In pursuit of plant power
Published: 25 September 2012 (GMT+10)
Long before the current emphasis on ‘green energy’, scientists have been on a quest to mimic the way that plants convert sunlight into fuel. In leaves, photosynthesis converts carbon dioxide (CO2) and water (H2O) into oxygen and carbohydrates such as glucose. The energy transfer efficiency rate of approximately 97% is the envy of engineers striving to produce ‘artificial photosynthesis’ solar energy harvesters.
(Note that artificial photosynthesis differs from photovoltaics, the method used in conventional solar panels, which generates an electrical current that can’t be easily stored but must be loaded onto the electrical grid.)
The benefits of such plant-mimicking energy harvesters are very clear to researchers: “The production of hydrogen using nothing but water and sunlight offers the possibility of an abundant, renewable, green source of energy for the future,” enthused Tom Mallouk, a Pennsylvania State University professor of chemistry and physics.1
However, there’s a long way to go yet. In fact, the chemistry of nature’s highly complex and efficient photosynthetic apparatus has not even been fully worked out yet, let alone copied! We have periodically reported on the new discoveries in recent years of the brilliant design of the plant photosynthetic apparatus and associated structures. For example, plants have a ‘dimmer switch’, super-sensitive to changes in light conditions, and plants also ‘know’ when to make ‘sunscreen’ when conditions warrant.2
One of the major hurdles to solve is the mystery of how plants manage to break apart the water molecule into hydrogen and oxygen without destroying themselves in the process. (Just think of the 1937 Hindenburg disaster where a Zeppelin caught fire, and burned the hydrogen gas into water. To break up water, this amount of energy has to be ‘put back’.) As a 1999 article in New Scientist, highlighting a limited breakthrough made by Yale University chemists Gary Brudvig and Robert Crabtree, explained:
“The oxygen is released by splitting water molecules, a reaction that in the lab requires such violence that it would tear any living system apart. So how can plants do it, using only energy from the sun?
“Try breaking water apart in one go and you’d need a huge blast of energy. To do the job with heat alone, for example, you’d need to raise the temperature of water by thousands of degrees—more than enough to vapourise a geranium.”3
But of course we don’t see geraniums or other greenery exploding, so obviously plants have a mechanism that can split water into hydrogen and oxygen at normal temperatures. To Brudvig and Crabtree’s credit though, they actually succeeded in making an artificial system that managed to produce oxygen. However, as they had not worked out how to use light energy, Brudvig and Crabtree instead used the chemical energy of powerful bleaches. But even then, their system could produce only 100 O2 molecules before being destroyed. As Gary Brudvig conceded:
“This is one of the drawbacks of the artificial system. It can’t constantly regenerate itself.”2
So how much do we know about how plants do it? Here’s a short extract from an earlier article4 by our resident PhD physical chemist, Jonathan Sarfati:
It turns out that in leaves there is a special assembly called Photosystem II (named because it was discovered second). A photon strikes this, and it is channeled into a type of chlorophyll called P680. There it knocks out an electron from an atom, and this energetic electron eventually helps make sugars from CO2. But then, the P680 must replenish the lost electron. This is a big problem for artificial photosynthesis— human chemists have also so far been unable to produce a system that replenishes the electrons knocked out by the photons. Photosynthesis would have quickly ground to a halt without this, so how are the electrons replaced?
For readers with the chemistry interest to continue perusing Dr Sarfati’s subsequent technical explanation, click on: Green power (photosynthesis). But having now given a background overview of some of the difficulties in pursuing the goal of artificial photosynthesis, it’s instructive to get an update on the current state of knowledge from one researcher in this field, Julian Eaton-Rye. Here’s how ABC science presenter Robyn Williams introduced him in an interview recently on The Science Show radio program:5
Robyn Williams: People all over the world are looking for alternative power sources. Professor Julian Eaton-Rye is a biochemist at the University of Otago in Dunedin in New Zealand and he’s interested in adapting photosynthesis to provide power, hydrogen power. He is working on Photosystem II.
Williams and Eaton-Rye then begin their discussion about how Photosystem II is used to break water molecules. Here’s some of the ensuing dialogue after Williams mentions that “it normally happens at normal temperatures.”
Julian Eaton-Rye: It does and I guess that’s the trick of Photosystem II, that it can break water molecules down at ambient temperatures, whereas if you wanted to break water you would have to heat it to about 2,000°C in order to break it down, so you’re not boiling the water, it’s not steam you want, you want to actually decompose the water.
Robyn Williams: So if you weren’t using an electric current, if you just wanted to break it down into hydrogen and oxygen, 2,000°C is a hell of a hot temperature, isn’t it.
Julian Eaton-Rye: Yes, it is. I guess perhaps that’s good for us because it means water is very stable and we need a lot of it and we’ve got a lot of it.
Robyn Williams: And we don’t blow up.
Julian Eaton-Rye: Right, exactly, yes.
