Carey Gates
March 24, 2008
FYS paper #2
GREEN SCUM AND RED CARPETS
As the “ecomobililty provider” for the Rome Film Festival, BMW offered its 7-series Hydrogen cars to transport the VIPs from their five-star hotels to the red carpet[1]. In addition, the Virgin Atlantic transportation service will be switching to hydrogen powered limousine vehicles to carry their premium class clients, and have placed a $2.6 million dollar order for a hydrogen powered airplane engines[2]. As classy as it sounds, the fuel in these vehicles comes from the less than appealing pond algae you may have seen around the neighborhood. Its capability to produce inordinate amounts of hydrogen ions has launched massive research and application efforts of harnessing pure hydrogen fuel from the simple process of photosynthesis.
Driven by the gene expression of the hydrogenase protein, photosynthesis is an anaerobic process in green algae. The family enzymes called hydrogenase catalyze the oxidation of hydrogen as it removes the electrons from the molecule by the equilibrium reaction 2H++2e- ⇌ H2. This molecular machine was discovered in the 1930’s. Further research in the 1950’s revealed two distinct types of hydrogenase, which differ in function and in accordance with their metallic component. The diiron hydrogenase [Fe-Fe] is less prominent in nature, found in microorganisms that produce hydrogen. Nickel-Iron hydrogenase exists in those that consume hydrogen.[3]
As photosynthesis occurs, Photosystem I collects energy from the sun, and typically sends the excited electrons to another molecular machine known as ferredoxin in order to create sugar, the form of energy useful to plant cells. However if excessive electrons accumulate in Photosystem I, they are sent instead to the hydrogenase enzyme. Hydrogenase then uses this energy to split water molecules and release molecular hydrogen as a waste product of photosynthesis. This natural process does not create significantly large amounts of hydrogen, but its simplicity and renewability make it a hugely viable energy source. Scientists today are interested in artificially emulating the process and genetically altering photosynthetic organisms to facilitate hydrogen production, having already found ways to breed and multiply the algae.
The first group to ever successfully directly manufacture and harness hydrogen fuel from a hydrogenase based molecular machine was led by Japanese efforts in 2006. A hybrid enzyme, crossed between hydrogenase from β-proteobacterium and Photosystem I subunit from cyanobacterium, was engineered by removing the subunit PsaE from the Photosystem I and attaching it to the hydrogenase. When placed near each other, these two artificially fashioned molecules spontaneously fused to create a single hybrid. The hydrogenase-PsaE-Photosystem I complex was confirmed as a complete molecular machine by sugcrose-gradient ultracentrifuge and immunoblot analysis.
While the structure had the potential to produce hydrogen at a rate of 1.2 μmol H2 · mg chlorophyll-1· h-1, the maximum was not reached. Factors such as insufficient electron supply from Photosystem I allowed the direct light-to-energy conversion of at a rate of .58 μmol H2 · mg chlorophyll-1· h-1. Although it only represents half of the ideal production, the complex did accelerate the electron transfer by five times the natural rate. This research group also intends to engineer a photosynthetic organism that unites hydrogenase, Photosystem I, and Photosystem II to increase hydrogen production even more. [4]
Professor Anastasios Melis of the
With all this impressive technology, it seems ridiculous that these processes are not yet applied in the mainstream economy. Yet as with all research endeavors, there are small issues that delay or prevent major successes. One inhibitor that scientists have incurred in using hydrogenase to create hydrogen fuel is its extreme sensitivity to oxygen. As a strictly anaerobic process, it is an arduous task to provide appropriate conditions for hydrogenase to function in order to produce hydrogen. Another frustrating aspect is that the photosynthetic process prefers to use the energy for sugar production. Photosystem I more naturally sends electrons to the ferredoxin to supply energy for the Calvin-Benson-Bassham cycle. In addition to being the underdog in the competition for energy, the constant electron transfer between Photosystem I and hydrogenase has not been finessed at this juncture. While they are challenging obstacles for making hydrogen fuel efficient enough for widespread use, the direct conversion of light to energy through artificial photosynthesis is still a very high priority in the international research field. Hydrogen as a primary fuel source has even sparked competition between the
The BioSolarH2 program is funded by the Air Force Office of Scientific Research to integrate traditional science and engineering to target and resolve issues faced by the U.S. Department of Defense. Led by Dr. Charles Dismukes of
The European Union’s initiative for implementing hydrogenase in effective hydrogen production is manifest in the Solar-H networking program. It was established to promote collaboration between existing researchers to provide support and to share expertise across the field. Solar-H objectives are classified into four team goals: the first to study living cyanobacteria and to alter its metabolic rate at the genetic level; the second to determine the mechanisms of natural photosynthesis, the third to artificially simulate those mechanisms at the molecular level, and finally to physically measure the pertinent reactions.[7] The programs of the
Hydrogenase and Photosystem I are obvioulsly applicable to real world issues and are extremely useful molecular machines. In conjunction, their capabilities present a potential and promising solution to the current energy crisis. Because using solar energy is probably the best possible option for a clean, renewable, abundant alternative energy source, this type of biofuel would be an exceptionally long term solution with outstanding benefits and virtually no downfalls. In fact, resolving oxygen inhibitors is not necessary for the process to work, only for facilitated use. Even preceding this advancement, the knowledge and application of natural and artificial hydrogenase enzymes present an optimistic, confident future for the production of fuel and energy.
BIBLIOGRAPHY
Ihara, Masaki, et. Al. “Light-driven Production by a Hybrid Complex of a [Ni-Fe]-Hydrogenase and the Cyanobacterial Photosystem I.” Photochemistry and Photobiology. 2006, 82: pgs. 676-682. March 16, 2006
Jaffe, Sam. “Mutant Algae Is Hydrogen Factory.” Wired Science.com.February 23, 2006. http://www.wired.com/science/discoveries/news/2006/02/70273
Lachance, Molly. “Biofuel research could result in alternative energy source.” AFOSR Public Affairs. March 11, 2008. www.afmc.af.mil/news
Melis, Anastasios.
Navarro, Xavier. “Glamor post of the week: BMW Hydrogen 7 is official limo for Rome Film Festival.” AutoblogGreen. September 27, 2008. http://www.autobloggreen.com/2007/09/27/glamor-post-of-the-week-bmw-hydrogen-7-is-official-limo-for-rom/
“New Euro Research Program for Bio, Solar H2.” Green Car Congress. March 1, 2005 www.greencarcongress.com
“Virgin
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