Intermolecular forces are the fundamental architects of supramolecular structure, where subtle interplays of charge distribution, entropy, and sterics determine the outcome. In aromatic molecules, the distribution of delocalised π electrons is modulated by the substituents, affecting their intermolecular interactions and introducing “holes” in the π orbitals. While increasingly well-understood in the solid state, the influence of π-holes on solvation and miscibility in the liquid remains unknown. Here, total neutron scattering and modelling-based refinement reveal the solvation of phenol, aniline, and p-nitrophenol in water. The in-plane solvation is dominated by strong classical hydrogen bonds between water and the substituents. Out of the ring plane, perpendicular OH···π weak hydrogen bonds between water and phenol or aniline are cooperative and modulated by differences in electron density. By contrast, in p-nitrophenol, the presence of the electron-withdrawing nitro group enhances the overall molecular dipole, and introduces a pronounced π-hole that significantly disrupts the overall out-of-plane solvation. The latter is dominated by close water-O···N contacts at ≈ 3.35 Å resulting from localized charge depletion accompanied by O···π* motifs (≈ 3.96 Å). These interactions template the structure of the surrounding water, redefining the solubility of these aromatics in water and underscoring the complex solvation of organic molecules. The influence of π-holes on solvation and miscibility of aromatic molecules in water remains unclear. Here, the authors show that aromatic hydration is dominated by weak OH···π hydrogen bonds rather than by conventional hydrogen bonds via the substituents.

Amorphous solid water (ASW), formed via vapour deposition under low temperature and pressure conditions, has been the focus of physical- and astro-chemists for some time as it represents the most likely formation process for interstellar ices. The porous structure of ASW has been found to be significantly impacted by deposition conditions, with little literature on the specific impacts of deposition temperature. This work utilises total neutron scattering (TNS) and small angle neutron scattering (SANS) to provide direct experimental evidence that deposition temperature does indeed have a significant impact on the structure of grown ASW. At low deposition temperatures, the ASW structure is highly porous and seemingly in the form of nanoporous islands/grains with voids between them - with these two populations of pores making up the total porosity. With increasing deposition temperatures, the nanopores in the islands become smaller until they are no longer present at temperatures above 80 K, whereby the voids start to dominate. Therefore, even at higher deposition temperatures, there is still porosity present from void volume, rather than being a fully compact ice.

Total neutron scattering (TNS) has emerged as a powerful experimental method for characterising structural properties of liquids confined at nanoscale in porous materials, yet its application to studying room-temperature gas adsorption remains relatively unexplored. This work investigates the feasibility and sensitivity of TNS in detecting subtle structural responses for adsorption of gases including N₂, O₂, simulated Air, and CO₂ in zeolite 13X, under conditions typical of pressure swing adsorption (1 and 5 bar) utilised in medical oxygen concentrators (MOCs). Experimental results illustrate the capability of TNS to detect minor structural alterations induced by gas adsorption, thereby validating its potential as an insightful analytical method. Although the observed changes confirm known molecular interactions and adsorption behaviours, the precise molecular-level interpretation and mechanistic insights will predominantly derive from subsequent advanced molecular simulations. Future research will prioritise the development of quantitative TNS approaches through refined modelling protocols, aiming to accurately describe the spatial distribution of adsorbed gas molecules within zeolite frameworks. Thus, this work positions TNS not merely as a supportive technique but as a critical approach for deepening our fundamental understanding of molecular interactions of fluids confined in porous systems.

Intermolecular forces are the fundamental architects of supramolecular structure. From liquid miscibility to the formation of organic crystals and biological structures, subtle interplays of charge distribution determine the outcome. Aromatic rings are a key motif in organic chemistry that provide rigid and highly directional interactions in proteins and nucleic acids. The distribution of the aromatic delocalised π electrons is strongly modulated by the substituents, giving rise to complex charge patterns across the molecule that affect reactivity and intermolecular interactions. These patterns range from axial dipoles to localised "holes" in the delocalized π network. While increasingly well-understood in the solid state, their influence on solvation and miscibility in the liquid remains unknown. We exploited neutron total scattering and experimentally constrained Monte Carlo simulations to picture the solvation of three aromatics in water: phenol, aniline, and p-nitrophenol. We observe the expected strong classical hydrogen bonds between the water and the OH, NH2, and NO2 substituents. Out of the ring plane, the solvation of phenol and aniline is centred around perpendicular, non-classical OH···π interactions. By contrast, for p-nitrophenol, the presence of the electron-withdrawing nitro group enhances the overall molecular dipole, and introduces a pronounced π hole on the nitro group that significantly disrupts the out-of-plane solvation. The latter is dominated by a close O···N contact (3.44 Å) accompanied by longer O···centroid interactions (~4.00 Å) resulting from localized charge depletion in the ring. These interactions begin to explain the complex solubility behaviour of these systems and highlight the complexity of the solvation of organic molecules.

