Macrocycles with both acidic and basic functionalities

4 Macrocycles with both acidic and basic functionalities 

Many polyazamacrocycles have been alkylated with chloroacetic acid leading to compounds which contain both amine and carboxylic acid functions, e.g. [63] (Stetter et al., 1981). These compounds are similar to EDTA (ethylenediamine tetraacetate). Although the ring size of this class of macrocycles and the number of N—CH2—COOH groups has been modified 

In the polyazamacrocyclic phenols [64], an acidic function, the phenol group, has an intra-annular orientation while the basic units, the nitrogen atoms of the macrocycles, have no defined orientation. In water at 25°C, the pATa values of the phenols were measured and compared with those of other macrocyclic and non-macrocyclic phenols (Kimura et al., 1987a,b). Because the nitrogen atoms and the phenol function both possess acid-base properties, more than one pXg value could be measured. By the use of UV measurements, the values of the phenol group could be distinguished from those of the amines. 

When the neutral macrocycles [64] were dissolved in solvents other than water, equilibria between the neutral forms and betaine structures were also found. In ethanol, the equilibrium between a phenol and a betainic 

There are some examples where acids and bases are both incorporated in intra-annular fashions in the same macrocycle (Cram and Trueblood, 1981 Bell et al., 1982 Uiterwijk et al., 1986). In Table 28 such a macrocycle [66] is compared with compounds discussed in Sections 2 and 3. 

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