Professor Shuichi Hiraoka, leader of the laboratory at the University of Tokyo Graduate School of Arts and Sciences along with his team claims to have identified the weak molecular forces that hold together a tiny, self-assembling box with powerful possibilities. The study demonstrates a practical application of a force common in biological systems and advances the pursuit of artificial chemical life.
The formation of DNA and proteins are biological examples of self-assembly, but the forces or processes controlling how these natural molecules come together also remain undefined. Investigations by Hiraoka’s team contribute to chemical understanding of how natural molecules might self-assemble and reveal techniques for mimicking those processes in the future.
To understand self-assembly systems the team developed artificial self-assembling cubes which helped them to understand how biological systems function. They identified the forces holding together the sides of their tiny boxes as van der Waals forces, mainly dispersion forces. These forces are weak attractions between molecules created when electrons temporarily group together on one side of an atom. Geckos can walk up walls in part due to van der waals forces.
Each side of the cube is formed from one molecule i.e. 2 nanometres in diameter and shaped like a six-pointed snowflake. Each side is about one-four-thousandth the size of a human blood cell. The weak forces holding the sides of the cube together make the box slightly flexible, so it adjusts to best accommodate guest molecules based on their size, shape, and atomic charge. The box can bulge to hold large or long contents and contract to eliminate extra space when hosting guest molecules with negative charge(s).
The tiny boxes were made out of molecules of hexaphenylbenzene. The individual molecules exist as a dry, white powder. When mixed with water, the molecules spontaneously self-assemble into cubes.
A cube that can self-assemble in water has the potential for future biological applications. The hexaphenylbenzene cube also holds together even above the boiling temperature of water, remaining stable up to 130 degrees Celsius (266 degrees Fahrenheit).
The six points of the snowflake-shaped hexaphenylbenzene molecules lock together when they assemble into a cube. Researchers describe the design of this molecular box as resembling the Japanese wood joining technique called hozo, where pieces of wood are held together without adhesives or hinges, using only intricate interlocking designs.
“We do not have the data yet, but the logical conclusion is that long chain like guest molecules somehow fold to get inside the box,” said Hiraoka.
The study is published in Nature Communications.