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Processing of the data allows calculation of
Δ
H, K (equilibrium constant) and
Δ
S. ITC also provides the number of sites (for macromolecules binding more
than one ligand). One may, for example, compare binding of different ligands.
3.2.3. Thermodynamics of dilute
solutions:
Fundamentals
(keywords)
Dilute solution: The term ‘dilute’ refers to a concentration range where the
interactions between individual macromolecules are negligible. The molecules
are then separated in space. The concentration by which interactions become
significant is called the critical overlap concentration (c*), and is defined above
(figure/text box).
The definition of dilute solution (c < c*) takes advantage of the fact that the
(easily observable and measurable) viscosity of the solution changes quite
abruptly when c reaches c* (c.f. Fig. 14.2 in the textbook).
Dilute solutions are primarily a research tool. They are mainly used to obtain
information about individual macromolecules such as M, R
G
, [
η
] etc., because
many mathematical formulae are much simplified and do not have to take into
account interactions between polymers. Note also the common practise to
extrapolate results (osmometry, light scattering, intrinsic viscosity) to zero
concentration to obtain accurate estimates.
DILUTE SOLUTION:
c < c*
SEMIDILUTE
SOLUTION:
c* < c < c**