Almost all of the chemical energy found in Earth’s living things can be traced back to the sun. This is because “light-harvesting” (LH) supramolecules (two or more molecules held together by intermolecular forces) help plants and some types of bacteria (usually as a food source) using sunlight to drive photosynthesis. In order for these supramolecules to be effective, they need to have many pigments, such as chlorophyll, arranged in specific structures that vary from species to species.
For example, green photosynthetic bacteria have LH antennas where chlorophyll molecules form spiral structures, which in turn assemble into large tubular supramolecules. On the other hand, purple photosynthetic bacteria, such as Rhodobacter sphaeroides, shows different types of LH antennas in which chlorophyll pigments are arranged in ring-shaped structures. Although researchers have been able to create tubular chlorophyll aggregates in the laboratory by self-assembly, their ring-shaped counterparts have not been produced artificially so far.
In a recent study published in Chemical Bonding on January 26, 2023, a group of scientists from Japan managed to solve this knowledge gap. They discovered that mixing a mixture of chlorophyll and naphthalenediamide in organic matter led to the formation of dimers that self-assembled into ring-shaped structures, e ‘ each a few hundred nanometers in diameter. The team included Professor Hitoshi Tamiaki from Ritsumeikan University and Associate Professor Shogo Matsubara from Nagoya Institute of Technology.
Intrigued by their initial discovery, the team sought to better understand the formation of ring-containing nanostructures and their properties. When they took a closer look using an atomic force microscope, they noticed that chlorophyll dimers, molecules made of two chlorophyll units linked by naphthalene, had originally joined together to form a wavy structure. stable nanofibers. When they heated the nanofibers at 50°C, they split into smaller precursors whose ends fused to form the desired nanorings.
Interestingly, this nanofiber-nanoring transition was dependent on external influences. Temperature was found to play a major role, along with dimer pressure. Prof. Tamiaki explains: “In the lower regions, ring-shaped aggregates were obtained by the special combination of one fiber supramolecule. go up to the nanostructures of the network.”
In general, the findings of this study reveal a straightforward way to synthesize the LH supramolecule that has eluded scientists for a long time. Happy with the results, Dr. Matsubara says: “Our self-made assemblies allow for better absorption of sunlight as well as transfer of excitatory energy. LH materials for devices such as solar cells.” Furthermore, the structural change from nanofiber to nanoring induced by an external stimulus can help to realize new smart materials with flexible properties.
The team said that further research on the optical properties of the self-contained nanorings is ongoing. To find out what interesting applications this knowledge will lead us to, stay tuned for future articles!