Power Merger

English
Nanocrystals that convert two low-energy photons into a single high-energy one, under an electron microscope
 

 

 
Solar power could supply all the energy the world needs, yet it still accounts for only a tiny fraction of the global energy market. One major hurdle is low efficiency: Almost all the energy is lost, for example, when solar cells convert sunlight into electricity. In particular, about a fourth is lost because the cells can absorb light particles, or photons, only above a certain energy level. All the lower-energy photons that hit the cell are therefore wasted, reducing its efficiency and driving up the cost of energy production.

A potential solution is to convert pairs of low-energy photons into a single high-energy particle that can be absorbed by the cell – a process known in technical terms as “upconversion.” This task poses an enormous challenge: Just as it’s much easier to break a vase than to put it together from pieces, so it is easier to split a particle into lower energy components than to merge two particles into one. It is particularly difficult to achieve upconversion tuned to specific colors, or energy levels. Now Weizmann Institute scientists have developed an innovative system that overcomes this difficulty. The study, reported in Nature Nanotechnology, was performed by Dr. Dan Oron with research students Zvicka Deutsch and Lior Neeman of the Physics of Complex Systems Department.
 
(l-r) Lior Neeman, Ben Leshem, Dr. Dan Oron, Zvicka Deutschand and Osip Schwartz
 

 

 
Using solution-based chemistry procedures that resemble stir-frying in hot oil, the scientists built nanocrystals shaped like rods about 50 nanometers (50 billionths of a meter) in length. The area of the period at the end of this sentence could include about a billion such crystals. At one end of the nanorod, an electron absorbs photons one by one: It is first excited by one photon, then pushed to a higher energy level by the next photon. The resulting high-energy electron is transferred to the other end of the rod, where it emits a photon whose energy is higher than that of each of the two absorbed ones.

In the study, the scientists managed to convert two red-light photons, which have relatively low energy, into a single green-light photon, whose energy is higher. In fact, the system can be tuned to virtually any color because its design allows for great flexibility, as the properties of the nanorods can be controlled by their radius.

To help their nanocrystals make the transition from the lab to industry, the scientists are currently working to increase their efficiency as upconverters and to obtain better control of their colors. In the future, such crystals could be used in combination with more conventional materials, such as silicon, the material of choice for most commercial solar cells. Since silicon does not absorb photons from the infrared range down, these low-energy photons could be captured by the nanocrystals.

 

Through Thick and Thin

A neuron under a two-photon microscope, visualized using an unscattered laser beam (left), a temporally focused beam (middle) and a beam without temporal focusing (right)
 

 

 
When it comes to brain research, enlightening studies can be performed using literally enlightening techniques – ones that involve shining light on neurons. Using a light beam, it is possible, for example, to excite an individual brain neuron in order to determine with which other neurons it communicates. Ultimately, in this manner scientists can trace entire neuronal networks that underlie everything, from memories and emotions to movement and behaviors.

Neuronal networks are often studied using electrodes, but light beams are less invasive and easier to move around. The only problem is that when a light is directed at a region deep inside the brain, it illuminates the entire region, not only the targeted neuron.

In a study conducted in collaboration with French researchers, Dr. Dan Oron and his team have found a solution. As reported in Nature Photonics, they managed to excite deeply embedded neurons – inside a slice of mouse brain tissue more than 200 microns thick – with the help of short laser pulses. Oron’s team consisted of research student Ben Leshem and postdoctoral fellow Dr. Osip Schwartz of the Weizmann Institute’s Physics of Complex Systems Department. They collaborated with the team of Dr. Valentina Emiliani of Paris Descartes University: Dr. Eirini Papagiakoumou and graduate student Aurelien Begue, as well as her university colleagues Drs. Brandon Stell and Jonathan Bradley.

The study made use of an approach called temporal focusing, developed earlier at Weizmann. As its name suggests, it works by controlling the focus of a laser light beam in time rather than in space: Light is beamed at the sample in long pulses, which shorten when the beam reaches the desired plane, producing the needed illumination. As a result, only the targeted neuron, which has been genetically engineered to respond to the short pulse but not to the long ones, is excited. Moreover, this neuron is illuminated in a uniform manner, with its borders sharply delineated, which is optimal for its excitation. This happens because temporal focusing dramatically reduces the scattering of light within brain tissue: The scattered photons don’t interfere with the excitation process as they don’t hit the brain tissue at the instant in which the targeted neuron is illuminated. The method allows for such outstanding precision because the pulses last only about a hundred femtoseconds – each femtosecond is a millionth of a billionth of a second.

Thanks to this method, it might now be possible to study neuronal networks by exciting individual neurons with short laser pulses.
 
Dr. Dan Oron’s research is supported by Dana and Yossie Hollander; the Leona M. and Harry B. Helmsley Charitable Trust; the European Research Council; and the Crown Photonics Center. Dr. Oron is the incumbent of the Recanati Career Development Chair of Energy Research in Perpetuity.
 
 
Space & Physics
English
  • Alternative Energy
  • Dan Oron
  • Microscopy
  • Nanoscience
  • Photon
  • Physics of Complex Systems
  • Solar Energy

Weizmann Institute Solar Technology to Convert Greenhouse Gas into Fuel

English

An Israeli-Australian venture will use solar technology developed at the Weizmann Institute of Science to reduce carbon dioxide emissions from the burning of brown coal. The venture has been recently launched in Israel by NewCO2Fuels Ltd., a subsidiary of the Australian company Greenearth Energy Ltd., which has acquired an exclusive worldwide license for the solar technology from Yeda, the Weizmann Institute’s technology transfer arm.


