Anomalous rotational-symmetry breaking in proton arrangement of surface-confined cyclic hydrogen bonds revealed by atomic force spectroscopy

Sep 30, 2026

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Hydrogen-bonded systems and biosystems rely on microscopic proton ordering, shaped by the quantum nature of protons, to govern phase transitions, chemical reactions, biomolecular functions, and collective proton transfer. Resolving proton arrangements and quantum behavior at atomic scale is difficult because protons are extremely small and effective characterization methods are limited. Here, bond-resolved AFM/AFS probes proton-order signatures in surface-confined benzimidazole assemblies, revealing anomalous rotational-symmetry breaking and quantum proton delocalization.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages11

Reading Time28 min

AccessFree to download

Introduction

Background on nuclear quantum effects and proton ordering

Challenges in detecting quantum proton behavior

| | | | | | --- | --- | --- | --- | | Article [https://doi.org/10.1038/s41467-025-66848-9](https://doi.org/10.1038/s41467-025-66848-9) | | | | | Anomalous rotational-symmetry breaking in proton arrangement of surface-conﬁned cyclic hydrogen bonds revealed by atomic force spectroscopy | | | | | Received: 24 December 2024
Accepted: 16 November 2025 Check for updates | Feng Gao1,2,10, Chunlei Yang 1,2,10, Yuanhao Lyu1,2, Luhao Zhang3,
Peng Cheng 1,2, Lan Chen 1,2, En-Ge Wang 3,4,5, Svetlana Klyatskaya6, Cui Zhang 1,2 , Mario Ruben 6,7,8 , Sheng Meng 1,2,9 , Kehui Wu 5 & Yi-Qi Zhang 1,2
In hydrogen-bonded materials and biosystems, microscopic proton ordering, which is strongly inﬂuenced by the quantum nature of protons, underpins diverse macroscopic phenomena, including phase transitions, chemical reactions, biomolecular processes and collective proton transfer. Yet resolving proton arrangementsand characterizing their quantum behavior atthe atomic scale remain challenging due to the small size of protons and the lack of effective approaches. Here, we exploit bond-resolved atomic force microscopy and spectroscopy (BR-AFM/AFS) to probe signatures of proton ordering in surface-conﬁned benzimidazole (BI) assemblies. By performing BR-AFS along the apparent H-bond between proton donor and acceptor nitrogen atoms, we extract information consistent with H-bonding directionality and signatures compatible with quantum proton delocalization. We observe anomalous rotational-symmetry breaking in the proton order of the cyclic hexamers, arising from the coexistence of both localized and quantumdelocalized protons. The chirality of a single hexamer can be reversibly switched by altering its adsorption registry combined with collective transfer of six protons. Path-integral molecular dynamics calculations unravel that nuclear quantum effects promote proton delocalization and concomitant reduction of donor-acceptor distance. Our ﬁndings enable atomic-level detection of complex proton orders, engineering proton-based quantum states, and elucidation of long-range proton transfer mechanisms in molecular architectures. | | | | Hydrogen bonds are profoundly inﬂuenced by nuclear quantum effects (NQEs) owing to the low mass of the proton1–3. To fully understand many fundamental biological and chemical processes mediated by H-bonds–such as enzymatic reactions4–6, signaling7, and | | the dynamics of water8–the quantum nature of protons must be considered. In two-or three-dimensional molecular crystals, where intermolecular H-bonding motifs create speciﬁc proton arrangements9–12, NQEs can signiﬁcantly impact proton ordering, thereby dramatically | | A full list of afﬁliations appears at the end of the paper. e-mail: [cuizhang@iphy.ac.cn](cuizhang@iphy.ac.cn); [mario.ruben@kit.edu](mario.ruben@kit.edu); [smeng@iphy.ac.cn](smeng@iphy.ac.cn); [khwu@tias.ac.cn](khwu@tias.ac.cn); [yiqi.zhang@iphy.ac.cn](yiqi.zhang@iphy.ac.cn) altering structural and physical properties. For example, quantum delocalization drives proton order-disorder transition and H-bondsymmetrization in high-pressure phases of ice13, and promotes hightemperature superconductivity in sulphur hydrides14. Recent highresolution scanning probe studies of small molecules on atomically ﬂat surfaces in ultrahigh vacuum (UHV) have provided preliminary evidences for proton sharing, including water-hydroxyl complexes on Cu(110)15, long-range-ordered Zundel cations on Au(111) and Pt(111)16, and H-bonded one-dimensional 2,5-diamino-1,4-benzoquinonediimines chains on Au(111)17. However, these observations have so far relied primarily on imaging, while complementary spectroscopic evidence remains limited. Another challenge is to extend the investigation of proton ordering and NQEs from small interfacial molecular systems, such as water18, to those with heavier skeletons10. In this regard, the imidazole ring represents an ideal candidate. Capable of both donating and accepting a

FAQs

Why is proton arrangement and its quantum behavior hard to resolve at the atomic scale?

Protons are extremely small, and there is a lack of effective approaches to characterize their quantum behavior directly.

How does bond-resolved AFM/AFS reveal proton ordering in benzimidazole assemblies?

By performing bond-resolved AF spectroscopy along the apparent hydrogen bond, the study extracts information consistent with hydrogen-bond directionality and signatures compatible with quantum proton delocalization.

What phenomenon did the authors observe in the cyclic hexamers of surface-confined hydrogen bonds?

Anomalous rotational-symmetry breaking in the proton order, originating from the coexistence of localized and quantum-delocalized protons.

Sep 30, 2026

Upload by Kyle