The availability of crown ethers with cavities of different sizes allows specific cations to be solvated with a high degree of selectivity. From this point of view, this chapter is divided into five sections focusing on the properties of the compounds as well as the synthesis of macrocycles: (1) preparation of macrocycles, (2) macrocycles as molecular receptors for complexation, recognition, and sensing, (3) interlocked molecules such as rotaxanes and catenanes, (4) calixarenes and porphyrins containing crown ethers, (5) conjugated macrocycles. Synthesis of the sucrose-based di-aza-crown ethers 60.
The host-pair reagent (HR/HS-d6 = 1/1) is mixed with the guest compound (G, which represents the pure guest enantiomer or various compositions) and is ionized using FAB-MS or ESI-MS. Two diastereomeric H-G complex ions simultaneously appear in the single-stage MS spectrum. Ionophores such as valinomycin also display a marked preference for the potassium cation over other cations. Crown ethers are useful for dissolving ionic substances such as KMnO4 in organic solvents such as isopropanol [(CH3)2CHOH] (Figure 18.7.1). Another effort used a similar strategy in which tartaric acid subunits within the central macrocycle comprised the central unit and scaffold for the membrane spanning chains <1989JA767>. Chem. Synthesis of pyranoside-containing macrocycles 9–11. Examples of Separations Obtained on a (+)-(18-Crown-6)-2,3,11,12-Tetracarboxylic Acid-Based CSP. Ainsi, le 18-couronne-6 a une forte affinité pour le cation potassium K+, le 15-couronne-5 pour le cation sodium Na+ et le 12-couronne-4 pour le cation lithium Li+. Chiral linear hosts using peracetylated 2derivatives: (a) R = COCH3; (b) R = CH3 [88]. We use cookies to help provide and enhance our service and tailor content and ads. For more information contact us at info@libretexts.org or check out our status page at https://status.libretexts.org. Fig. The term "crown" refers to the resemblance between the structure of a crown ether bound to a cation, and a crownsitting on a person's head. Note how the cation is nestled within the central cavity of the molecule and interacts with lone pairs of electrons on the oxygen atoms. L'introduction du radioisotope du fluor (à savoir le 18F) sur des traceurs organiques destinés à la médecine peut être réalisé grâce aux éthers couronne. Copyright © 2020 Elsevier B.V. or its licensors or contributors. Gokel, E.K. Macrocycles of type 12, based on methyl 4,6-di-O-butyl-α-d-glucopyranoside, were prepared in an analogous way.38 Bakó et al. Scheme 4. CS-D1202. All crown ethers have a central cavity that can accommodate a metal ion coordinated to the ring of oxygen atoms., cyclic compounds with the general formula (OCH 2 CH 2) n. Crown ethers are named using both the total number of atoms in the ring and the number of oxygen atoms.