Genetically Engineered Protein Can Split Water into Hydrogen and Oxygen
01 December 2006
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Scientists have combined two molecules that occur naturally in blood to engineer a molecular complex that uses solar energy to split water into hydrogen and oxygen. The research is published today in the Journal of the American Chemical Society.
Professors Tsuchida and Komatsu from Waseda University, Japan, in collaboration with Imperial College London, synthesized a large molecular complex from albumin (a protein molecule that is found at high levels in blood serum) and porphyrin (a molecule which is used to carry oxygen around the body and gives blood its deep red color).
Porphyrin molecules are normally found combined with metals, and in their natural state in the blood they have an iron atom at their center. The scientists modified the porphyrin molecule to swap the iron for a zinc atom in the middle, which completely changed the chemistry and characteristics of the molecule.
This modified porphyrin molecule was then combined with albumin; with the albumin molecule itself being modified by genetic engineering to enhance the efficiency of the process. The resulting molecular complex was proven to be sensitive to light, and can capture light energy in a way that allows water molecules to be split into molecules of hydrogen and oxygen.
The efficiency of the photoproduction of H2 was greater than that of the system using the well-known organic chromophore, tetrakis(1-methylpyridinium-4-yl)porphinatozinc(II) (ZnTMPyP4+), under the same conditions.
This work has shown that it is possible to manipulate molecules and proteins that occur naturally in the human body by changing one small detail of their make-up, such as the type of metal at the heart of a porphyrin molecule, as we did in this study.
It’s very exciting to prove that we can use these biological structures as a conduit to harness solar energy to separate water out into hydrogen and oxygen. In the long term, these synthetic molecules may provide a more environmentally friendly way of producing hydrogen, which can be used as a “green” fuel.
—Dr Stephen Curry, Imperial College London
Resources:
“Photosensitized reduction of water to hydrogen using human serum albumin complexed with zinc protoporphyrin IX”; Teruyuki Komatsu, Rong-Min Wang, Patricia A Zunszain, Stephen Curry, Eishun Tsuchida; Journal of the American Chemical Society ASAP Article 10.1021/ja0656806 S0002-7863(06)05680-0
Any word on the efficiency of this process?
Posted by: Neil | 01 December 2006 at 08:49 AM
How do you separate the Hydrogen and Oxygen gasses after they have come out of solution? Do you just kind of let them settle, and take the H2 off the top?
Posted by: Hal | 01 December 2006 at 11:18 AM
and what is the efficentie
this very interesting.
Posted by: tibi | 01 December 2006 at 02:05 PM
The relevant efficiency measure in this context is the number of quantum yield of hydrogen, relative to solar irradiation spectrum at the earth's surface.
The key element of any chemical photosystem is an organic dye molecule that holds one metal ion inside a ring-shaped cage. Porphyrins are actually a whole class of molecules: the one in blood cells is called haeme, based on iron and stabilized by the protein globin. Other natural porphyrins include rhodopsin (in retinal cells) and xantophylls (visible in fall foliage as the dominant chlorophyll is broken down first). Chlorophyll is based on magnesium.
For reference, chlorophyll-based photosynthesis will yield one O2 molecule for every ~10 solar quanta.
ZnTMPyP4+ is an artificial molecule used in artificial photosystems. These are much simpler, because the target result is hydrogen rather than glucose. The oxygen is just a by-product in both cases. Using a combination of ZnTMPyP4+, EDTA and a catalyst (platinum particles) kept finely dispersed with Carbowax 20M, an optimum quantum yield of 0.07 has been reported for 1/2H2, i.e. ~14.3 photons per hydrogen atom. Relative to one unit of 2H2+O2, I'm guessing that translates to ~57 photons, about 6 times as many as photosynthesis needs. Evolution evidently works very well!
Of course, a plant can only use a fraction of the surface area of each leaf for chlorophyll, so relative to total incident sunlight at temperate latitudes, efficiency is only about 2%.
Artificial photosystems do not suffer from this drawback, allowing them to overcompensate for the poor efficiency through higher porphyrin density per unit area. Since both hydrogen and oxygen are produced, you end up with detonating gas (2H2 + O2). This cannot be transported safely: either it has to be combusted on site (usually not useful) or, the hydrogen has to be separated, e.g. via adsorption in a matrix. Once the hydrogen fraction is low enough, the residual gas can be ignited and then chilled to condense out the water, yielding pure oxygen that can be bottled and put to industrial uses. Desorption of the hydrogen obviously has to occur in a separate location in the absence of oxygen.
So far, though, industrial-scale applications of artificial photosystems are still a distant prospect.
http://www.rsc.org/publishing/journals/article.asp?doi=f29817701939
Posted by: Rafael Seidl | 01 December 2006 at 07:53 PM
Rafael:
Reported technology is part of long-term investment of DOE into so-called advanced photovoltaics. Considering recent advances in genetic engineering and molecular biotechnology, it offers mind-bogging possibilities.
Produced hydrogen molecules were never supposed to leave advanced solar panel. The main idea is to combine functions of photovoltaic electricity generation, hydrogen production for energy storage (producing electricity at night and at low-sunlight days), and in most advanced application to produce liquid hydrocarbon fuel from surplus of energy. All in one panel at same time. In the wildest dreams, such combination of technologies into one roof-mounted panel could provide electricity, serve as energy storage, and produce liquid transportation fuel – all in flexible combination. However fictional it sounds, it is actually emerging.
Posted by: Andrey | 02 December 2006 at 02:41 AM
Synthetic/artificial leaf/eye. Both the leaf (chloroplast) and the eye (rods and cones) take light and convert it for use. One makes chemical energy for food/building blocks, the other makes chemicals for neuro ionic signals-sort of electrical. Cyanobacteria/blue green algae have a system w/no chloroplasts, but do have similar/same chemicals and systems for photosynthesis as plants/true algaes.
_Matching the sun's spectrum output would be another step. Currently, photosynthesis is most efficient at red and blue, not yellow and green. There are some pigments that absorb/transfer wavelengths, but they do not work efficienctly and leave large frequency gaps.
http://en.wikipedia.org/wiki/Chlorophyll
http://en.wikipedia.org/wiki/Image:MODIS_ATM_solar_irradiance.jpg
Posted by: allen_Z | 02 December 2006 at 07:44 AM
Does anyone know if this protein spends out or degrades over time? It seems the zinc would degrade to zinc oxide.
Posted by: Bob.B | 04 December 2006 at 08:46 PM