Electrochemical SEIRAS Analysis of Imidazole-Ring-Functionalized Self-Assembled Monolayers

Abstract

An essential amino acid, histidine, has a vital role in the secondary structure and catalytic activity of proteins because of the diverse interactions its side chain imidazole (Im) ring can take part in. Among these interactions, hydrogen donating and accepting bonding are often found to operate at the charged interfaces. However, despite the great biological significance, hydrogen-bond interactions are difficult to investigate at electrochemical interfaces due to the lack of appropriate experimental methods. Here, we present a surface-enhanced infrared absorption spectroscopy (SEIRAS) and density functional theory (DFT) study addressing this issue. To probe the hydrogen-bond interactions of the Im at the electrified organic layer/water interface, we constructed Au-adsorbed self-assembled monolayers (SAMs) that are functionalized with the Im group. As the prerequisite for spectroelectrochemical investigations, we first analyzed the formation of the monolayer and the relationship between the chemical composition of SAM and its structure. Infrared absorption markers that are sensitive to hydrogen-bonding interactions were identified. We found that negative electrode polarization effectively reduced hydrogen-bonding strength at the Im ring at the organic layer–water interface. The possible mechanism governing such a decrease in hydrogen-bonding interaction strength is discussed.

Diblock Copolymers of Methacryloyloxyethyl Phosphorylcholine and Dopamine Methacrylamide: Synthesis and Real-Time Adsorption Dynamics by SEIRAS and RAIRS

“…SEIRAS experimental details were described elsewhere . In short, the surface of the mechanically polished face-angled Si crystal was subjected to 2% HF for 1 min and then coated with gold by applying a plating mixture for 4 min at room temperature.…”

“…SEIRAS experimental details were described elsewhere. 48 In short, the surface of the mechanically polished face-angled Si crystal was subjected to 2% HF for 1 min and then coated with gold by applying a plating mixture for 4 min at room temperature. In order to increase the mechanical resistance of the gold film, the film was removed with aqua regia, and the gold film plating was repeated.…”

Formation of tethered bilayer lipid membranes on gold surface probed by in situ SEIRAS

“…SEIRAS substrate preparation and experiment details have been described elsewhere [22]. In short, the polished face-angled Si crystal was reduced with 1 mL HF (2 wt%) and then coated with an Au film by applying a plating mixture for 4 min at room temperature.…”

“…Surface-enhanced infrared absorption spectroscopy (SEIRAS) is one of the most promising tools for probing the structure, adsorption peculiarities, and the orientation of adsorbed molecules at the electrochemical interface with molecular specificity and submonolayer sensitivity [20,21]. The analysis of a secondary structure of adsorbed peptides, the conformation of self-assembled monolayers, and the function of surface attached biosensors were successfully accomplished by employing of the in situ SEIRAS approach [20,[21][22][23].…”