Final Report Summary - IEFACP (Novel Calix[4]arene Based Macrocyclic Heteroditopic Receptor Molecules for Ion-Pair Recognition and Interlocked Molecules Capable of Induced Molecular Motion.)
The design and application of new heteroditopic receptor systems capable of the simultaneous coordination of both cationic and anionic guest species has recently attracted a great deal of interest, as these systems have the potential to act as salt solubilisation, extraction, and membrane transport agents and sensors. Stimulated by the potential uses mechanically bonded molecules may have as molecular switches, sensors and machines, the interest being shown in discovering new imaginative and high yielding templation methods for their construction is ever increasing. The use of rotaxane and catenane cavities as binding domains for the recognition and sensing of guest species remains underdeveloped which is surprising given their unique three-dimensional topological interlocked cavity design. In addition such mechanically bonded 'host' molecules have the possibility of exhibiting unprecedented host-guest binding behaviour.
In this project we have prepared novel calix[4]arene based macrocyclic heteroditopic receptor molecules for ion-pair recognition and interlocked host molecules using halogen bonding (XB) anion templation.
Halogen bonding, is the attractive non-covalent interaction between an electron-deficient, polarized halogen atom, commonly bromine or iodine, and a Lewis base. Anions have been exploited extensively as XB acceptors in the solid state crystal engineering of conducting, magnetic and liquid crystalline materials. Given XB's complementary analogy to hydrogen bonding in terms of stringent directionality and bond strength, it is surprising that solution phase applications of XB in molecular recognition processes such as protein-ligand complexes, anion receptor chemistry and catalysis are only now beginning to emerge. In order to demonstrate the potential application of XB in anion and ion-pair recognition and it´s use in the anion templated construction of interlocked host systems, we have synthesized a novel bidentate halogen-bonding bromoimidazoliophane receptor which, via cooperative action of two preorganised bromine halogen bond donor atoms, is capable of selectively binding bromide strongly in competitive aqueous solvent media (Figure 1).
Importantly by comparison, the protic imidazoliophane receptor analogue is a non-selective weak binder of halide anions (Table 1)
A series of new potential XB threading components, 2-iodo-imidazolium halide ion-pair salts were successfully prepared and both solution phase and X-ray solid state structure determinations provided evidence of halide anion binding via halogen bonding (Figure 2).
1H NMR titration experiments between these XB salts and various isophthalamide containing macrocycles proved that the 2-iodo-imidazolium motif was capable of forming pseudorotaxanes, with an observed preference for chloride as the templating anion (Figure 3).
Taking into account these precedents, the first XB catenane (Figure 4) was synthesized via chloride and bromide anion templation.
After halide anion template removal 1H NMR titration experiments revealed the catenane host to selectively recognize chloride and bromide anions solely by halogen bonding, via cooperative action of two bromine halogen bond donor atoms.
Furthermore by virtue of the naphthalene groups the XB catenane was shown to optically sense Cl- and Br- anions using fluorescence spectroscopy.
A heteroditopic calix[4]diquinone macrocycle was demonstrated to form a series of ion-pair templated interpenetrated and interlocked molecular assemblies (Figure 5)
Building upon these promising results, a recently awarded ERC Advanced Grant will focus on the design of novel heteroditopic receptor molecules for lanthanide cation- anion ion pair recognition, which have a potentially powerful application in high contrast magnetic resonance imaging, and interlocked systems capable of sensing and analyte induced molecular motion.
In this project we have prepared novel calix[4]arene based macrocyclic heteroditopic receptor molecules for ion-pair recognition and interlocked host molecules using halogen bonding (XB) anion templation.
Halogen bonding, is the attractive non-covalent interaction between an electron-deficient, polarized halogen atom, commonly bromine or iodine, and a Lewis base. Anions have been exploited extensively as XB acceptors in the solid state crystal engineering of conducting, magnetic and liquid crystalline materials. Given XB's complementary analogy to hydrogen bonding in terms of stringent directionality and bond strength, it is surprising that solution phase applications of XB in molecular recognition processes such as protein-ligand complexes, anion receptor chemistry and catalysis are only now beginning to emerge. In order to demonstrate the potential application of XB in anion and ion-pair recognition and it´s use in the anion templated construction of interlocked host systems, we have synthesized a novel bidentate halogen-bonding bromoimidazoliophane receptor which, via cooperative action of two preorganised bromine halogen bond donor atoms, is capable of selectively binding bromide strongly in competitive aqueous solvent media (Figure 1).
Importantly by comparison, the protic imidazoliophane receptor analogue is a non-selective weak binder of halide anions (Table 1)
A series of new potential XB threading components, 2-iodo-imidazolium halide ion-pair salts were successfully prepared and both solution phase and X-ray solid state structure determinations provided evidence of halide anion binding via halogen bonding (Figure 2).
1H NMR titration experiments between these XB salts and various isophthalamide containing macrocycles proved that the 2-iodo-imidazolium motif was capable of forming pseudorotaxanes, with an observed preference for chloride as the templating anion (Figure 3).
Taking into account these precedents, the first XB catenane (Figure 4) was synthesized via chloride and bromide anion templation.
After halide anion template removal 1H NMR titration experiments revealed the catenane host to selectively recognize chloride and bromide anions solely by halogen bonding, via cooperative action of two bromine halogen bond donor atoms.
Furthermore by virtue of the naphthalene groups the XB catenane was shown to optically sense Cl- and Br- anions using fluorescence spectroscopy.
A heteroditopic calix[4]diquinone macrocycle was demonstrated to form a series of ion-pair templated interpenetrated and interlocked molecular assemblies (Figure 5)
Building upon these promising results, a recently awarded ERC Advanced Grant will focus on the design of novel heteroditopic receptor molecules for lanthanide cation- anion ion pair recognition, which have a potentially powerful application in high contrast magnetic resonance imaging, and interlocked systems capable of sensing and analyte induced molecular motion.