Chemistry Breakthrough: Cancer-Targeting Compounds Developed
Chemists at St. Petersburg University have created new iridium compounds that could help scientists design “smart” cancer drugs in the future. These drugs could be turned on directly inside tumor cells and tracked in real time because they would change the color of their glow. The study was published in the journal Inorganic Chemistry.
How these special molecules work
Some molecules can change their properties when light shines on them. One important process behind this is called Excited-State Intramolecular Proton Transfer (ESIPT). In simple terms, this means that inside one molecule, a tiny particle called a proton can quickly move from one part of the molecule (the donor) to another part (the acceptor) after the molecule absorbs light.
When light hits the molecule, its electrons shift. This causes the proton to “jump.” This process happens very fast. It is important in nature, including in the glowing of some living organisms, and it is also used in industry.
Problems with older systems
Until now, most of these light-sensitive systems were made only from organic molecules. But they often did not glow brightly enough and were not very stable.
Scientists tried adding metal atoms to make the molecules stronger and give them new properties. However, this usually failed. The metal would push out the proton and stop the switching process completely.
So, researchers wanted to create a metal-containing molecule where the metal would help the proton move, instead of stopping it. This was a big challenge.
What the researchers achieved
The team at St. Petersburg University succeeded. They built a new iridium complex with a special organic structure. This structure includes an acyclic diaminocarbene ligand and a pyrazine fragment with two nitrogen atoms that acts like a “trap” for the proton.
In this molecule, the iridium atom plays a key role. When the molecule absorbs light, the iridium shifts electron density toward the pyrazine. This makes the pyrazine strongly attract the proton. As a result, the proton jumps.
When this happens, the color of the glow changes from blue-green to orange-red. The shift in light is about 100 nanometers.
This is the first known example of a glowing organometallic molecule where the metal directly controls the proton transfer, and where the donor and acceptor parts are located in different places in the molecule.
How they proved it works
The scientists carried out several tests.
First, they saw that the glow depends on the surroundings. In some solvents, the compound glows orange. In alcohol, it turns green again because alcohol blocks the proton transfer.
Second, computer calculations showed that the proton transfer is energetically favorable and should cause this color change.
Finally, they replaced normal hydrogen with its heavier form, deuterium. When they did this, the orange glow disappeared. This proved that the color change is really caused by proton transfer and not something else.
Why this matters
Professor Mikhail Kinzhalov from the Department of Physical Organic Chemistry explained that such compounds could one day be used to create drugs or special agents that react to the environment inside tumor cells. In theory, the molecule could change color only inside a tumor cell.
This would make it possible to treat the cancer locally and also watch what is happening to the drug inside cells in real time.
For now, the research is still at a basic stage. The main goal was to prove that a metal can help proton transfer instead of blocking it. The team has shown for the first time that this is possible.
In the future, these switchable glowing molecules could be used not only in cancer therapy, but also in medical diagnostics and in creating new electronic materials.
