Photosynthesis: Lessons from nature
Photosynthesis is one of nature's finest miracles. Through the
photosynthetic process, green plants absorb sunlight in their leaves and
convert the photonic energy into chemical energy that is stored as
sugars in the plants' biomass. If we can learn from nature and develop
an artificial version of photosynthesis we would have an energy source
that is absolutely clean and virtually inexhaustible. (September 23, 2011)
 |
| Through the miracle of photosynthesis, plants absorb sunlight in
their leaves and convert the photonic energy into chemical energy that
is stored as sugars in the plants' biomass. (Credit: Photo by Roy
Kaltschmidt, Berkeley Lab) |
"Solar energy is forecasted to provide a significant fraction of the
world's energy needs over the next century, as sunlight is the most
abundant source of energy we have at our disposal," says Graham Fleming,
Vice Chancellor for Research at the University of California (UC)
Berkeley who holds a joint appointment with Lawrence Berkeley National
Laboratory (Berkeley Lab).
"However, to utilize solar energy harvested
from sunlight efficiently we must understand and improve both the
effective capture of photons and the transfer of electronic excitation
energy."
Photosynthesis: Evolutionary perspective
Photosynthesis is one of the fundamental processes of life on Earth. The
evolutionary transition from anoxygenic (no oxygen produced) to
oxygenic (oxygen-producing) photosynthesis resulted in the critical
development of atmospheric oxygen in amounts large enough to allow the
evolution of organisms that use oxygen, including plants and mammals.(April 3, 2012)
 |
| Ferns. Photosynthesis is one of the fundamental processes of life on
Earth. The evolutionary transition from anoxygenic (no oxygen produced)
to oxygenic (oxygen-producing) photosynthesis resulted in the critical
development of atmospheric oxygen. One of the outstanding questions of
the early Earth is how ancient organisms made this transition. (Credit: ©
Pontus Edenberg / Fotolia) |
Plants and algae, as well as cyanobacteria, use photosynthesis to
produce oxygen and "fuels," the latter being oxidizable substances like
carbohydrates and hydrogen. There are two pigment-protein complexes that
orchestrate the primary reactions of light in oxygenic photosynthesis:
photosystem I and photosystem II.
"In photosynthesis, the oxygen is produced at a special metal site
containing four manganese and one calcium atom connected together as a
metal cluster," explains professor James Allen. "This cluster is bound
to the protein called photosystem II that provides a carefully
controlled environment for the cluster."
On illumination, two water molecules bound at the cluster are split
into molecular oxygen and four protons. Since water molecules are very
stable, this process requires that the metal cluster be capable of
efficiently performing very energetic reactions.
Allen, Williams and coworkers are trying to understand how a
primitive anoxygenic organism that was capable of performing only simple
low energy reactions could have evolved into oxygen-producing
photosynthesis.
They have been manipulating the reaction center of the purple bacterium Rhodobacter sphaeroides
encouraging it to acquire the functions of photosystem II. In the
recent publication, they describe how a mononuclear manganese bound to
the reaction center has gained some of the functional features of the
metal cluster of photosystem II.
Although the mononuclear manganese cannot split water, it can react
with reactive oxygen species to produce molecular oxygen. These results
suggest that the evolution of photosynthesis might well have proceeded
through intermediates that were capable of oxygen production and served
until a protein with a bound manganese-calcium cluster evolved.
Carotenoids Can Capture Blue/Green Light and Pass Energy On to Chlorophylls
Pigments found in plants and
purple bacteria employed to provide protection from sun damage do more
than just that. Researchers from the University of Toronto and
University of Glasgow have found that they also help to harvest light
energy during photosynthesis. (April 4, 2013)
 |
| Advanced optical probes using femtosecond lasers enable light
harvesting processes to be examined in exquisite detail. Anticlockwise
from top right: Purple bacteria and the structure of the light
harvesting complex that gives these cells their distinctive purple
color. This special protein incorporates molecules of
bacteriochlorophyll and carotenoid to capture the energy from sunlight.
The lower part of the figure shows the protein data recorded from
two-dimensional laser spectroscopy. (Credit: Evgeny Ostroumov) |
A series of experiments showed that a special "dark state" of the
carotenoid -- a hidden level not used for light absorption at all --
acts as a mediator to help pass the energy it absorbs very efficiently
to a chlorophyll pigment.
