2(H2O)6]·2H2O was established. This complex compound crystallizes with eight water molecules, six of which are the hydration shell of the Mg2+ cation, and two more molecules bind the [Mg(H2O)6]2+ aquacation with ionized ligand molecules by intermolecular hydrogen bonds. The packing of molecules in the crystal lattice is stabilized by a branched system of hydrogen bonds with the participation of solvate water molecules and oxygen atoms of various functional groups of ionized ligand molecules. With regard to the biological activity of magnesium comenate, a neuroprotective, stress-protective, and antioxidant effect was established in in vitro and in vivo models. In in vitro experiments, magnesium comenate protected cerebellar neurons from the toxic effects of glutamate and contributed to the preservation of neurite growth parameters under oxidative stress caused by hydrogen peroxide. In animal studies, magnesium comenate had a stress-protective and antioxidant effect in models of immobilization-cold stress. Oral administration of magnesium comenate at a dose of 2 mg/kg of animal body weight for 3 days before stress exposure and for 3 days during the stress period led to a decrease in oxidative damage and normalization of the antioxidant system of brain tissues against the background of induced stress. The obtained results indicate the advisability of further studies of magnesium comenate as a compound potentially applicable in medicine for the pharmacological correction of conditions associated with oxidative and excitotoxic damage to nerve cells.

New yttrium tropolonato-based complexes: synthesis, X-ray crystal structures and thermal properties

New yttrium complexes containing HT (tropolone, 2-hydroxy-2,4,6-cycloheptatrien-1-one) and its anion, [Y(H2O)2T3]·0.5H2O, [Y(H2O)2(HT)T2]·NO3·0.5HNO3 and [Y(HT)T3]2, were synthesized and structurally characterized. In all compounds, the coordination number (CN) of yttrium is 8 and the coordination mode is YO8. In reactions with bidentate N-donor ligands, phen (1,10-phenantroline) and Bath (4,7-diphenyl-1,10-phenanthroline), anhydrous, non-hygroscopic, heteroleptic mononuclear complexes [Y(phen)T3] and [Y(Bath)T3]·0.5EtOH with CN = 8 and YO6N2 coordination mode were obtained. During thermolysis of [Y(H2O)2T3]·0.5H2O, the removal of coordinated and solvate water molecules leads to the formation of anhydrous YT3 remaining stable up to 320° C, which is also characteristic of [Y(HT)T3]2 thermolysis. Decomposition of tropolonate complexes containing phenanthroline occurs at temperatures >300 °C.

Syntheses, crystal structures and Hirshfeld surface analysis of three salts of 1-(4-nitro-phenyl)-piperazine.

The structures and Hirshfeld surface analysis of three salts of 1-(4-nitro-phenyl)-piperazine are discussed. In 4-(4-nitro-phen-yl)piperazin-1-ium salicylate (C10H14N3O2 +·C7H5O3 -), there are strong hydrogen bonds between cation and anion and the 4-nitro-phenyl substituent occupies an equatorial position in the piperazinium ring. The cation and anion are linked together by supra-molecular inter-actions [graph-set notation of hydrogen bonding (6) propagating in the a-axis direction]. Additionally, there is π-π stacking involving the salicylate anion and the piperazinium cation in adjacent asymmetric units as well as a C-H⋯π inter-action between a hydrogen atom on the piperazine ring and the phenyl ring within the salicyclate anion. In bis-[4-(4-nitro-phen-yl)piperazin-1-ium] bis-(4-fluoro-benzoate) trihydrate (2C10H14N3O2 +·2C7H4FO2 -·3H2O), there are two cations, two anions, and three water mol-ecules of solvation in the asymmetric unit, all linked by hydrogen bonds [graph-set notation of hydrogen bonding R 2 2(20) between adjacent cations and R 3 3(9) between a cation and its adjacent anion]. In the anion, the 4-nitro-phenyl ring occupies an axial substitution position in the piperazinium ring, which is relatively rare. Within the asymmetric unit, the phenyl groups in the cations show an offset π-π inter-action. Additionally, there is a C-H⋯π inter-action between a hydrogen atom on the phenyl ring within a cation and the phenyl ring within an anion. In 4-(4-nitro-phen-yl)piperazin-1-ium 3,5-di-nitro-benzoate (C10H14N3O2 +·C7H4N2O6 -), there is a strong N-H⋯O hydrogen bond linking the cation and anion and the 4-nitro-phenyl ring occupies an axial substitution position in the piperazinium ring, as seen in the previous structure. In the crystal, the cation and the anion form a complex three-dimensional hydrogen-bonded array involving R 2 2(8), R 4 4(12) and R 4 4(20) rings propogating in the a-axis direction. The nitro-phenyl group is disordered with occupancies of 0.806 (10) and 0.194 (10).

