تثبيت النيتروجين: الفرق بين النسختين
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[[ملف:عقد جذرية.JPG|تصغير|عقد مستجذرات جذرية على نباتات الفصة الحولية - لاحظ النبات على يسار الصورة لا يحتوي عقداً جذرية نظراً لعدم القيام بتلقيحه بالمستجذرة]]
'''تثبيت النيتروجين''' {{إنج|Nitrogen fixation}} هو العملية التي يتحول فيها النيتروجين (N<sub>2</sub>) الموجود في الجو إلى أمونيوم<ref name=postgate>{{cite book |author=Postgate, J. |year=1998 |title=Nitrogen Fixation, 3rd Edition |publisher=Cambridge University Press, Cambridge UK}}</ref> النيتروجين الجوي أو النيتروجين الجزيئي (N<sub>2</sub>) هو خامل نسبياً: فلا يتفاعل مع مواد كيميائية أخرى مولداً مركبات جديدة. تقوم عملية تثبيت النيتروجين على تحويله من الشكل الثنائي (N<sub>2</sub>) حتى يستخدم بطرق أخرى.
تثبيت النيتروجين الطبيعي والصناعي هو جوهري لجميع أشكال الحياة لأنه ضروري للتكوين البيولوجي لكتل البناء الأساسية في النباتات والحيوانات وغيرها من أشكال الحياة. مثلا: [[نوكليوتيد|النوكليوتيدات]] و[[حمض نووي|الحمض النووي]] و[[حمض أميني|الحموض الأمينية]] للبروتينات. لذا فإن تثبيت النيتروجين هام للزراعة وصناعة الأسمدة. كما أنه هام في صناعة المتفجرات (مثل [[بارود|البارود]] و[[ديناميت|الديناميت]] و[[تي إن تي (مادة كيميائية)|التي إن تي]]). يحدث تثبيت النيتروجين بشكل طبيعي عند حدوث البرق.<ref>{{cite book|last=Slosson|first=Edwin|title=Creative Chemistry|year=1919|publisher=The Century Co.|location=New York|pages=19–37}}</ref><ref>http://www.biology.ed.ac.uk/archive/jdeacon/microbes/nitrogen.htm</ref>
كما يشير تثبيت النيتروجين إلى تحويلات حيوية أخرى للنيتروجين، كتحويله إلى [[ثنائي أكسيد النيتروجين]]. الميكروبات التي بإمكانها تثبيت النيتروجين هي [[بدائيات النوى]] ([[بكتيريا]] و[[عتائق]] معاً موزعين في ممالكهم الخاصة) تدعى [[دايازتروف]]. طورت بعض النباتات والحيوانات (مثل [[أرضة]]) علاقة [[تعايش (أحياء)|تعايش]] مع الدايازتروف.
== التثبيت الحيوي للنيتروجين ==
[[File:Nitrogen Cycle.svg|thumb|320px|left|مخطط توضيحي [[دورة النيتروجين|لدورة النيتروجين]] تم إهمال تثبيت النيتروجين للاأحيائي.]]
اكتشف التثبيت الحيوي للنيتروجين كل من المهندس الزراعي الألماني [[هيرمان هيلريغل]] وعالم الميكروبات الهولندي [[مارتينوس بايرينك]]. يحدث التثبيت الحيوي للنيتروجين ('''BNF''') عندما يتحول النيتروجين الجوي إلى أمونيا عن طريق أنزيمات [[نيتروجيناز|النيتروجيناز]].<ref name=postgate/> وتفاعل التثبيت الحيوي للنيتروجين هو:
<div style="direction:ltr;">
: N<sub>2</sub> + 8 H<sup>+</sup> + 8 e<sup>−</sup> → 2 NH<sub>3</sub> + H<sub>2</sub>
</div>
العملية مقرونة [[حلمهة|بحلمهة]] 16 مكافئ من [[ثلاثي فوسفات الأدينوسين]] ويرافقها تشكل جزيئ H<sub>2</sub>. في الدايازتروف التي تعيش بشكل حر تهضم الأمونيا التي ولدها النيتروجيناز إلى غلوتامات عن طريق أنزيم [[غلوتامين سينثيتاز]].
