BIOMIMETIC ION-BINDING MONOLAYERS ON GOLD AND THEIR CHARACTERIZATION BY AC-IMPEDANCE SPECTROSCOPY

Novel ion-binding monolayers on gold surfaces are presented where the molecular design is based upon the natural ion binder ferrichrome. The new ion binders possess hydroxamate coordinating groups arranged in C -2 symmetry (bishydroxamate binder, BHB) or C-3 symmetry (trishydroxam ate binder, THB), and a separate dialkyl sulfide moiety, which serves as an anchor to the gold substrate. The separation between the ion-bin ding cavity and the attachment site to the gold allows each parameter to be controlled separately, namely, cavity size, its symmetry and ext ernal envelope. as well as,he functional group used for immobilization . The monolayers were characterized with respect to ellipsometric thic kness, wettability (advancing and receding contact angles (CAs) for wa ter), and surface coverage; the latter is determined by metal underpot ential deposition (UPD). It is shown that the introduction of hydropho bic side chains (i-butyl) improves the CAs, thickness, and surface cov erage of the monolayers. A detailed analysis of the alternating-curren t (AC) impedance spectra is presented for THB monolayers on gold elect rodes, where the impedance data are fitted to an equivalent circuit mo del. It is shown that the AC response in a wide frequency range can be used to probe ion binding and release in monolayer systems on electro des.