In recent years, it has been shown that deep eutectic solvents (DES) and similar mixtures solvate and allow for self-assembly of surfactants, serving as potential "green" alternatives as solvents for, for example, templating nanomaterials or drug delivery applications. Which surfactants are soluble and how they self-assemble depends strongly on the mixture components and their molar ratio. Here, we present the surfactant behavior in halogen-free citric acid: glycerol-based systems and show how a change in the molar ratio can affect the micellization of cationic surfactants. We also study micellization of nonionic ethylene oxide surfactants, which are insoluble in the most common hydrophilic choline chloride-based DES, such as choline chloride: urea and choline chloride: glycerol, in the absence of water. We find that the cationic C12TANO3 and C16TANO3 form spherical micelles with significantly higher intermicellar interactions than in comparable choline chloride-based DES, indicating that less charge screening due to the solvent components takes place. The nonionic Brij L23 (main component C12EO23) is also found to form spherical micelles in 1:2 citric acid: glycerol, while the nonionic Brij L4 (main component C12EO4) forms less clearly structured phases at similar concentrations.

Due to their high reactivity, organolithium and organomagnesium addition to ketones is usually performed under inert atmosphere at low temperature. Recent work has shown that, by dissolving the substrate in deep eutectic solvents (DES), these processes can be carried out on the benchtop, in air at room temperature. Surprisingly, the organometallic reagent, added to the DES from an organic solution, works in these conditions and gives better yields than in the standard setup. Here, we investigated acetophenone in a (1:2) choline chloride:glycerol (ChCl:Gly) DES solution by experimental liquid diffraction, neutron reflectometry, NMR, interfacial tension measurements, and by computational modelling. Our data show that this DES is a poor solvent for the ketone and promotes its accumulation at the surface of the liquid or its escape into the organic solvent. Molecular dynamics simulations of Grignard reagent i-PrMgCl in the (ChCl:Gly)/tetrahydrofuran biphasic system indicate also preference for its localisation at the interface. These results pinpoint why this combination of solvents promote the reaction, require stirring, and accounts for the lack of rapid decomposition of the organometallic reagents.

The concentration dependent structure of ethylene glycol/water mixtures at room temperature was investigated. Mixtures with concentrations XEG = 1, 0.9, 0.46, 0.11 were examined by total neutron scattering. The neutron scattering data was then used to constrain molecular simulations of the studied systems to allow for in depth analysis of the systems' structures. It was found that at low ethylene glycol concentrations (XEG = 0.11) water structure was preserved, and ethylene glycol molecules were well hydrated. At the intermediate concentrations (XEG = 0.46) the tetrahedral ordering of water was lost and water molecules existed as interconnected string-like structures. At high concentrations (XEG = 0.9), water molecules were completely isolated mostly existing as single molecules or dimers. This behaviour is in contrast to aqueous mixtures of mono-alcohols such as methanol, isopropanol, tert-butanol where water structure can be found to persist even at high alcohol concentrations. Evidence for intra-molecular hydrogen bonding in ethylene glycol was found at all concentrations but became much more significant in the more diluted mixtures. These structural features of the ethylene glycol/water mixtures may explain their cryoprotectant or antifreeze properties as well as other concentration dependent properties.

The wide range of properties, relative ease and low cost of using Deep Eutectic Solvents garners them interest in an ever expanding range of applications. Among common DES components many are naturally occurring chiral molecules. Here we present the liquid structure of either single enantiomeric or racemic tartaric acid with choline chloride with (molar ratio of 2 choline chloride to 1 tartaric acid), as well as the influence of low amounts of added water (2:1:2) from neutron scattering data with H/D isotropic substitution, refined using empirical potential structure refinement. We show that the overall structure remains the same between the different enatiomeric compositions, with small differences in interactions only occurring between the tartaric acid molecules. The overall structure is also robust towards hydration, similar to what has been found in other DES. We also compare our structures to the structures of DES comprising of similar carboxylic acids (1:1 choline chloride - malic acid, 1:1 choline chloride - oxalic acid), finding overall similar dominant interactions, with differences that may be attributable to the number of available hydrogen bonding sites and steric effects.