الجينات الميكروبية المطلوبة لتثبيت النيتروجين موزعة على نطاق عريض في البيئات المتنوعة. <ref>{{cite journal|author=Gaby, J.C.; Buckley, D.H.|title=A global census of nitrogenase diversity.|journal=Environmental Microbiology |year=2011|pages=1790–1799|doi=10.1111/j.1462-2920.2011.02488.x|volume=13|issue=7}}</ref><ref>{{cite journal|author=Hoppe, B.; Kahl, T.; Karasch, P.; Wubet, T.; Bauhus, J.; Buscot, F.; Krüger, D.|title=Network analysis reveals ecological links between N-fixing bacteria and wood-decaying fungi.|journal=PLoS ONE|year=2014|pages=e88141|doi=10.1371/journal.pone.0088141|volume=9|issue=2}}</ref>
الأنزيمات المسئولة عن عمل النيتروجيناز حساسة جداً للتخريب بالأوكسيجين. كثير من البكتيريا تتوقف عن إنتاج الأنزيمات في وجود الأوكسيجين.<ref name=postgate/> توجد الكثير من أحياء تثبيت النيتروجين فقط في ظروف لا هوائية، وتتنفس لإنقاص معدلات الأوكسيجين، أو تربطة ببروتين مثل [[ليغيموغلوبين]].<ref name=postgate/>
=== الميكروبات التي تثبت النيتروجين ===
{{main|دايازتروف}}
ميكروبات الدايازتروف هي [[زراقم]] مثل [[trichodesmium]] و [[خضربيات|الخضربيات]] و [[azotobacteraceae]] و [[ريزوبيا|الريزوبيا]] و [[فرانكيا|الفرانكيا]].
[[Cyanobacteria]] inhabit nearly all illuminated environments on Earth and play key roles in the carbon and [[nitrogen cycle]] of the [[biosphere]]. In general, [[cyanobacteria]] are able to utilize a variety of inorganic and organic sources of combined nitrogen, like [[nitrate]], [[nitrite]], [[ammonium]], [[urea]], or some [[amino acid]]s. Several cyanobacterial strains are also capable of [[diazotroph]]ic growth, an ability that may have been present in their last common ancestor in the [[Archaea]]n.<ref>"The evolution of nitrogen fixation in cyanobacteria" N. Latysheva, V. L. Junker, W. J. Palmer, G. A. Codd and D. Barker; ''Bioinformatics''; '''2012''': 28(5) pp 603–606; (Article) {{DOI|10.1093/bioinformatics/bts008}}</ref>
Nitrogen fixation by cyanobacteria in [[coral reef]]s can fix twice the amount of nitrogen than on land—around 1.8 kg of nitrogen is fixed per hectare per day. The colonial marine cyanobacterium ''[[Trichodesmium]]'' is thought to fix nitrogen on such a scale that it accounts for almost half of the nitrogen-fixation in marine systems on a global scale.<ref>{{cite journal|author=Bergman, B.; Sandh, G.; Lin, S.; Larsson, H.; and Carpenter, E. J.|title=''Trichodesmium'' – a widespread marine cyanobacterium with unusual nitrogen fixation properties|journal=FEMS Microbiology Reviews |year=2012|pages=1–17|doi=10.1111/j.1574-6976.2012.00352.x|volume=37|issue=3}}</ref>
=== تعايش العقد الجذرية ===
====عائلة البقول ====
Plants that contribute to nitrogen fixation include the [[legume]] family – [[Fabaceae]] – with taxa
such as [[kudzu]], [[clover]]s, [[soybean]]s, [[alfalfa]], [[lupin]]es, [[peanut]]s, and [[rooibos]]. They contain [[symbiosis|symbiotic]] bacteria called ''[[Rhizobia]]'' within [[root nodule|nodules]] in their [[root|root systems]], producing nitrogen compounds that help the plant to grow and compete with other plants. When the plant dies, the fixed
nitrogen is released, making it available to other plants and this helps to fertilize the [[soil]].<ref name=postgate/><ref>{{Cite book |author=Smil, V |year=2000 |title=Cycles of Life |publisher=Scientific American Library}}</ref> The great majority of legumes have this association, but a few genera (e.g., ''[[Styphnolobium]]'') do not. In many traditional and organic farming practices, fields are rotated through various types of crops, which usually includes one consisting mainly or entirely of clover or buckwheat (non-legume family ''[[Polygonaceae]]''), which are often referred to as "[[green manure]]".
