Quantum Effects Observed Powering Photosynthesis

Fmo_protein1Experiments in recent years have suggested that quantum effects were present in the light-harvesting antenna proteins of plant cells, but their precise role in processing incoming photons remained inconclusive.

In a new experiment published Dec. 6 in Proceedings of the National Academy of Sciences, a connection between coherence and energy flow is confirmed.  Coherence is when discrete molecules interact as one, separated by space but not time.

“There was a smoking gun before,” said study co-author Greg Engel of the University of Chicago. “Here we can watch the relationship between coherence and energy transfer. This is the first paper showing that coherence affects the probability of transport. It really does change the chemical dynamics.”

The new findings are the latest  to expand scientific understanding of photosynthesis, one of life’s fundamental processes.

Observations of coherence in antenna-protein chlorophylls from green sulfur bacteria  lasted far longer than anyone expected, long enough to hint at functional role.

Confronted with this unexpected coherence, researchers hypothesized a role in enabling ultra-efficient energy transfer. Energy from incoming photons could simultaneously explore every possible chlorophyll route from a protein’s surface to the reaction center at its core, then settle on the shortest path.

To see if that happened, a team led by Engel and Shaul Mukamel of the University of California, Irvine analyzed the fluctuation of lasers as they passed through antenna proteins. Depending on how they shifted, the researchers could track what happened inside.

They found a clear mathematical link between energy flows and fluctuations in chlorophyll coherence. The link was so clear it could be described in derivative sines and cosines, mathematical concepts taught in college trigonometry.

“The mounting evidence that quantum effects can be seen in natural systems when excited by lasers is compelling,” said Greg Scholes, a University of Toronto biophysicist who first found quantum effects in room temperature photosynthesis.

Further research is needed to understand the full role of quantum physics, said Scholes. “How much do they change our understanding? How much are they needed?” he said.

Engel sees a lesson in the importance of the antenna proteins in which chlorophyll molecules are embedded. “The protein does a lot more for this system than we thought,” he said. “It’s not just a simple structural element.”

In the image below, like ripples on water, energy absorbed from sunlight moves through the photosynthetic complex (gray-and-green molecular structure) with a wavelike motion. In this artist’s rendering, that motion creates interference signals that are analyzed in a spectrum (left).


The Daily Galaxy via wired.com

Image credit: Greg Engels and sciencewriter.org


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