Macrocyclic ligands classification

Macrocyclic ligands will be classified, for the purposes of this article, as rings with at least nine members and three or more donor atoms. In a number of cases of unique structural units, elegant descriptive names have developed, which more appropriately describe the macrocyclic shape. Macrocycles will be classified as to donor types and, within the donor types, specific classifications of macrocycles will be noted where applicable. 

The nature of the donor atoms is one of the most important characteristics of macrocyclic ligands [11] and has been employed as a criterion for a classification of macrocyclic compounds. The classification of the macropolycyclic encapsulating ligands is based on the nature of the donor atoms and the type of donor groups that appear to be the best. 

While this work did not involve the use of macrocyclic ligands, the classification system used reveals several principles which are pertinent to macrocycle-metal ion binding. Further study is required to determine if Ais system can be extended to the rational design of macrocyclic ligands. 

Poon and Mak have classified the reactivities of a range of macrocyclic ligand complexes of the type /ra 5-[Co(L)(X)(Y)]+ (L=quadridentate N-donor macrocycle X and Y unidentate anionic ligands with X the leaving group) into three categories as shown in Table 30. Those ions in classification I react with a rate-determining proton transfer and kon=ki reactions (30)—(32), and at... 

Different classifications for the chiral CSPs have been described. They are based on the chemical structure of the chiral selectors and on the chiral recognition mechanism involved. In this chapter we will use a classification based mainly on the chemical structure of the selectors. The selectors are classified in three groups (i) CSPs with low-molecular-weight selectors, such as Pirkle type CSPs, ionic and ligand exchange CSPs, (ii) CSPs with macrocyclic selectors, such as CDs, crown-ethers and macrocyclic antibiotics, and (iii) CSPs with macromolecular selectors, such as polysaccharides, synthetic polymers, molecular imprinted polymers and proteins. These different types of CSPs, frequently used for the analysis of chiral pharmaceuticals, are discussed in more detail later. 

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