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Photosystem II: The Water-Splitting Enzyme of Photosynthesis J
Some bacteria use Photosystem I and some use Photosystem II. More than two bya, and maybe more than three bya, cyanobacteria used both, and a miraculous instance of innovation tied them together. were then used to strip electrons from water. Although the issue is still controversial regarding when it happened and how, that instance of cyanobacteria's using manganese to strip electrons from water is responsible for oxygenic photosynthesis. It seems that some enzymes that use manganese may have been "drafted" into forming the manganese cluster responsible for splitting water in oxygenic photosynthesis. Water is not an easy molecule to strip an electron from, a single cyanobacterium seems to have “stumbled” into it, and it probably happened only . Once an electron was stripped away from water in Photosystem I, then stripping away a proton (a hydrogen nucleus) essentially removed one hydrogen atom from the water molecule. That proton was then used to drive a “turbine” that manufactures ATP, and wonderful show how those protons drive that enzyme turbine (). Oxygen is a waste product of that innovative ATP factory.
This innovative works that mimic the process of plants by splitting the water molecules and produce products of Hydrogen and oxygen only by using the energy from the sunlight.
Artificial photosynthesis for solar water-splitting
Thermochemical water splitting uses high temperatures—from concentrated solar power or from the waste heat of nuclear power reactions—and chemical reactions to produce hydrogen and oxygen from water. This is a long-term technology pathway, with potentially low or no greenhouse gas emissions.
The extra electron passed onto the second molecule will eventually be passedon to NADP+ to produce NADPH. The light reaction of photosynthesis in green plants is shown below. In this process, in a scheme that is reminiscent of electron transport in mitochondria, water is oxidized by photosystem II.
Catalytic solar water splitting inspired by …
All higher life on Earth depends on this process for its energy needs and PSII produces the oxygen we breathe, which ultimately keeps us alive.
The revealing of the mechanism of this water splitting process is essential for the development of artificial systems that mimic and surpass the efficiency of natural systems.
Thermochemical water splitting processes use high-temperature heat (500°–2,000°C) to drive a series of chemical reactions that produce hydrogen. The chemicals used in the process are reused within each cycle, creating a closed loop that consumes only water and produces hydrogen and oxygen. The necessary high temperatures can be generated in the following ways:
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Catalytic solar water splitting inspired by photosynthesis
Photosynthetic water splitting is the breakdown of two water molecules into two H2 molecules plus an O2. The reaction takes place in two steps: 1) water oxidation and 2) proton reduction. Chemically speaking, both steps are difficult, but for this study, the researchers focused only on speeding up the second step. The tough part of proton reduction involves forming a bond between two hydrogens to form H2, a process called hydrogen evolution, so that’s where a catalyst can help. There are many hydrogen-evolving catalysts, but none rival biological enzymes, and most have additional drawbacks as well. Most existing catalysts aren’t soluble in water, which is a problem since the end goal is to use the catalyst to turn water into fuel. Another factor is cost; many catalysts rely on the electron-moving properties of expensive metals, such as platinum or rhodium. In this study, the researchers examined the reaction pathways of a water-soluble hydrogen-evolving catalyst with a lower-cost cobalt center.
Photosynthetic water splitting is the breakdown of ..
Humans can learn a lot from plants. With energy from the sun, protein catalysts in plants efficiently split water to generate oxygen, storing the energy as carbohydrates. Scientists would like to perform a similar trick, using solar energy to split water and produce hydrogen fuel. Hydrogen fuel burns clean, producing only water as a byproduct, but splitting water is not an efficient task for humans. Researchers have taken baby steps toward artificial photosynthesis, building solar-powered water-splitting catalysts in the laboratory, but so far these catalysts remain far less efficient than their vegetal counterparts. One reason it's difficult to improve catalytic efficiency is that scientists don't fully understand the catalysts’ water-splitting mechanism. To examine the reaction pathway of a cobalt-based catalyst in unprecedented detail, researchers collected x-ray absorption spectra at the U.S. Department of Energy’s Advanced Photon Source (APS), an Office of Science user facility at Argonne National Laboratory. The data revealed electronic and structural features of the catalyst, offering clues for how the researchers can tweak the catalyst to run the reaction more efficiently. Such advances could bring down the cost of producing hydrogen fuel, making a hydrogen economy—a world run on water—a possibility for the future.
Splitting of water during photosynthesis | scholarly search
In addition to producing NADPH, the light dependent reactions also produce oxygen as a waste product. When the special chlorophyll molecule at the reaction centre passes on the electrons to the chain of electron carriers, it becomes positively charged. With the aid of an enzyme at the reaction centre, water molecules within the thylakoid space are split. Oxygen and H+ ions are formed as a result and the electrons from the splitting of these water molecules are given to chlorophyll. The oxygen is then excreted as a waste product. This splitting of water molecules is called photolysis as it only occurs in the presence of light.
Splitting of water during photosynthesis ..
Numerous solar thermochemical water-splitting cycles have been investigated for hydrogen production, each with different sets of operating conditions, engineering challenges, and hydrogen production opportunities. In fact, more than 300 water-splitting cycles are described in the literature. For more information, see .
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