Ruthenium bipyridine complexes for the recognition of glucose

Bipyridine ligands containing pendant methyl, amino and amino-boronic acid groups were synthesized. Coordination complexes of these ligands with ruthenium were prepared straightforwardly and in good yield. The luminescence behavior of the Ru complexes was studied as a function of pH and exposure to various concentrations of glucose. The methyl bipyridine complex showed no change in luminescence with pH; the amino derivative showed a rapid decrease from low pH to neutral, and the amino-boronate derivative showed a gradual decrease from pH 4 to 10. Luminescence quenching was observed at high pH as expected on the basis of a photoinduced electron transfer (PET) signaling mechanism. This behavior can be explained on the basis of the first oxidation and reduction potentials of these complexes. Glucose testing showed a significant dependence on the solvent system used. In pure methanol, the ruthenium boronate complex exhibits a 4 and 10% luminescence intensity increase upon increasing glucose concentration from 0 to 400 and 0 to 1600 mg/dl, respectively. However, in 50 vol.% methanol/phosphate buffered saline, none of the complexes showed significant response in the glucose range of physiological interest.