Abstract
The present work reports the synthesis and complexation properties of five mixed bridge P=O/P=S cavitands toward N,N-methyl butyl ammonium chloride (1) as prototype guest. The influence of number and position of P=O and P=S groups on the affinity of phosphonate cavitands toward 1 is assessed via ITC titrations in DCE as solvent. Comparison of the resulting Kass values, the enthalpic and entropic contributions to the overall binding with those of the parent tetraphosphonate Tiiii and tetrathiophosphonate TSiiii cavitands allows one to single out the simultaneous dual H-bond between the cavitand and the salt as the major player in complexation.
Highlights
Tetraphosphonate cavitands represent an interesting class of synthetic receptors featuring peculiar molecular recognition properties toward methyl ammonium guests [1,2]
Mixed-bridged phosphonate cavitands, featuring both P=O and P=S bridges, have been investigated in the context of alcohol sensing with Quartz Crystal Microbalance (QCM) transducers [8]
In the present work we investigate the influence of number and position of P=O and P=S groups on the affinity of phosphonate cavitands toward methyl ammonium salts as target guests
Summary
Tetraphosphonate cavitands represent an interesting class of synthetic receptors featuring peculiar molecular recognition properties toward methyl ammonium guests [1,2]. The origin of this selectivity has been identified in the synergistic presence of three different interactions, namely (i) N+O=P cation-dipole interactions; (ii) CH3-π interactions of the acidic +N-CH3 group with the π basic cavity [3];. One key issue which remains to be addressed is which is the influence of number and relative position of the P=O bridges on the receptor selectivity. Complete substitution of the P=O units with either P=S or methylene bridges has been shown to completely switch off complexation toward this class of guests [6,7].
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