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'''Oxygen''' '''evolution''' is the process of generating molecular [[oxygen]] through [[chemical reaction]]. Mechanisms of oxygen evolution include the [[oxidation]] of [[water]] during oxygenic [[photosynthesis]], [[electrolysis]] of water into oxygen and [[hydrogen]], and electrocatalytic oxygen evolution from [[oxide]]s and [[oxoacid]]s. | |||
==Oxygen evolution in nature== | |||
Photosynthetic oxygen evolution is the fundamental process by which breathable oxygen is generated in earth's [[biosphere]]. The reaction is part of the [[light-dependent reaction]]s of photosynthesis in [[cyanobacteria]] and the [[chloroplast]]s of [[green algae]] and [[plant]]s. It utilizes the energy of [[light]] to split a water molecule into its [[proton]]s and [[electron]]s for photosynthesis. Free oxygen is generated as a by-product of this reaction, and is released into the [[Earth's atmosphere|atmosphere]]. | |||
===Biochemical reaction=== | |||
Photosynthetic oxygen evolution occurs via the light-dependent oxidation of water to molecular oxygen and can be written as the following simplified chemical reaction: | |||
2H<sub>2</sub>O <math>\longrightarrow</math> 4e<sup>-</sup> + 4H<sup>+</sup> + O<sub>2</sub> | |||
The reaction requires the energy of four [[photon]]s. The electrons from the oxidized water molecules replace electrons in the P<sub>680</sub> component of [[photosystem|photosystem II]] that have been removed into an [[electron transport chain]] via light-dependent [[excited state|excitation]] and [[resonance energy transfer]] onto [[plastoquinone]].<ref name="Raven">{{cite book | last = Raven | first = Peter H. | coauthors = Ray F. Evert, Susan E. Eichhorn | title = Biology of Plants, 7th Edition | publisher = W.H. Freeman and Company Publishers | date = 2005 | location = New York | pages = 115–127 | isbn = 0-7167-1007-2}}</ref> Photosytem II, therefore, has also been referred to as water-plastoquinone oxido-reductase.<ref name="Raval">{{cite journal |author=Raval M, Biswal B, Biswal U |title=The mystery of oxygen evolution: analysis of structure and function of photosystem II, the water-plastoquinone oxido-reductase |journal=Photosynthesis Research |volume=85 |issue=3 |pages=267–93 |year=2005 |pmid=16170631| doi=10.1007/s11120-005-8163-4}}</ref> The protons are released into the [[thylakoid lumen]], thus contributing to the generation of a proton gradient across the thylakoid membrane. This proton gradient is the driving force for [[Adenosine triphosphate|ATP]] synthesis via [[photophosphorylation]] and coupling the absorption of light energy and oxidation of water to the creation of chemical energy during photosynthesis.<ref name="Raven"/> | |||
===Oxygen-evolving complex=== | |||
Water oxidation is catalyzed by a [[manganese]]-containing [[Cofactor (biochemistry)|cofactor]] contained in [[photosystem II]] known as the [[oxygen-evolving complex]] (OEC) or water-splitting complex. Manganese is an important [[Cofactor (biochemistry)|cofactor]], and [[calcium]] and [[chloride]] are also required for the reaction to occur.<ref name="Raven"/> | |||
[[X-ray crystallography|X-ray crystallogra]] is structure of the oxygen-evolving complex and its manganese cluster.<ref name="Ferreira">{{cite journal |author=Ferreira K, Iverson T, Maghlaoui K, Barber J, Iwata S |title=Architecture of the photosynthetic oxygen-evolving center |journal=Science |volume=303 |issue=5665 |pages=1831–8 |year=2004 |pmid=14764885| doi=10.1126/science.1093087}}</ref> Based on structural and [[spectroscopy|spectroscopic]] experiments, oxygen evolution involves a core three-plus-one cluster of three manganese [[ion]]s and one calcium ion, with one additional manganese, which are oxidized via intermediate states called ''S-states''. The O-O bond of molecular oxygen is formed between manganese-ligated oxygen atoms at the most oxidized, or S4, state.<ref name="Robblee">{{cite journal |author=Robblee J, Cinco R, Yachandra V |title=X-ray spectroscopy-based structure of the Mn cluster and mechanism of photosynthetic oxygen evolution |journal=Biochimica et Biophysica Acta |volume=1503 |issue=1-2 |pages=7–23 |year=2001 |pmid=11115621 |doi=10.1016/S0005-2728(00)00217-6 }}</ref> | |||
===History of discovery=== | |||
