Shape-selective sensing of lipids in aqueous solution by a designed fluorescent molecular tube.

The design, synthesis, and recognition properties of two isomeric calixnaphthalene-type molecular tubes is described. The anti isomer showed strong fluorescence quenching upon titration with various simple lipid guests in water, in which the more hydrophobic guests associated with higher affinity. The syn isomer bound long straight-chain guests tightly with a similar fluorescence-quenching response. However, the syn isomer was more selective, giving an increase in fluorescence upon titration of guests which could not thread through the tube. Thus, the syn isomer is a selective fluorescent sensor for long straight-chain lipids.