Page 184 - Chiral Separation Techniques

162 6 Enantiomer Separations using Designed Imprinted Chiral Phases

Fig. 6-5. Model of the binding site for L-PA based on spectroscopic and chromatographic characteri-
zation of the prepolymerization monomer–template assemblies.

6.4 Adsorption Isotherms and Site Distribution

Adsorption isotherms can yield important information concerning binding energies,
modes of binding and site distributions in the interaction of small molecule ligands
with receptors [40]. In the case of MIPs, a soluble ligand interacts with binding sites
in a solid adsorbent. The adsorption isotherms are then simply plots of equilibrium
concentrations of bound ligand (adsorbate) versus concentration of free ligand. The
isotherms can be fitted using various models where different assumptions are made.
The most simple is the Langmuir-type adsorption isotherm (Equation (1)), where the
adsorbent is assumed to contain only one type of site, where adsorbate–adsorbate
interactions are assumed not to occur, and where the system is assumed ideal. This
isotherm depends on two parameters: the saturation capacity (site density), q , and
s
the adsorption energy, b [41, 42].

q = aC (1)
1
1 + bC
1
q = aC + aC (2)
1
2
1 + bC 1 + bC
2
1
q = aC 1/ n a ( and n = numerical parameters) (3)
The bi-Langmuir model (Equation (2)) or tri-Langmuir model, the sum of two or
three Langmuir isotherms, correspond to models that assume the adsorbent surface