Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Lab-made complexes are “sun sponges”

22.08.2013
A ring of protein and pigments, half synthetic and half natural, can be used to quickly prototype light-harvesting antennas that absorb more sunlight than fully natural ones

In diagrams it looks like a confection of self-curling ribbon with bits of bling hung off the ribbon here and there. In fact it is a carefully designed ring of proteins with attached pigments that self-assembles into a structure that soaks up sunlight.


HUNTER/Holten/PARC

The dyad modules assemble into rings (side view, above left, and top view, above right) that pack many pigments together for light harvesting. Because of the additional pigments attached to the dyads, the antennas absorb more of the sun’s light than natural systems.

The scientists who made it call it a testbed, or platform for rapid prototyping of light-harvesting antennas–structures found in plants and photosynthesizing bacteria–that take the first step in converting sunlight into usable energy. The antennas consist of protein scaffolding that holds pigment molecules in ideal positions to capture and transfer the sun’s energy. The number and variety of the pigment molecules determines how much of the sun’s energy the antennas can grab and dump into an energy trap.

In the August 6, 2013 online edition of Chemical Science, a new publication of the Royal Society of Chemistry, the scientists describe two prototype antennas they’ve built on their testbed. One incorporated synthetic dyes called Oregon Green and Rhodamine Red and the other combined Oregon Green and a synthetic version of the bacterial pigment bacteriochlorophyll that absorbs light in the near-infrared region of the spectrum.

Both designs soak up more of the sun’s spectrum than native antennas in purple bacteria that provided the inspiration and some components for the testbed. The prototypes were also far easier to assemble than synthetic antennas made entirely from scratch. In this sense they offer the best of both worlds, combining human synthetic ingenuity with the repertoire of robust chemical machinery selected by evolution.

One day a two-part system (consisting of an antenna and a second unit called a reaction center) might serve as a miniature power outlet into which photochemical modules could be plugged. The sun’s energy could then be used directly to split water, generate electricity, or build molecular-scale devices.

The project was organized by the Photosynthetic Antenna Research Center (PARC) at Washington University in St. Louis, one of 46 Energy Frontier Research Centers funded by the Department of Energy in 2009. The team tapped the expertise of many PARC-affiliated scientists, including Dewey Holten and Christine Kirmaier of Washington University in St. Louis, Paul Loach and Pamela Parkes-Loach of Northwestern University, Jonathan Lindsey of North Carolina State University, David Bocian of the University of California, Riverside, and Neil Hunter of University of Sheffield in the United Kingdom.

Designer pigments
Nature has evolved many different systems to capture the sun’s energy, but they all rely on pigments, molecules that appear strongly colored because they are selectively absorbing some wavelengths, or colors, of light in the solar spectrum.

The pigment we are most familiar with is chlorophyll, the molecule that makes plants appear green. But that green color is a tipoff about the plant’s solar absorption. We see plants as green because they’re reflecting the green part of the spectrum and absorbing in the violet and the red parts of the spectrum instead.

Not only do plants miss the middle of the visible spectrum, they also miss light at wavelengths longer than we can see, including near-infrared photons absorbed by photosynthetic bacteria. The accessory pigments such as carotenoids that give leaves their splendid fall colors fill some gaps but large swaths of the solar spectrum pass through untouched.

“Since plant pigments actually reject a lot of the light that falls on them,” Hunter said, “potentially there’s a lot of light you could gather that plants don’t bother with.”

The team relies on Jonathan Lindsey to design and synthesize pigments that can absorb at wavelengths that will fill some of the holes in the absorption of natural systems. “It can’t be done from first principles,” Lindsey said, “but we have a large database of known absorbers and so drawing on that and reasoning by analogy we can design a large variety of pigments.”

More than one synthetic or natural pigment can be attached to the protein scaffolding. “The prototypes in the Chemical Science paper both have two but ultimately we’d like to add three or four or even more,” said Lindsey. “One of our goals is to understand to what extent the protein can be derivatized with pigments.”

“The effectiveness of the design depends not only on having extra pigments but also pigments able to talk to one another, so that energy that lands on any one of them is able to hop onto the next pigment and then to the next one after that. They have to work together,” Hunter explained.

“The energy cascades down like a waterfall,” Hunter said. “So you pour the energy at the top of the waterfall and it hits one pigment and jumps to the next and the next and finally to the pigment at the bottom, which in terms of energy is the pigment that is reddest in color.”

Self assembly line
If broad spectral coverage was one goal of the project, another was to avoid the laborious synthesis typically required to make designer light-harvesting antennas.

Fortunately light-harvesting antennas from purple bacteria are modular devices that self assemble under appropriate conditions, conditions that have been worked out by team members Paul Loach and Pamela Parkes-Loach. The basic module is a pair of peptides (short proteins) called alpha and beta that in turn house two bacteriochlorophyll molecules that both absorb light and act as the trap for all the harvested energy.

Thanks to the chemical affinities of the components, they self-assemble into dyads when added together in detergent (detergent is used instead of water alone because parts of the peptides shun water). By adjusting the detergent concentration and temperature, the dyads form rings, which in native antenna contain up to 16 alpha/beta dyads and thus as many as 32 bacteriochlorophylls.

In the testbed, the scientists use peptides that have been slightly modified from the native amino acid sequence for attachment of the extra pigments to increase solar spectral coverage. The attachment sites were chosen to avoid disrupting the self assembly of the components into dyads and dyads into rings.

“This is an example of what the field would refer to as semi-synthesis,” Lindsey said. “We take naturally occurring materials and combine them with synthetic ones to make something that doesn’t exist in nature. By taking lots of material from nature we can make molecules that are architecturally more complex than those we can make from scratch.”

Once assembled, the antenna are sent to the Holten/Kirmaier lab, where a variety of spectroscopic methods including ultra-fast laser spectroscopy are used to excite each pigment molecule and to follow the energy transfer from one pigment to the next and down to the target bacteriochlorophyll. Given the right pigments in the right locations, this transfer is extremely efficient, and little energy is lost on the way.

Samples also went to the Bocian laboratory where they are probed for structural integrity and to the Hunter laboratory where images are made of the rings, which are only 11 to 16 nanometers (a billionth of a meter) across and must be magnified tens of thousands of times to be visible.

“I’ve been working in photosynthesis for 50 years,” said Loach, “and I can’t think of many other times when there were so many good people with so many different talents coming together to try to solve problems. It’s fun to be part of it and to see what comes out of the collaboration.”

Diana Lutz | EurekAlert!
Further information:
http://www.wustl.edu

More articles from Life Sciences:

nachricht Scientists uncover the role of a protein in production & survival of myelin-forming cells
19.07.2018 | Advanced Science Research Center, GC/CUNY

nachricht NYSCF researchers develop novel bioengineering technique for personalized bone grafts
18.07.2018 | New York Stem Cell Foundation

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Future electronic components to be printed like newspapers

A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.

The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

A smart safe rechargeable zinc ion battery based on sol-gel transition electrolytes

20.07.2018 | Power and Electrical Engineering

Reversing cause and effect is no trouble for quantum computers

20.07.2018 | Information Technology

Princeton-UPenn research team finds physics treasure hidden in a wallpaper pattern

20.07.2018 | Materials Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>