Water Under Extreme Confinement
Synchrotron infrared spectroscopy shows that water confined to a single molecular layer forms a weakened, frustrated hydrogen-bond network
Water confined to a single molecular layer has been directly probed by infrared absorption spectroscopy, offering experimental evidence for how its hydrogen-bonding network changes under extreme two-dimensional confinement. Led by researchers at The University of Manchester, the study used Ångström-scale slit capillaries built from van der Waals heterostructures to hold water in channels only a few atoms high.
To boost the weak signal from so few water molecules, the team used van der Waals capillaries with a reflective graphite base and a hexagonal boron nitride top layer that acted as an infrared waveguide. Synchrotron infrared microspectroscopy in reflectance mode then allowed the confined-water signal to be compared with empty capillaries and bulk water regions.
The resulting spectra tracked the O–H stretching band of water across capillaries of different thicknesses. As the channels narrowed toward the monolayer limit, the band shifted to higher frequencies, indicating a disrupted and weakened hydrogen-bonding network. The transition was most pronounced below roughly 1.4 nm, where geometric confinement began to dominate over conventional interfacial effects.
Density functional theory–based molecular dynamics simulations helped interpret the spectral shifts. In the monolayer regime, the simulations suggested a frustrated, mosaic-like hydrogen-bond network with fewer hydrogen bonds per water molecule than in bulk water, alongside a notable population of free, non-hydrogen-bonded O–H groups. The authors frame this as a structurally distinct form of two-dimensional water, rather than simply interfacial water squeezed thinner.
Beyond confined water itself, the work shows how nanofabricated heterostructures could extend far-field infrared absorption measurements to molecular populations that would otherwise be too small to probe.
Tracking Battery Damage Below the Surface
Depth-sensitive X-ray photoelectron spectroscopy tracks oxygen-driven degradation at a buried solid-state battery interface
A study of solid-state battery half-cells has linked early capacity loss to oxygen-containing species that migrate during cycling and react near the cathode current collector, forming a TiOx-rich degradation layer at the buried interface.
The team studied cells made with a titanium disulfide cathode and a lithium yttrium chloride (Li₃YCl₆) solid electrolyte using a custom operando setup that maintained relevant stacking pressure while allowing X-ray access to the electrode through a perforated current collector. Hard X-ray photoelectron spectroscopy (HAXPES) provided depth-sensitive chemical information from buried regions of the electrode, while complementary soft X-ray photoelectron spectroscopy helped distinguish near-surface changes from deeper interfacial processes.
During discharge, HAXPES tracked lithiation of the titanium disulfide cathode through shifts in titanium and sulfur core-level spectra, while also detecting reduction of the Li₃YCl₆ solid electrolyte. Across the same discharge sequence, the measurements showed a growing titanium oxide contribution near the current collector interface, with the oxygen-containing Ti-related overlayer increasing from roughly 2 nm in the pristine state to around 5–6 nm by the end of discharge.
Longer-term cycling supported the operando picture. Ex situ microscopy and energy-dispersive X-ray analysis showed oxygen enrichment near the surface of cycled cathodes, while electrochemical data showed increasing polarization and capacity fade. The authors attribute this to oxygen-containing species, likely already present within cell components, forming an amorphous TiOx-rich degradation layer.
“We have gained some surprising insights, particularly regarding the harmful role played by intrinsic oxygen,” said Katherine Mazzio in a press release. The findings point to oxygen control as one route to improving interfacial stability in solid-state batteries, especially in sulfide-based systems where buried reactions remain difficult to access directly.
Infrared Spectra from a Single Droplet
SiDDIRAS records vibrational spectra from a single levitated droplet by tracking laser-induced displacement during evaporation
A new infrared action spectroscopy method can record vibrational spectra from a single levitated aqueous microdroplet by tracking how the droplet moves during laser-induced evaporation. Called single droplet displacement infrared action spectroscopy (SiDDIRAS), the approach is designed to probe well-defined, substrate-free microdroplets that are difficult to study by conventional Fourier-transform infrared spectroscopy.
The method traps a charged droplet in a linear quadrupole electrodynamic balance, where alternating and direct-current fields hold it in place under controlled humidity. When infrared light from a quantum cascade laser reaches an absorption frequency, the droplet warms, loses a small amount of water, and shifts upward. Mapping that displacement against infrared frequency produces an action spectrum of the individual droplet.
