Molecular recognition of nucleosides and nucleotides by a water-soluble cyclo-bis-intercaland receptor based on acridine subunits

The macrocyclic bisacridine receptor 1 prepared by diamine-dialdehyde condensation has been found to complex nucleotides strongly in water. The important changes of the fluorescence properties of 1 upon complexation revealed the remarkable ability of the receptor to discriminate between the two types of nucleobase: addition of purine nucleotides produced a strong quenching of the emission whereas a considerable enhancement of the fluorescence intensity was induced by pyrimidine nucleotides. By comparison with the binding properties of the acyclic monochromophoric reference compound 7 these opposite variations of the fluorescence have been interpreted in terms of electronic interaction (π/π stacking) and conformational changes of the receptor 1 (increase of the interchromophoric distance). The stability constants were determined by fluorescence measurements and high values ranging from 104 to 108 M−1 were obtained for the 1/1 complexes. The selectivities observed were shown to be dependent on both electrostatic and structural factors.