Ligand-exchange chromatography metal ions

Chiral ligand-exchange chromatography resolves enantiomers on the basis of their ability to complex with transition metal ions, such as copper, zinc, and cadmium, as illustrated by the separation of amino acid racemates using copper102 (Fig. 2.21). The principle of exchange is similar to that... 

Further examples of separation techniques that exploit the asymmetric distribution of amino acid residues at the surface of folded proteins include metal ion affinity chromatography (HP-IMAC), ligand exchange chromatography (HP-LEC), immunoaffinity chromatography (HP-IAC), hydrophilic chromatography (HP-HILIC), and the various modes of biospecific (HP-BAC), and biomimetic (HP-BMC) chromatography. For example, the... 

In separation science, ligand-exchange chromatography indeed exploits the rapid and reversible formation of metal complexes to separate compounds, which can donate electrons and coordinate to complexed metal ions immobilised on a solid support [11]. Retention of a given species is directly related to the stability of the mixed ligand complex it forms with the immobilised metal complex. Utilisation of this principle for the separation of chiral molecules, as well as large biological macromolecules such as proteins, has been successfully demonstrated. 

Chiral ligand-exchange chromatography is based on the formation of diastereomeric ternary complexes that involve a transition metal ion (M), usually copper II a single enantiomer of a chiral molecule (L), usually an amino acid and the eitantiomers of the racemic solute R and S). The diastereomeric mixed chelate complexes formed in this system are represented by the formulas L-M-R and L-M-S. When these complexes have different stabilities, the less stable complex is eluted first, and the enantiomeric solutes are separated. 

Chiral separation using ligand-exchange chromatography involves the reversible complexation of metal ions and chiral complexing agents. The central ion, usually or forms a bis complex with bidentates ligands. 

In ligand-exchange chromatography (LEC), the separation of analytes is due to the exchange of ligands from the mobile phase with other ligands coordinated to metal ions immobilized on a stationary phase. LEC has been used successfully for the resolution of free amino acids, amino acid derivatives, and for enantiomeric resolution of racemic mixtures [3]. 

Walton and co-workers reported the analysis of various alkaloids by means of ligand--exchange chromatography. As stationary phases, ion-exchange materials loaded with metal-ions that are capable of giving ammonia complexes (Cu++,N1++,Zn++ and Ag+) were used. 

Another form of ion chromatography is ligand exchange chromatography where a cation exchange resin is used to separate analytes that can form coordination complexes with the metal attached to the resin. 

Chiral ligand-exchange chromatography is based on the formation of diastereomeric ternary complexes that involve a transition metal ion, chiral ligand, and the amino acid enantiomers. Among transition metals, Cu(II) formed the most stable complexes... 

Chiral ligand exchange chromatography can be performed either on an achiral stationary phase with a chiral mobile phase or on a chiral stationary phase IMAC is performed on the metal ion immobilized stationary phase. The latter two stationary phases may be symbolized by the same formula as... 

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