As a demonstration, the team measured a single aqueous droplet containing sodium chloride and sodium azide, using azide as an infrared vibrational probe of the droplet’s ionic environment. The SiDDIRAS spectrum captured a blue-shifted, broadened azide asymmetric stretch relative to dilute bulk solution, along with a water bend–libration combination band linked to disruption of the hydrogen-bonding network. Mie scattering–based sizing and refractive-index measurements supported the interpretation that the droplet remained aqueous but was supersaturated with salt.
Future studies could tune droplet charge, size, and vibrational probe chemistry to help separate surface effects from bulk-like behavior in microdroplet and aerosol chemistry.
Structure Solving at Scale
Deep learning and fragment-based optimization help move from one-dimensional NMR spectra to testable molecular structures
A computational framework called NMR-Solver has been developed to automate small-molecule structure elucidation from one-dimensional proton and carbon nuclear magnetic resonance spectra, addressing a task that remains slow, expertise-dependent, and difficult to scale in synthetic chemistry.
The approach combines large-scale spectral retrieval with a physics-guided molecular optimization workflow. Candidate structures are first drawn from a simulated NMR database built from around 106 million PubChem-derived molecules, each annotated with predicted ¹H and ¹³C chemical shifts. The system then uses a fragment-based optimization strategy to iteratively recombine and refine candidate molecules, scoring them against the experimental spectra. Rather than searching chemical space randomly, the workflow uses atomic-level structure–spectrum relationships to guide each structural change.
The workflow uses NMRNet, a deep learning model, to predict atom-level chemical shifts from molecular structure. During optimization, NMR-Solver uses faster inherited fragment-level shift estimates for screening, followed by more precise prediction and spectral scoring for higher-ranked candidates. The system can also incorporate experimental constraints, known reactants, molecular formulas, or expert-proposed scaffolds, allowing it to operate either automatically or as part of a human-guided analysis.
Tested on experimental spectra curated from recent synthetic chemistry papers, NMR-Solver outperformed a previous NMR-to-structure method and improved further when reactant information was included, reflecting how chemists often interpret spectra in practice. The framework was also applied to laboratory and literature cases involving unanticipated products, regioisomer assignments, and previously misassigned structures.
For synthetic workflows, the approach could provide a more systematic way to move from experimental spectra to testable structural assignments.
The Hidden Nitrogen of Primitive Asteroids
The study suggests primitive asteroids store nitrogen not only in organics and salts, but also in ammoniated phyllosilicates
Analysis of material returned from the asteroids Ryugu and Bennu has identified ammonium-rich phyllosilicate grains, suggesting that nitrogen in primitive asteroid samples is not limited to organics or salts.
The assignment comes from near- and mid-infrared spectroscopic analysis, beginning with MicrOmega near-infrared hyperspectral microscopy of Ryugu samples returned by JAXA’s Hayabusa2 mission and Bennu samples returned by NASA’s OSIRIS-REx mission. The measurements were carried out inside JAXA’s extraterrestrial sample curation facility under nitrogen-purged conditions, allowing the samples to be analyzed without terrestrial atmospheric exposure.
Across the collections, the researchers identified 13 ammonium-rich regions of interest in Ryugu samples and 12 in Bennu samples, typically tens to hundreds of micrometers across. MicrOmega spectra linked these bright regions to both Mg-rich phyllosilicates and N–H-bearing material through paired absorptions near 2.7 µm and 3.06 µm. Their similar spectral profiles in both asteroid collections pointed to the same nitrogen-bearing phase rather than isolated, sample-specific inclusions.
Complementary mid-infrared spectra of selected Bennu regions strengthened that assignment. A diagnostic NH₄⁺ bending band near 7 µm appeared alongside a pronounced phyllosilicate Si–O band near 10 µm, while spectral features expected for organic nitrogen compounds or common ammonium salts were absent. Together, the near- and mid-infrared data support the interpretation that ammonium is incorporated into phyllosilicate structures.
The authors argue that these ammoniated phyllosilicates likely formed during aqueous alteration, when mobile ammonium ions were incorporated into clay-like mineral layers. Together with previously identified ammonium-rich phosphate grains, the findings suggest that primitive asteroids may have carried nitrogen in multiple stable inorganic forms, some of which may be difficult to detect from remote spectra alone.
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