Complexation chromatography ligand exchange

Type IV When the solute is part of a diastereomeric metal complex (chiral ligand-exchange chromatography)... 

Chiral ligand-exchange chromatography (CLEC) ° separates enantiomers by the formation of diastereomeric metal complexes. In a first instance the technique was mainly used for the separation of amino acids. Impressive results of the first separations gave rise to intensive investigation in the field and numerous publications appeared in the literature, which have been reviewed. 

Based on preliminary results from Helfferich130, further developments by Davankov and co-workers5 131 133 turned the principle of chelation into a powerful chiral chromatographic method by the introduction of chiral-complex-forming synlhetie resins. The technique is based on the reversible chelate complex formation of the chiral selector and the selectand (analyte) molecules with transient metal cations. The technical term is chiral ligand exchange chromatography (CLEC) reliable and complete LC separation of enantiomers of free a-amino acids and other classes of chiral compounds was made as early as 1968 131. 

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... 

Ligand exchange chromatography is a very powerful method for separating enantiomers. However, it is limited to enantiomeric compounds that are able to undergo metal complexes with the chiral stationary phase such as amino acids, amino acid derivatives, and amino alcohols. 

V. A. Davankov, Ligand exchange chromatography of chiral compounds, in D. Cagniant (ed.), Complexation Chromatography, Marcel Dekker, New York, 1992, p. 197. 

A. M. Rizzi, Efficiency in chiral high performance ligand exchange chromatography. Influence of complexation process, flow rate and capacity factor, J. Chromatogr. A 542 (1991), 221. 

Another molecular rect nition force is the metal-complex formation realized in chiral ligand-exchange chromatography (CLEC). The technique was first proposed by Helf-ferich ]400] and was turned into a powerful chromatographic technique by Davankov and co-workers [8,401 j. This technique is based on a reversible chelate-complex forma-... 

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. 

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