Calcium diglutamate
{{chembox
| ImageFile = Calcium diglutamate.svg
| IUPACName = Calcium bis[(2S)- 2-amino-4-carboxy-butyrate]
| OtherNames = {{Unbulleted list|Calcium biglutamate|L-Glutamic acid calcium salt}}
|Section1={{Chembox Identifiers
| Abbreviations = CDG, CBG
| index_label = anhydrous
| index1_label = tetrahydrate
| ChemSpiderID = 2766261
| InChIKey = ZKUDDWCZGPUNQH-VDEFSOALBX
| CASNo = 5996-22-5
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNo1 = 69704-19-4
| CASNo1_Ref = {{cascite|correct|CAS}}
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 9FA5OTO85L
| UNII1_Ref = {{fdacite|correct|FDA}}
| UNII1 = IPW75840KB
| EINECS =
| PubChem = 3527266
| PubChem1 = 71310219
| SMILES = C(CC(=O)[O-])C(C(=O)[O-])N.C(CC(=O)[O-])C(C(=O)[O-])N.[Ca+2]
| InChI = 1/2C5H9NO4.Ca.2H/c2*6-3(5(9)10)1-2-4(7)8;;;/h2*3H,1-2,6H2,(H,7,8)(H,9,10);;;/p-4/t2*3-;;;/m00.../s1/r2C5H9NO4.CaH2/c2*6-3(5(9)10)1-2-4(7)8;/h2*3H,1-2,6H2,(H,7,8)(H,9,10);1H2/p-4/t2*3-;/m00./s1
| Beilstein = 11158966
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|Section2={{Chembox Properties
| Ca=1 | C=10 | H=16 | N=2 | O=8
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|Section7={{Chembox Hazards
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Calcium diglutamate, sometimes abbreviated CDG and also called calcium biglutamate, is a compound with formula Ca(C5H8NO4)2. It is a calcium acid salt of glutamic acid. CDG is a flavor enhancer (E number E623)—it is the calcium analog of monosodium glutamate (MSG). Because the glutamate is the actual flavor-enhancer, CDG has the same flavor-enhancing properties as MSG but without the increased sodium content.{{Cite journal| first1 = P.| last2 = Woodward | first2 = D. | first3 = T.| last4 = Shoobridge| last3 = Beard | first4 = A. | first5 = M.| title = Calcium diglutamate improves taste characteristics of lower-salt soup| type = Free full text| last1 = Ball| last5 = Ferrier| journal = European Journal of Clinical Nutrition| volume = 56| issue = 6| pages = 519–523| date=Jun 2002 | issn = 0954-3007| pmid = 12032651| doi = 10.1038/sj.ejcn.1601343| doi-access = }} Notably, only the L isomer is used in flavouring as D-glutamate does not have an umami/savoury flavour.{{cite journal | last1=Kawai | first1=Misako | last2=Sekine-Hayakawa | first2=Yuki | last3=Okiyama | first3=Atsushi | last4=Ninomiya | first4=Yuzo | title=Gustatory sensation of L- and D-amino acids in humans | journal=Amino Acids | volume=43 | issue=6 | date=2012 | issn=0939-4451 | doi=10.1007/s00726-012-1315-x | pages=2349–2358| pmid=22588481 }}{{cite journal | last1=Schiffman | first1=S | last2=Sennewald | first2=K | last3=Gagnon | first3=J | title=Comparison of taste qualities and thresholds of D- and L-amino acids | journal=Physiology & Behavior | volume=27 | issue=1 | date=1981 | doi=10.1016/0031-9384(81)90298-5 | pages=51–59| pmid=7267802 }}
As a soluble source of calcium ions, this chemical is also used as a first-aid treatment for exposure to hydrofluoric acid.{{cite web |url= http://www.ee.byu.edu/cleanroom/first_aid.phtml |title= First Aid for Chemical and Cleanroom Laboratories |accessdate= 2009-06-10 |archive-date= 2009-04-30 |archive-url= https://web.archive.org/web/20090430024822/http://www.ee.byu.edu/cleanroom/first_aid.phtml |url-status= dead }}
Synthesis and reactions
Calcium di-glutamate can be prepared by reacting calcium carbonate with two molar equivalents of glutamic acid:{{cite journal | last1=Sakata | first1=Yoshiki | last2=Horikawa | first2=Toshiyuki | last3=Takenouchi | first3=Kuniharu | title=Alkaline Earth Salts of Glutamic Acid and Optical Resolution of their Racemic Modifications | journal=Agricultural and Biological Chemistry | volume=27 | issue=7 | date=1963 | issn=0002-1369 | doi=10.1080/00021369.1963.10858140 | pages=518–525}}
:CaCO3 + 2 HOOC(CH2)2CH(NH2)COOH → Ca(OOC(CH2)2CH(NH3)COO)2 + H2O + CO2↑
Concentration of the solution to a syrup under reduced pressure, followed by gradual crystallisation, affords the monohydrate. Structurally, the glutamate anion is zwitterionic, with the amino group protonated (pKa = 9.47) and both carboxylic-acid groups (pKa = 2.10, 4.07) in their deprotonated carboxylate form.{{cite journal | last1=Einspahr | first1=H. | last2=Bugg | first2=C. E. | title=Calcium binding to α-amino acids: the crystal structure of calcium di-L-glutamate tetrahydrate | journal=Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry | volume=35 | issue=2 | date=1979-02-15 | doi=10.1107/S0567740879003435 | pages=316–321}}
Calcium di-L-glutamate can be used to prepare other glutamates through metathesis with a soluble sulfate, carbonate or hydroxide salt. For example, manganese(II) di-L-glutamate can be prepared through metathesis with manganese(II) sulphate:{{cite journal | last1=Devereux | first1=Michael | last2=Jackman | first2=Maura | last3=McCann | first3=Malachy | last4=Casey | first4=Michael | title=Preparation and catalase-type activity of manganese(II) amino acid complexes | journal=Polyhedron | volume=17 | issue=1 | date=1998 | doi=10.1016/S0277-5387(97)00211-8 | pages=153–158}}
:Ca(OOC(CH2)2CH(NH3)COO)2 + MnSO4 → Mn(OOC(CH2)2CH(NH3)COO)2 + CaSO4↓