Kanazawa University Research: From Molecular Interactions to Material Function: Unraveling Water's Effect on Chitin Nanocrystals

KANAZAWA, Japan, Oct. 20, 2025 /PRNewswire/ -- Researchers at the Nano Life Science Institute (WPI-NanoLSI), Kanazawa University, report in the Journal of the American Chemical Societythe use of three-dimensional atomic force microscopy (AFM) and molecular dynamics simulations to determine the structure of water in the hydration of different types of chitin nanocrystals, and how this affects their mechanicalproperties, reactivities, and interactions with enzymes and reactants.

Chitin is a naturally occurring polymer with a number of attractive mechanical and chemical properties that many are seeking to mimic in bioengineered materials. Naturally occurring chitin has one of two crystal structures known as α – with the molecules aligned antiparallel – and β – with the molecules aligned in parallel. The nanoscale structure of chitin greatly affects the chemical and mechanical properties of the material, and here the structure that water forms around the fibres when they are hydrated can play a significant role. However, until now, the details of these different structures were not well understood. Now, researchers led by Ayhan Yurtsever and Takeshi Fukuma at Nano Life Science Institute (WPI-NanoLSI), Kanazawa University, together with collaborators Kazuho Daicho, Tsuguyuki Saito, and Noriyuki Isobe from the University of Tokyo, and molecular dynamics experts led by Fabio Priante and Adam S. Foster from Aalto University, Finland, have used 3D AFM and molecular dynamics to study the different structures and how water forms on them when they are hydrated for different pH levels (Fig. 1) The results of this study provide explanations for differences in how the two structures interact with enzymes and reactants.

Atomic force microscopy gauges surface topography and chemical information by monitoring the strength of forces exerted on a nanoscale tip attached to a cantilever. The researchers used a modified AFM known as 3D-AFM, which enabled them not only to image the morphology of chitin nanocrystals but also to investigate the three-dimensional local organization of water molecules surrounding these nano structures. In their report, they noted a high degree of long-range order in the β chitin fibres, whose structure has so far been less thoroughly explored. They describe how the occasional breaks in that order "lead to a structure resembling partially bitten corncobs or a brickwork pattern". Their AFM imaging also showed how the molecular arrangement runs right through the fibre. "These different structural components are not merely external aggregates;" they explain in the report. "Instead, they constitute an integral part of the chitin fiber (Fig. 2)."

The researchers also investigated the structures under different pHs, to see how this might affect the hydrated architectures of the chitin fibres. They found that the high level of crystallinity observed was preserved in acetic acid buffer solutions pH 3-5. Some of the most significant insights came from studying the water structure and hydrogen bonding on the two crystalline types of chitin (Fig. 3). They showed how the larger grooves in α chitin allowed greater accumulation of water, which formed a hydration barrier for interactions with external ions and molecules, making them less reactive. The repulsive forces for hydration were also higher for α chitin. They suggest this may explain why certain enzymes react with chitin in only one crystalline form and not the other. Furthermore, they propose that the lower energetic penalty associated with the structured hydration environment of β-chitin facilitates more rapid enzymatic access and substrate turnover. These insights could inform the development of bioprotonic applications – devices based on the transport of protons as opposed to electrons – and hydrogels since the hydration layer affects ion and molecular diffusion.

"Collectively, this work links nanoscale interfacial structure to rational design strategies, advancing the effective development of sustainable, bio-based nanomaterials for energy and biomedical applications," they conclude in their report. "Additionally, it provides valuable insights for the computational modeling of chitin surface interactions, crystallosolvate formation, and enzymatic hydrolysis, supporting the development of future material design strategies."

Glossary

Atomic force microscopy

This imaging technique uses a nanosized tip at the end of a cantilever that is scanned over a sample. It can be used to determine the topography of a sample surface from the change in the strength of forces between the tip and the sample with distance, and the resulting deflection of the cantilever. It was first developed in the 1980s but a number of modifications have augmented the functionality of the technique since. It is better suited to imaging biological samples than the scanning tunnelling microscope that had been previously developed, because it does not require a conducting sample.

Chitin

Chitin is a polysaccharide that comprises a substantial component of the shells of marine crustaceans, insect exoskeletons and cell walls in fungi and algae, among other living organisms. Among the attributes that have attracted so much interest in the material are its nontoxicity, antibacterial properties, its tunability in terms of surface structure and chemistry and the nematic crystalline form of hydrated chitin. Potential applications include drug delivery, bone-tissue engineering, sensing, photonic devices, green electronics, self-healing hydrogels, shape-memory bionanocomposites among many others.

The parallel alignment of the fibres in β chitin result in weaker bonds between chitin sheets that enhance the chemical reactivity and allow water to intercalate within the crystal structure. However, until this study there were critical gaps in the understanding of β chitin structures, particularly how water intercalates into the structures.