The Weizmann technology makes use of concentrated solar energy to dissociate carbon dioxide (CO2) to carbon monoxide (CO) and oxygen (O2). This method, developed at the Weizmann Institute by Prof. Jacob Karni, also makes it possible to dissociate water (H2O) to hydrogen (H2) and oxygen (O2) at the same time it dismantles the CO2.


Carbon monoxide (CO), or its mixture with hydrogen called Syngas, can then be used as gaseous fuel, for example, in power plants, or converted to liquid fuel such as methanol, which can be stored, transported or used to power motor vehicles.


The method has proved successful in laboratory trials. NewCO2Fuels Ltd. is now building a solar reactor for the conversion of CO2 on an industrial scale. Part of the development is being performed in collaboration with the Canadian Institute for the Energies and Applied Research at the Weizmann Institute of Science.


Greenearth Energy expects the new Israeli-Australian venture to help harness the vast brown coal resources in the State of Victoria in south-eastern Australia, whose use has been limited until now by the high CO2 emission content from this type of coal. The possibility of converting CO2 to fuel in a clean and efficient manner will turn brown coal into a source of environmentally friendly fuel.

 

Canadian Institute for the Energies and Applied Research
 
 

Prof. Jacob Karni’s research is supported by the Israel Strategic Alternative Energy Foundation.

 


 

Canadian Institute for the Energies and Applied Research
Environment
English
  • Canadian Institute for the Energies and Applied Research
  • Industrial application
  • Jacob Karni
  • Solar Energy
  • Yeda

A Place in the Sun

English

(l-r) Prof David Cahen and Dr. Pabitra Nayak. Setting limits

“One of my dreams for the field of alternative energy is to see the day when all homes will be covered in ‘solar paint’,” says Prof. David Cahen of the Weizmann Institute’s Materials and Interfaces Department (Faculty of Chemistry).

“The trick,” says Cahen, “is to understand the limitations, as well as the capabilities, of each type of solar cell and then find a suitable niche for its use.” Current solar cell technologies are relatively expensive – unable to convert the sun’s energy into electricity with cost-effective efficiency. Although the solar energy that reaches Earth in just one hour equals the entire energy needs of the world for a whole year, calculations show that even the best solar cell can never reach an efficiency of more than about 31% – and this figure is lower in practice. Simple economics shows that solar cells with low efficiency are worthwhile only if they are also cheap.

Half a century ago, William Shockley and Hans Queisser identified three factors limiting the efficiency of the commonly used “sandwich-layered” solar cell: 1) It has a limited spectrum of light absorption; 2) much of the absorbed light energy is lost as heat; and 3) electric current is lost in the cell before it can be used. Newer generations of solar cells have been constructed from organic, molecular and polymeric materials, but even in optimal lab conditions, their performance is lower than that of most of today’s commercial solar cells. Are there other factors, beyond the SQ limits (named for their proposers), that need to be taken into account?

To find out, Cahen and postdoctoral fellow Dr. Pabitra Nayak (a graduate of the Tata Institute of Fundamental Research, India), with the help of Prof. Juan Bisquert of Universitat Jaume I, Spain, analyzed and compared various criteria of all the different types of solar cells. Their findings, recently published in Advanced Materials suggest that there are indeed additional limiting factors beyond the SQ limits – at least for solar cells made with organic materials – that can explain the extra energy loss.

A “typical” solar cell is made from two layers of inorganic semiconducting material – most commonly, crystalline silicon. One of the layers is electron-rich, the other electron-deficient. Stacking these two layers creates a region with an electric field. When light strikes the semiconductor, freeing electrons from their bonds, electricity is generated. The electric field acts as a one-way gate, allowing the “free” electrons to travel through a wire connecting the two layers, thus creating an electric current.

The three SQ limits come into play as the light strikes the material. The “limited spectrum of light absorption” means that some of the light does not possess enough energy to free electrons in any given material and passes through the cell unused. If, on the other hand, the light has more energy than the amount needed to free electrons, the extra energy is lost as heat – limiting factor number two. The third limiting factor involves freed electrons that return to their bound states before they can escape through the wire.
 
Will solar paint replace some traditional photocells? Traditional silicon photocell. Image: Stephan Kambor, Wikimedia Commons
But materials made of organic molecules have an entirely different structure than the non-molecular, inorganic materials currently used for solar cells, and this, according to Cahen, may contain clues to their lower efficiency values. For example, organic materials are more disordered – a state that requires more energy to free electrons and create a current. Some energy is also lost in the form of bond vibration as an electron is freed in the interaction of light with organic materials. Weaker bonding between organic molecules also leads to reduced electron movement through the semiconductor layer, and this causes some of the freed electrons to lose energy. These latter two phenomena occur in all solar cells, but they are small to negligible in the classic, inorganic cells.

Should researchers give up on organic-molecule-based solar cells? Or should they continue seeking ways to improve their efficiency? That, says Cahen, might be akin to pushing dyslexic students to excel in literature: “Instead of investing time and effort trying to reach unrealistic efficiencies, knowing their limitations up front leads to more reasonable expectations of what the cell can do, and it can therefore be put to a more suitable use. For example, molecular-type cells could be perfect for use in solar paints despite their lower efficiency, and they can be much cheaper to produce than silicon-based solar cells, which are not even an option for such applications. Organic molecules also may be well suited for exploiting specific parts of the solar spectrum.”

Additionally, Cahen views his research as very relevant for artificial photosynthetic systems – in which solar energy is converted to chemicals. “Solar cells are like a beta site for learning about artificial photosynthesis. If we can realize both artificial photosynthesis and solar paint, we will have added some very significant pieces to the mosaic that will make up our energy future.”
 
