ELECTROCHEMICAL DETECTION OF ELECTROCHEMICALLY INACTIVE CATIONS BY SELF-ASSEMBLED MONOLAYERS, OF CROWN-ETHERS

Self-as sembled monolayers (SAMs) of 2-[(6-mercaptohexyl)oxy]methyl-12 -crown-4 (1) and 2-[(6-mercaptohexyl)oxy]methyl-15-crown-5 (2) on gold are able to bind cations reversibly from aqueous solutions. This bind ing of the electrochemically inactive cations is monitored by cyclic v oltammetry and impedance spectroscopy using the redox couple Ru(NH3)(6 )(2+/3+) as ''reporter ion''. Gold electrodes modified with 1 detect N a+ even in the presence of a 100-fold excess of K+; SAMs of 2 are K+ s elective. As a result of the high surface density of crown ethers, san dwich complexes are formed. Reduced surface concentrations of receptor s in mixed monolayers of 2 with heptanethiol prevent the sandwich comp lexation and decreases the K+/Na+ selectivity of the SAM.