An unusual observation made during laboratory experiments led researchers to a discovery that could mark an entire career.
After years of trying to induce the behavior, unravel its mechanism and define its scope, a team led by Flinders University, in Australia, announced what it describes as a great discovery: a hitherto unknown type of reaction exchange between sulfur-sulfur bonds.
What makes this reaction remarkable is the fact that sulfur-sulfur bonds require, as a rule, heat, light or catalysts to be made to reorganize into molecules. The new “trisulfide metathesis reaction” occurs without additional reagents or any other external stimulus.
Instead, occurs spontaneously at room temperature when molecules containing chains of three sulfur atoms — trisulfides — are placed in certain solvents.
The discovery was presented in a published this Friday in the magazine Nature Chemistry.
“It is rare to discover an entirely new reaction, and even rarer that it can be useful in so many areas and applications”, says the chemist Justin Chalker, a researcher at Flinders University who has been studying sulfide polymers for more than a decade and co-senior author of the paper, cited by .
“Understanding this new reaction has allowed us to apply it to several high-value uses — including selective modification of a drug antitumor and the production of a new plastic that can be shaped, used and then ‘undone’ when it is necessary to recycle it”, details Chalker.
Sulfur-sulfur bonds are essential in many different moleculesincluding peptides, proteins, polymers and drugs. Part of the usefulness of this link lies in its ability to break and form again in response to a wide range of stimuli. Typically, they are molecular chains with two sulfur atoms — disulfides — that are used in these reactions.
Os organic trisulfidesin which three sulfur atoms form a chain with a different fragment at each end (normally represented as RSSSR, where R means “the rest of the molecule”), are less studied, but continue to be important. They are used, for example, in products such as vulcanized rubber and antitumor drugs.
But getting trisulfides to rearrange themselves has traditionally been difficult. Previous work has shown that exchanging these sulfur bonds generally requires high temperatures, often between about 80 and 150 degrees Celsius — and even then, the reactions can take hours or days to achieve balance.
A trisulfide metathesis reaction Now discovered, it behaves in a way very different. In certain solvents, sulfur chains begin exchanging fragments within seconds at room temperature, without the need for heat, light or additional reagents.
When studying sulfur-containing polymers, the team observed that certain trisulfide molecules quickly reorganized when dissolved in solvents such as in dimethylformamidecommon in chemistry experiments.
Instead of needing heat or catalyststhe sulfur chains began to exchange fragments for themselves.
In this reaction, two trisulfide molecules can exchange the chemical groups attached to their ends, changing, in practice, partners and forming new combinations of molecules. Chemists call put yourself to this type of partner exchange process.
In a typical metathesis, a pair of molecules with the arrangement:
‹ R1–S–S–S–R1 ›
‹ R2–S–S–S–R2 ›
go to:
‹ R1–S–S–S–R2 ›
‹ R2–S–S–S–R1 ›
Under the right conditions, this exchange occurs with remarkable rapidity: sometimes reaches equilibrium in a few seconds, at room temperature. Furthermore, it is easily reversible.
Researchers have already put the reaction to the testa, using it to modify the antitumor compound calicheamicin. They also used it to create a plastic made of chains linked by trisulfide bonds, which could be easily disassembled into its building blocks.
“I’m excited to see how this chemistry will be adopted, expanded and applied in ways we haven’t even imagined yet”, says the chemist Harshal Patelfrom Chalker’s laboratory at Flinders University, and co-author of the study.
“Coming across a new reaction is excitingand we have already demonstrated several relevant applications in biomolecular and materials chemistry”, adds the researcher.
Because it is fast, selective and reversible, this reaction could give chemists a new way to build molecules capable of rearranging themselves under mild conditions — something that could prove useful in areas ranging from drug discovery to materials science.
“I think the examples we show of what is possible to do with this chemistry are just the tip of the iceberg”, says the chemist Tom Hasellfrom the University of Liverpool, in the United Kingdom, and also co-author of the study.
