Metal ion recognition and molecular templating in self-assembled monolayers of cyclic and acyclic polyethers

Abstract

Our recent work with cyclic and acyclic polyether self-assembled monolayers (SAMs) on gold is presented. A series of dithia-crowntetrathiafulvalene derivatives with one or two disulfide groups has been prepared, and their SAMs on gold have been characterized by electrochemistry and by reflection-absorption infrared spectroscopy. These SAMs are extremely stable on repeated electrochemical potential scans and can selectively recognize alkali metal ions. Acyclic polyether derivatives can also self-assemble on gold to yield selective metal ion recognition domains. Impedance spectroscopy data for these SAMs fit the Langmuir isotherm and allow the determination of ion association constants. Some of the SAMs prepared with new acyclic polyether derivatives are able to detect potassium cations selectively when templated in their presence. These structures are believed to be a consequence of ion ''imprinting'' during the process of SAM formation.T he easy preparation, stability, and versatility of self-assembled monolayers (SAMs) has resulted in considerable activity in this field since the first publication by Nuzzo and Allara (1). Molecular recognition is especially relevant on surfaces because it allows the control of the exchange of signals, structures, and energy through the interfaces (2-4). SAMs allow the introduction of functional groups in the adsorbates, thus offering a powerful way to develop systems that have applications as sensors, devices, and switches (5). Some recent articles have reported surface structures with hydrophobic and hydrophilic properties arranged in nano-strips and honeycomb or homogeneous structures (6), whereas others have detected photo and electrochemical conversion of cis to trans forms within the SAM (7). Other examples have shown the formation of chiral imprinted sites (8). SAM structures have also been prepared for the recognition and sensing of metal ions (9), some of which are electrochemically active (10-18).Relatively recently, and Bryce et al. (23,24) reported, almost simultaneously, the incorporation of crownether groups into SAMs and their use as potential metal ion sensors. The Reinhoudt group used electrochemical impedance spectroscopy (EIS) for SAM characterization and to study the ion recognition processes (19)(20)(21)(22). This technique enables the detection of interfacial ion recognition phenomena when both guest ion and host monolayer are electrochemically inactive, by detecting changes of the charge-transfer resistance induced by metal ion binding (see Fig. 1a; refs. 25 and 26). The report by Bryce et al. (23,24) described SAMs of crown-annelated tetrathiafulvalene (TTF) derivatives, which showed, by cyclic voltammetry (CV), a redox potential shift of the electroactive, surface-confined, crown-TTF group on ion complexation (23, 24). The first TTF-crown SAMs reported by this group were apparently unstable after several electrochemical scans (23). However, in a subsequent report they demonstrated that the stability and electrochemical behavior of the SAMs can be improv...

Electron Transport through Cyclic Disulfide Molecular Junctions with Two Different Adsorption States at the Contact: A Density Functional Theory Study

“…The density functional theory (DFT) QM calculations on finite clusters (Au 28 ) were carried out using Jaguar v5.5 software. 46 The three-layer 28-atom cluster Au 28 (9,10,9) (as shown below in Figure 3, section 3.2) has been established to be the minimum cluster size required for an accurate representation of the (111) surface of the fcc metal. 47 It was cut from a bulk Au crystal with an experimental lattice parameter of 4.08 Å, which corresponds to the nearest-neighbor AusAu distance of 2.88 Å.…”

“…3 Compounds such as 1,2-dithiolane-3-pentanoic acid (also known as thioctic acid, lipoic acid, or 1,2-dithiolane-3-valeric acid) have been used for various applications such as molecular switches, molecular machines, sensors, and protein immobilization. [4][5][6][7][8][9][10][11][12][13][14] A prominent example is the bistable Stoddart-Heath-type [2]rotaxane (1) anchored to gold electrodes, 4,15 which has already proved useful as a molecular switch. 15,16 The switch 1 is turned on and off reversibly upon the redoxinduced shuttling of the cyclobis-(paraquat-p-phenylene) (CB-PQT, blue) ring between two stations, tetrathiafulvalene (TTF, green) and 1,5-dioxynaphthalene (DNP, red).…”

Adsorption of crown ethers on single and polycrystalline platinum-electrodes

“…The complex formation was only indirectly monitored by measuring the influence of the incorporated cations on the redox current of [Ru(NH 3 ) 6 ] 2+, 3+ as ''report ion''. Besides cyclic polyethers, like different dithia-crown-tetrathiafulvalene, acyclic polyether had been investigated on gold bead electrodes [5]. Here, by a way of ''imprinting'' during the formation of the self assembled monolayers SAMS, in the presence of the cations, selective, chemically modified electrodes had been created.…”

Studying the binding of Cd2+ by ω-mercaptoalkanoic acid self assembled monolayers by cyclic voltammetry and scanning electrochemical microscopy (SECM)

“…Systems for the simultaneous detection of Cd 2+ and Zn 2+ [12], Pb 2+ and Hg 2+ [13] and other combinations [1,11,[14][15][16][17][18][19][20][21][22] have been reported. Significant work has been carried out in designing selective interfaces for various metal ions [23][24][25][26][27][28][29][30][31][32][33] using SAMs bearing crown ethers.…”