Stoichiometric displacement model

Drager, R. R. and Regnier, F. E., Application of the stoichiometric displacement model of retention to anion-exchange chromatography of nucleic acids,... 

A stoichiometric model can conveniently be invoked to explain the ion-exchange retention process [43 6]. As discussed in detail in these cited papers on ion-exchange theory, useful information about the involved ion-exchange process can be deduced from plots of log k vs. the log of the counterion concentration [X], which commonly show linear dependencies according to the stoichiometric displacement model (Equation 1.1)... 

A thorough study on the ion-exchange mechanism and the effect of distinct counterions in this PO mode was recently presented by Gyimesi-Forras et al. [41]. A large variety of distinct acid additives to methanol, acetonitrile, and tetrahydrofuran (Table 1.1) (without any base added) was investigated in view of the stoichiometric displacement model and their effect on the enantiomer separation of 2-methoxy-2-(l-naphthyl)propionic acid. The stoichiometric displacement model (Equation 1.1) was obeyed also in the PO mode, as revealed by linear plots of log k vs. acid concentration. The slopes and intercepts along with the concentration ranges used with the distinct competitor acids are summarized in Table 1.1. 

Influence of Acid Additives on Retention Characteristics of 2-Methoxy-2-(1-Naphthyl)Propionic Acid on a 0-9-(tert-ButylcarbamoyOQuinine CSP as Assessed by the Characteristic Parameters of the Stoichiometric Displacement Model (Slopes and Interc ... 

According to the stoichiometric displacement model, the equilibrium constant for peptide adsorption with the solvated nonpolar ligands can be expressed as follows ... 

Although the stoichiometric displacement model does not describe the physical situation rigorously enough, it has been widely used and corrected for some shortcomings. Whitley et al.m 89 have corrected the model since not all charges are accessible for the protein. They have introduced a correction... 

The basic principles of ion exchange have been discussed by Walton [78]. However, this discussion was mainly limited to the case of small inorganic ions. For the separation of biomolecules, e stoichiometric displacement model (SDM, next subsection) is of particular interest. This model is based on the assumption that ion exchange is the only mechanism of retention of the components studied and that the ion-exchange process can be modeled as a stoichiometric "reaction" described by the mass action principle. 

The state of equilibrium in ion exchange chromatography is currently described by stoichiometric models where the solute, for example a protein, displaces a stoichiometric number of salt ions bound on the ion exchanger. A basic concept is the stoichiometric displacement model developed by Kopaciewicz et al. (1983). For monovalent counterions the reaction is described as follows ... 

The importance of three-dimensional structure to chromatographic behavior is reflected in the nonmechanistic model, the stoichiometric displacement model (SDM). The central hypothesis of the SDM is that the displacement of a solute from a surface is accompanied by the adsorption of a stoichiometric amount of displacing agent. The process may be described by the equilibrium expression ... 

Extensive literature has developed related to the preferential interaction of different solvents with proteins or peptides in bulk solution.156-5X1 Similar concepts can be incorporated into descriptions of the RPC behavior of peptides and employed as part of the selection criteria for optimizing the separation of a particular peptide mixture. As noted previously, the dependency of the equilibrium association constant, /CassoCji, of a peptide and the concentration of the solvent required for desorption in RPC can be empirically described1441 in terms of nonmechanistic, stoichiometric solvent displacement or preferential hydration models, whereby the mass distribution of a peptide P, with n nonpolar ligands, each of which is solvated with solvent molecules Da is given by the following ... 

Use of the Stoichiometric Solvent Displacement Model in Peptide Isolation by Reversed-Phase Chromatography... 

According to this theoretical treatment, the slope of the plots of In k versus the solvent concentration, [3]m, can be employed to derive the contact area associated with the peptide-nonpolar ligand interaction. The retention and elution of a peptide in RPC can then be treated as a series of microequilibriums between the different components of the system, as represented by eq 6. The stoichiometric solvent displacement model addresses a set of considerations analogous to that of the preferential interaction model, but from a different empirical perspective. Thus, the affinity of the organic solvent for the free peptide P, in the mobile phase can be represented as follows ... 

This influence of the valence and activity coefficients of the displacer salt on the retention behavior of polypeptides and proteins can be anticipated from theoretical treatments of the ion-exchange chromatographic separation of proteins. According to the nonmechanistic stoichiometric model of protein retention behavior in HP-IEX80,82-85 the influence of a divalent cation salt such as CaCl2 on the retention behavior of a protein in HP-IEC can be evaluated in terms of the following relationships ... 

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