From: csaez <csaez@CCTR.UMKC.EDU>
  To  : rasmb@bbri.harvard.edu
  Date: Mon, 18 Aug 1997 13:34:36 -0500

Van't Hoff Plots ...

Background:
A well known method to determine thermodynamic
parameters from AU data is using a van't Hoff plot.
In this way, the enthalpy and entropy change can be
obtained from the slope and and the intercept,
respectively .... provided is linear. If the plot is not
linear, i.e: when the enthalpy change is dependent of
temperature, the plot should be fit with a quadratic
equation.

My situation:
I'm working on the induced self-association of the
complement component C8 by Suramin. A van't
Hoff Plot of AU data in the temperature range 8-
37 degrees is nicely linear, however, it presents a
brake at 20 degrees, which is reproducible. In other
words, I have two straight lines with very different
slopes. Obviously, this is a result of the poor
stability of the complex at higher temperatures.

My Questions:
1. Should I consider my plot NOT linear ?
2. Since there's no doubt I'm capable to fit
    all data into 2 different straight lines, what
    would be the right  interpretation (from a
    themodymamic point of view) ?

I thank you in advance for your time, and any
comment that you might have on this regard.

Cristian Saez
University of Missouri-Kansas City
email: csaez@cctr.umkc.edu