Hi Francis
I guess it depends on how much residual high-affinity binder you have in the 
mixture and what the difference in affinity is between Y and deriv-Y. Another 
issue is of course whether Y and derY compete for the same binding site and 
have the same stoichiometry. A well designed displacement ITC experiment and 
comparisons thereof with ITC data for your high-affinity binder should lead to 
some good answers.  Knowing the ratio of Y vs deriv-Y in your starting compound 
solution will be an advantage.

A very useful reference in thinking about and carrying out displacement ITC in 
our group has been the one by Velazquez-Campoy and Freire. This article was 
specifically written to address the application of displacement titrations in 
ITC. We have applied this approach to address several types of questions 
concerning interactions in the uM-pM range.
Velazquez-Campoy A, Freire E.
Isothermal titration calorimetry to determine association constants for 
high-affinity ligands
Nat Protoc. 2006;1(1):186-91. 

Best regards

Savvas Savvides
Unit for Structural Biology @ L-ProBE
Ghent University
K.L. Ledeganckstraat 35, 9000 Ghent, Belgium
Ph. +32  (0)472 928 519 http://www.LProBE.ugent.be/xray.html

On 24 Aug 2010, at 17:11, Francis E Reyes wrote:

> Hi All
> I'm curious the effect of small impurities in commercially synthesized 
> compounds on ITC and its analysis. Say if compound Y is the high affinity 
> binder, but you make a derivative that differs from a single functional group 
> from Y (you used Y to make this new compound) and you never are able to 
> completely get rid of Y. How does this affect the analysis of determining the 
> derivative's affinity by ITC?
> References or personal experience is appreciated!
> F
> ---------------------------------------------
> Francis E. Reyes M.Sc.
> 215 UCB
> University of Colorado at Boulder
> gpg --keyserver pgp.mit.edu --recv-keys 67BA8D5D
> 8AE2 F2F4 90F7 9640 28BC  686F 78FD 6669 67BA 8D5D

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