Pyrrolidine-Derived Phenanthroline Diamides: An Influence of Fluorine Atoms on the Coordination of Lu(III) and Some Other f-Elements and Their Solvent Extraction.

Three pyrrolidine-derived phenanthroline diamides were studied as ligands for lutetium trinitrate. The structural features of the complexes have been studied using various spectral methods and X-ray. The presence of halogen atoms in the structure of phenanthroline ligands has a significant impact on both the coordination number of lutetium and the number of solvate water molecules in the internal coordination sphere. The stability constants of complexes with La(NO3)3, Nd(NO3)3, Eu(NO3)3, and Lu(NO3)3 were measured to demonstrate higher efficiency of fluorinated ligands. NMR titration was performed for this ligand, and it was found that complexation with lutetium leads to an approximately 13 ppm shift of the corresponding signal in the 19F NMR spectrum. The possibility of formation of a polymeric oxo-complex of this ligand with lutetium nitrate was demonstrated. Experiments on the liquid-liquid extraction of Am(III) and Ln(III) nitrates were carried out to demonstrate advantageous features of chlorinated and fluorinated pyrrolidine diamides.

Solvation effects on glyphosate protonation and deprotonation states evaluated by mass spectrometry and explicit solvation simulations.

Glyphosate is a widely used herbicide, and its protonation and deprotonation sites are fundamental to understanding its properties. In this work, the sodiated, protonated, and deprotonated glyphosate were evaluated in the gas phase by infrared multiple photon dissociation spectroscopy to determine the exact nature of these coordination, protonation, and deprotonation states in the gas phase. In this context, Natural Bond Orbital analyses were carried out to unravel interactions that govern glyphosate (de)protonation states in the gas phase. The solvent effect on the protonation/deprotonation equilibria was also investigated by implicit (Solvation Model Based on Density and polarizable continuum models) and explicit solvation models (Monte Carlo and Molecular Dynamics simulations). These results show that glyphosate is protonated in the phosphonate group in the gas phase because of the strong hydrogen bond between the carboxylic oxygen (O7) and the protonated phosphonate group (O8-H19), while the most stable species in water is protonated at the amino group because of the preferential interaction of the NH2 + group and the solvent water molecules. Similarly, deprotonated glyphosate [Glyp-H]- was shown to be deprotonated at the phosphonate group in the gas phase but not in solution, also because of the preferential solvation of the NH2 + group present in the other deprotomers. Therefore, these results show that the stabilization of the protonated amino group by the solvent molecules is the governing factor of the (de)protonation equilibrium of glyphosate in water.

Zooming into the Inner Helmholtz Plane of Pt(111)-Aqueous Solution Interfaces: Chemisorbed Water and Partially Charged Ions.

The double layer on transition metals, i.e., platinum, features chemical metal-solvent interactions and partially charged chemisorbed ions. Chemically adsorbed solvent molecules and ions are situated closer to the metal surface than electrostatically adsorbed ions. This effect is described tersely by the concept of an inner Helmholtz plane (IHP) in classical double layer models. The IHP concept is extended here in three aspects. First, a refined statistical treatment of solvent (water) molecules considers a continuous spectrum of orientational polarizable states, rather than a few representative states, and non-electrostatic, chemical metal-solvent interactions. Second, chemisorbed ions are partially charged, rather than being electroneutral or having integral charges as in the solution bulk, with the coverage determined by a generalized, energetically distributed adsorption isotherm. The surface dipole moment induced by partially charged, chemisorbed ions is considered. Third, considering different locations and properties of chemisorbed ions and solvent molecules, the IHP is divided into two planes, namely, an AIP (adsorbed ion plane) and ASP (adsorbed solvent plane). The model is used to study how the partially charged AIP and polarizable ASP lead to intriguing double-layer capacitance curves that are different from what the conventional Gouy-Chapman-Stern model describes. The model provides an alternative interpretation for recent capacitance data of Pt(111)-aqueous solution interfaces calculated from cyclic voltammetry. This revisit brings forth questions regarding the existence of a pure double-layer region at realistic Pt(111). The implications, limitations, and possible experimental confirmation of the present model are discussed.