[[Inga alley farming]] relies on the leguminous [[genus]] ''[[Inga]]'', a small tropical, tough-leaved, [[nitrogen-fixing]] tree.<ref name=Elkan>Elkan, Daniel. "Slash-and-burn farming has become a major threat to the world's rainforest". ''[[The Guardian]]'', 21 April 2004.</ref>
==== غير بقولي ====
[[Image:A sectioned alder root nodule gall.JPG|right|thumb|<Center>A sectioned alder tree root nodule.]]
Although by far the majority of plants able to form nitrogen-fixing root nodules are in the legume family [[Fabaceae]], there are a few exceptions:
* ''Parasponia'', a tropical genus in the [[Cannabaceae]] also able to interact with rhizobia and form nitrogen-fixing nodules<ref>{{cite journal |first=Rik |last=Op den Camp |title=LysM-Type Mycorrhizal Receptor Recruited for Rhizobium Symbiosis in Nonlegume ''Parasponia'' |journal=[[Science (journal)|Science]] |volume=331 |issue=6019 |pages=909–912 |doi=10.1126/science.1198181 |year=2010 |first2=A. |last3=De Mita |first3=S. |last4=Cao |first4=Q. |last5=Polone |first5=E. |last6=Liu |first6=W. |last7=Ammiraju |first7=J. S. S. |last8=Kudrna |first8=D. |last9=Wing |first9=R. |displayauthors=2 |last2=Streng |last10=Untergasser |first10=A. |last11=Bisseling |first11=T. |last12=Geurts |first12=R. }}</ref>
* [[Actinorhizal plant]]s such as [[alder]] and [[bayberry]] can also form nitrogen-fixing nodules, thanks to a symbiotic association with ''[[Frankia]]'' bacteria. These plants belong to 25 genera<ref>{{cite book |chapter=Ecology of actinorhizal plants |first=J. O. |last=Dawson |title=Nitrogen-fixing Actinorhizal Symbioses |volume=6 |pages=199–234 |doi=10.1007/978-1-4020-3547-0_8 |year=2008 |publisher=Springer }}</ref> distributed among 8 plant families.
