Investigating the conversion from coordination bond to electrostatic interaction on self-assembled monolayer by SECM

Investigating the conversion of various kinds of weak interactions on protein surfaces may provide new insights in developing rational drugs. Herein, conversion from coordination bonds to electrostatic interactions occurring on the cysteine self-assembled monolayer (Cys SAM), a simplified protein surface, was investigated using scanning electrochemical microscopy (secm). On the Cys SAM electrode surface, the coordination bonds between Cys and copper (Cu [II]) were characterized by positive feedback. With the introduction of aspartic acid (Asp) on the electrode surface, the trend of positive feedback declined until it eventually presented negative feedback, indicating the conversion from the original coordination bonds to electrostatic interactions formed by Cys and Asp. This conversion phenomenon was driven by a higher binding affinity between Cys and Asp than between Cys and Cu (II). The conversion ratio was assessed to be about 89 %, based on the changes of the integral area of the Cu (II) reduction peak presented by cyclic voltammetry. Moreover, the binding specificity of Asp in electrostatic interaction with Cys compared to the other three amino acids was deemed to be structural matching. This work may facilitate the comprehension of the underlying mechanism of conversion phenomena on the biological surface at a molecular level.