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Figure 1. High-resolution AFM images of β-chitin nanocrystal surfaces and the interfacial molecular organization of water near these surfaces.

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Figure 2: (A) AFM topography image, showing individual β-chitin NCs on mica, acquired in water. (B–F) High-resolution AFM images recorded along the fiber axis (across the shaded region in (A)), each covering an area of 20–30 nm × 20–30 nm, revealing the structural variations across the crystal surface. Ellipses highlight regions with fluctuating disordered domains on the surface, indicating the boundary between vertically stacked chitin sheets.

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Figure 3: Comparison between water-oxygen density maps and experimentally obtained vertical ∆f maps. (A–C) Vertical 2D-xz ∆f maps taken along the chitin chain direction. (D–F) Simulated vertical 2D water-oxygen density maps along the chain direction at different lateral positions on the (1-20) crystalline plane of the β-chitin NC. The red, blue, and green arrows indicate the identical hydration features between the simulation and experiment. (G–I) Water-oxygen density snapshots (40) with overlaid chitin molecular structures. (J–L) Hydrogen-bonding networks formed between water molecules and the underlying chitin substrate.

The copyright for all figures in this article is attributed as follows:
© 2025 American Chemical Society.

Reference

Ayhan Yurtsever, Kazuho Daicho, Fabio Priante, Keisuke Miyazawa, Mohammad Shahidul Alam, Kazuki Miyata, Akinori Yabuki, Noriyuki Isobe, Tsuguyuki Saito, Adam S. Foster and Takeshi Fukuma, Interplay between β-Chitin Nanocrystal Supramolecular Architecture and Water Structuring: Insights from Three-Dimensional Atomic force Microscopy Measurements and Molecular Dynamics Simulations, Journal of the American Chemical Society 2025

DOI: 10.1021/jacs.5c08484

URL: https://doi.org/10.1021/jacs.5c08484

Funding

This work was primarily supported by Grants-in-Aid for Scientific Research (21H05251, 20K05321, 22J01001, 22KJ1473, and 25K18274) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan (MEXT), World Premier International Research Center Initiative (WPI), MEXT, Japan JST-CREST Program (JPMJCR22L3; JPMJCR24A4), the New Energy and Industrial Technology Development Organization (NEDO) program (JPNP18016 and PJ-ID 20001845), Japan JST-ASPIRE Program (JPMJAP2310), and JST-PRESTO Program (JPMJPR2508). The computing resources from the Aalto Science-IT project, CSC, and Helsinki are gratefully acknowledged. We thank the captain and crew of R/V Yokosuka for their great support of scientific activity during the expedition YK21-18C (PI: Dr. Hidetaka Nomaki). We extend thanks to the DSV Shinkai 6500 team. We thank the NIES for providing us the culture of Phaeocystis globosa NIES‑1396. 

Contact:
Kimie Nishimura (Ms)
Project Planning and Outreach, NanoLSI Administration Office
Nano Life Science Institute, Kanazawa University
Email: nanolsi-office@adm.kanazawa-u.ac.jp
Kakuma-machi, Kanazawa 920-1192, Japan

About Nano Life Science Institute (WPI-NanoLSI), Kanazawa University:

Understanding nanoscale mechanisms of life phenomena by exploring 'uncharted nano-realms'.

Cells are the basic units of almost all life forms. We are developing nanoprobe technologies that allow direct imaging, analysis, and manipulation of the behavior and dynamics of important macromolecules in living organisms, such as proteins and nucleic acids, at the surface and interior of cells. We aim at acquiring a fundamental understanding of the various life phenomena at the nanoscale.

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About the World Premier International Research Center Initiative (WPI):

The WPI program was launched in 2007 by Japan's Ministry of Education, Culture, Sports, Science and Technology (MEXT) to foster globally visible research centers boasting the highest standards and outstanding research environments. Numbering more than a dozen and operating at institutions throughout the country, these centers are given a high degree of autonomy, allowing them to engage in innovative modes of management and research. The program is administered by the Japan Society for the Promotion of Science (JSPS).

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About Kanazawa University:

As the leading comprehensive university on the Sea of Japan coast, Kanazawa University has contributed greatly to higher education and academic research in Japan since it was founded in 1949. The University has three colleges and 17 schools offering courses in subjects that include medicine, computer engineering, and humanities.

The University is located on the coast of the Sea of Japan in Kanazawa, a city rich in history and culture. The city of Kanazawa has a highly respected intellectual profile since the time of the fiefdom (1598-1867). Kanazawa University is divided into two main campuses: Kakuma and Takaramachi for its approximately 10,200 students, including 600 from overseas.

http://www.kanazawa-u.ac.jp/en/