Editing Glutamic acid (section)

===Ionization===
[[File:Glutamic Acid at physiological pH V2.svg|class=skin-invert-image|thumb|left|The glutamate monoanion.]]
When glutamic acid is dissolved in water, the [[amine|amino group]] (−{{chem|N|H|2}}) may gain a [[proton]] ({{chem|H|+}}), and/or the [[carboxylic acid|carboxyl groups]] may lose protons, depending on the [[pH|acidity]] of the medium.

In sufficiently acidic environments, both carboxyl groups are protonated and the molecule becomes a [[cation]] with a single positive charge, HOOC−CH({{chem|N|H|3|+}})−({{chem|C|H|2}})<sub>2</sub>−COOH.<ref name=neub>{{cite journal|pmc=1263308 |date=1936 |last1=Neuberger |first1=A. |title=Dissociation constants and structures of glutamic acid and its esters |journal=Biochemical Journal |volume=30 |issue=11 |pages=2085–2094 |doi=10.1042/bj0302085 |pmid=16746266 }}</ref>

At [[pH]] values between about 2.5 and 4.1,<ref name=neub/> the carboxylic acid closer to the amine generally loses a proton, and the acid becomes the neutral zwitterion <sup>−</sup>OOC−CH({{chem|N|H|3|+}})−({{chem|C|H|2}})<sub>2</sub>−COOH. This is also the form of the compound in the crystalline solid state.<ref name=roda>{{cite journal | last1 = Rodante | first1 = F. | last2 = Marrosu | first2 = G. | year = 1989 | title = Thermodynamics of the second proton dissociation processes of nine α-amino-acids and the third ionization processes of glutamic acid, aspartic acid and tyrosine | journal = Thermochimica Acta | volume = 141 | pages = 297–303 | doi = 10.1016/0040-6031(89)87065-0 | bibcode = 1989TcAc..141..297R }}</ref><ref name=cryst>{{cite journal | last1 = Lehmann | first1 = Mogens S. | last2 = Koetzle | first2 = Thomas F. | last3 = Hamilton | first3 = Walter C. | year = 1972 | title = Precision neutron diffraction structure determination of protein and nucleic acid components. VIII: the crystal and molecular structure of the β-form of the amino acidl-glutamic acid | journal = Journal of Crystal and Molecular Structure | volume = 2 | issue = 5| pages = 225–233 | doi = 10.1007/BF01246639 | bibcode = 1972JCCry...2..225L | s2cid = 93590487 }}</ref>  The change in protonation state is gradual; the two forms are in equal concentrations at pH 2.10.<ref name=ionpH/>

At even higher pH, the other carboxylic acid group loses its proton and the acid exists almost entirely as the glutamate anion <sup>−</sup>OOC−CH({{chem|N|H|3|+}})−({{chem|C|H|2}})<sub>2</sub>−COO<sup>−</sup>, with a single negative charge overall. The change in protonation state occurs at pH 4.07.<ref name=ionpH/> This form with both carboxylates lacking protons is dominant in the [[physiological pH]] range (7.35–7.45).

At even higher pH, the amino group loses the extra proton, and the prevalent species is the doubly-negative anion <sup>−</sup>OOC−CH({{chem|N|H|2}})−({{chem|C|H|2}})<sub>2</sub>−COO<sup>−</sup>. The change in protonation state occurs at pH 9.47.<ref name=ionpH>William H. Brown and Lawrence S. Brown (2008), ''Organic Chemistry'' (5th edition). Cengage Learning. p. 1041. {{ISBN|0495388572|978-0495388579}}.</ref>