Chelant
<p ><b>Chelation</b> is the formation or presence of two or more separate <a href="http://en.wikipedia.org/wiki/Coordinate_bond" title="Coordinate bond" class="mw-redirect" >coordinate bonds</a> between a <a href="http://en.wikipedia.org/wiki/Denticity" title="Denticity" >polydentate</a> (multiple bonded) <a href="http://en.wikipedia.org/wiki/Ligand" title="Ligand" >ligand</a> and a single central atom.<sup id="cite_ref-IUPAC_0-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Chelates#cite_note-IUPAC-0" >[1]</a></sup> Usually these <a href="http://en.wikipedia.org/wiki/Ligand" title="Ligand" >ligands</a> are <a href="http://en.wikipedia.org/wiki/Organic_compound" title="Organic compound" >organic compounds</a>, and are called chelants, chelators, chelating agents, or sequestering agents.</p>
<p>
The ligand forms a <b>chelate complex</b> with the substrate. Chelate complexes are contrasted with <a href="http://en.wikipedia.org/wiki/Coordination_complex" title="Coordination complex" >coordination complexes</a> composed of <a href="http://en.wikipedia.org/wiki/Denticity" title="Denticity" >monodentate ligands</a>, which form only one bond with the central atom.</p>
<p>
Chelants, according to <a href="http://en.wikipedia.org/wiki/ASTM" title="ASTM" class="mw-redirect" >ASTM</a>-A-380, are "chemicals that form soluble, complex molecules with certain metal ions, inactivating the ions so that they cannot normally react with other elements or ions to produce precipitates or scale."</p>
<p>
The word chelation is derived from <a href="http://en.wikipedia.org/wiki/Greek_language" title="Greek language" >Greek</a> χηλή, <i>chelè</i>, meaning claw; the ligands lie around the central atom like the claws of a<a href="http://en.wikipedia.org/wiki/Lobster" title="Lobster" >lobster</a>.<sup id="cite_ref-1" class="reference" ><a href="http://en.wikipedia.org/wiki/Chelates#cite_note-1" >[2]</a></sup></p>