It was not until the end of the 18th century that [[Joseph Priestley]] discovered by accident the ability of plants to "restore" air that had been "injured" by the burning of a candle. He followed up on the experiment by showing that air "restored" by [[vegetation]] was ''"not at all inconvenient to a [[mouse]]."'' He was later awarded a medal for his discoveries that: ''"...no vegetable grows in vain... but cleanses and purifies our atmosphere."'' Priestley's experiments were followed up by [[Jan Ingenhousz]], a Dutch physician, who showed that "restoration" of air only worked in the presence of light and green plant parts.<ref name="Raven"/> | |||
Ingenhousz suggested in 1796 that CO<sub>2</sub> ([[carbon dioxide]]) is split during photosynthesis to release oxygen, while the [[carbon]] combined with water to form [[carbohydrate]]s. While this hypothesis was attractive and reasonable and thus widely accepted for a long time, it was later proven incorrect. Graduate student [[C.B. Van Niel]] at [[Stanford University]] found that [[purple sulfur bacteria]] reduce carbon to carbohydrates, but accumulate [[sulfur]] instead of releasing oxygen. He boldly proposed that, in analogy to the sulfur bacteria's forming elemental sulfur from H<sub>2</sub>S ([[hydrogen sulfide]]), plants would form oxygen from H<sub>2</sub>O (water). In 1937, this hypothesis was corroborated by the discovery that plants are capable of producing oxygen in the absence of CO<sub>2</sub>. This discovery was made by [[Robin Hill (biochemist)|Robin Hill]], and subsequently the light-driven release of oxygen in the absence of CO<sub>2</sub> was called the ''Hill reaction''. Our current knowledge of the mechanism of oxygen evolution during photosynthesis was further established in experiments tracing [[isotopes of oxygen]] from water to oxygen gas.<ref name="Raven"/> | |||
==Technological oxygen evolution== | |||
<!-- Deleted image removed: [[Image:Hoffman voltameter.jpg|thumb|300px|Hoffman electrolysis apparatus used in electrolysis of water{{puic|Image:Hoffman voltameter.jpg|log=2008 April 26}}]] --> | |||
Oxygen evolution occurs as a byproduct of [[hydrogen production]] via [[electrolysis of water]]. While oxygen production is not the main focus of industrial applications of water electrolysis, it becomes essential for [[life support system]]s in situations that require the generation of oxygen for air revitalization. Human exploration of regions that lack breathable oxygen, such as the deep sea or outer space, requires means of reliably generating oxygen apart from earth's atmosphere. [[Submarine]]s and [[spacecraft]] utilize either an [[electrolysis|electrolytic]] mechanism (water or solid oxide electrolysis) or [[chemical oxygen generator]]s as part of their life support equipment. | |||
==References== | |||
{{reflist}} | |||
==External links== | |||
*Plant Physiology Online, 4th edition: [http://4e.plantphys.net/article.php?ch=7&id=72 Topic 7.7 - Oxygen Evolution] | |||
*[http://www.life.uiuc.edu/crofts/bioph354/lect25.html Oxygen evolution] - Lecture notes by Antony Crofts, UIUC | |||
*[http://www.globalchange.umich.edu/globalchange1/current/lectures/samson/evolution_atm/ Evolution of the atmosphere] – Lecture notes, Regents of the University of Michigan | |||
*[http://www.wikihow.com/Make-Oxygen-and-Hydrogen-from-Water-Using-Electrolysis How to make oxygen and hydrogen from water using electrolysis] | |||
[[Category:Photosynthesis]] | |||
[[Category:Breathing gases]] | |||
[[Category:Oxygen]] | |||
[[Category:Evolution]] | |||
[[Category:Geological history of Earth]] | |||
[[Category:Biological evolution]] | |||
Revision as of 15:27, 8 August 2013
Oxygen evolution is the process of generating molecular oxygen through chemical reaction. Mechanisms of oxygen evolution include the oxidation of water during oxygenic photosynthesis, electrolysis of water into oxygen and hydrogen, and electrocatalytic oxygen evolution from oxides and oxoacids.
Oxygen evolution in nature
Photosynthetic oxygen evolution is the fundamental process by which breathable oxygen is generated in earth's biosphere. The reaction is part of the light-dependent reactions of photosynthesis in cyanobacteria and the chloroplasts of green algae and plants. It utilizes the energy of light to split a water molecule into its protons and electrons for photosynthesis. Free oxygen is generated as a by-product of this reaction, and is released into the atmosphere.
