Supramolecular plasticity: The remarkable host–guest properties of phosphonate cavitands have been exploited in the self‐assembly of supramolecular polymers (see picture) that feature guest‐triggered reversibility and template‐driven conversion from linear into star‐branched forms. The structurally similar but complexation‐inefficient thiophosphonate cavitand acts as chain stopper to control the degree of polymerization.
This Communication reports the highly selective monomethylation of primary amines through host-guest product sequestration. Complete control of the outcome of the N-methylation reaction has been achieved by adding to the reaction medium stoichiometric amounts of a teraphosphonate phosphonate cavitand Tiiii, capable of selectively and quantitatively trapping the monomethylated ammonium salt formed. The synergistic combination of ion-dipole, H-bonding, and CH(3)-pi interactions provide the high association constants (K(ass) > 10(9)) and the specific complexation mode necessary for the exclusive sequestration of the monomethylated intermediate reaction product.
We report here the monitoring of reversible guest inclusion in phosphonate cavitands through a large increase in luminescence intensity caused by the modulation of the exoergonicity of an electron-transfer reaction.
Turning molecular recognition into an effective mechanical response is critical for many applications ranging from molecular motors and responsive materials to sensors. Herein, we demonstrate how the energy of the molecular recognition between a supramolecular host and small alkylammonium salts can be harnessed to perform a nanomechanical task in a univocal way. Nanomechanical Si microcantilevers (MCs) functionalized by a film of tetra-phosphonate cavitands were employed to screen as guests the compounds of the butylammonium chloride series 1-4, which comprises a range of low molecular weight (LMW) molecules (molecular mass< 150 Da) that differ from each other by one or a few N-methyl groups (molecular mass 15 Da). The cavitand surface recognition of each individual guest drove a specific MC bending (from a few to several tens of nanometer), disclosing a direct, label-free, and real-time mean to sort them. The complexation preferences of tetraphosphonate cavitands toward ammonium chloride guests 1-4 were independently assessed by isothermal titration calorimetry. Both direct and displacement binding experiments concurred to define the following binding order in the alkylammonium series: 2 > 3 ≈ 1 ≫ 4. This trend is consistent with the number of interactions established by each guest with the host. The complementary ITC experiments showed that the host-guest complexation affinity in solution is transferred to the MC bending. These findings were benchmarked by implementing cavitand-functionalized MCs to discriminate sarcosine from glycine in water.
Supramolekulare Plastizität: Die bemerkenswerte Wirt‐Gast‐Chemie von Phosphonatcavitanden wurde zum Aufbau selbstorganisierter supramolekularer Polymere genutzt (siehe Bild), die reversibel auf die Bindung von Gastspezies hin entstehen und je nach Templat von der linearen in eine sternförmig verzweigte Form wechseln. Ein Thiophosphonatcavitand mit ähnlicher Struktur, aber ohne Komplexierungsvermögen wirkt als Kettenende und bestimmt den Polymerisationsgrad.
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