Nanocapsules of unprecedented internal volume seamed by calcium ions

The inception of an unprecedented class of voluminous Platonic solids displaying hierarchical geometry based on pyrogallol[4]arene moieties seamed by divalent calcium ion is described. Single-crystal X-ray structural determination has established the highly conserved geometry of two original Ca2+-seamed nanocapsules to be essentially cubic in shape with C-ethylpyrogallol[4]arene units located along the twelve edges of the cube which are then bridged by metallic polyatomic cations ([Ca4Cl](7+) or [Ca(HCO2)Na-4](5+)) at the six cube faces. The accessible volume of the nanocapsules is ca. 3500 & ANGS;(3) and 2500 & ANGS;(3) and is completely isolated from the exterior of the capsules. These remarkable nanocapsule discoveries cast a spotlight on a marginalized area of synthetic materials chemistry and encourage future exploration of diversiform supramolecular assemblies, networks, and capsules built on calcium, with clear benefits deriving from the intrinsic biocompatibility of calcium. Finally, a proof-of-concept is demonstrated for fluorescent reporter encapsulation and sustained release from the calcium-seamed nanocapsules, suggesting their potential as delivery vehicles for drugs, nutrients, preservatives, or antioxidants.

Automated summary

A new class of voluminous crystalline compounds formed by divalent calcium ion binding to pyrogallol[4]arene-based hierarchical geometries has been discovered. The structures of these nanocapsules, determined through single-crystal X-ray analysis, show a highly conserved cubic shape with C-ethylpyrogallol[4]arene units along the cube edges, bridged by metallic polyatomic cations. The nanocapsules have an isolated volume of approximately 3500 &ANGS;(3) and 2500 &ANGS;(3). This discovery opens up possibilities for exploring diverse supramolecular assemblies, networks, and capsules using calcium, with potential applications in drug delivery, nutrition, preservation, and antioxidants.