Biochemical reaction
Photosynthetic oxygen evolution occurs via the light-dependent oxidation of water to molecular oxygen and can be written as the following simplified chemical reaction:
The reaction requires the energy of four photons. The electrons from the oxidized water molecules replace electrons in the P680 component of photosystem II that have been removed into an electron transport chain via light-dependent excitation and resonance energy transfer onto plastoquinone.[1] Photosytem II, therefore, has also been referred to as water-plastoquinone oxido-reductase.[2] The protons are released into the thylakoid lumen, thus contributing to the generation of a proton gradient across the thylakoid membrane. This proton gradient is the driving force for ATP synthesis via photophosphorylation and coupling the absorption of light energy and oxidation of water to the creation of chemical energy during photosynthesis.[1]
Oxygen-evolving complex
Water oxidation is catalyzed by a manganese-containing cofactor contained in photosystem II known as the oxygen-evolving complex (OEC) or water-splitting complex. Manganese is an important cofactor, and calcium and chloride are also required for the reaction to occur.[1]
X-ray crystallogra is structure of the oxygen-evolving complex and its manganese cluster.[3] Based on structural and spectroscopic experiments, oxygen evolution involves a core three-plus-one cluster of three manganese ions and one calcium ion, with one additional manganese, which are oxidized via intermediate states called S-states. The O-O bond of molecular oxygen is formed between manganese-ligated oxygen atoms at the most oxidized, or S4, state.[4]
History of discovery
It was not until the end of the 18th century that Joseph Priestley discovered by accident the ability of plants to "restore" air that had been "injured" by the burning of a candle. He followed up on the experiment by showing that air "restored" by vegetation was "not at all inconvenient to a mouse." He was later awarded a medal for his discoveries that: "...no vegetable grows in vain... but cleanses and purifies our atmosphere." Priestley's experiments were followed up by Jan Ingenhousz, a Dutch physician, who showed that "restoration" of air only worked in the presence of light and green plant parts.[1]
Ingenhousz suggested in 1796 that CO2 (carbon dioxide) is split during photosynthesis to release oxygen, while the carbon combined with water to form carbohydrates. While this hypothesis was attractive and reasonable and thus widely accepted for a long time, it was later proven incorrect. Graduate student C.B. Van Niel at Stanford University found that purple sulfur bacteria reduce carbon to carbohydrates, but accumulate sulfur instead of releasing oxygen. He boldly proposed that, in analogy to the sulfur bacteria's forming elemental sulfur from H2S (hydrogen sulfide), plants would form oxygen from H2O (water). In 1937, this hypothesis was corroborated by the discovery that plants are capable of producing oxygen in the absence of CO2. This discovery was made by Robin Hill, and subsequently the light-driven release of oxygen in the absence of CO2 was called the Hill reaction. Our current knowledge of the mechanism of oxygen evolution during photosynthesis was further established in experiments tracing isotopes of oxygen from water to oxygen gas.[1]
Technological oxygen evolution
Oxygen evolution occurs as a byproduct of hydrogen production via electrolysis of water. While oxygen production is not the main focus of industrial applications of water electrolysis, it becomes essential for life support systems in situations that require the generation of oxygen for air revitalization. Human exploration of regions that lack breathable oxygen, such as the deep sea or outer space, requires means of reliably generating oxygen apart from earth's atmosphere. Submarines and spacecraft utilize either an electrolytic mechanism (water or solid oxide electrolysis) or chemical oxygen generators as part of their life support equipment.
References
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External links
- Plant Physiology Online, 4th edition: Topic 7.7 - Oxygen Evolution
- Oxygen evolution - Lecture notes by Antony Crofts, UIUC
- Evolution of the atmosphere – Lecture notes, Regents of the University of Michigan
- How to make oxygen and hydrogen from water using electrolysis
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A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running
The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more
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In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang
Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules
Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.
A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running
The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more
There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang - ↑ One of the biggest reasons investing in a Singapore new launch is an effective things is as a result of it is doable to be lent massive quantities of money at very low interest rates that you should utilize to purchase it. Then, if property values continue to go up, then you'll get a really high return on funding (ROI). Simply make sure you purchase one of the higher properties, reminiscent of the ones at Fernvale the Riverbank or any Singapore landed property Get Earnings by means of Renting
In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang
Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules
Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.
A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running
The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more
There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang