Photosynthetic algae have been their light-capture technology for millions of years of improvement. Thus, these algae have powerful light-harvesting systems - proteins that absorb light and then convert it into energy - scientists have long been eager to understand the mechanisms and imitate it for use in renewable energy sources.
Now, researchers at Princeton University have uncovered a mechanism that can improve the light capture efficiency of the cryptophytes Chroomonas mesostigmatica. Cryptic algae usually live under other organisms that absorb most of the sun's rays. Correspondingly, these algae evolved to thrive on light that was not captured by their neighbors - mainly yellowish green. These algae collect this yellow-green light energy and transfer it to a molecular network that converts it into red light, in which chlorophyll molecules need to perform important photosynthetic chemistry.
The speed of energy through the system is both impressive and confusing to the scientists who study them. Scholes's prediction is always three times slower than the observed rate. "These energies go through the time scale of the protein - and we will never understand why this process can go so fast," says author Gregory Scholes, an honorary professor of chemistry at Princeton University.
In 2010, Scholes's team found evidence that the reason behind these fast rates is a strange phenomenon called quantum coherence, in which molecules can share electron excitation and transfer energy according to the laws of quantum mechanical probability rather than classical physics. But the team has not been able to accurately explain how coherence is speeding up until now.
By using a sophisticated ultrafast high power laser pointer method, researchers are able to measure the light absorption of molecules and fundamentally track the energy flow in the system. Under normal circumstances, the absorption signal will overlap, so that they can not be assigned to specific molecules within the protein complex, but the group by cooling the protein to a very low temperature can improve the signal contrast, Jacob Dean said he was the The lead author of the paper and a postdoctoral fellow at the Scholes Laboratory.
Researchers have observed that the energy of the system shifts from one molecule to another, from high-energy green light to low-energy red light, and excess energy is lost in the form of vibrational energy. Dean said that these experiments revealed a specific spectral pattern, which is a conclusive evidence of vibrational resonance or vibration matching between donor and acceptor molecules.
This matching of vibrations allows the transfer of energy much faster than the speed that can be transmitted by the distribution of light excitation between molecules. This effect provides a mechanism for previously reported quantum coherence. Taking into account this redistribution, the researchers recalculated their predictions and arrived at a rate almost three times faster.
"At long last, the forecast is roughly correct," Scholes said. "It turns out that it requires this completely different and surprising mechanism." Scholes Laboratories plans to study the proteins involved to explore whether this mechanism works in other photosynthetic organisms. Ultimately, scientists hope to draw inspiration and design principles from these precisely tuned but very powerful photoproteins to create a light-harvesting system with perfect energy transfer properties. "This mechanism is a more powerful exposition of the optimality of these proteins," Scholes said.