Iron oxide: Difference between revisions

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| year = 2003
| publisher = Wiley VCH
| isbn = 978-3-527-30274-31
}}</ref>
 
* Oxide of Fe<sup>II</sup>
** FeO: [[iron(II) oxide]], [[wüstite]]
** FeO<sub>2</sub>:<ref>{{Cite journal|last=Hu|first=Qingyang|last2=Kim|first2=Duck Young|last3=Yang|first3=Wenge|last4=Yang|first4=Liuxiang|last5=Meng|first5=Yue|last6=Zhang|first6=Li|last7=Mao|first7=Ho-Kwang|date=June 2016|title=FeO<sub>2</sub> and (FeO)OH under deep lower-mantle conditions and Earth’sEarth's oxygen–hydrogen cycles|url=http://www.nature.com/doifinder/10.1038/nature18018|journal=Nature|language=En|volume=534|issue=7606|pages=241–244|doi=10.1038/nature18018|pmid=27279220|issn=1476-4687|bibcode=2016Natur.534..241H}}</ref> [[iron dioxide]]
* Mixed oxides of Fe<sup>II</sup> and Fe<sup>III</sup>
** Fe<sub>3</sub>O<sub>4</sub>: [[Iron(II,III) oxide]], [[magnetite]]
** Fe<sub>4</sub>O<sub>5</sub><ref>{{cite journal|title=Discovery of the recoverable high-pressure iron oxide Fe4O5|date=Oct 2011 | doi=10.1073/pnas.1107573108 |pmid=21969537 | volume=108|issue=42|journal=Proceedings of the National Academy of Sciences|pages=17281–17285|bibcode=2011PNAS..10817281L|pmc=3198347|last1=Lavina |first1=B. |last2=Dera |first2=P. |last3=Kim |first3=E. |last4=Meng |first4=Y. |last5=Downs |first5=R. T. |last6=Weck |first6=P. F. |last7=Sutton |first7=S. R. |last8=Zhao |first8=Y. }}</ref>
** Fe<sub>5</sub>O<sub>6</sub><ref>{{cite webjournal|url=http://advances.sciencemag.org/content/1/5/e1400260|title = Synthesis of Fe5O6|journal = Science Advances|volume = 1|issue = 5|pages = e1400260|doi = 10.1126/sciadv.1400260|pmid = 26601196|year = 2015|last1 = Lavina|first1 = Barbara|last2 = Meng|first2 = Yue}}</ref>
** Fe<sub>5</sub>O<sub>7</sub><ref name = "oxides">{{cite webjournal|url=http://www.nature.com/ncomms/2016/160211/ncomms10661/abs/ncomms10661.html| title = Structural complexity of simple Fe2O3 at high pressures and temperatures| journal = Nature Communications| volume = 7| pages = 10661| doi = 10.1038/ncomms10661| pmid = 26864300| pmc = 4753252| year = 2016| last1 = Bykova| first1 = E.| last2 = Dubrovinsky| first2 = L.| last3 = Dubrovinskaia| first3 = N.| last4 = Bykov| first4 = M.| last5 = McCammon| first5 = C.| last6 = Ovsyannikov| first6 = S. V.| last7 = Liermann| first7 = H. -P.| last8 = Kupenko| first8 = I.| last9 = Chumakov| first9 = A. I.| last10 = Rüffer| first10 = R.| last11 = Hanfland| first11 = M.| last12 = Prakapenka| first12 = V.}}</ref>
** Fe<sub>25</sub>O<sub>32</sub><ref name="oxides" />
**Fe<sub>13</sub>O<sub>19</sub><ref>{{cite web|url=http://www.degruyter.com/view/j/ammin.2015.100.issue-8-9/am-2015-5369/am-2015-5369.xmljournal| title = The crystal structures of Mg2Fe2C4O13, with tetrahedrally coordinated carbon, and Fe13O19, synthesized at deep mantle conditions| journal = American Mineralogist| volume = 100| issue = 8–9| pages = 2001–2004| doi = 10.2138/am-2015-5369| year = 2015| last1 = Merlini| first1 = Marco| last2 = Hanfland| first2 = Michael| last3 = Salamat| first3 = Ashkan| last4 = Petitgirard| first4 = Sylvain| last5 = Müller| first5 = Harald}}</ref>
* Oxide of Fe<sup>III</sup>
** Fe<sub>2</sub>O<sub>3</sub>: [[iron(III) oxide]]
==Microbial degradation ==
 
Several species of [[Dissimilatory metal-reducing bacteria|bacteria]], including ''Shewanella oneidensis'', ''Geobacter sulfurreducens'' and ''Geobacter metallireducens'', metabolically utilize solid iron oxides as a terminal electron acceptor, reducing Fe(III) oxides to Fe(II) containing oxides.<ref>{{cite journal|last1=Bretschger|first1=O.|last2=Obraztsova|first2=A.|last3=Sturm|first3=C. A.|last4=Chang|first4=I. S.|last5=Gorby|first5=Y. A.|last6=Reed|first6=S. B.|last7=Culley|first7=D. E.|last8=Reardon|first8=C. L.|last9=Barua|first9=S.|last10=Romine|first10=M. F.|last11=Zhou|first11=J.|last12=Beliaev|first12=A. S.|last13=Bouhenni|first13=R.|last14=Saffarini|first14=D.|last15=Mansfeld|first15=F.|last16=Kim|first16=B.-H.|last17=Fredrickson|first17=J. K.|last18=Nealson|first18=K. H.|title=Current Production and Metal Oxide Reduction by Shewanella oneidensis MR-1 Wild Type and Mutants|journal=Applied and Environmental Microbiology|date=20 July 2007|volume=73|issue=21|pages=7003–7012|doi=10.1128/AEM.01087-07|pmid=17644630|pmc=2223255}}</ref>
 