Says Scholes. "It is amazing that nature uses so many aspects of a whole
range of quantum mechanical states in carotenoid molecules, moreover,
and puts those states to use in such diverse ways."
cientists Swap Key Metal Necessary For Turning Sunlight Into Chemical Energy
Scientists Swap Key Metal Necessary For Turning Sunlight Into Chemical Energy
Photosynthesis is a remarkable biological process that supports life on
earth. Plants and photosynthetic microbes do so by harvesting light to
produce their food, and in the process, also provide vital oxygen for
animals and people.(May 23, 2009)
 |
| The reactions that convert light to chemical energy happen in a
millionth of a millionth of a second, which makes experimental
observation extremely challenging. A premier ultrafast laser
spectroscopic detection system established at the Biodesign Institute,
with the sponsorship of the National Science Foundation, acts like a
high-speed motion picture camera. It splits the light spectrum into
infinitesimally discrete slivers, allowing the group to capture vast
numbers of ultrafast frames from the components of these exceedingly
rapid reactions. These frames are then mathematically assembled,
allowing the group to make a figurative "movie" of the energy transfer
events of photosynthesis. (Credit: Arizona State University Biodesign
Institute) |
In all plant chlorophylls, only one particular metal, magnesium, is held tightly within the molecule's center.
During photosynthesis, plants have two photosystems that work in
tandem: photosystem I and photosystem II. To peer at the inner workings
of photosynthesis, the team used a hardy, well-studied, photosynthetic
bacterium called Rhodobacter sphaeroides. An organism similar to this
purple bacterium was likely one of the earliest photosynthetic bacteria
to evolve. The purple bacteria possess a simplified system similar to
photosystem II.
The center stage of photosynthesis is the reaction center, where light
energy is funneled into specialized chlorophyll binding proteins. The
research team had previously demonstrated that the movement of the
reaction center proteins during photosynthesis facilitates the
light-driven movement of electrons between molecules in the reaction
center, helping the plant or bacteria to harness light energy
efficiently even if conditions aren't optimal. Every time the team
introduced disruptions into this electron pathway, the proteins were
able to compensate by moving and energetically guiding the electrons
through their biological circuit.
Photosynthesis: A new source of electrical energy
Biofuel cell works in cactus
Scientists in France have transformed the chemical energy generated by
photosynthesis into electrical energy by developing a novel biofuel
cell. The advance offers a new strategy to convert solar energy into
electrical energy in an environmentally-friendly and renewable manner.
In addition, the biofuel cell could have important medical applications. (February 18,2008)
 |
| Biofuel cell inserted in a cactus and graph showing the course of
electrical current as a function of illumination of the cactus (black:
glucose, red: O2). |
The researchers showed that a biofuel cell inserted in a cactus leaf could generate power of 9 μW per cm2. Because this yield was proportional to light intensity, stronger illumination accelerated the production of glucose and O2
(photosynthesis), so more fuel was available to operate the cell. In
the future, this system could ultimately form the basis for a new
strategy for the environmentally-friendly and renewable transformation
of solar energy into electrical energy.
Artificial Photosynthesis
Researchers from the Department of Chemistry at the Royal Institute of
Technology (KTH) in Stockholm, Sweden, have managed to construct a
molecular catalyzer that can oxidize water to oxygen very rapidly. In
fact, these KTH scientists are the first to reach speeds approximating
those is nature's own photosynthesis. The research findings play a
critical role for the future use of solar energy and other renewable
energy sources. (April 12, 2012)
 |
| Grass. Scientists have imitated natural photosynthesis and created a
record-fast molecular catalyzer. (Credit: © Nejron Photo / Fotolia) |
Researchers all over the world, including the US, Japan, and the EU,
have been working for more than 30 years on refining an artificial form
of photosynthesis. The results have varied, but researchers had not yet
succeeded in creating a sufficiently rapid solar-driven catalyzer for
oxidizing water.
But now, together with research colleagues, he has imitated natural
photosynthesis and created a record-fast molecular catalyzer. The speed
with which natural photosynthesis occurs is about 100 to 400 turnovers
per seconds. The KTH have now reached over 300 turnovers per seconds
with their artificial photosynthesis.
"This is clearly a world record, and a breakthrough regarding a
molecular catalyzer in artificial photosynthesis," says Licheng Sun.
"When it comes to renewable energy sources, using the sun is one of the best ways to go," says Sun.
Artificial Leaf
Scientists have claimed one of the milestones in the drive for
sustainable energy -- development of the first practical artificial
leaf. Speaking in Anaheim, California at the 241st National Meeting of
the American Chemical Society, they described an advanced solar cell the
size of a poker card that mimics the process, called photosynthesis,
that green plants use to convert sunlight and water into energy. (March 28, 2011)
 |
| Living tree leaves. Scientists have just claimed one of the
milestones in the drive for sustainable energy -- development of the
first practical artificial leaf. (Credit: iStockphoto) |
"A practical artificial leaf has been one of the Holy Grails of
science for decades," said Daniel Nocera, Ph.D., who led the research
team. "We believe we have done it. The artificial leaf shows particular
promise as an inexpensive source of electricity for homes of the poor in
developing countries. Our goal is to make each home its own power
station," he said. "One can envision villages in India and Africa not
long from now purchasing an affordable basic power system based on this
technology."
Following sites referred thankfully and reference for further detail:
http://www.sciencedaily.com, the journal Analytical Chemistry.
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