Prof. David Cahen's research is supported by the Mary and Tom Beck Canadian Center for Alternative Energy Research, which he heads; the Nancy and Stephen Grand Research Center for Sensors and Security; the Helen and Milton A. Kimmelman Center for Biomolecular Structure and Assembly; the Gerhardt M.J. Schmidt Minerva Center on Supramolecular Architectures, which he heads; the Carolito Stiftung; the Wolfson Family Charitable Trust; Dr. Monroe Burk, Columbia, MD; the estate of Theodore E. Rifkin; the Jacob and Charlotte Lehrman Foundation; and the Irving and Varda Rabin Foundation of the Jewish Community Foundation. Prof. Cahen is the incumbent of the Rowland and Sylvia Schaefer Professorial Chair in Energy Research.

 
 
 
(l-r) Prof David Cahen and Dr. Pabitra Nayak. Setting limits
Environment
English
  • Alternative Energy
  • David Cahen
  • Materials and Interfaces
  • Organic molecule
  • Solar Energy

A Source of Safe Energy

English

 

 

 
illustration: Sunshine
 

 

 

 

 

 

 

 

 

 

 

 

Containing no corrosive chemicals, giving off no pollution and able to generate electricity indefinitely just by lying in the sun, solid state photocells -- commonly known as "solar batteries" -- are a promising source of safe energy. Projects under way at the Weizmann Institute may spur the wider use of these environmentally benign devices.

In one of them, a novel photoetching technique for modifying the surface of silicon has been developed by Prof. Reshef Tenne and co-workers in collaboration with French researchers. Their approach increases the efficiency of silicon photocells by reducing the amount of light they reflect and by limiting "surface recombination," the trapping of electrons in the semiconductor before they can exit as an electric current.

An inexpensive new method for removing problematic transition-metal impurities from semiconductors has also been designed by Prof. Tenne. Here, an infra-red laser is used to ionize impurity atoms, causing their rapid movement through the semiconductor and enabling their removal from the crystal surfaces by simple chemical procedures. This technique may find numerous economically feasible applications for improving photovoltaics of various kinds.

A novel photovoltaic cell, operating on a principle differing radically from that underlying standard photocells, has been devised by Dr. Gary Hodes. The cell is made of easily produced films of semiconductor nanocrystallites which are less than one-hundredth the size of the crystallites present in standard photovoltaics.

Hodes, collaborating with Tenne, is also designing solar cells containing thin films of layered, well-ordered semiconductors such as molybdenum disulfide and tungsten diselenide -- materials that are far more stable than widely used amorphous silicon.

In other work, a theoretical approach has been developed by Dr. David Cahen that explains why pre-heating polycrystalline solar cells in air helps reduce energy-conversion losses due to decreased current loss on crystallite surfaces. Cahen has also succeeded in identifying and analyzing the basic mechanisms by which solar energy is lost as heat in solar cells, and in measuring such losses experimentally. In addition, working with Drs. Lev Margulis and Gary Hodes, he showed that thermal mismatch between components of solar cells made of polycrystalline thin films is a major problem in the manufacture and performance of such cells; the scientists went on to demonstrate that this mismatch can be virtually eliminated by using a cheaper type of glass as substrate for the cell.

Cahen has also collaborated with Prof. Amnon Yogev, who heads a project in which highly concentrated sunlight is split into two different parts (spectral ranges), one used to drive solar powered lasers and the other converted into electricity by "concentrator" solar cells. Experiments are now under way to convert all of the concentrated sunlight into electricity by splitting it into a number of spectral ranges, each matched to a different type of solar cell.

Some of these Institute developments are already being closely examined by solar cell manufacturers in Europe.
 
sunlight concentration apparatus; Mirror concentrating light on solar cell
 
 

 

 
 
illustration: Sunshine
Environment
English
  • Amnon Yogev
  • David Cahen
  • Gary Hodes
  • Materials science
  • Reshef Tenne
  • Solar Energy
  • Solar laser

Saving Up Sunshine

English

 

 

Prof. Igor Lubomirsky. New energy: Turning excess CO2 into fuel

 

 

 

 

 

 

 

 

 

 

 

 

One of the unsolved technical challenges holding back the global use of such renewable energy resources as solar or wind is that they’re not always able to deliver power when and where it’s needed. There’s plenty of sun and wind – enough to run all the factories, computers and air conditioners in the world; but supplying that energy on demand is still problematic.

If only we had a way to save the sun’s energy for a rainy day. Coal, for instance, is a form of stored energy: It can be burned at will to create steam, which, in turn, produces electricity. In contrast, solar panels and windmills convert sunshine and wind directly to electricity – useful for powering our homes, but hard to stockpile. Many solutions have been proposed, but most (oversized batteries, for example, or pumping large quantities of water uphill) remain expensive, unwieldy or impractical in other ways. One promising avenue that scientists have been exploring is that of converting the energy obtained from the sun or wind into a form that can be stored, transported and burned at a later date. In the 1980s and 1990s, Weizmann scientists began pursuing methods for storing solar energy in chemical bonds, using highly concentrated solar energy created in the Institute’s solar tower (thermochemical heat pipe).

Now, Prof. Igor Lubomirsky of the Institute’s Materials and Interfaces Department in the Faculty of Chemistry has come up with a novel alternative for converting solar energy into fuel. What’s more, his method is comparatively inexpensive, produces no environmentally hazardous waste and is very efficient. Rather than coal (which takes millions of years to be created and emits pollutants when burned), the new method produces carbon monoxide (CO) – a non-corrosive gas that can be burned directly in turbines or generators, or converted on-site into liquid fuel. Although it’s toxic in high concentrations, CO has been used for over a hundred years as an intermediate chemical product; tens of millions of tons are synthesized each year from coal or wood in one of the most developed of industrial processes.

