CO2 capture by multivalent amino-functionalized calix[4]arenes: self-assembly, absorption, and QCM detection studies.

The reactivity of CO(2) with polyamino substrates based on calix[4]arenes and on a difunctional, noncyclic model has been studied. All the compounds react with CO(2) in chloroform to form ammonium carbamate salts. However, the number, topology, and conformational features of the amino-functionalized arms present on the multivalent scaffold have a remarkable influence on the reaction efficiency and on the product composition.

Supramolecular control of single-crystal-to-single-crystal transformation through selective guest exchange.

Guest-switchable crystals: A solid-state guest exchange of the tetraphosphonate cavitand Tiiii[H,CH(3),Ph] as host promotes single-crystal-to-single-crystal transformations (see graphic). The strong preference for methanol over water is observed in all three phases (gas, liquid, solid), thus demonstrating the fundamental role played by the preorganized cavity through synergistic H-bonds and C-H⋅⋅⋅π interactions.

Formation of tetrameric water clusters driven by a cavitand template.

We describe an innovative approach to the generation of tetrameric water clusters in the solid state. The specific H-bond pattern induced by the tetraphosphonate cavitand template via its rigidly preorganized P=O acceptor groups leads to the exclusive formation of the unique cyclic homodromic water tetramer of C(4) symmetry.

Molecular recognition on a cavitand-functionalized silicon surface.

A Si(100) surface featuring molecular recognition properties was obtained by covalent functionalization with a tetraphosphonate cavitand (Tiiii), able to complex positively charged species. Tiiii cavitand was grafted onto the Si by photochemical hydrosilylation together with 1-octene as a spatial spectator. The recognition properties of the Si-Tiiii surface were demonstrated through two independent analytical techniques, namely XPS and fluorescence spectroscopy, during the course of reversible complexation-guest exchange-decomplexation cycles with specifically designed ammonium and pyridinium salts.

Supramolecular sensing with phosphonate cavitands.

Phosphonate cavitands are an emerging class of synthetic receptors for supramolecular sensing. The molecular recognition properties of the third-generation tetraphosphonate cavitands toward alcohols and water at the gas-solid interface have been evaluated by means of three complementary techniques and compared to those of the parent mono- and diphosphonate cavitands. The combined use of ESI-MS and X-ray crystallography defined precisely the host-guest association at the interface in terms of type, number, strength, and geometry of interactions.