Recognition properties of phosphorylated cavitands

Phosphonate cavitands

Phosphonate cavitands are an emerging class of synthetic receptors for supramolecular sensing. We have developed the chemistry of these original hosts for several years. In the last decade we have established collaboration with the group of E. Dalcanale in Parma (Italy), where are developed different sensor devices for the detection of various analytes. In this context, our experience in the synthesis of phosphorylated cavitands allowed to investigate further their extraordinary complexation properties. Recently, the molecular recognition properties of the 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. Quartz Crystal Microbalance (QCM) measurements then validated the predictive value of such information for sensing applications. The importance of energetically equivalent multiple interactions on sensor selectivity has been demonstrated by comparing the molecular recognition properties of tetraphosphonate cavitands with those of their mono and diphosphonate counterparts (Chem. Eur. J. 2008).

Phosphorylated cavitands form strong associations with ammonium partners. We used this property to elaborate supramolecular association with original structure and properties. For instance, in this context iii-phosphorylated cavitands incorporating a N-methyl-pyridinium guest moiety as fourth bridging unit form supramolecular associations by inclusion of the charged CH3N⁺-pyridinium head into a neighboring host cavity. The dimeric association is favored in solution and was characterized by NMR, mass spectrometry, DOSY experiments and single crystal X-ray analysis (J. Org. Chem. 2009).

In the same way, four tetra-phosphorylated TiiiiPO cavitands encapsulated the pyridinium heads of a tetra-(N-methylpyridinium)-porphyrin iodide to form a 4:1:4 (host)₄/guest⁴⁺/4I^- complex. The single crystal X-ray diffraction analysis shows the arrangement of the four cavities bound to the CH3N⁺ groups of the porphyrin moiety and the four iodide anions nested between the phenethyl substituents of the hosts. ¹H-NMR investigations show that the structure is preserved in chloroform solution and underline the effect of the counter-anions (J. Org. Chem, 2007).