The ability of trimethylamine N-oxide to resist pressure induced perturbations to water structure.

Trimethylamine N-oxide (TMAO) protects organisms from the damaging effects of high pressure. At the molecular level both TMAO and pressure perturb water structure but it is not understood how they act in combination. Here, we use neutron scattering coupled with computational modelling to provide atomistic insight into the structure of water under pressure at 4 kbar in the presence and absence of TMAO.

Microscopic Structure of Liquid Nitric Oxide.

The microscopic structure of nitric oxide is investigated using neutron scattering experiments. The measurements are performed at various temperatures between 120 and 144 K and at pressures between 1.1 and 9 bar.

The nano- and meso-scale structure of amorphous calcium carbonate.

Understanding the underlying processes of biomineralization is crucial to a range of disciplines allowing us to quantify the effects of climate change on marine organisms, decipher the details of paleoclimate records and advance the development of biomimetic materials. Many biological minerals form via intermediate amorphous phases, which are hard to characterize due to their transient nature and a lack of long-range order. Here, using Monte Carlo simulations constrained by X-ray and neutron scattering data together with model building, we demonstrate a method for determining the structure of these intermediates with a study of amorphous calcium carbonate (ACC) which is a precursor in the bio-formation of crystalline calcium carbonates.

Bridging Structure, Dynamics, and Thermodynamics: An Example Study on Aqueous Potassium Halides.

Aqueous salt systems are ubiquitous in all areas of life. The ions in these solutions impose important structural and dynamic perturbations to water. In this study, we employ a combined neutron scattering, nuclear magnetic resonance, and computational modeling approach to deconstruct ion-specific perturbations to water structure and dynamics and shed light on the molecular origins of bulk thermodynamic properties of the solutions.

Adsorption of simple gases into the porous glass MCM-41.

The porous glass MCM-41 is an important adsorbent to study the process of adsorption of gases onto a cylindrical surface. In this work, we study the adsorption of oxygen, nitrogen, deuterium, and deuteriated methane gases into MCM-41 using a combination of neutron diffraction analysis and atomistic computer modeling to interpret the measured data. Adsorption is achieved by immersing a sample of MCM-41 in a bath of the relevant gas, keeping the gas pressure constant (0.

Solute Specific Perturbations to Water Structure and Dynamics in Tertiary Aqueous Solution.

Liquid water is known as the "universal" solvent, capable of dissolving a wide variety of different solutes. While much is now understood about the impact of solutes on the water structure in binary solutions, it is much more challenging to deconvolute the potentially competing effects of more complex solutions. Here, we present a correlative NMR and neutron diffraction study to examine the solute induced perturbation of water structure and dynamics in a tertiary solution containing the naturally occurring osmolyte trimethylamine N-oxide (TMAO) and magnesium perchlorate (Mg(ClO)).

Experimental and modeling evidence for structural crossover in supercritical CO_{2}.

The physics of supercritical states is understood to a much lesser degree compared to subcritical liquids. Carbon dioxide, in particular, has been intensely studied, yet little is known about the supercritical part of its phase diagram. Here, we combine neutron scattering experiments and molecular dynamics simulations and demonstrate the structural crossover at the Frenkel line.

Trimethylamine N-oxide (TMAO) resists the compression of water structure by magnesium perchlorate: terrestrial kosmotrope vs. Martian chaotrope.

The presence of magnesium perchlorate (Mg(ClO4)2) as the dominant ionic compound in the Martian regolith and the recent discovery of a subsurface lake on Mars suggests that beneath the Martian surface may lie an aqueous environment suitable for life, rich in chaotropic ions. Closer to Earth, terrestrial organisms use osmolytes, such as trimethylamine N-oxide (TMAO), to overcome the biologically damaging effects of pressure. While previous studies have revealed that Mg(ClO4)2 acts to modify water structure as if it has been pressurized, little is known about the competing effects of chaotropes and kosmotropes.

Temperature-Dependent Segregation in Alcohol-Water Binary Mixtures Is Driven by Water Clustering.

Previous neutron scattering work, combined with computer simulated structure analysis, has established that binary mixtures of methanol and water partially segregate into water-rich and alcohol-rich components. It has furthermore been noted that, between methanol mole fractions of 0.27 and 0.

Trehalose in Water Revisited.

Trehalose, commonly found in living organisms, is believed to help them survive severe environmental conditions, such as drought or extreme temperatures. With the aim of trying to understand these properties, two recent neutron scattering studies investigate the structure of trehalose water solutions but come to seemingly opposite conclusions. In the first study, which looks at two concentrations of trehalose-water mole ratios of 1:100 and 1:25, the conclusion is that trehalose hydrogen-bonds to water rather weakly and has a relatively minor impact on the structure of water in solution compared to bulk water.

Comment on "Maxima in the thermodynamic response and correlation functions of deeply supercooled water".

Kim recently measured the structure factor of deeply supercooled water droplets (Reports, 22 December 2017, p. 1589). We raise several concerns about their data analysis and interpretation.

Structures of a Clathrate Hydrate Former, Inhibitor, and Synergist in Water.

SANS studies are reported for aqueous THF at the 1:17 clathrate hydrate-forming composition and on aqueous solutions of the synergist 2-butoxyethanol. Addition of the clathrate hydrate inhibitor polyvinylcaprolactam and a dimeric model compound, 1,3-bis(caprolactamyl)butane, show that the inhibitors do not significantly affect the solution structures of these two important species in clathrate hydrate formation and inhibition. The SANS studies show that 1,3-bis(caprolactamyl)butane is a good model for polyvinylcaprolactam, and both the polymer and model compound exhibit hydrogen bonding interactions with water but do not interact significantly with 2-butoxyethanol in aqueous solution.