In Lubomirsky’s approach, the CO is generated from CO2 in a relatively straightforward chemical process using a setup that’s something like a large, hot battery. Inside a special cell, a chemical compound is heated to around 900°C and an electric current is passed through the compound. When CO2 is continuously fed into the cell, the result is pure CO and oxygen.

“CO could be produced right at the smokestack of a power plant or other CO2 source,” says Lubomirsky, “so the greenhouse gases released from the plant would be removed and recycled before they have a chance to hit the atmosphere. The metal used in the process is off-the-shelf titanium, which is many times cheaper and more available than such precious metals as platinum that are often used in similar devices.” Other advantages of the method include a thermodynamic efficiency of over 85% (not counting the energy needed to heat the system), which is almost unheard of in the world of energy conversion, and the ease of transporting and burning CO.

Lubomirsky: “In the future, this method might be used to harvest solar or wind energy in places where it’s plentiful, convert it to CO and store or convert it into a liquid fuel such as methanol. This research is 100% the fruit of Weizmann Institute scientists and resources, especially the Institute’s Alternative Energy Research Initiative (AERI), which supports a number of important research projects in the field.”

Yeda, Ltd., the technology transfer arm of the Weizmann Institute, has applied for a patent for the method, and preliminary tests are planned for the near future.

Prof. Igor Lubomirsky’s research is supported by the Nancy and Stephen Grand Research Center for Sensors and Security; the Phyllis and Joseph Gurwin Fund for Scientific Advancement; Yossie Hollander, Israel; Martin Kushner Schnur, Mexico; Rowland Schaefer, New York; and the Wolfson Family Charitable Trust.

Freeze and Heat

Can one freeze water by heating it? In research that recently appeared in Science, Lubomirsky, working with then research student David Ehre and Prof. Meir Lahav, demonstrated that water can turn solid at different temperatures, depending on the electric charge of the surface underneath. By creating conditions for the charge to be reversed, they found that ice could even form as the surface heated up.

The experiment was based on a long-standing conjecture that an electric charge could promote freezing by causing the water molecules to align with the charge. When water freezes at 0° Celsius, the ice crystals start to coalesce around dust particles or other impurities. But so-called super-cooled water, such as that in high clouds, can stay liquid well below the freezing point if nothing sets off crystallization. Testing the theory was problematic, however, as materials that hold a charge – mostly metals – also act as nuclei for ice formation.

The team solved the problem by placing the water on a special surface made of pyroelectric crystals; these can carry a charge when heated or cooled, but do not provide a nucleus for ice crystals. To their surprise, they found that whereas on a positively charged surface, the water froze at -7°C and on the uncharged surface at -12.5°C; on the negatively charged material, it only turned to ice at -18°C. When they put liquid water on the negatively charged surface, the water turned to ice when that surface was heated from -11°C to -8°C.

Prof. Igor Lubomirsky
Environment
English
  • Alternative Energy
  • Chemistry
  • Igor Lubomirsky
  • Materials and Interfaces
  • Meir Lahav
  • Solar Energy
  • Yeda

Just Add Water

English
 
Prof. David Milstein. Hydrogen in three easy steps

 

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Take a metal complex. Add water and heat to 100°C for three days, stirring occasionally. Then add a generous amount of light and continue to “simmer” at room temperature for a further two days. The resulting hydrogen and oxygen are now ready to be “served.”
 
This is the gist of a unique new strategy devised by Prof. David Milstein and his colleagues in the Weizmann Institute’s Organic Chemistry Department; and it represents the first steps toward obtaining a clean, sustainable source of hydrogen for fuel. While today’s methods of producing hydrogen using sunlight are inefficient and often discharge chemical waste, the new system relies on a metal complex that is “reset” for reuse at the end of the procedure. In the process, the team demonstrated a new mode of bond generation between oxygen atoms and they even defined the mechanisms by which this takes place. In fact, says Milstein, the production of oxygen gas through the pairing of oxygen atoms that have been split off from water molecules – a crucial step in the process – has proven to be a bottleneck. Their results have recently been published in Science.
 
Nature has taken a very different path to producing free oxygen: It’s a byproduct of the photosynthesis carried out by plants. Spurred on by plants’ “green” example, vast worldwide efforts have been devoted to the creation of artificial photosynthetic systems. The ones Milstein develops are based on metal complexes that serve as catalysts (substances that increase the rate of a chemical reaction without getting used up themselves).
 
The new approach devised by the Weizmann team is divided into a stepwise sequence of reactions, beginning with water splitting. Milstein’s “secret ingredient” is a complex of the element ruthenium designed by his group in previous studies. This is a “smart” synthetic complex composed of a metal center and an organic (carbon-based) component; the two cooperate in cleaving the water molecule. This complex not only breaks the chemical bond between hydrogen and oxygen, but prevents them from getting back together by binding one hydrogen atom to its organic part and the remaining hydrogen and oxygen atoms (an OH group) to its metal part, creating a new metal complex.
 
The second stage – the heat stage – involves heating the resulting complex in water to 100°C, leading to the release of hydrogen gas – a potential source of clean fuel – and creating another chemical structure on the metal complex, this one containing two OH groups.
 
“But the most interesting part is the third, light-driven stage,” says Milstein. “When we exposed the third version of the complex to light at room temperature, not only was oxygen gas produced but the metal complex also reverted back to its original state, and this could be recycled for use in further reactions.”
 
These results have garnered a fair amount of interest in their field, as bonding between two oxygen atoms promoted by a man-made metal complex was previously a very rare event and its mechanism had been a mystery. Milstein and his team succeeded, for the first time, in identifying an unprecedented mechanism for this process. Their experiments indicated that during the third stage, the energy provided by the light causes the two OH groups to get together and form hydrogen peroxide (H2O2), which then quickly breaks up into oxygen and water. “Because hydrogen peroxide is considered a relatively unstable molecule, scientists have generally deemed this step implausible; but we have shown otherwise,” says Milstein. The team also challenged another misconception, providing evidence that the bond between the two oxygen atoms is generated within a single molecule, involving just one metal center, and not between oxygen atoms residing on separate molecules as was commonly thought.
 
