How many Mg2+ ions can EDTA bind?

Martin Offterdinger a8803349 at unet.univie.ac.at
Wed Dec 17 03:15:43 EST 1997


On Tue, 16 Dec 1997 17:34:31 -0600, James Akowski
<akowski at anl.spam.me.not.gov> wrote:

>Hello,  I need to re-adjust the [Mg2+] in my PCR rxns to correct for
>EDTA carryover.  Different people have told me, each with great
>certainty, that one molecule of EDTA (pKa's 2.0, 2.7, 6.1, and 10.2) at
>pH 9 will chelate one, two, or four Mg2+ ions.  I, myself, have no idea
>how EDTA coordinates Mg2+. Can someone give a definitive stoichiometry
>or point me to any references?
>Thanks for your help. 
>.....................................................................
>.....  James Akowski                    e-mail akowski at anl. gov    ..
>....   Center for Mechanistic Biology                             ...
>...    Argonne National Laboratory      phone  (630)252-3806     ....
>..     Argonne, IL  60439               FAX    (630)252-1868    .....
>.....................................................................
>Hi! I'm a .sig virus, v.3G2 Please append me to your .signature file!
EDTA forms complexes with 2 and 3 valent kations 1:1, so in other
words one EDTA molecule will omplex one Mg 2+ ion! The pH value does
not change the stoichiometry of the reaction but only the
efficiency-if the pH is not optimal the equilibrium will be shifted to
the right side leaving more free Mg2+ and EDTA!
Martin



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