Water may be one of the most familiar substances on Earth, but under extreme confinement it reveals hidden behaviors that challenge our understanding of matter. A new study by researchers at Tokyo University of Science has uncovered a previously unexplored phase of confined water known as the “premelting state”, a strange condition where water behaves as if it is both freezing and melting at once.
When trapped in extremely small spaces inside proteins, minerals, or nanomaterials, water no longer behaves like its bulk liquid form. These confinement effects are crucial for natural processes like ion transport through cell membranes and for technologies in nanofluidics.
Yet studying these dynamics has been notoriously difficult. While X-ray diffraction can reveal the positions of many atoms, it struggles to capture the ultrafast rotational motion of hydrogen or the individual movements of water molecules on the picosecond scale.
Led by Professor Makoto Tadokoro, with Lecturer Fumiya Kobayashi and PhD student Tomoya Namiki, the research team turned to static solid-state deuterium nuclear magnetic resonance (NMR) spectroscopy to probe water confined within the hydrophilic nanopores of a molecular crystal.
Their work, published in the Journal of the American Chemical Society on August 27, 2025, revealed a hierarchical, three-layered structure in the water trapped inside quasi-one-dimensional nanopores just 1.6 nm wide. Distinct NMR signals showed that each water layer had unique movements and hydrogen-bonding interactions, proving that the confined water organizes itself in a far more complex way than bulk liquid.
Even more remarkably, the team discovered that water in these nanopores freezes into an unusual structure, then begins to melt through a distorted hydrogen-bonded network giving rise to the elusive premelting state.
To observe this phase, the researchers slowly warmed the water-filled crystal. As the temperature increased, the NMR spectra showed dramatic changes, signaling a new, transitional state of matter.
As Prof. Tadokoro explained: “The premelting state involves the melting of incompletely hydrogen-bonded H?O before the completely frozen ice structure starts melting during the heating process. It essentially constitutes a novel phase of water in which frozen H?O layers and slowly moving H?O coexist.”
Measurements of rotational mobility confirmed the paradox: while the molecules remained fixed in place like a solid, their rotational motion was extremely fast and liquid-like, echoing the behavior of bulk water.
This breakthrough not only sheds light on how confined water behaves but also opens possibilities for practical applications. For example, tailoring water’s freezing and melting could advance both biological and industrial technologies.
Prof. Tadokoro highlighted the potential: “By creating new ice network structures, it may be possible to store energetic gases such as hydrogen and methane and develop water-based materials such as artificial gas hydrates.”
