Complexation of Trace Metal Ions by Ligands Anchored to Gold Surfaces Different than by Ligands Dissolved in Homogeneous Solutions

While the homogenous binding of metal ions by a wide range of organic and inorganic ligands has been studied using numerous methods and comprehensive data of the homogenous association constants are available for many metal ions, ligands and solvent systems, complied data involving heterogeneous binding by surface bound ligands do not exist. Only few methods have been developed and applied for studding and determining the heterogeneous stability constants of trace metal ions by organic ligands contain mercapto, amino, amide and carboxylate groups. We wish to report on new approaches for the determination of the heterogeneous binding constants of trace metal ions by ligands anchored to the gold surfaces. Yet, in order to extract reliable and meaningful thermodynamic values it is crucial that the interfaces be well-defined and homogenous otherwise the surface heterogeneous will allow extracting only the average of the thermodynamic values. Thiols and dithols, which have been the subject of intensive research and characterization during last two decades, appear to provide this prerequisite. Functionalized thiols have been used quite thoroughly for selectively interacting and extracting metal ions. Three different methods have been developed and include IR spectroscopy, electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SEM). Here we will use other new technique, the electrochemical quartz crystal nanobalance (EQCN). The EQCN, which is based on monitoring the mass of a metal ion (ng) bound to the ligand, is sensitive to changes in the total mass of the monolayer on gold electrode as a result of metal ion binding.