So far, Milstein’s team has demonstrated a three-step mechanism for the formation of hydrogen and oxygen from water using light, without the production of chemical waste. For their next study, they plan to combine these stages to create an efficient catalytic system, bringing those in the field of alternative energy one step closer to realizing the goal of a clean, efficient method for producing hydrogen fuel from water using sunlight.
 
Participating in the research were former postdoctoral fellow Dr. Stephan Kohl, research student Leonid Schwartsburd and Yehoshoa Ben-David, all of the Organic Chemistry Department, together with Drs. Lev Weiner, Leonid Konstantinovski, Linda Shimon and Mark Iron of Chemical Research Support.

 

Prof. David Milstein’s research is supported by the Mary and Tom Beck-Canadian Center for Alternative Energy Research; the Helen and Martin Kimmel Center for Molecular Design; and the Bernice and Peter Cohn Catalysis Research Fund. Prof. Milstein is the incumbent of the Israel Matz Professorial Chair of Organic Chemistry.

 
Prof. David Milstein. Hydrogen in three easy steps
Chemistry
English
  • Alternative Energy
  • Catalyst
  • David Milstein
  • Green Chemistry
  • Organic Chemistry

Shedding Light

English

(l-r) Iris Margalit, Dr. Ilit Cohen-Ofri, Dr. Joanna Grzyb, Dr. Dror Noy and Dr. Jebasinga Tennyson. Custom-built proteins

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
If “older is wiser,” then photosynthetic organisms, including plants, algae and various types of bacteria, must be wise indeed – at least when it comes to efficiently converting sunlight, water and carbon dioxide into sugars and other energy-rich molecules to fuel their biological activities.
 
Dr. Dror Noy, a plant scientist at the Weizmann Institute of Science, has plans to harness the ancient art of photosynthesis – mastered by organisms over millions of years – in new ways, to create clean and renewable alternatives to fossil fuels.
 
Using natural biological building blocks and the living photosynthetic apparatus as a starting “blueprint,” Noy intends to design and engineer functional solar energy conversion systems. The building blocks of these systems will be small, robust protein scaffolds known as maquettes, which were first developed by the University of Pennsylvania group Noy joined as a postdoctoral student. Maquettes are assembled from natural amino acids, but their design is different from any natural protein. Now Noy hopes to customize new types of maquettes, endowing them with pigments and other cofactors found in the photosynthetic apparatus.
 
Noy focuses on the initial stages of photosynthesis – the so-called light reactions. In protein complexes known as photosystems, the pigments in leaves or organisms absorb sunlight and transfer this light energy to a nearby reaction center. In the reaction centers, this energy causes the release of electrons, which then pass through a chain of reactions, producing chemical energy for further conversion into oxygen and carbohydrates in the final stages of photosynthesis. To return the lost electrons to the photosystems, new electrons are split from water molecules, freeing up oxygen molecules and positively charged protons.
 
“Although the process of photosynthesis is highly efficient for photosynthetic organisms, they store their converted energy in sugars that are poor fuel products,” explains Noy. He is trying to sift through the evolutionary “noise” of functions that have been lost, gained or duplicated over the aeons to identify the minimal requirements necessary for photosynthesis, and to build maquettes that will harness its energy for making better fuels.
 
As for the design, Noy and his group have an initial advantage: The photosynthetic apparatus is one of the best-characterized systems in the field of biology. The distance between pigments has been measured down to the near-atomic scale, and the dynamics of energy transfer down to fractions of picoseconds. The precise 3-D arrangement of pigments, however, is critical for the process to work efficiently, and in practice, manipulating structures at such small scales has proven difficult. The photosystem proteins provide the scaffold that maintains this spatial organization, and this, in turn, is determined by the sequence of their amino acids. Thus the key to success lies in finding the right amino acid sequence for each protein – an incredible challenge, given that there are millions of possible combinations.
 
Yet Noy’s group is starting to make headway. Using genetic engineering, they “program” the bacterium E. coli to produce new proteins with specifically designed amino acid sequences for assembling pigments and cofactors into simpler analogs of natural photosynthetic proteins. By iteratively testing and redesigning the new proteins, they are beginning to understand how sequences of amino acids translate into the required 3-D structures. They have already managed to build prototype maquettes containing a few light-harvesting pigments that are able to carry out some reactions, and they are hoping to further tweak the design to contain many more pigments. Another group is working on ways to tap into the process of photosynthesis at the “junction” where light energy can be diverted to converting protons into hydrogen molecules that could be used for fuel.
 
Noy: “These studies will hopefully open the way to the design of stand-alone energy conversion as well as such light-activated devices as protein-based solar cells, which make use of biological elements in a non-biological context. Insights gained from this research will also advance our understanding of the way plants harvest and store solar energy. This understanding should make it possible to introduce custom-built proteins into plants to increase the production of such plant-based fuels as biodiesel or ethanol, as well as enabling the production by plants of such ‘inorganic’ fuels as hydrogen.”
 
