Electrochemical Investigations into the Binding of Some Nonredox Active Metal Ions to Surface-Bound Glutamic Acid Conjugates

Abstract

A number of ferrocene glutamic acid cystamine conjugates suitable for the preparation of thin film on gold were prepared and fully characterized electrochemically and spectroscopically. In this study, we evaluate the interactions of nonelectroactive metal ions such as Ca2+ and Tb3+ ions using a combined electrochemical and spectroscopic approach. Cyclic voltammetry studies show a reversible one-electron redox behavior associated with the ferrocene group. These peptide interfaces exhibit a considerable affinity to bind Ca2+ and Tb3+ ions from aqueous solutions with log K ∼ 3. In the presence of metal ion, the charge associated with oxidation of the ferrocene group decreases in line with a blockage of the formation of Fc+/ClO4 - ion pair by the formation of an overlayer on top of the film, which essentially shuts down the oxidation of the Fc group. The resulting increase in the film thickness is monitored by X-ray photoelectron spectroscopy (XPS) and by a decrease in the capacitance as monitored by electrochemical impedance spectroscopy. XPS measurements show that the metal ions bind exclusively to the carboxylic acid and that the amide group is not involved in metal binding.

Ferrocene-peptido conjugates: From synthesis to sensory applications

“…17). 88 The bidentate coordination mode of Ca(II) and Tb(III) Fig. 15 Structure of Fc-conjugates as probes for the study of host-guest interactions.…”

“…Fig 17. Schematic representation of interactions between surface-bound Fc-Glu derivatives(50)(51) and Tb(III) and Ca(II) metal ions 88. …”

Voltammetric studies of dendrimer multilayers: Layer‐by‐layer assembly of metal‐peptide dendrimers multilayers

“…83,84 Effect of non-redox intervening dendrimer layers on electron transfer Schlenoff et al have shown that electron transfer through multilayer films was via electron hopping between neighboring sites which is facilitated by interpenetrating of alternate layers. 85,86 According to Schlenoff, upon reduction a negative charge is introduced into the multilayer and this is compensated by the intake of positive ions which they proved with the use of 45 Ca 2þ in solution. 87 Studies by Uosaki and coworkers on multilayer of gold nanoclusters (MG), ferrocenylhexanthiol-gold nanocluster (MGF), and polycation polyallylamine on MUA-Au electrode or Cu 2þ ion have shown that a quasi reversible redox peak with a constant charge corresponding to the redox reaction of the ferrocene was observed whether the MGF was placed closest to the electrode (first layer) or on the outermost layer.…”

“…Additionally, we have reported the synthesis of cystamine functionalized glutamic acid dendrimer analogues and demonstrated their deposition and interaction of metal cations Ca 2þ and Tb 3þ at the gold electrode interfaces. [45][46][47] The materials display strong intramolecular as well as intermolecular Hydrogen bonding with carboxylate interfaces and that the redox properties of the core are attenuated by the increase in the peptide dendritic sphere and metal ion interactions. In this study, we explore the use of these metal ions to assemble LbL films of peptide dendrimers.…”

“…We have recently reported the synthesized Fc based glutamic acid ester dendrimers and prepared their deposition on MUA functionalized monolayers on gold electrodes. Additionally, we have reported the synthesis of cystamine functionalized glutamic acid dendrimer analogues and demonstrated their deposition and interaction of metal cations Ca 2+ and Tb 3+ at the gold electrode interfaces 45–47. The materials display strong intramolecular as well as intermolecular Hydrogen bonding with carboxylate interfaces and that the redox properties of the core are attenuated by the increase in the peptide dendritic sphere and metal ion interactions.…”