Calix[5]arenes Based Supramolecular Capsules Via Mulitple Hydrogen Bonding Mediated Self-assembly

Container molecules with isolated,nanometer-sized cavities,especially reversible supramolecular capsules mediated by noncovalent interactions such as hydrogen bonding,electrostatic interaction,halogen bonding,hydrophobic interaction,and metal coordination et c.,have become a hot research topic in supramolecular chemistry,mainly because of their irreplaceable role in the study of special physical and chemical behavior of guest molecules in confined space and potential applications in the fields of controlled drug release,catalysis,materials science and biomedicine et c.In the current thesis,we designed and synthesized a series of calix[5]arenes endowed with multiple hydrogen binding sites to study their self-assembly behavior of forming supramolecular capsules in non-polar solvents.In the first part of the thesis,we synthesized calix[5]arenes with five UPy motifs and five NAPy motifs.¹H NMR study confirmed preliminarily that hydrogen bonding mediated random aggregates were formed in non-polar solvents.After the addition of competitive solvents such as CF₃COOH or DMSO,the aggregates were destroyed to release free monomers.A lot of guest molecules including C₆₀,C₇₀,tetrabutyl ammonium halide,pyridine-N-oxide,et c,could not induce penta?UPy?calix[5]arene to form a homo dimeric supramolecular capsule.¹H NMR study returned no evidence for formation of a hetero dimeric supramolecular capsule upon 1:1 mixing penta?UPy?calix[5]arene and penta?NAPy?calix[5]arene in non-polar solvent.Further efforts are needed for the discovery of self-assembly conditions.In the second part of the thesis,two calix[5]arenes equipped with five Hamilton receptor motifs and five cyanuric acid guest motifs respectively,were synthesized and their structures were confirmed by ¹H NMR,¹³C NMR and MALDI-TOF MS.After screening different types of potential guest molecules via ¹H NMR,we found finally that 4-methylpyridine-N-oxide could be encapsulated as a guest in the hetero dimeric supramolecular capsule formed from Penta?Hamilton receptor?calix[5]arene and Penta?cyanuric acid?calix[5]arene.Hydrogen bonding between NHs on the capsule and N⁺-O^-on the guest,and C-H···?interaction from CH₃ on the guest and aromatic on the capsule are the critic driving forces for guest encapsulation by the capsule.Addition of hydrogen bonding competitive solvent such as DMSO can disrupt the capsule to release the guest molecule.The optimal ratio of the guest and the capsule was determined to be 15:1 via NMR titration experiment.The guest induced formation of the supramolecular capsule was further confirmed via UV-vis spectroscopy.