Researchers can now predict the properties of disordered polymers

Through a team of researchers from the University of Illinois at Urbana-Champaign and from the University of Massachusetts at Amherst, scientists are able to read models on long chains of molecules for understand and predict the behavior of disordered strands of proteins and polymers. The results could, among other things, pave the way for the development of new materials from synthetic polymers.

The laboratory of Charles Sing, an assistant professor in chemical and biomolecular engineering in Illinois, provided the theory behind the discovery, which was then verified by experiments conducted in the laboratory of Sarah Perry, assistant professor in Chemical Engineering at UMass Amherst and Illinois. The collaborators detailed their results in an article entitled "Design of electrostatic interactions via a polyelectrolyte monomer sequence" published in ACS (American Chemical Society) Central Science.

Colleagues began to understand the physics behind the precise sequence of charged monomers along the chain and its impact on the polymer's ability to create self-assembling liquid materials, called complex coacervates.

"What fascinates me about this work is that we are inspired by a biological system," Sing said. "The typical image of a protein shows that it folds into a very precise structure, but this system is based on intrinsically disordered proteins."

This paper builds on the earlier findings of Perry and Sing in 2017, which ultimately aim to help advance intelligent material design.

"Our previous article showed that these sequences were important, it shows why," says Sing. "The first showed that different sequences gave different properties in complex coacervation, what we can now do is use a theory to actually predict why they behave in this way."

Unlike structured proteins, which interact with very specific binding partners, most synthetic polymers do not.

"They are more confused because they will react with a wide range of molecules in their environment," explained Sing.

They found that despite this fact, the precise sequence of monomers along a protein (amino acids) really made a difference.

"It has been obvious to biophysicists that the sequence makes a big difference if it forms a very precise structure," Sing said. "Ultimately, forming imprecise structures makes all the difference."

Even unstructured proteins have a precision that is associated with them. Monomers, the basic elements of complex molecules, are the links in the chain. Sing's group theorized that by knowing the sequence of polymers and monomers and the charge (positive, negative or neutral) associated with them, one can predict the physical properties of complex molecules.

"Although researchers know that if they put different charges at different locations of any of these inherently disordered proteins, the actual thermodynamic properties change," Sing said.

"What we can show is that you can actually change the strength of this by changing it very specifically in the sequence.In some cases, changing the sequence by a single monomer (a single link in that chain), can to radically change the way these things can be formed, and we have also proven that we can predict the outcome. "

Sing adds that this information is valuable for biophysicists, bioengineers and materials scientists. This discovery will help engineers understand a broad class of proteins and adjust proteins to change their behavior. This gives them a new way to put information into molecules to build new materials and better guess the behavior of these properties.

Material scientists can, for example, use this information to control a material and assemble it into very complex structures or to create membranes that accurately filter contaminants in the water. They hope that scientists, inspired by biopolymers, will be able to use this ability to predict physical behaviors simply by reading the sequence in order to design new intelligent materials in this way.

"This in a way brings together biology and synthetic polymers," Sing said. "For example, at the end of the day, there is no major chemical difference between protein and nylon, biology uses this information to explain how life is going, and if you can identify precisely these different valuable information for a number of other applications ".