The ability to fix nitrogen is far from universally present in these families. For instance, of 122 genera in the [[Rosaceae]], only 4 [[genera]] are capable of fixing nitrogen. All these families belong to the [[order (biology)|order]]s [[Cucurbitales]], [[Fagales]], and [[Rosales]], which together with the [[Fabales]] form a clade of [[eurosid]]s. In this clade, Fabales were the first lineage to branch off; thus, the ability to fix nitrogen may be [[plesiomorphic]] and subsequently lost in most descendants of the original nitrogen-fixing plant; however, it may be that the basic [[genetics|genetic]] and [[physiological]] requirements were present in an incipient state in the [[last common ancestor]]s of all these plants, but only evolved to full function in some of them:
{{Clear}}
{|
|- valign=top
|'''Family: Genera'''
[[Betulaceae]]: ''[[Alnus]]'' (alders)
[[Cannabaceae]]: ''[[Trema (genus)|Trema]]''
[[Casuarinaceae]]:
:''[[Allocasuarina]]''
:''[[Casuarina]]''
:''[[Ceuthostoma]]''
:''[[Gymnostoma]]''
|
<span style="color:white;">......</span>
|
<br>
[[Coriariaceae]]: ''[[Coriaria]]''
[[Datiscaceae]]: ''[[Datisca]]''
[[Elaeagnaceae]]:
:''[[Elaeagnus]]'' (silverberries)
:''[[Hippophae]]'' (sea-buckthorns)
:''[[Shepherdia]]'' (buffaloberries)
|
<span style="color:white;">......</span>
|
<br>
[[Myricaceae]]:
:''[[Comptonia]]'' (sweetfern)
:''[[Morella (plant)|Morella]]''
:''[[Myrica]]'' (bayberries)
|
<span style="color:white;">......</span>
|
<br>
[[Rhamnaceae]]:
:''[[Ceanothus]]''
:''[[Colletia]]''
:''[[Discaria]]''
:''[[Kentrothamnus]]''
:''[[Retanilla]]''
:''[[Talguenea]]''
:''[[Trevoa]]''
|
<span style="color:white;">......</span>
|
<br>
[[Rosaceae]]:
:''[[Cercocarpus]]'' (mountain mahoganies)
:''[[Chamaebatia]]'' (mountain miseries)
:''[[Dryas (plant)|Dryas]]''
:''[[Purshia]]/Cowania'' (bitterbrushes/cliffroses)
|}
There are also several nitrogen-fixing symbiotic associations that involve [[cyanobacteria]] (such as ''[[Nostoc]]''):
* Some lichens such as ''[[Lobaria]]'' and ''[[Peltigera]]''
* [[Mosquito fern]] (''[[Azolla]]'' species)
* [[Cycad]]s
* ''[[Gunnera]]''
== التثبيت الصناعي للنيتروجين ==
The possibility that atmospheric nitrogen reacts with certain chemicals was first observed by Desfosses in 1828. He observed that mixtures of [[alkali metal]] oxides and carbon react at high temperatures with nitrogen. With the use of [[barium carbonate]] as starting material the first commercially used process became available in the 1860s developed by Margueritte and Sourdeval. The resulting [[barium cyanide]] could be reacted with steam yielding [[ammonia]]. In 1898 [[Adolph Frank]] and [[Nikodem Caro]] decoupled the process and first produced [[calcium carbide]] and in a subsequent step reacted it with nitrogen to [[calcium cyanamide]]. The [[Ostwald process]] for the production of [[nitric acid]] was discovered in 1902. [[Frank-Caro process]] and Ostwald process dominated the industrial fixation of nitrogen until the discovery of the Haber process in 1909.<ref>{{cite journal | title = Die Umwandlungsgleichung Ba(Cn)<sub>2</sub> → BaCN<sub>2</sub> + C Im Temperaturgebiet von 500 Bis 1000 °C | first1 = H. last1 = Heinrich | first2 = Rolf | last2= Nevbner | journal =Zeitschrift für Elektrochemie und angewandte physikalische Chemie | volume = 40 | issue = 10 | pages = 693–698 | year = 1934 | url = | doi = 10.1002/bbpc.19340401005| doi_inactivedate = 2014-01-29 }}</ref><ref>{{cite book | url = http://books.google.de/books?id=87XQAAAAMAAJ | title = Fixed nitrogen | author1 = Curtis | first1 = Harry Alfred | year = 1932}}</ref>
