EDTA affinity for zinc

tfitzwater at gilead.com tfitzwater at gilead.com
Mon Aug 14 13:26:11 EST 2000

>Subject: EDTA affinity for zinc
>From: Johannes Graumann (j_graumann at hotmail.com)
>Date: Sun 13 Aug 2000 - 17:35:42 BST

>Could somebody please give me a hint where to find the affinity of EDTA
>for zinc at pH 7.5?

>Thank you, Johannes

The apparent log stability constants for EDTA at pH 7.5 are Mg:  5.9, Ca:
7.8, Zn:  13.6.  The Ki at pH 7.5 is the "apparent" value at a particular
pH which considers all forms of complexing species, rather than only the
most anionic.  EDTA has 4 pKa values and for example, at pH 7.0, a =
2.08e3, so that log a = 3.3.  For Mg++:EDTA at pH 7.0: log Ki (apparent) =
8.7 - 3.3 = 5.4.
See R. M. C. Dawson, D. C. Elliot, W. H. Elliot and K. M. Jones 1969 Data
for Biochemical Research.  Oxford Univ. Press, New York for more

Tim Fitzwater
Principal Research Associate
Gilead Sciences
2860 Wilderness Pl.
Boulder, CO 80301


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