Resorcinarenes are cyclic tetramers that are synthesized by the condensation of resorcinol and various aldehydes. The upper and lower rims can be modified with substituents that provide specific selectivity and other chemical features. In this work, resorcinarene-based macrocyclic ligands with specific selectivities have been designed, synthesized and applied to chiral amine discrimination and transition metal ion separations.These resorcinarenes fall into two categories. In the first type, the upper rims of resorcinarenes were modified with amino acid groups, including chiral alanine groups. The lower rims were modified with --CH3, or --C11H23 groups. The structures were studied by nuclear magnetic resonance (NMR), mass spectrometry (MS), dynamic light scattering (DLS), and sustained off-resonance irradiation collision induced dissociation (SORI-CID) techniques in Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). The binding strength between the resorcinarenes with amines was studied by 1H NMR titration. Among these new resorcinarenes, the chiral alanine undecyl resorcinarenes acid (AUA) showed chiral discrimination among chiral secondary amines. The AUA ligands were adsorbed onto 55% cross-linked styrene-divinylbenzene resin and used as cation-exchangers in ion chromatography (IC) for transition metal ion separations. The AUA IC column showed selectivity for Cu2+ when no chelating eluent was used in the eluent, a selectivity which was not observed with a commercial column containing standard cation-exchangers. Six metal ions (Cu2+, Mn2+, Co2+, Ni2+, Cd2+, and Zn2+) were separated on the AUA column within a reasonable time with a simple oxalic acid gradient eluent. The second type of resorcinarene-based ligand, cyclenbowl, contains four cyclen units on the upper rim and four --C11H23 chains on the lower rim. The column packed with cyclenbowl adsorbed onto polystyrene showed selectivity for Cu2+ over five other transition metal ions including Mn2+, Co2+, Ni2+, Cd2+, and Zn2+ ions. The preconcentration of Cu2+ at the parts per billion level from a high concentration matrix of Mn2+, Co2+, Ni2+, Cd2+, and Zn2+ ions was achieved using HNO3 eluent. Recovery of Cu2+ was greater than 98%. Furthermore, the other five transition metal ions were well separated on the cyclenbowl column with an oxalic acid eluent gradient.



College and Department

Physical and Mathematical Sciences; Chemistry and Biochemistry



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resorcinarene, chiral recognition, ion chromatography, selectivity, transition metal ions, preconcentration, macrocyclic ligands, separations