Right: Actual molecular structures of natural protein complexes:a photosynthetic reaction center (top) and a cytochrome. Left: Artificial proteins that are analogous to the natural ones, with details of their “assistant molecules” (far left)
 
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

Getting the Green Light


 
Born in Tel Aviv, in 1967, Dr. Dror Noy served in the Israel Air Force, reaching the rank of lieutenant. After receiving a B.Sc. in chemistry from Tel Aviv University in 1992, he pursued his M.Sc. and Ph.D. studies at the Weizmann Institute under the guidance of Prof. Avigdor Scherz, then went on to postdoctoral studies at the University of Pennsylvania in the laboratory of Prof. P. Leslie Dutton. Upon returning to Israel in 2004, he worked as a post-doctoral fellow and later as a staff scientist with Prof. Irit Sagi in the Weizmann Institute’s Structural Biology Department. “Although I focused on different aspects of research at each stage of my studies, the repertoire of scientific and technical knowledge thus gained has allowed me to integrate them into a new line of research.” Noy joined the Plant Sciences Department as a senior scientist in 2007.

Noy is a recipient of the 2006 Career Development Award from the internationally based Human Frontier Science Program. He is married and is the father of four children, aged 10, 7 and twins of 3½ years.
 


Dr. Dror Noy’s research is supported by the Chais Family Fellows Program for New Scientists; the Koret Foundation; the estate of Louise G. Perlmuter, Brookline, MA; Ilan Gluzman, Secaucus, NJ; and Dr. and Mrs. Robert Zaitlin, Los Angeles, CA.
 

 

 
(l-r) Iris Margalit, Dr. Ilit Cohen-Ofri, Dr. Joanna Grzyb, Dr. Dror Noy and Dr. Jebasinga Tennyson. Custom-built proteins
Environment
English
  • Alternative Energy
  • Genetic engineering
  • Photosynthesis
  • Plant Sciences

Paint Power

English

Dr. Boris Rybtchinski. borrowing from biology

 
 
 
 
 
 
 
 

 

 

 

Alternative energy promises a bright future thanks, in part, to dark paint. Our buildings, cars, ships and airplanes could one day be powered by a thin coat of special paint that will convert solar energy to electricity or fuel. Preference will be given to dark hues, which are better at absorbing sunlight. Thus a new Ferrari might, alas, come in black instead of red.

Making such futuristic energy concepts a reality will take radically new scientific approaches. “We haven’t made much progress in our use of energy,” says Dr. Boris Rybtchinski of the Weizmann Institute’s Organic Chemistry Department. “Our resources of oil and coal are limited, yet we continue to burn these fossil fuels and pollute the environment. In the meantime, the world’s demand for energy is soaring and the threat of global warming looms. There’s a huge gap between the enormity of the problem and the progress in finding alternative energy sources. We badly need fresh, creative ideas.”

Rybtchinski’s team is working on one such idea. He draws his inspiration from photosynthesis, the process by which plants and certain bacteria convert sunlight into chemical energy by employing an organic “paint” – chlorophyll. Certain artificial pigments are already more effective than chlorophyll, but combining them into functional systems is no simple matter. Rybtchinski seeks to create “well-connected” molecular systems that will harvest sunlight in clever ways intended to generate solar electricity and fuels.

Solar cells, which convert sunlight into electricity, are already available commercially; but their use is limited, in part, by their high cost and the difficulty of storing the energy, as these cells work only when the sun shines. The storage problem could be overcome by converting sunlight into chemical energy. In other words, fuels might be created using sunlight – just what photosynthesis achieves in nature.

Rybtchinski seeks to build artificial photosynthetic systems from cheap and readily available organic materials. Such systems might be able to produce various fuels from freely available ingredients – for example, hydrogen from water, or methanol from water and carbon dioxide. Solar paint would be a type of artificial photosynthetic system.

Rybtchinski believes that a better understanding of natural photosynthesis, combined with advances in organic chemistry and nanotechnology, can lead to innovative solutions in this field of research. In his lab, one doesn’t see the familiar panels or mirrors of solar installations. In fact, without an electron microscope one doesn’t see much of anything at all, as his solar energy nano-systems measure only several millionths of a millimeter.

To manufacture these systems, he takes a cue from yet another natural process – self-assembly – which governs the emergence of biological systems, from proteins to living organisms. Water plays a key structural role in self-assembly: Various biological molecules are either repelled or attracted to water molecules, and this property determines their position in living cells and tissues. With the help of an array of advanced technologies, Rybtchinski uses sophisticated molecular methods to exploit the hydrophobic – that is, “water-hating” – properties of certain organic molecules, manipulating them to self-assemble into efficient solar-energy-converting units.

In one of their projects, Rybtchinski’s group builds molecular “wires” that must perform three types of function, in rising order of complexity: moving photons while absorbing the energy of sunlight (a step occurring at the beginning of photosynthesis); moving electrons to convey an electric current in solar cells; and, finally, moving both electrons and protons to generate solar fuels.

In parallel, Rybtchinski collaborates with a number of other Institute scientists on creating hybrid solar conversion systems composed of organic molecules, catalysts and nano-particles. “In this work, we are solving basic science questions that are key to finding practical alternative energy solutions,” he says. “The need to find such solutions is what ultimately motivates us all.”

The long-term goal is not just to achieve plants’ efficiency at using sunlight – already a formidable challenge – but to overtake them. “Plants don’t run around the way we do, so our energy needs are vastly higher,” Rybtchinski explains. “Therefore, we need to generate much more energy and with greater efficiency.”   

 On a Personal Note

Born in Kiev, Ukraine, Dr. Boris Rybtchinski received a B.Sc. in chemistry from Kiev State University in 1992. He then immigrated to Israel and, in 1993, embarked on graduate studies at the Weizmann Institute under the guidance of Prof. David Milstein. After serving in the medical corps of the Israel Defense Forces, he earned his Ph.D. with distinction in 2002. He conducted postgraduate research at Northwestern University for three years and joined the Weizmann faculty in the fall of 2005. He has received a number of prestigious awards, including the Sir Charles Clore Prize. He lives in Tel Aviv with his wife, Revital, whom he met when both were students at Weizmann, and their son, Gal, several months old. He enjoys sports and reading history books.
 

