The effect of surface attachment on ligand binding: studying the association of Mg²⁺, Ca²⁺and Sr²⁺by 1-thioglycerol and 1,4-dithiothreitol monolayers

Abstract

The difference in the heterogeneous binding of Mg(2+), Ca(2+) and Sr(2+) ions by 1-thioglycerol (TG) and 1,4-dithiothreitol (DTT) spontaneously adsorbed monolayers on Au has been studied following the changes in the double layer capacity. A mathematical treatment, based on calculating the electrochemical potential difference at the monolayer-electrolyte interface, has followed our recent work which dealt with the acid-base equilibrium at the interface as a means of calculating the pK of ionizable SAMs and their binding with Cd(2+). Experimentally, spontaneously adsorbed monolayers of TG and DTT were assembled on Au surfaces and studied by impedance spectroscopy and alternating current voltammetry (ACV). The capacity was measured for each of the modified surfaces at increasing concentrations of the divalent metal ions separately. The goal of this study has been to examine the effect of metal ion binding by similar ligands that are differently attached onto the surface. TG and DTT monolayers differ in their flexibility, which is a result of their attachment to the surface through one and two arms, respectively. The general trend of the apparent heterogeneous association constants of the divalent metal ions, which were calculated from the capacity measurements, was substantially different from the classical Irving-Williams series that is applicable to homogeneous systems. This difference could be nicely explained by the reduction of the degree of freedom and flexibility of the attached ligands.

Self-assembled dithiothreitol on Au surfaces for biological applications: phospholipid bilayer formation

“…1). DTT SAMs have been used to bind Ag + cations, 26 to immobilize gold nanoparticles, 27 to study heterogeneous binding of divalent metals, 28 and also to provide an hydroxylated substrate for sol-gel synthesis. 29 It has been reported that DTT self-assembly on Au(111) changes the contact angles of a water droplet on gold from 501 to 381.…”

Alkylthiol self-assembled monolayers on Au(111) with tailored tail groups for attaching gold nanoparticles

“…For example, -CH3 and -CF3 as tail groups make the SAM surface hydrophobic, metallophobic and highly anti-adherent, [36], while -COOH, -NH2 or -OH tail groups yield hydrophilic surfaces with good metal ion and protein binding properties [3,25,45]. Among tail groups a very popular one is the -SH (thiol) end-group since it allows attaching various nanoobjects (noble metal 3 nanoparticles, nanorods, etc) to a gold substrate or cross-link them between each other [5,6,18,27,32,34,48].…”

Electrochemical Renewal of Stationary Mercury Drop or Meniscus Electrodes

“…Dithiothreitol (DTT) -a four carbon a-w dithiol with hydroxyl groups on the second and third carbons -is frequently used as a reducing agent in isolation and storing of proteins in their reduced state. Electrochemical behavior of DTT was studied at gold [10], silver [39] as well as at mercury electrodes [40]. In this paper we measured the dependence of peak S (at about À 0.45 V) of DTT (Figs.…”