Scientists at the U.S. Department of Energy’s Argonne National Laboratory and the Notre Dame Radiation Laboratory at the University of Notre Dame have tied quantum physics and chemistry of photosynthesis in biology.
Using ultrafast spectroscopy to see what happens at the subatomic level during the very first stage of photosynthesis, two branches of science that could not be more different seem to be working together.
The result of the study could significantly influence efforts by chemists and nanoscientists to create artificial materials and devices that can imitate natural photosynthetic systems. Yet scientists have a long way to go before they will be able to create devices that match the light harvesting efficiency of a plant.
Argonne biochemist David Tiede said, “If you think of photosynthesis as a marathon, we’re getting a snapshot of what a runner looks like just as he leaves the blocks. We’re seeing the potential for a much more fundamental interaction than a lot of people previously considered.”
Different species of plants, algae and bacteria have evolved a variety of different mechanisms to harvest light energy, they all share a feature known as a photosynthetic reaction center. Pigments and proteins found in the reaction center help organisms perform the initial stage of energy conversion.
These pigment molecules, or chromophores, are responsible for absorbing the energy carried by incoming light. After a photon hits the cell, it excites one of the electrons inside the chromophore.
As the Argonne scientists observed the initial step of the process, they saw something no one had observed before: a single photon appeared to excite different chromophores simultaneously.
Tiede explains, “The behavior we were able to see at these very fast time scales implies a much more sophisticated mixing of electronic states. It shows us that high-level biological systems could be tapped into very fundamental physics in a way that didn’t seem likely or even possible.”
Chemist Gary Wiederrecht at Argonne’s Center for Nanoscale Materials takes up the potential, “The quantum effects observed in the course of the experiment hint that the natural light-harvesting processes involved in photosynthesis may be more efficient than previously indicated by classical biophysics. It leaves us wondering: how did Mother Nature create this incredibly elegant solution?”
Currently artificial photosynthesis experiments have not been able to replicate the molecular matrix that contains the chromophores.
Tiede resumes explaining, “The level that we are at with artificial photosynthesis is that we can make the pigments and stick them together, but we cannot duplicate any of the external environment. The next step is to build in this framework, and then these kinds of quantum effects may become more apparent.”
Today the problem is when the quantum effect occurs is so short-lived – less than a trillionth of a second – scientists will have a hard time ascertaining biological and physical rationales for their existence in the first place. That circumstance is what keeps the absolute certainty of the research out of reach.
Tiede said, “It makes us wonder if they are really just there by accident, or if they are telling us something subtle and unique about these materials. Whatever the case, we’re getting at the fundamentals of the first step of energy conversion in photosynthesis.”
The original study paper published back in March, now almost 2 ½ months ago. The press release came out last week and took nearly a week for distribution. It’s quite rare to have so much time go by in research announcements. That leaves the question, is it just an oversight or has something in the way of confirmation happened?
On the answer, the time doesn’t really matter; regular readers with an interest in the field of the journal Proceedings of the National Academy of Sciences would have taken notice. What will be interesting is checking the Citing Articles in a few months to see what else has turned up by others.
The noteworthy point beyond the quantum effects is that science is looking at chemistry at the quantum level, and seeing things. ‘What’ exactly, might be open for discussion for a while, but the breakthrough in sensor technology is going to open a whole new vista on chemistry with a restart on the potential of chemistry technology with great effects on biology.