Understanding the nature of intermediates/active species in reactions is a major challenge in chemistry. This is because spectator species typically dominate the experimentally derived data and consequently active phase contributions are masked. Transient methods offer a means to bypass this difficulty. In particular, modulation excitation with phase-sensitive detection (ME-PSD) provides a mechanism to distinguish between spectator and reacting species. Herein, modulation excitation (ME) time-resolved (energy dispersive) X-ray absorption spectroscopy, assisted by phase sensitive detection (PSD) analysis, has been applied to the study of a liquid phase process; in this case the classic ferrocyanide/ferricyanide redox couple. Periodic switches of the electrical potential (anodic/cathodic) enabled the use of the ME approach. Structural changes at fractions as low as 2 % of the total number of electroactive species were detected within the X-ray beam probe volume containing ~30 pmol of Fe(II)/Fe(III).

Eutectic mixtures of choline chloride, urea, and water in deep eutectic solvent (DES)/water molar hydration ratios (w) of 2, 5, and 10, with dissolved cerium salt, were measured using neutron diffraction with isotopic substitution. Structures were modeled using empirical potential structure refinement (EPSR). Ce3+ was found to form highly charged complexes with a mean coordination number between 7 and 8, with the shell containing mostly chloride, followed by water. The shell composition is strongly affected by the molar ratio of dilution, as opposed to the mass or volume fraction, due to the high affinity of Cl- and H2O ligands that displace less favorable interactions with ligands such as urea and choline. The presence of Ce3+ salt disrupted the bulk DES structure slightly, making it more electrolyte-like. The measured coordination shell of choline showed significant discrepancies from the statistical noninteracting distribution, highlighting the nonideality of the blend. Cluster analysis revealed the trace presence of percolating water clusters (25 ≥ n ≥ 2) in solvent compositions of 5 and 10w for the first time.

In this work, H/D isotopic substitution neutron diffraction was combined with empirical potential structure refinement (EPSR) and DFT-based quantum calculations to study the interactions between B(OH)3 boric acid molecules, B(OH)4- metaborate ions, water molecules, and potassium cations in borate solutions. The results show that the solute ions and molecules have a marked effect on the second coordination shell of the water molecules, causing a greater deviation from a tetrahedral structure than is observed for pure water. Potassium ions and trans-B(OH)3 tend to form a monodentate contact ion pair (MCIP) with a K-B distance ∼3.8 Å, which remains constant upon changing the solution concentration. Potassium ions and cis-B(OH)3 form both a MCIP at K-B ∼3.8 Å and a bidentate contact ion pair (BCIP) at K-B ∼3.4 Å. As the solution concentration increases, there is a BCIP to MCIP transformation. Boric acid molecules can undergo hydration in one of three ways: direct hydration, interstitial hydration, and axial hydration. The energetic hydration preference is direct hydration → interstitial hydration → axial hydration. Nine water molecules are required when all water molecules directly interact with the -OH groups of B(OH)4-, and a tenth water molecule is located at an interstitial position. The hydrogen bonding between boric acid molecule/metaborate ion and water molecules is stronger than that between water molecules in the hydration layer.

Calcium silicate hydrate (C-S-H) is a disordered, nanocrystalline material that acts as a primary binding phase in Portland cement. Thin films of water are present on the surfaces and in nanopores of C-S-H, impacting many of its chemical and mechanical properties, such as ion transport, creep, or thermal behavior. Despite decades of research, a full understanding of the structural details of adsorbed, confined, and bulk water in C-S-H remains elusive. In this work, we applied a multitechnique study involving molecular dynamics (MD) simulations validated by neutron diffraction with isotopic substitution (NDIS) and X-ray scattering methods to investigate the structure of water in C-S-H and C-A-S-H (an Al-bearing, low-CO2 C-S-H substitute). Direct comparison of NDIS data with the MD results reveals that the structure of confined and interfacial water differs significantly from the bulk water and exhibits a larger degree of mesoscale ordering for more hydrated C-S-H structures. This observation suggests an important role of water as a stabilizer of the atomistic-level structure of C-S-H.

