Sensing of molecular chirality on an electrode modified with a clay-metal complex hybrid film

A chiral sensing electrode has been prepared by coating an indium tin oxide (ITO) substrate with a hybrid film of metal complexes and a clay layer (montmorillonite). By applying the combined method of the Langmuir-Blodgett and self-assembly techniques, a monolayer of a water-soluble chiral metal complex (A[Os(phen)3] 21), which acted as a mediator of oxidizing a target molecule, was fixed electrostatically onto a single-layered clay film. Chiral sensing was demonstrated by monitoring a photocurrent when the electrode was in contact with an aqueous NaClO4 solution of 1,1 '-2-binaphthol. As a result, the S-1,1 '-2-binaphthol gave a photocurrent 1.8 times higher than the R-isomer at the applied potential of 700 mV (vs Ag vertical bar AgCl vertical bar KCl-(sat)). Detection limit was determined to be 40 mu M from the concentration dependence of a response current. Mechanisms for chiral sensing effect were explained in terms of the stereoselective binding of 1,1 '-2-binaphthol with adsorbed Lambda-[Os(phen)(3)](2+) on a clay surface.