Smart supramolecular assemblies

Self-assembly of complex molecules is essential for a wide array of biological structures, including proteins, cell membranes, or even entire viruses. Supramolecular chemistry is a field of study that attempts to build large molecules out of a discrete number of smaller building blocks. By altering the strength of attraction between different polymers, complexes can be constructed on demand, leading to the development of 'smart materials' that respond to changes in their environment, such as the addition of a new chemical. However, many aspects of supramolecular chemistry remain poorly understood.

Now, in a study published in Scientific Reports, researchers from Osaka University showed how additives can promote the self-assembly of spherical microparticles made of a super absorbent polymer, poly(sodium acrylate), as well as control the macroscopic shape of the resulting assemblies. Some of the polymer molecules were functionalized with the specific chemical, β-cyclodextrin (βCD), and others with adamantane (Ad) residues. However, the microparticles did not assemble until a critical threshold concentration of the additive 1-adamantanamine hydrochloride (AdNH₃Cl) was introduced. The researchers took inspiration from biological proteins, which consist of long chains of smaller units called amino acids. Certain attractions or repulsion between amino acids, including hydrogen bonding, electrostatic interaction, or hydrophobic interactions, can control the folded shape of the resulting protein. Similar effects can occur among other large biomolecules, including DNA, polysaccharides, and lipids.

"In a certain sense, all living organisms are just collections of supramolecular polymers with sophisticated functions," lead author of the study Akihito Hashidzume says.

The team analyzed the behavior of the macroscopic assembly of spherical microparticles, and found that the resulting shape, whether more spherical or elongated, could be controlled based on the AdNH₃Cl concentration. This suggests that stimuli, such as heat and force, can be used to control the shape of the assemblies.

"The results in this study might help us understand the origin of various shapes of organisms," senior author Akira Harada says. This research could also assist in future work on the control of macroscopic assemblies based on microscopic interactions, as well as novel active materials that change depending on their situation.