Prior to 1900, [[Nikola Tesla]] also experimented with the industrial fixation of nitrogen "by using currents of extremely high frequency or rate of vibration".<ref>http://www.tfcbooks.com/tesla/1900-06-00.htm</ref> <ref>THE PROBLEM OF INCREASING HUMAN ENERGY</ref>
=== عملية هابر ===
{{main|عملية هابر-بوش}}
Artificial fertilizer production is now the largest source of human-produced fixed nitrogen in the [[Earth]]'s [[ecosystem]]. Ammonia is a required precursor to [[fertilizer]]s, [[explosive]]s, and other products. The most common method is the [[Haber process]]. The Haber process requires high pressures (around 200 atm) and high temperatures (at least 400 °C), routine conditions for industrial catalysis. This highly efficient process uses natural gas as a hydrogen source and air as a nitrogen source.<ref>http://www.epa.gov/watertrain/nitroabstr.html US Enivronmental Protection Agency: Human Alteration of the Global Nitrogen Cycle: Causes and Consequences by Peter M. Vitousek, Chair, John Aber, Robert W. Howarth, Gene E. Likens, Pamela A. Matson, David W. Schindler, William H. Schlesinger, and G. David Tilman</ref>
Much research has been conducted on the discovery of catalysts for nitrogen fixation, often with the goal of reducing the energy required for this conversion. However, such research has thus far failed to even approach the efficiency and ease of the Haber process. Many compounds react with atmospheric nitrogen to give [[dinitrogen complex]]es. The first dinitrogen [[Complex (chemistry)|complex]] to be reported was based on [[ruthenium]],[Ru(NH<sub>3</sub>)<sub>5</sub>(N<sub>2</sub>)]<sup>2+</sup>.<ref>{{cite journal
| title = Nitrogenopentammineruthenium(II) complexes
| author = A. D. Allen, C. V. Senoff
| journal = Journal of the Chemical Society, Chemical Communications
| volume =
| issue = 24
| pages = 621
| year = 1965
| url =
| doi = 10.1039/C19650000621}}</ref>
=== انقاص النيتروجين الجوي ===
Catalytic chemical nitrogen fixation at temperatures considerably lower than the Haber process is an ongoing scientific endeavor. Nitrogen was converted to ammonia and hydrazine by [[Alexander E. Shilov]] in 1970.<ref>"Catalytic reduction of molecular nitrogen in solutions" A. E. Shilov ''Russian Chemical Bulletin'' Volume 52, Number 12, 2555–2562, {{DOI|10.1023/B:RUCB.0000019873.81002.60}}</ref><ref>"Reduction of dinitrogen" Richard R. Schrock ''PNAS'' 14 November 2006 vol. 103 no. 46 17087 {{DOI|10.1073/pnas.0603633103}}</ref>
Few compounds will cleave the N<sub>2</sub> molecule. Under an atmosphere of nitrogen, lithium metal converts to [[lithium nitride]]. Treatment of the resulting nitride gives ammonia. Another example of [[homolysis (chemistry)|homolytic cleavage]] of dinitrogen under mild conditions was published in 1995. Two equivalents of a [[molybdenum]] complex reacted with one equivalent of dinitrogen, creating a [[triple bond]]ed MoN complex.<ref>"Dinitrogen Cleavage by a Three-Coordinate Molybdenum(III) Complex" Catalina E. Laplaza and Christopher C. Cummins ''Science'' 12 May 1995: 861–863.[[Digital object identifier|10.1126/science.268.5212.861]]</ref> Since then, this triple bonded complex has been used to make [[nitriles]].<ref>"A Cycle for Organic Nitrile Synthesis via Dinitrogen Cleavage" John J. Curley, Emma L. Sceats, and Christopher C. Cummins ''J. Am. Chem. Soc.'', 2006, 128 (43), pp. 14036–14037 {{DOI|10.1021/ja066090a}}</ref>
[[Trimethylsilyl chloride]], lithium, and nitrogen molecule react to give [[tris(trimethylsilyl)amine]], under catalysis by [[nichrome]] wire or [[chromium trichloride]] in tetrahydrofuran.
