Organic iron-sulfur framework stabilises clusters and raises carbon fixation in chloroplasts

Researchers at the Institute of Biophysics and the Institute of Genetics and Developmental Biology, both part of the Chinese Academy of Sciences, have made a synthetic material that holds discrete iron-sulfur clusters in a stable, layered framework. When the material was combined with isolated chloroplasts, carbon fixation activity was higher than in chloroplasts alone. The work, led by Haolin Cao and colleagues, appears in the journal Small.

The problem with iron-sulfur clusters

Iron-sulfur clusters are ancient cofactors found across biology. They carry electrons in respiration and photosynthesis and play a part in the catalytic activity of many enzymes. Outside the protein environment that protects them, however, they are sensitive to oxygen and unstable. That fragility has limited attempts to use them in engineered or hybrid systems.

Building the framework

The team used a hydrothermal synthesis route. They added terephthalic acid as an organic linking ligand, which interrupted the dense lattice typical of conventional iron sulfide minerals. The result was a nanosheet-like material, termed a condensed organic iron-sulfur framework (OISF), in which iron-sulfur clusters remain separate from one another. The design borrows the stability of condensed metal-organic framework (MOF)-like structures while keeping the clusters themselves intact.

The structure was checked with several techniques, including X-ray diffraction analysis, synchrotron radiation methods and Mössbauer spectroscopy. These confirmed the framework and its [2Fe-2S] cluster core, the same type of two-iron, two-sulfur unit found in many natural proteins.

Electron transfer and stability

The OISF was found to transfer electrons readily, donating them to a range of electron acceptors, and its redox behaviour can be tuned by changing chemical conditions. Structural analysis suggested that electron transfer involves the dynamic formation of S–S bonds between clusters in neighbouring layers.

Compared with conventional iron sulfide minerals, the framework showed higher redox activity and good stability in the presence of oxygen. The authors note that this combination makes it better suited to integration with biological systems.

Combination with chloroplasts

To test that idea, the researchers combined the OISF with isolated chloroplasts, producing what they call an OISF-chloroplast complex (OCC). In their experiments, the complex showed higher carbon fixation activity than chloroplasts without the material. The source does not give the size of the increase, the conditions used or whether the effect has been tested beyond isolated chloroplasts, so the result should be read as an early, laboratory-scale demonstration.

Why it matters

The study offers a design approach for biomimetic materials that keep the redox activity of natural iron-sulfur clusters without their usual fragility. It also adds experimental and theoretical support for the use of nanozymes, meaning nanomaterials with enzyme-like function, to enhance photosynthetic carbon fixation.

Open questions include how the framework behaves over longer periods, how it interacts with intact cells or whole plants, and how far the gains in carbon fixation can be extended. Answers to these would show whether such hybrids are useful beyond isolated-chloroplast experiments, whether for studying photosynthetic electron transport or for work on artificial photosynthesis.

Source: New organic iron-sulfur framework boosts photosynthesis and carbon fixation (Phys.org, 11 November 2026).

Image: AI-generated illustration.