== Environmental effects ==
 
=== Methanogenesis replacement by iron oxide reduction ===
Under conditions favoring iron reduction, the process of iron oxide reduction can replace at least 80% of methane production occurring by [[methanogenesis]].<ref name=":4">{{Cite journal|last=Sivan|first=O.|last2=Shusta|first2=S. S.|last3=Valentine|first3=D. L.|date=2016-03-01|title=Methanogens rapidly transition from methane production to iron reduction|url=http://onlinelibrary.wiley.com/doi/10.1111/gbi.12172/abstract|journal=Geobiology|language=en|volume=14|issue=2|pages=190–203|doi=10.1111/gbi.12172|issn=1472-4669}}</ref> This phenomenon occurs in a nitrogen-containing (N<sub>2</sub>) environment with low sulfate concentrations. Methanogenesis, an [[Archaea]]n driven process, is typically the predominate form of carbon mineralization in sediments at the bottom of the ocean. Methanogenesis completes the decomposition of organic matter to methane (CH<sub>4</sub>).<ref name=":4" /> The specific electron donor for iron oxide reduction in this situation is still under debate, but the two potential candidates include either Titanium (III) or compounds present in yeast. The predicted reactions with Titanium (III) serving as the electron donor and [[Phenazine|phenazine-1-carboxylate]] (PCA) serving as an electron shuttle is as follows:
:Ti(III)-cit + CO<sub>2</sub> + 8H<sup>+</sup> → CH<sub>4</sub> + 2H<sub>2</sub>O + Ti(IV) + cit&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ΔE = &ndash;240 + 300 mV
:Ti(III)-cit + PCA (oxidized) → PCA (reduced) + Ti(IV) + cit&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;ΔE = &ndash;116 + 300 mV
 
=== Hydroxyl radical formation ===
On the other hand when airborne, iron oxides have been shown to harm the lung tissues of living organisms by the formation of hydroxyl radicals, leading to the creation of alkyl radicals. The following reactions occur when Fe<sub>2</sub>O<sub>3</sub> and FeO, hereafter represented as Fe<sup>3+</sup> and Fe<sup>2+</sup> respectively, iron oxide particulates accumulate in the lungs.<ref name=":9">{{Cite journalbook|last=Hartwig|first=A.|last2=MAK Commission 2016|first2=|date=July 25, 2016|title=Iron oxides (inhalable fraction) [MAK Value Documentation, 2011]|url=|journal=The MAK Collection for Occupational Health and Safety|publisher=Wiley-VCH Verlag GmbH & Co. KGaA.|volume=1|pages=1804–1869|doi=10.1002/3527600418.mb0209fste5116|via=|isbn=9783527600410}}</ref>
: {{oxygen|2}} + {{e-}} → {{oxygen|2|•&thinsp;&ndash;}}<ref name=":9" />
The formation of the superoxide anion ({{oxygen|2|•&thinsp;&ndash;}}) is catalyzed by a transmembrane enzyme called [[NADPH oxidase]]. The enzyme facilitates the transport of an electron across the plasma membrane from cytosolic NADPH to extracellular oxygen (O<sub>2</sub>) to produce {{oxygen|2|•&thinsp;&ndash;}}. [[Nicotinamide adenine dinucleotide phosphate|NADPH]] and [[Flavin adenine dinucleotide|FAD]] are bound to cytoplasmic binding sites on the enzyme. Two electrons from NADPH are transported to FAD which reduces it to FADH<sub>2</sub>. Then, one electron moves to one of two heme groups in the enzyme within the plane of the membrane. The second electron pushes the first electron to the second heme group so that it can associate with the first heme group. For the transfer to occur, the second heme must be bound to extracellular oxygen which is the acceptor of the electron. This enzyme can also be located within the membranes of intracellular organelles allowing the formation of {{oxygen|2|•&thinsp;&ndash;}} to occur within organelles.<ref name=":2">{{Cite journal|last=Bedard|first=Karen|last2=Krause|first2=Karl-Heinz|date=2007-01-01|title=The NOX Family of ROS-Generating NADPH Oxidases: Physiology and Pathophysiology|url=http://physrev.physiology.org/content/87/1/245|journal=Physiological Reviews|language=en|volume=87|issue=1|pages=245–313|doi=10.1152/physrev.00044.2005|issn=0031-9333|pmid=17237347}}</ref>
: 2{{oxygen|2|•&thinsp;&ndash;}} + 2{{H+}} → {{chem|H|2|O|2}} + O<sub>2</sub> <ref name=":9" /><ref name=":7">{{Cite journal|last=Chapple|first=Iain L. C.|last2=Matthews|first2=John B.|date=2007-02-01|title=The role of reactive oxygen and antioxidant species in periodontal tissue destruction|url=http://onlinelibrary.wiley.com/doi/10.1111/j.1600-0757.2006.00178.x/abstract|journal=Periodontology 2000|language=en|volume=43|issue=1|pages=160–232|doi=10.1111/j.1600-0757.2006.00178.x|pmid=17214840|issn=1600-0757}}</ref>
The formation of hydrogen peroxide ({{chem|H|2|O|2}}) can occur spontaneously when the environment has a lower pH especially at pH 7.4.<ref name=":7" /> The enzyme superoxide dismutase can also catalyze this reaction. Once {{chem|H|2|O|2}} has been synthesized, it can diffuse through membranes to travel within and outside the cell due to its nonpolar nature.<ref name=":2" />
: Fe<sup>2+</sup> + {{chem|H|2|O|2}} → Fe<sup>3+</sup> + HO{{sup|•}} + {{OH-}}
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