Specific Supramolecular Interactions between Zn2+-Salophen Complexes and Biologically Relevant Anions

Recognition of inorganic phosphates PO4 3-, P2O74-, and P3O105- and nucleotides AMP2-, ADP3-, and ATP4- by Zn2+-salophen complexes 1 and 2 in ethanol was investigated by different spectroscopic techniques. 31P NMR and mass spectrometry showed that anions of both series are bound by 1 and 2, while absorption and emission studies revealed that only nucleotides produce relevant changes in the spectral properties of the two hosts. 1H NMR studies proved that the adenine aromatic group is involved in the complexation, thus pointing out the role of supramolecular ditopic receptors played by salophen derivatives toward this class of biologically relevant substrates. The lifetime of the photogenerated triplet state of the Zn2+-salophen compounds was measured by nanosecond laser flash photolysis, and the observed changes upon increasing the concentration of nucleotides allowed the identification of the formation of a 1:0.5 host/guest intermediate complex additionally to the formation of a 1:1 complex.