The molecular components of nature's photosynthetic machinery take a beating from high-energy photons, ultraviolet light, and highly oxidizing (i.e., degrading) byproducts. When damage occurs, cellular processes recognize and cut off the damaged part of photosynthetic protein complex, remove the intact section to the outer regions of the cell where it can be fully repaired, and then return to its original site and function.Edit Summary
"The sun's rays can be brutal, even for a leaf that's harvesting them. When photosynthesis is going full blast, a leaf is constantly building new photosynthetic reaction centers to replace those damaged by harsh oxygen species and other destructive molecules generated by intense ultraviolet light.
"So rather than trying to make solar cells that are extremely durable, the team decided to take a literal leaf from nature's book and go the route of self-repair, says chemical engineer Michael Strano of MIT, who led the project. He and Stephen Sligar and Colin Wraight of the University of Illinois at Urbana-Champaign, along with other colleagues, designed a system where damaged parts could be easily replaced.
"The researchers began with light-harvesting reaction centers from a purple bacterium. Then they added some proteins and lipids for structure, and carbon nanotubes to conduct the resulting electricity.
"These ingredients were added to a water-filled dialysis bag--the kind used to filter the blood of someone whose kidneys don't work--which has a membrane that only small molecules can pass through. The soupy solution also contained sodium cholate, a surfactant to keep all the ingredients from sticking together.
"When the team filtered the surfactant out of the mix, the ingredients self-assembled into a unit, capturing light and generating an electric current.
"The spontaneous assembly occurs thanks to the chemical properties of the ingredients and their tendency to combine in the most energetically comfortable positions. The scaffolding protein wraps around the lipid, forming a little disc with the photosynthetic reaction center perched on top. These discs line up along the carbon nanotube, which has pores that electrons from the reaction center can pass through.
"Adding the sodium cholate back into the mix disassembles the complexes. But filtering it out again brings them right back together." (Ehrenberg 2010)