:3 Me<sub>3</sub>SiCl + 3 Li + 1/2 N2 → (Me<sub>3</sub>Si)<sub>3</sub>N + 3 LiCl
Tris(trimethylsilyl)amine can then be used for reaction with α,δ,ω-tri[[ketone]]s to give tricyclic [[pyrrole]]s.<ref>{{cite book|last=Brook|first=Michael A.|title=Silicon in Organic, Organometallic, and Polymer Chemistry|year=2000|publisher=John Wiley & Sons, Inc.|location=New York|pages=193–194}}</ref>
Catalytic systems for converting nitrogen to ammonia have been developed since the 1980s.<ref>C. J. Pickett, "The Chatt Cycle and the Mechanism of Enzymic Reduction of Molecular Nitrogen", ''J. Biol. Inorg. Chem.'' 1996 1, 601–606.</ref> In 2003 another was reported based on molybdenum compound, a proton source, and a strong [[reducing agent]].<ref>''Synthesis and Reactions of Molybdenum Triamidoamine Complexes Containing Hexaisopropylterphenyl Substituents'' Dmitry V. Yandulov, [[Richard R. Schrock]], Arnold L. Rheingold, Christopher Ceccarelli, and William M. Davis Inorg. Chem.; '''2003'''; 42(3) pp 796–813; (Article) {{DOI|10.1021/ic020505l}}</ref><ref>"Catalytic Reduction of Dinitrogen to Ammonia at a Single Molybdenum Center" Dmitry V. Yandulov and Richard R. Schrock ''[[Science (journal)|Science]]'' 4 July '''2003''': Vol. 301. no. 5629, pp. 76–78 {{DOI|10.1126/science.1085326}}</ref><ref>The catalyst is based on [[molybdenum(V) chloride]] and [[tris(2-aminoethyl)amine]] substituted with three very bulky hexa-isopropylterphenyl (HIPT) groups. Nitrogen adds end-on to the molybdenum atom, and the bulky HIPT substituents prevent the formation of the stable and nonreactive Mo-N=N-Mo [[Dimer (chemistry)|dimer]], and the nitrogen is reduced in an isolated pocket. The proton donor is a [[pyridinium]] cation, which is accompanied by a [[tetraborate]] counter ion. The [[reducing agent]] is [[decamethylchromocene]]. All ammonia formed is collected as the HCl salt by trapping the distillate with a HCl solution</ref><ref>Note also that, although the dinitrogen complex is shown in brackets, this species can be isolated and characterized. Here the brackets do not indicate that the intermediate is not observed.</ref> However, this catalytic reduction fixates only a few nitrogen molecules.
[[Image:NitrogenReduction.png|center|500px|Synthetic nitrogen reduction Yandulov 2006]]
In 2011 Arashiba et al. reported yet another system with a catalyst again based on [[molybdenum]] but with a diphosphorus [[pincer ligand]].<ref>Kazuya Arashiba, Yoshihiro Miyake Yoshiaki Nishibayashi "A molybdenum complex bearing PNP-type pincer ligands leads to the catalytic reduction of dinitrogen into ammonia" ''Nature Chemistry'' Volume: 3, Pages: 120–125 Year published:(2011) {{DOI|10.1038/nchem.906}}</ref>
== انظر أيضاً ==
* [[Birkeland–Eyde process]]: an industrial fertiliser production process
* [[Denitrification]]: an organic process of nitrogen release
* [[George Washington Carver]]: an American botanist
* [[Nif gene]]: a gene found in nitrogen fixing bacteria
* [[Nitrification]]: biological production of nitrogen
* [[Nitrogen cycle]]: the flow and transformation of nitrogen through the environment
* [[Nitrogen deficiency]]
* [[Nitrogenase]]: enzymes used by organisms to fix nitrogen
* [[Ostwald process]]: a chemical process for making nitric acid HNO<sub>3</sub>
* [[Push–pull technology]]: the use of both repellent and attractive organisms in agriculture
== المراجع ==
{{Reflist|30em}}
== روابط خارجية ==
* [http://www.mcdb.ucla.edu/Research/Hirsch/imagesb/HistoryDiscoveryN2fixingOrganisms.pdf "A Brief History of the Discovery of Nitrogen-fixing Organisms", Ann M. Hirsch (2009)]
* [http://dornsife.usc.edu/labs/capone Marine Nitrogen Fixation laboratory at the University of Southern California]
{{Use dmy dates|date=July 2012}}
[[تصنيف:استقلاب]]
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