Scientists at the Pacific Northwest National Laboratory developed a novel technique to study and observe in real time electron transfer reactions. In an article, published in the latest Chemical Communications, Eric Ackerman et al report combining single-molecule fluorescence spectroscopy with conventional electrochemical methods to study single molecule electron transfer dynamics. Because such reactions are fundamental to the existence of life and many of its processes, such research can have profound consequences for future clinical and scientific efforts.
When studying these reactions, chemists generally look at a whole group of molecules reacting and measure the average energy they give off, much like looking at a whole organization of workers and averaging their productivity. More useful is knowing which of your coworkers are workaholics and which are asleep on the job, and, hopefully, why.
The team combined two well-established techniques to zoom in on electron transfer reactions. In one, called cyclic voltammetry, a molecule fluoresces when zapped with electricity. The PNNL team chose a dye called cresyl violet: at a particular voltage, the dye molecule loses an electron and in the process sends out a flash of white light.
But traditional cyclic voltammetry allows studying such molecules only in big batches. Being able to watch individual molecular reactions would be like being able to see the details in the frames of a film.
To view single molecules, PNNL chemists Chenghong Lei and Dehong Hu combined forces. Lei built an electrochemical cylinder about the size of a brazil nut that held a drop of dye. The team fitted this onto Hu’s single-molecule fluorescent microscope at EMSL, DOE’s Environmental Molecular Sciences Laboratory on the PNNL campus. This set-up resulted in a new instrument capable of performing both techniques simultaneously.
By rapidly cycling the voltage up and down, the team found that some individual molecules were a bit erratic. Although most of the molecules behaved as expected, some that should have been lit, weren’t. And turning off the electricity, all should have blinked out but some kept burning in the absence of a voltage.
"What we want to know is what causes these variations. And can we control these variations in a favorable way with external experimental and environmental conditions?" said Lei.
Studying molecules one at a time can provide insights into chemical reactions that can’t be observed by studying them en masse. Such insights could help chemists improve upon the design that nature gave them. Their new instrument provides a way to study and control the molecules.
"If we could make a desired molecule consistently work at its maximum rate, that would be a big improvement," said Ackerman.
In addition, the researchers said they plan to use cresyl violet or another fluorescent molecule side-by-side, or even incorporated into proteins of interest, such as those involved in electron transfer reactions that generate biofuels. As the proteins gain or lose electrons, the fluorescent components would lose or gain theirs to reveal what is going on . . . in a flash.