Editing Chelation (section)

== In nature ==

Numerous [[biomolecules]] exhibit the ability to dissolve certain metal [[cation]]s. Thus, [[protein]]s, [[polysaccharide]]s, and polynucleic acids are excellent polydentate ligands for many metal ions.  Organic compounds such as the amino acids [[glutamic acid]] and [[histidine]], organic diacids such as [[malate]], and polypeptides such as [[phytochelatin]] are also typical chelators. In addition to these adventitious chelators, several biomolecules are specifically produced to bind certain metals (see next section).<ref>{{cite journal |last1=Krämer |first1=Ute |last2=Cotter-Howells |first2=Janet D. |last3=Charnock |first3=John M. |last4=Baker |first4=Alan J. M. |last5=Smith |first5=J. Andrew C. |name-list-style=vanc |title=Free histidine as a metal chelator in plants that accumulate nickel |journal=Nature |volume=379 |issue=6566 |year=1996 |pages=635–8 |bibcode=1996Natur.379..635K |doi=10.1038/379635a0 |s2cid=4318712}}</ref><ref>{{cite journal |vauthors=Magalhaes JV |title=Aluminum tolerance genes are conserved between monocots and dicots |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=103 |issue=26 |pages=9749–50 |date=June 2006 |pmid=16785425 |pmc=1502523 |doi=10.1073/pnas.0603957103 |bibcode=2006PNAS..103.9749M |doi-access=free}}</ref><ref>{{cite journal |vauthors=Ha SB, Smith AP, Howden R, Dietrich WM, Bugg S, O'Connell MJ, Goldsbrough PB, Cobbett CS |title=Phytochelatin synthase genes from Arabidopsis and the yeast Schizosaccharomyces pombe |journal=The Plant Cell |volume=11 |issue=6 |pages=1153–64 |date=June 1999 |pmid=10368185 |pmc=144235 |doi=10.1105/tpc.11.6.1153}}</ref><ref name="Lippard" />

Virtually all metalloenzymes feature metals that are chelated, usually to peptides or cofactors and prosthetic groups.<ref name="Lippard">{{cite book |vauthors=Lippard SJ, Berg JM |title=Principles of Bioinorganic Chemistry |publisher=University Science Books |location=Mill Valley, Calif. |year=1994 |isbn=978-0-935702-73-6}}.{{page needed|date=December 2015}}</ref>  Such chelating agents include the [[porphyrin]] rings in [[hemoglobin]] and [[chlorophyll]].  Many microbial species produce water-soluble pigments that serve as chelating agents, termed [[siderophores]]. For example,  species of ''[[Pseudomonas]]'' are known to secrete [[pyochelin]] and [[pyoverdine]] that bind iron. [[Enterobactin]], produced by ''[[Escherichia coli|E. coli]]'', is the strongest chelating agent known. The marine [[mussel]]s use metal chelation, especially Fe<sup>3+</sup> chelation with the [[L-DOPA|Dopa]] residues in mussel foot protein-1 to improve the strength of the threads that they use to secure themselves to surfaces.<ref>{{cite journal |vauthors=Das S, Miller DR, Kaufman Y, Martinez Rodriguez NR, Pallaoro A, Harrington MJ, Gylys M, Israelachvili JN, Waite JH |title=Tough coating proteins: subtle sequence variation modulates cohesion |journal=Biomacromolecules |volume=16 |issue=3 |pages=1002–8 |date=March 2015 |pmid=25692318 |pmc=4514026 |doi=10.1021/bm501893y}}</ref><ref>{{cite journal |vauthors=Harrington MJ, Masic A, Holten-Andersen N, Waite JH, Fratzl P |title=Iron-clad fibers: a metal-based biological strategy for hard flexible coatings |journal=Science |volume=328 |issue=5975 |pages=216–20 |date=April 2010 |pmid=20203014 |pmc=3087814 |doi=10.1126/science.1181044 |bibcode=2010Sci...328..216H}}</ref><ref>{{cite journal |vauthors=Das S, Martinez Rodriguez NR, Wei W, Waite JH, Israelachvili JN |title=Peptide Length and Dopa Determine Iron-Mediated Cohesion of Mussel Foot Proteins |journal=Advanced Functional Materials |volume=25 |issue=36 |pages=5840–5847 |date=September 2015 |pmid=28670243 |pmc=5488267 |doi=10.1002/adfm.201502256}}</ref>

In earth science, chemical [[weathering]] is attributed to organic chelating agents (e.g., [[peptide]]s and [[sugar]]s) that extract [[metal ions]] from minerals and rocks.<ref>{{cite web |title=Introduction to the Lithosphere: Weathering |first=Michael |last=Pidwirny |name-list-style=vanc |location=University of British Columbia Okanagan |url=http://www.physicalgeography.net/fundamentals/10r.html}}</ref>  Most metal complexes in the environment and in nature are bound in some form of chelate ring (e.g., with a [[humic acid]] or a protein). Thus, metal chelates are relevant to the mobilization of [[metals]] in the [[soil]], the uptake and the accumulation of [[metals]] into [[plants]] and [[microorganism]]s. Selective chelation of [[heavy metals]] is relevant to [[bioremediation]] (e.g., removal of [[Caesium-137|<sup>137</sup>Cs]] from [[radioactive waste]]).<ref>{{cite book |last1=Prasad  |first1=MNV |name-list-style=vanc |title=Metals in the Environment: Analysis by Biodiversity |date=2001 |publisher=Marcel Dekker |location=New York |isbn=978-0-8247-0523-7}}{{page needed|date=December 2015}}</ref>