Exactly right. Water is an amazing substance, just right for life. Because it is designed that way.6 However, neither Williams nor Eaton-Rye acknowledge such Designer-created design—instead they both pay homage to evolution. But as the following short dialogue shows, with references to ‘architecture’, ‘essential’, ‘repair’, ‘design’, ‘delicate’, ‘machinery’, ‘efficient’, and ‘work seamlessly’, it’s evident that Williams and Eaton-Rye sure have a lot of faith that ‘evolution did it’:
Robyn Williams: And so the secret is presumably an enzyme or more than one enzyme or what?
Julian Eaton-Rye: The secret is a metal centre composed of manganese and calcium, four manganese and one calcium, and they are put together in an architecture and a protein environment that holds them in a certain configuration, which simply allows that to act as the catalyst to drive this reaction. And one of the great challenges is to understand that architecture so that it can be mimicked so that we can make machines that will split water, because we talked about the electrons and the oxygen but of course you also have those protons, and those protons can become hydrogen, and hydrogen is a fuel.
Robyn Williams: And hydrogen would be great to have, but the great thing about enzymes is that when you’ve had the reaction, they are still there at the end, which is nice, isn’t it.
Julian Eaton-Rye: It is nice. In the case of Photosystem II, there’s a slight twist because this is a machine that works at the edge and there’s quite a bit of energy involved from the light that is absorbed, and while that’s splitting water it also causes damage to the actual protein architecture that is essential to hold everything in place to make it work. And what has happened in evolution is that the organisms that house the enzyme have developed a system to constantly repair the photosystem to sustain this reaction, and therefore Photosystem II offers an interesting model to look at how you might design a machine that repairs itself in a chemical way that would sustain this reaction in a synthetic operation.
Robyn Williams: So instead you’ve got a very delicate machine here which can easily break down. In other words, the enzyme can go bust, and you’re trying to see whether there is a way in which you can harness all this and maintain a vigour … the enzyme or something else, so that you don’t have the whole thing break down in about two seconds.
Julian Eaton-Rye: The enzyme doesn’t go bust, and I think that’s its success, is that this machinery that repairs itself is so efficient that the enzyme continues to work seamlessly, and therefore the mechanism involved is a very intriguing one, and if we were able to reproduce it in biomimetic systems then we would be able to have sustained water oxidation panels on our roof that light shines on that continue to make us hydrogen and electrons as a fuel source.
The notion that such a complex system as Photosystem II (not to mention the rest of the plant, complete with its capacity to reproduce itself many times over) could have arisen without intelligent design input is surely bizarre. No wonder that Romans 1:20 says that men are “without excuse” for saying “There is no God” (Psalm 14:1, 53:1).
Are Julian Eaton-Rye and other researchers around the world any closer to being able to copy photosynthesis than they were ten years ago?
Julian Eaton-Rye: That’s perhaps a little bit out there in the future, but the understanding of the chemistry to split water has received a big boost in just the last 12 months with an important X-ray crystal structure of the photosystem from a group in Japan, and there are many people around the world working on the manganese operation. Our own lab works on the protein environment that surrounds that manganese system, and the polypeptides that are necessary to continually turn over the photosystem. I think that the future is promising and the biochemistry is very interesting, and we hope that in the next five to ten years … perhaps just five actually, the real chemistry of the reaction will be understood, and to therefore reproduce it in a sustained way becomes a reasonable goal.
If man, one day, does succeed in copying (note: re-engineering) what plants can do, it won’t have been the result of time-and-chance processes, but intelligent design, and the researchers so credited will no doubt be worthy of the honour likely to be bestowed on them. So how much more honour is due to the supremely Intelligent Designer who designed the plants in the first place?!
When Robyn Williams asked Julian Eaton-Rye about the probable payoff if the research into the chemical workings of Photosystem II and other aspects of photosynthesis is successful, Eaton-Rye replied:
Julian Eaton-Rye: The payoff is clearly that if you can actually make hydrogen from water, you would have solved many, many issues surrounding pollution and sustained energy production. There is no pollution from using water as a source of fuel. So in that sense it’s a very wonderful opportunity that we might be able to pursue.
Man, in pursuit of ‘plant power’: sustained energy production from water and the sun with the added benefit of no pollution from using water as a fuel!
Sounds like a great idea. Wonder who thought of it first?
- Boyd, R., Scientists seek to make energy as plants do, www.physorg.com/news144307026.html, 27 October 2008. Return to text.
- How plants ‘know’ when to make sunscreen, Creation 34(1):9, 2012; reporting on: Experts reveal why plants don’t get sunburn, University of Glasgow news, www.gla.ac.uk, 30 March 2011. Return to text.
- Burke, M., Green miracle, New Scientist 163(2199):27–30, 14 August 1999. Return to text.
- Sarfati, J., Green power (photosynthesis): God’s solar power plants amaze chemists, Journal of Creation 19(1):14–15, 2005. Return to text.
- Copying plants’ ability to split water—Robyn Williams interviews Otago University Associate Professor Julian Eaton-Rye, ABC Radio National (Australian Broadcasting Corporation), The Science Show broadcast Saturday 19 May 2012; transcript at http://www.abc.net.au/radionational/programs/scienceshow/copying-plantse28099-ability-to-split-water/4019830. Return to text.
- See Sarfati, J., The wonders of water, Creation 20(1):44–47, 1997. Return to text.