Three new zinc(II) 4′-chloro-2,2′:6′,2ʺ-terpyridine (4′-Cltpy)-based complexes: synthesis, spectroscopic and structural studies, thermal behavior, and Hirshfeld surface analysis

Three new ZnII complexes with the ligand 4′-chloro-2,2′:6′,2ʺ-terpyridine (4′-Cltpy), [Zn(4′-Cltpy)(N3)2] (1), [Zn(4′-Cltpy)(NCS)2] (2) (two 1:1 metal/ligand complexes) and a 1:2 metal/ligand complex, [Zn(4′-Cltpy)2](NO3)2·2H2O (3), have been synthesized and characterized by elemental analysis, IR, 1H NMR spectroscopy and single-crystal X-ray diffraction. The structures of 1 and 2 contain a ZnN5 coordination sphere, which includes coordination from three nitrogen donors of the 4′-Cltpy ligand and two nitrogen atoms of two terminal azide or two terminal thiocyanate ligands, respectively. Addison’s τ value suggests a distorted square pyramidal coordination of ZnII in 1 and intermediate between square pyramidal and trigonal bipyramidal in 2. In the complex cation of 3, the ZnII center is coordinated by six nitrogen atoms from two 4′-Cltpy ligands in a distorted octahedral coordination geometry. In this structure, two non-coordinating nitrate anions serve as counterions, and there are two non-coordinating solvent water molecules. Hirshfeld surface analysis was employed to clarify the nature and extent of intermolecular interactions. In addition, the thermal stabilities of the compounds were evaluated by thermogravimetric analysis (TGA).

Microsolvation of phenol in water: structures, hydration free energy and enthalpy

ABSTRACT In this work, we have studied the microsolvation of phenol in water. We started by identifying initial configurations of phenol-water clusters using classical molecular dynamics. The configurations are optimised at the ωB97XD/aug-cc-pVDZ level of theory. To understand the interaction between phenol and the solvating water molecules, we performed a quantum theory of atoms in molecules (QTAIM) analysis. The results show that the structures of phenol-water clusters are similar to those of neutral water clusters. The QTAIM analysis shows that the structures of phenol-water clusters are stabilised by strong OH··· O hydrogen bondings, weak CH··· O hydrogen bondings, and OH bonding interactions. The located structures of phenol-water clusters have been used to calculate the absolute hydration free energy and enthalpy of phenol for temperatures between 20 and 400 K. The hydration energies are calculated using the cluster continuum solvation model. It has been found that the explicit solvation has negligible effects on the hydration free energy and enthalpy of phenol. Furthermore, the hydration free energy of phenol is found to be linearly varying with increasing temperature, while the hydration enthalpy is found to be temperature independent. The estimated hydration free energy of phenol is slightly underestimated as compared to a previously reported experimental estimate.

Two metal-free perovskite molecules with different 3D frameworks show reversible phase transition, dielectric anomaly and SHG effect.

