Recognition and Sensing of Nucleoside Monophosphates by a Dicopper(II) Cryptate

The dicopper complex of a bis-tren cryptand in which the spacer consists of two furane subunits connected in 2,2' by a -CH2- fragment selectively recognizes guanosine monophosphate with respect to other nucleoside monophospates (NMPs) in a MeOH/water solution at pH 7. Recognition is efficiently signaled through the displacement of the indicator 6-carboxyfluorescein bound to the receptor, monitoring its yellow fluorescent emission. Titration experiments evidenced the occurrence of several simultaneous equilibria involving 1:1 and 2:1 receptor/NMP and receptor/indicator complexes. It was demonstrated that the added NMP displaces the indicator from the 2:1 receptor/indicator complex, forming the 1:1 receptor/ analyte inclusion complex. Recognition selectivity is thus ascribed to the nature of nucleotide donor atoms involved in the coordination and their ability to encompass the CuII-CuII distance within the cryptate.