High-pressure chemistry

Most of our knowledge about the chemical composition of the Earth’s interior is primarily retrieved by indirect observations, experiments and calculations that are limited to simple compositions. Here, the authors present the investigation of inclusions trapped in super deep diamonds as an alternative source of a wealth of information on the chemical state of the Earth’s interior through time.

Trimethylamine N-oxide (TMAO) protects organisms from the damaging effects of deep-sea high pressure, but it is not well understood how pressure and TMAO in combination perturb the water structure. Here, the authors use neutron scattering coupled with computational modelling of water at 25 bar and 4 kbar in the presence and absence of TMAO to propose an “osmolyte protection ratio” at which pressure and TMAO-induced energy changes effectively cancel out, which translates across scales to the organism level.

Enzymes may behave differently at high pressures found in environments such as the ocean floor, but molecular dynamics force fields are not well characterized at high pressures. Here the CHARMM36m force field is validated against NMR data at variable pressures up to 2500 bar, using ubiquitin as a model protein.

Fatty acid membranes are implicated in several hypotheses about the origins of life, but whether their stability towards extremes of temperature, pressure, and ionic strength is sufficient to enable primitive biochemistry remains unclear. Here branched and linear alkanes are shown to stabilise a common model primordial membrane towards high temperatures and pressures

Compression is a common densification method for solid-state materials, but the structural evolution of compressed non-equilibrium oxide materials such as glasses and zeolites remains somewhat elusive. Here, the authors show that siliceous zeolite single-crystals cold-compressed at 20 GPa yield permanently densified glassy silica, while cold-compressed siliceous zeolite powder and glassy silica are metastable.

Water can form a vast number of topological frameworks owing to its hydrogen-bonding ability, with 19 different forms of ice experimentally confirmed at present. Here, the authors comment on open questions and possible future discoveries, covering negative to ultrahigh pressures.

Understanding the mechanical properties of metal–organic frameworks (MOFs) is crucial for their industrial application, but the compressibility of structurally dynamic MOFs under pressure remains unclear. Here, in situ variable pressure powder X-ray diffraction experiments on two families of dynamic MOFs find that increased structural flexibility results in enhanced mechanical resilience.

Antimonite (Sb₂S₃) has potential applications for solar energy, but how its layered structure changes under pressure is incompletely understood. Here diamond anvil cell experiments supported by first principles calculations offer a structural explanation for experimentally observed phase transitions.

CO₂ is prominent in the Earth’s and exoplanetary atmospheres, but its excited state photochemistry is not yet fully understood. Here the authors identify gradual quenching of the diffuse vibrational structure in supercritical CO₂ electronic spectra under pressures up to 137 bar.

The lower decomposition barriers of cyclo-N₆ anions hinder their application as high-energy-density materials. Here, first-principles calculations reveal that enhancing the covalent component of the interaction between cyclo-N₆ anions and cations can effectively improve stability at high pressure.

Recent high-pressure studies have uncovered many types of chemical bonds present in noble gas compounds. Here, by extrapolating what has been found so far, the authors discuss which future discoveries can be expected and recommend further avenues of exploration.

The chemical stability of alkali halides has caused them to be exploited as inert media in high-pressure, high-temperature experiments. Here, NaCl and KCl are unexpectedly found to react with yttrium, dysprosium and iron oxide in a laser-heated diamond anvil cell, producing Y₂Cl, DyCl, Y₂ClC and Dy₂ClC at ~40 GPa and 2000 K and FeCl₂ at ~160 GPa and 2100 K.

Hydrogen sulfide and ammonia form molecular mixtures that could open up new routes towards hydrogen-rich high-pressure/high-temperature superconductors, but their mixing propensity under pressure is not well understood. Here, the authors identify stable nitric sulfur hydrides at high pressure using first-principles crystal structure prediction methods.

Collision theory predicts the spectral peak of the sodium D-line to have a red-shift dependent on pressure and temperature. Using the serendipitous presence of sodium in octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), the authors calibrate the D-line shift up to 1.5 GPa during deflagration.