EDTA

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[[Image:EDTA with ligand.png|right|thumb|200px|'''EDTA''' (black) with coordinate bonds to a metal ion (red)]]
[[Image:EDTA with ligand.png|right|thumb|200px|'''EDTA''' (black) with coordinate bonds to a metal ion (red)]]
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'''EDTA''' stands for '''ethylene-diamine-tetraacetic acid'''. It chelates divalent cations and is therefore used in many buffers. Its relative [[EGTA]] has a higher affinity for calcium than EDTA.
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'''EDTA''' stands for '''ethylene-diamine-tetraacetic acid'''. It chelates divalent cations and is therefore used in many buffers. Its relative [[EGTA]] has a higher affinity for calcium than for magnesium ions.
==Purpose==
==Purpose==

Revision as of 06:40, 16 June 2009

chemical structure of EDTA - ethylene-diamine-tetraacetic acid
chemical structure of EDTA - ethylene-diamine-tetraacetic acid
EDTA (black) with coordinate bonds to a metal ion (red)
EDTA (black) with coordinate bonds to a metal ion (red)

EDTA stands for ethylene-diamine-tetraacetic acid. It chelates divalent cations and is therefore used in many buffers. Its relative EGTA has a higher affinity for calcium than for magnesium ions.

Contents

Purpose

  • EDTA is a synthetic amino acid and chelating agent for divalent metals.
  • Most enzymes that synthesize or modify nucleic acids (e.g. polymerases, ligases, kinases, nucleases) are Mg2+-dependent. The addition of EDTA is a convenient way to stop these reactions.
  • EDTA is a component of many buffers used to store DNA, such as TE buffer, where the EDTA removes the metal cofactors (typically Mg++ required for activity of DNAses and other DNA damaging enzymes.

Procurement

  • Usually sold as the disodium salt (CAS 6381-92-6) (Sigma E1644).

Use

  • Molecular Weight, disodium salt dihydrate: 372.24
  • EDTA is essentially insoluble in water, and will only dissolve when neutralized with sodium hydroxide to a pH = 8.0
  • Standard stock solutions are 0.5M at pH 8.0. A 1M solution cannot be made. Autoclave.
  • Making the standard solution from disodium EDTA (the typical form sold) requires approximately 1 molar equivalent of NaOH
  • pK1 = 1.99
  • pK2 = 2.67
  • pK3 = 6.16
  • pK4 = 10.26

EDTA stock solution recipes

0.5 M EDTA stock

  • 16.81 g EDTA (Sodium Salt)
  • dH2O to 90 ml
  • adjust pH to 7.0
  • adjust volume to 100 ml

0.5M 500ml pH 8.0 with NaOH pre-calculated

  • 93.05g of Na2.EDTA (FW 372.2)
  • 10.14g of NaOH (FW 40)
  • 500 ml dH2O

[1]

Storage and stability

  • store at room temperature
  • stable for years

Interesting facts

  • Here's an article that speaks of the wonders of EDTA and how it can help treat Aunt Edna's cardiovascular disease, enhance your enjoyment of the Friday night happy hour, and act as a "get out of jail free" card.
  • EDTA helps you determine the hidden contents of your hard water.

Safety

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References

  • Here's a great page about EDTA, including formation constant (Kf) values for metal-EDTA complexes. Note that many heavy metal ions (like Fe3+, Co2+, and Zn2+) are chelated much more strongly than Mg2+. A little bit of EDTA in your reaction will go a long way to keep these evildoers out of trouble and away from your precious biomolecules without interfering with your Mg2+-dependent reactions.
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