Chemists Turn Gold to Purple — On Purpose
Professor Richard Watt and his chemistry students suspected that a common protein could potentially react with sunlight and harvest its energy — similar to what chlorophyll does during photosynthesis.
The story of how they proved it sounds as colorful as the legend of the leprechaun who hid his pot of gold at the end of the rainbow.
They started with citric acid from oranges and mixed it with the protein. Next they dissolved gold powder into the solution. Then they put vials of the yellow-colored mixture in direct sunlight and crossed their fingers in the hope that it would turn purple.
Here’s the reason why: If it turned purple, that would signal that the gold atoms had received electrons and used the donated energy to bunch together as small, purple-colored nanoparticles. And that would mean that the protein used the sunlight to excite the citric acid and trigger a transfer of energy.
While direct sunlight did the trick in about 20 minutes, a high-powered tungsten mercury lamp worked much faster.
“We set the system up, turned on the light, and the solution turned purple,” Watt said. “We knew that we’d proved the concept.”