Formation of Methane Hydrate in the Presence of Natural and Synthetic Nanoparticles.

Natural gas hydrates occur widely on the ocean-bed and in permafrost regions, and have potential as an untapped energy resource. Their formation and growth, however, poses major problems for the energy sector due to their tendency to block oil and gas pipelines, whereas their melting is viewed as a potential contributor to climate change. Although recent advances have been made in understanding bulk methane hydrate formation, the effect of impurity particles, which are always present under conditions relevant to industry and the environment, remains an open question.

Highly compressed water structure observed in a perchlorate aqueous solution.

The discovery by the Phoenix Lander of calcium and magnesium perchlorates in Martian soil samples has fueled much speculation that flows of perchlorate brines might be the cause of the observed channeling and weathering in the surface. Here, we study the structure of a mimetic of Martian water, magnesium perchlorate aqueous solution at its eutectic composition, using neutron diffraction in combination with hydrogen isotope labeling and empirical potential structure refinement. We find that the tetrahedral structure of water is heavily perturbed, the effect being equivalent to pressurizing pure water to pressures of order 2 GPa or more.

Water in a Soft Confinement: Structure of Water in Amorphous Sorbitol.

The structure of water in 70 wt % sorbitol-30 wt % water mixture is investigated by wide-angle neutron scattering (WANS) as a function of temperature. WANS data are analyzed using empirical potential structure refinement to obtain the site-site radial distribution functions (RDFs). Orientational structure of water is represented using OW-OW-OW triangles distributions and a tetrahedrality parameter, q, while water-water correlation function is used to estimate size of water clusters.

Structural evidence for solvent-stabilisation by aspartic acid as a mechanism for halophilic protein stability in high salt concentrations.

Halophilic organisms have adapted to survive in high salt environments, where mesophilic organisms would perish. One of the biggest challenges faced by halophilic proteins is the ability to maintain both the structure and function at molar concentrations of salt. A distinct adaptation of halophilic proteins, compared to mesophilic homologues, is the abundance of aspartic acid on the protein surface.

Hydrophilic Association in a Dilute Glutamine Solution Persists Independent of Increasing Temperature.

Recent studies suggest that hydrophilic interactions play an important role in controlling self-assembly in biological processes. To explore the effect of temperature on this interaction, we extend our previous work on the glutamine-water system at 24 °C (at a mole ratio of 1 glutamine to 269 water molecules) and present additional neutron diffraction data, at the same concentration, at 37 and 60 °C, using hydrogen/deuterium substitution on the water and glutamine, coupled with further extensive empirical potential structure refinement computer simulations. Taking all the possible hydrophilic couplings between glutamine molecules into account, we find that nearly one-fifth of the glutamines in solution are linked by hydrogen bonds at any one time.

A Neutron Diffraction Study of the Electrochemical Double Layer Capacitor Electrolyte Tetrapropylammonium Bromide in Acetonitrile.

Neutron diffraction with isotopic substitution has been used to characterize the bulk liquid structure of the technologically relevant electrolyte solution, 1 M tetrapropylammonium bromide (TPA Br) in acetonitrile (acn), and of pure deuterated acetonitrile. Empirical potential structure refinement modeling procedures have been used to extract detailed structural information about solvent-solvent, solvent-ion, and ion-ion correlations. Analysis of the refined data shows the expected local dipolar conformation of acn in the pure solvent.

Disordered Atom Molecular Potential for Water Parameterized against Neutron Diffraction Data. Application to the Structure of Ice Ih.

A disordered atom molecular potential (DAMP) for water is described that accurately accounts for the observed neutron interference differential scattering cross sections for light water, heavy water, and two different mixtures of these liquids (x = 0.5 and x = 0.64, where x is the mole fraction of light water in the mixtures) at T = 283 K.

Observation of interstitial molecular hydrogen in clathrate hydrates.

The current knowledge and description of guest molecules within clathrate hydrates only accounts for occupancy within regular polyhedral water cages. Experimental measurements and simulations, examining the tert-butylamine + H2 + H2O hydrate system, now suggest that H2 can also be incorporated within hydrate crystal structures by occupying interstitial sites, that is, locations other than the interior of regular polyhedral water cages. Specifically, H2 is found within the shared heptagonal faces of the large (4(3)5(9)6(2)7(3)) cage and in cavities formed from the disruption of smaller (4(4)5(4)) water cages.

Radical re-appraisal of water structure in hydrophilic confinement.

The structure of water confined in MCM41 silica cylindrical pores is studied to determine whether confined water is simply a version of the bulk liquid which can be substantially supercooled without crystallisation. A combination of total neutron scattering from the porous silica, both wet and dry, and computer simulation using a realistic model of the scattering substrate is used. The water in the pore is divided into three regions: core, interfacial and overlap.

A hybrid neutron diffraction and computer simulation study on the solvation of N-methylformamide in dimethylsulfoxide.

The solvation of N-methylformamide (NMF) by dimethylsulfoxide (DMSO) in a 20% NMF/DMSO liquid mixture is investigated using a combination of neutron diffraction augmented with isotopic substitution and Monte Carlo simulations. The aim is to investigate the solute-solvent interactions and the structure of the solution. The results point to the formation of a hydrogen bond (H-bond) between the H bonded to the N of the amine group of NMF and the O of DMSO particularly strong when compared with other H-bonded liquids.

What happens to the structure of water in cryoprotectant solutions?

Cryoprotectant molecules are widely utilised in basic molecular research through to industrial and biomedical applications. The molecular mechanisms by which cryoprotectants stabilise and protect molecules and cells, along with suppressing the formation of ice, are incompletely understood. To gain greater insight into these mechanisms, we have completed an experimental determination of the structure of aqueous glycerol.