Three-dimensional (3D) hybrid organic-inorganic perovskites (HOIPs) have attracted tremendous research interest due to their unique structure and promising applications. However, research on the design, synthesis and properties of this kind of metal-free crystalline material is still in the exploratory stage. Herein, two 3D perovskite molecules [1,4-3.2.2-dabcn]NH4Br3 (1) and [1,4-3.2.2-dabcn]NH4I3·0.5H2O (2) were obtained by reacting 1,4-diazabicyclo[3.2.2]nonane (1,4-3.2.2-dabcn) with NH4X (X = Br and I) in the corresponding concentrated halogen acids. The single X-ray diffraction results demonstrated that the inorganic framework structures in compounds 1 and 2 constructed with NH4Br and NH4I are completely different, caused by the radius of the bromide ion being smaller than that of the iodide ion. The 3D framework of compound 1 is constructed with a coplanar dimer [(NH4)2Br6]2- as the basic building unit, leading to the expanded 3D perovskite framework structure with a larger cavity to accommodate the 1,4-3.2.2-dabcn molecule. Nevertheless, compound 2 adopts a familiar 3D crystal framework structure with corner-sharing [(NH4)I6] octahedra, where the [1,4-3.2.2-dabcn] cations and water solvent molecule are confined in the cavities enclosed by the octahedra. Notably, both compounds exhibit reversible phase transition, dielectric anomaly and the second harmonic generation (SHG) effect. From the perspective of molecular design, this work is of great significance to guide the construction of new 3D metal-free perovskite molecular materials with reversible properties.

Synthesis of interstellar propen-2-ol (CH3C(OH)CH2) - the simplest enol tautomer of a ketone.

Enols - tautomers of ketones or aldehydes - are anticipated to be ubiquitous in the interstellar medium and play a key role in the formation of complex organic molecules in deep space, but their fundamental formation mechanisms have remained largely elusive as of now. Here we present a combined experimental and computational study demonstrating the first preparation of propen-2-ol (CH3C(OH)CH2) and its isomer methyl vinyl ether (CH3OCHCH2) in low-temperature acetone (CH3COCH3) ices upon exposure to energetic electrons. Propen-2-ol is the simplest enol tautomer of a ketone. Exploiting tunable vacuum ultraviolet photoionization in conjunction with reflectron time-of-flight mass spectrometry, propen-2-ol and methyl vinyl ether were monitored in the gas phase upon sublimation during the temperature-programmed desorption process suggesting that both isomers are promising candidates for future astronomical searches such as via the James Webb Space Telescope. Electronic structure calculations reveal that the barrier of keto-enol tautomerization can be reduced by more than a factor of two (162 kJ mol-1) through the involvement of solvating water molecules under realistic conditions on interstellar grains. The implicit solvent effects, i.e., the influences of the solvent dipole field on the barrier height are found to be minimal and do not exceed 10 kJ mol-1. Our findings signify a crucial step toward a better understanding of the enolization of ketones in the interstellar medium thus constraining the molecular structures and complexity of molecules that form in extraterrestrial ices - ketones - through non-equilibrium chemistry.

Aldehyde Hydrogenation by Pt/TiO2 Catalyst in Aqueous Phase: Synergistic Effect of Oxygen Vacancy and Solvent Water.

The aldehyde hydrogenation for stabilizing and upgrading biomass is typically performed in aqueous phase with supported metal catalysts. By combining density functional theory calculations and ab initio molecular dynamics simulations, the model reaction of formaldehyde hydrogenation with a Pt/TiO2 catalyst is investigated with explicit solvent water molecules. In aqueous phase, both the O vacancy (Ov) on support and solvent molecules could donate charges to a Pt cluster, where the Ov could dominantly reduce the Pt cluster from positive to negative. During the formaldehyde hydrogenation, the water molecules could spontaneously protonate the O in the aldehyde group by acid/base exchange, generating the OH* at the metal-support interface by long-range proton transfer. By comparing the stoichiometric and reduced TiO2 support, it is found that the further hydrogenation of OH* is hard on the positively charged Pt cluster over stoichiometric TiO2. However, with the presence of Ov on reduced support, the OH* hydrogenation could become not only exergonic but also kinetically more facile, which prohibits the catalyst from poisoning. This mechanism suggests that both the proton transfer from solvent water molecules and the easier OH* hydrogenation from Ov could synergistically promote aldehyde hydrogenation. That means, even for such simple hydrogenation in water, the catalytic mechanism could explicitly relate to all of the metal cluster, oxide support, and solvent waters. Considering the ubiquitous Ov defects in reducible oxide supports and the common aqueous environment, this synergistic effect may not be exclusive to Pt/TiO2, which can be crucial for supported metal catalysts in biomass conversion.