Dr. Boris Rybtchinski’s research is supported by the Helen and Martin Kimmel Center for Molecular Design; the Alternative Energy Research Initiative; Mr. and Mrs. Yossie Hollander, Israel; the Robert Rees Applied Research Fund; Sir Harry Djanogly, CBE, UK; and Mr. and Mrs. Larry Taylor, Los Angeles, CA. Dr. Rybtchinski is the incumbent of the Abraham and Jennie Fialkow Career Development Chair.

 
 
 
Dr. Boris Rybtchinski.
Environment
English
  • Alternative Energy
  • Boris Rybtchinski
  • Nanotechnology
  • Organic Chemistry
  • Photosynthesis
  • Solar Energy

Going for Green

English
 
Prof. Uri Pick. better biofuel
 
Prof. Avihai Danon. Alga genetics
 
 
 
 

Oil from Algae

 

What are the best crops to grow for biofuels? Corn and sugarcane, presently converted to ethanol in Brazil and the USA, consume large amounts of petrochemicals and arable land in cultivation, and using them for fuel is already beginning to drive up the price of food. The contribution of soybean- and canola-based biodiesel in Europe to overall fuel consumption is small and cannot be extended. A better alternative, according to a number of scientists, may be lying under the nearest rock or floating on a stagnant pond: algae.
 
Algae have a number of advantages over other sources of biofuel. For one, they can be grown on marginal soil or in salt water, without draining water resources. For another, they grow rapidly and could be harvested regularly throughout the year. And there is no waste – no seeds, stems or roots to discard. Algae plantations placed near power plants would capture much of the emitted carbon dioxide to use as building blocks for biofuel, thus creating “green energy.”

 

Finally, some kinds of algae produce oil – up to 50% of their mass. This oil, says Prof. Avihai Danon of the Institute’s Plant Science Department, can be easily xtracted and converted to bio-diesel, which could be used in today’s diesel engines without significant investment. Algae could yield an estimated 30 times the oil output of the best crop plants, and could satisfy the fuel needs of the USA and other heavily industrialized countries around the world.
 
Danon and Prof. Uri Pick of the Biological Chemistry Department have begun a new project that aims to create strains of algae that will excel at generating oil for biofuel. Their first step is to understand how and when the algae produce the oil. Like green plants, algae get their energy from the sun and store it as sugars or oils. But there is a limit to how much energy one alga – a single-celled organism – can utilize. In fact, too much sunlight can overload the alga’s system, stimulating the production of free radicals that can harm or even kill the cell. This limit creates a trade-off between oil production and growth, and the cell must decide in which to invest its energy. The scientists suspect that it is in times of stress that the algae build up their stores of oil.
 
The researchers are working on several different strains of algae that grow in different conditions and have different traits. They are developing the tools to identify and compare the genes that regulate the algal metabolism, making decisions whether to stockpile oil or spread out, whether to take in additional sunlight or put up protective sunscreens. “Once we’ve identified the genes, we should be able to develop the means to control these processes in the algae ourselves,” says Danon, “and hopefully create algae that can be an excellent, environmentally friendly source of fuel.”    
 

Prof. Ed Bayer. Solving two problems with one bacterial complex

 
 

Recycled Fuel

 
While the debate rages over the ecological and economic value of using food crops to produce fuel, Weizmann Institute scientists are taking a different approach that could potentially solve two environmental problems with one stone – or at least one bacterial enzyme complex.
 
One of the obstacles to creating biofuels from organic substances such as agricultural waste is that they contain large amounts of tough materials – mainly cellulose – that do not break down easily. (Corn and sugarcane, on the other hand, are rich in starch and sugar that can easily be turned into ethanol.) Prof. Ed Bayer of the Biological Chemistry Department has been researching bacteria that chew up cellulose, converting it to sugar that they then feed on. In the 1980s Bayer, together with Prof. Raphael Lamed of Tel Aviv University, discovered how the bacteria’s cellulose-degrading machinery works. The cellulosome, as they dubbed this molecular machine, is a group of enzymes that work as a team to chop up the long chains of repeating sugar units in cellulose molecules into short sugars that can be dissolved in water.
 
About 50 percent of landfill material is cellulose, mostly in the form of paper, and it continues to pile up year after year.
 
Breakdown is slow, partly due to landfill conditions and partly because the cellulose in such man-made products as paper turns out to be particularly hard for the bacterial cellulosome to digest. Bayer began tinkering with cellulosomes, adapting the bacterial machinery for turning plant cellulose into sugar into an effective tool for recycling paper. He and Lamed used genetic engineering techniques to create hundreds of different versions of the cellulosome, mixing and matching parts in their search for those that excelled at their new task. Prof. Gideon Schreiber, an expert in designing and altering protein-protein interactions, and Prof. Dan Tawfik, an expert in enzyme evolution, have joined the team to help design artificial cellulosomes with improved activity. The most recent version of the artificial cellulosome can potentially turn a lab dish full of finely shredded paper into simple sugar syrup in about a day.
 
Recently, this research has taken on new urgency. The simple sugars churned out in the process are ideal for conversion to ethanol, and the artificial cellulosome might be adapted to other cellulose-rich energy resources such as agricultural waste. Much research remains to be done before the process can be recreated efficiently on the industrial scale, Bayer cautions. Nonetheless, one day our cars may run on ethanol brewed from recycled trash.

 

Prof. Dan Tawfik. Hydrogen-producing bacterium

 

 

Fuel of the Fittest

 

If algae and bacteria can be engineered to produce such bio-fuels as biodiesel and ethanol, might they also generate such futuristic energy resources as hydrogen? Hydrogen could be the cleanest fuel of all, as its combustion leaves behind only water. But most present-day methods of producing hydrogen still involve processing fossil fuels.
 
