Design, synthesis and recognition properties of urea-type anion receptors in low polar media

The binding efficiency of simple receptors bearing two NH hydrogen-bond donor groups, of general formula PhCH2NH-Y-NHPh (Y = C=N-Ts, SO2, CS, CO), towards selected anion guests has been evaluated in chloroform solution in order to assess the effect of the nature of different binding sites incorporated into the receptor scaffold. Experimental results together with molecular mechanics and quantum chemical calculations have revealed that the nature of the spacer Y induces important electronic effects and conformational changes that lead to different degrees of preorganisation of the NH binding groups. In addition, the synthesis and binding properties of new lipophilic urea-based receptors, having electron-withdrawing alkylsulfonyl substituents (SO2C8H17) and characterised by enhanced NH hydrogen-bond donor ability, is reported. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).