Frustrated ion-pair binding by heteroditopic macrocyclic receptors

Abstract

A series of Ag⁺ complexes of the macrocyclic heteroditopic receptor, 4-phenylurea-benzo-15-crown-5 (1) have been prepared from hydrophobic- (,) and oxo- (, ) anion salts. These complexes contain the Ag⁺ cation, partially interacting with the macrocyclic cavity and the anions H-bonded to urea moieties. Additional interactions of the Ag⁺ cation with a –C = O moiety of a neighbouring receptor 1 molecule or with the oxo-anions (, ) have been observed. K_ass values calculated for the resulted ion-pair macrocyclic complexes , , , were fitted with 1:1 model and correspond to the values of 140, 255, 660 and 980 M^− 1, respectively. The cooperative anion/urea and cation/macrocycle binding and their interaction favour the whole recognition process. This synergism is amplified by self-assembly and depends on the structural features of the anion. In the combined system, the cation–anion interactions are favourable for the stability of the whole system.

Keywords::

• ion-pair recognition
• crown-ethers
• silver salts
• H-bonding
• urea
• self-assembly

Notes

^1. Strong Ag⁺ binding behaviours have been reported for 18-crown-6 macrocycle, dimensionally adapted to fit the cation-see Ref. (2).

Additional information

Funding

This work was financially supported by DYNANO, PITN-GA-2011-289033 (http://www.dynano.eu); European Union's Seventh Framework Programme (FP7/2007-2013) [grant number 264115] – STREAM and by funds from the Romanian National Authority for Scientific Research, CNCS – UEFISCDI grant, project number PN-II-ID-PCCE-2011-2-0028 contract 4/30.05.2012.