We determine the structural origin of an "atomic-spring-like effect" in a glassy silica-helium composite, which exhibits this mechanical property that reversibly accumulates and restores energy at the subnanoscale based on a high-pressure experimental pair distribution function study combined with atom-scalemolecular simulations. These unexpected experimental results were obtained byusing a 3 mu m spot size 61 keV X-ray beam and large area detector and bysubtracting the scattered intensity due to helium outside the sample from the silicasignal at the same focal point for each pressure point. The compression behavior of the glassy silica-helium composite is characterized on a structural level by the change from a uni- to bimodal distribution in the inter-tetrahedral distances in the amorphous isotropic structure of silica. We propose a simple characterization of this atomic-spring-like glass property using impedance spectroscopy measurements

The structure of aqueous magnesium nitrate solution is gaining significant interest among researchers, especially whether contact ion pairs exist in concentrated solutions. Here, combining X-ray diffraction experiments, quantum chemical calculations and ab initio molecular dynamics simulations, we report that the [Mg(NO3)2] molecular structure in solution from the coexistence of a free [Mg(H2O)6]2+ octahedral supramolecular structure with a free [NO3(H2O)n]- (n = 11-13) supramolecular structure to an [Mg2+(H2O)n(NO3-)m] (n = 3, 4, 5; m = 3, 2, 1) associated structure with increasing concentration. Interestingly, two hydration modes of NO3--the nearest neighbor hydration with a hydration distance less than 3.9 Å and the next nearest neighbor hydration with hydration distance ranging from 3.9 to 4.3 Å-were distinguished. With an increase in the solution concentration, the hydrated NO3- ions lost outer layer water molecules, and the hexagonal octahedral hydration structure of [Mg(H2O)62+] was destroyed, resulting in direct contact between Mg2+ and NO3- ions in a monodentate way. As the concentration of the solution further increased, NO3- ions replaced water molecules in the hydration layer of Mg2+ to form three-ion clusters and even more complex chains or linear ion clusters.

Monitoring the dynamics of CO2-EOR, the pore accessibility and the structural properties of confined CO2 with neutron scattering.

Abstract Deep eutectic systems are currently under intense investigation to replace traditional organic solvents in a range of syntheses. Here, indole in choline chloride‐malic acid deep eutectic solvent (DES) was studied as a function of water content, to identify solute interactions with the DES which affect heterocycle reactivity and selectivity, and as a proxy for biomolecule solvation. Empirical Potential Structure Refinement models of neutron diffraction data showed [Cholinium]+ cations associate strongly with the indole π‐system due to electrostatics, whereas malic acid is only weakly associated. Trace water is sequestered into the DES and does not interact strongly with indole. When water is added to the DES, it does not interact with the indole π‐system but is exclusively in‐plane with the heterocyclic rings, forming strong H‐bonds with the ‐NH group, and also weak H‐bonds and thus prominent hydrophobic hydration of the indole aromatic region, which could direct selectivity in reactions.

The solution structure of 1.0 M Uranyl Chloride has been determined by the EPSR modelling of a combination of neutron scattering and EXAFS data. The experimental data show an equilibrium in solution between [UO2(H2O)5]2+ and [UO2Cl(H2O)4]+ with a stability constant of 0.23 ± 0.03 mol-1 dm-3. A much smaller fraction of the neutral [UO2Cl2(H2O)3] ion is also observed. The data also show, for the first time in solution, that the uranyl ion is a very poor hydrogen bond acceptor, but the coordinated waters show enhanced hydrogen bond ability compared to the bulk water.

Herein mixtures of cyclohexane and benzene have been investigated in both the bulk liquid phase and when confined in MCM-41 mesopores. The bulk mixtures have been studied using total neutron scattering (TNS), and the confined mixtures have been studied by a new flow-utilising, integrated TNS and NMR system (Flow NeuNMR), all systems have been analysed using empirical potential structure refinement (EPSR). The Flow NeuNMR setup provided precise time-resolved chemical sample composition through NMR, overcoming the difficulties of ensuring compositional consistency for computational simulation of data ordinarily found in TNS experiments of changing chemical composition—such as chemical reactions. Unique to the liquid mixtures, perpendicularly oriented benzene molecules have been found at short distances from the cyclohexane rings in the regions perpendicular to the carbon–carbon bonds. Upon confinement of the hydrocarbon mixtures, a stronger parallel orientational preference of unlike molecular dimers, at short distances, has been found. At longer first coordination shell distances, the like benzene molecular spatial organisation within the mixture has also found to be altered upon confinement.