In an ambitious project, a consortium of scientists from France, Spain, Sweden, the UK, Portugal and Israel, including Prof. Dan Tawfik of the Biological Chemistry Department, are investigating the possibility of creating a bacterium that will produce hydrogen cleanly and economically. The researchers have started with a strain of cyanobacteria (often called blue-green algae, though they are not true algae). These photosynthetic, single-celled organisms have a long history of producing materials we need: They’re credited with releasing oxygen into the early atmosphere (paving the way for the evolution of oxygen-breathing animals), and with fixing nitrogen in soils so that plants such as rice can absorb it.
 
The researchers plan to use a cutting-edge approach to developing the new bacteria. Rather than adapting one or two existing genes, they aim to equip the cyanobacteria with a whole new set of biological components engineered for specific functions. The multidisciplinary team will use a slew of techniques to accomplish this, including one developed by Tawfik – directing the evolution of enzymes in cell culture to produce cellular components that are highly efficient at carrying out desirable tasks.   

Prof. Ed Bayer’s research is supported by Mr. and Mrs. Yossie Hollander, Israel. Prof. Bayer is the incumbent of the Maynard I. and Elaine Wishner Chair of Bio-Organic Chemistry.
 
Prof. Avihai Danon’s research is supported by the Edward D. and Anna Mitchell Research Fund; and Mr. and Mrs. Yossie Hollander, Israel. Prof. Danon is the incumbent of the Henry and Bertha Benson Professorial Chair.
 
Prof. Uri Pick’s research is supported by Mr. and Mrs. Yossie Hollander, Israel.
Prof. Pick is the incumbent of the Charles and Louise Gartner Professorial Chair.
 
 
Prof. Gideon Schreiber’s research is supported by the Clore Center for Biological Physics; the Helen and Milton A. Kimmelman Center for Biomolecular Structure and Assembly; and Mr. and Mrs. Yossie Hollander, Israel.
 
Prof. Dan Tawfik’s research is supported by the J&R Center for Scientific Research; the Jack Wolgin Prize for Scientific Excellence; Mr. and Mrs. Yossie Hollander, Israel; Mr. Rowland Schaefer, New York, NY; and the estate of Fannie Sherr, New York, NY. Prof.  Tawfik is the incumbent of the Elaine Blond Career Development Chair.
 

 

Environment
English
  • Alga
  • Alternative Energy
  • Avihai Danon
  • Bacterial cells
  • Dan Tawfik
  • Ed Bayer
  • Genetic engineering
  • Uri Pick

Fueling the Future

English
Illustration: multidisciplinary research towards sustainable energy
 

 

"Developing alternative means of producing energy in the forms that humankind needs is crucial to dealing with the ongoing energy crisis,” Weizmann Institute President Prof. Ilan Chet said recently. He went on: “Creating fresh, sustainable methods of satisfying the world’s energy needs will be possible only if we can gain the knowledge to invent completely new technologies. The Weizmann Institute of Science has an obligation to take a lead in global efforts in this field. We believe we can help shape the planet’s future.”
 
Prof. Chet was referring to an ambitious multidisciplinary research initiative launched by the Weizmann Institute of Science. The scientists involved in the new Initiative for Research in Sustainable and Alternative Energy aim to significantly advance the search for solutions to the world’s most pressing energy problems. 
 
The global energy crisis is a complex problem that involves challenges on the political, economic and scientific fronts. The demand for energy has risen sharply in recent years, fueled by rapidly rising standards of living and expanding populations, especially in industrializing countries such as China and India. If nothing is done to change current patterns, energy demand will rise nearly 60% by the year 2030. Nonrenewable energy sources such as fossil fuels are running out; petroleum-based fuel supplies could be held hostage to political upheavals, affecting the peace and security of Israel and the entire world. The continuing upward spiral of oil prices also threatens the stability of the global economy. As long as energy consumption continues to rise, burning fossil fuels will be a major cause of air pollution, including the accumulation of greenhouse gases in the upper atmosphere, which may already be causing global warming.   
 
Many Weizmann Institute scientists are concerned about this state of affairs, and a number of them have recently made a commitment to join in the search for energy solutions. Says Prof. Mordechai Sheves, Dean of the Faculty of Chemistry: “The special nature of the Weizmann Institute, with its emphasis on multidisciplinary scientific cooperation, makes it one of the most promising places in which to pursue such solutions.” 
 
Institute scientists are already applying a number of original approaches to producing alternative energy. One example is the manufacture of methanol (currently extracted from fossil fuels) using the sun’s energy. If the method proves successful, it may in the future provide a relatively clean, renewable and environmentally friendly fuel. 
 
Scientists from many disciplines will conduct research under the aegis of the sustainable energy initiative. Various research groups in physics and chemistry, for example, will focus on energy conversion, storage and conservation, adding to several projects at the Institute that are already showing progress in converting the sun’s energy to electricity and fuel. A research team in the life sciences plans to investigate ways of utilizing plants and biomass as energy sources. Other scientists are carrying out basic research in nuclear fusion, while new lubricants containing nanomaterials developed at the Institute promise to increase the efficiency of machinery, thereby reducing fuel consumption.
 
The Weizmann Institute plans to raise significant funds for the Initiative so that cutting-edge energy research can move forward at the pace needed to find timely answers. The plan calls for recruiting promising young scientists as well as established researchers to join the effort and share their expertise with the Institute's multidisciplinary task force of leading scientists. With this impetus to advanced research and innovation, the Weizmann Institute intends to lead the way in finding new and better solutions to meet the world’s growing energy needs. 
Illustration: multidisciplinary research towards sustainable energy
Environment
English
  • Alternative Energy

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