Nanocapsules of unprecedented internal volume seamed by calcium ions

Nanotoroids or Coordination Networks: Molecular Constructs at the Mercy of Anions

Pyrogallol[4]arene (PgC) macrocycles, owing to their preorganized structures, are known to form dimeric (M8L2), hexameric (M24L6), and dodecameric (M24L12) nanocapsules, as well as coordination networks. However, the role of anions in the formation of varied geometries and stoichiometries of PgCs is understudied. In this study, we explore the assembly of pyrogallol[4]arene with strontium iodide, forming metal-organic nanotoroids (M10L8), and with strontium nitrate, which forms coordination networks. Preliminary fluorescence spectroscopy experiments with dyes such as coumarin 153 and Nile red confirm that these nanotoroidal channels can effectively host dye molecules, making them suitable for diverse applications, including drug delivery. Furthermore, the nanotoroids and surface defects of the crystals can serve as a template to grow gold nanosheets.

Supramolecular Handshakes: Characterization of Urea-Carboxylate Interactions Within Calixarene Frameworks

The research of molecular capsules offers high application potential and numerous benefits in various fields. With the aim of forming supramolecular capsules which can be reversibly assembled and dissociated by simple external stimuli, we studied interactions between calixarenes containing urea and carboxylate moieties. To this end two ureido-derivatives of p-tert-butylcalix[4]arene comprising phenylureido-moieties and diacetate-calix[4]arenes were prepared. The binding of acetate by ureido-derivatives of calixarene in acetonitrile was characterized, revealing high affinity of ureido-calixarenes for carboxylates. This suggested high potential for uniting the complementary calix[4]arenes via H-bonds between carboxylic groups and urea moieties. The assembly of calixarenes was examined in detail by means of UV, 1H NMR, ITC, DOSY, MS, and conductometry providing insight in the structure-stability relationship. The tetraureido-calixarene derivative formed the most stable heterodimers with diacetate-calix[4]arenes featuring practically quantitative association upon mixing the two calixarene counterparts. The possibility of controlling the formation of the heterodimer by protonating the carboxylates, thereby hindering the interactions critical for capsule assembly, was investigated. Indeed, the reversibility of breaking and re-forming the heterodimer by addition of an acid and base to the solution containing urea- and carboxylate-derivative calix[4]arene was demonstrated using NMR spectroscopy.

Hierarchical 2D honeycomb-like network from barium-seamed nanocapsules

We report on a two-dimensional hexagonal "honeycomb" network comprising barium-seamed metal-organic nanocapsules involving a hexameric assembly of pyrogallol[4]arene ligands. The incorporated barium ions act as spacers to generate a solvent-accessible void, hierarchical self-assembly having an individual void volume near 13 000 Å3. This work illustrates the surprising chemistry that remains to be discovered by integrating large or classically non-reactive metal ions within supramolecular assemblies, networks, and organic nanocapsules.