Electrosynthesis of Poly(alanine)-Like Peptides in Concentrated Alanine Based Electrolytes, Characterization Coupled to DFT Study and Application to pH Proton Receptor

The anodic oxidation of concentrated l-alanine on smooth electrodes such as platinum and glassy carbon electrodes was studied. Contrary to the previous studies performed up to now with diluted l-alanine, the electrochemical process generated here results in a completely different situation. The oxidation on smooth platinum was carried out by electrochemical quartz crystal microbalance (EQCM) coupled to cyclic voltammetry technique. The effects of concentration, scan rate, and pH (zwitterion at pH = 6 and alkaline media at pH = 13) on potential values were examined. Glassy carbon and smooth gold electrodes showed the same behavior as on smooth platinum electrode. Spectroscopic analysis such as attenuated total reflectance FT infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) were used to characterize the resulting thin film coatings. The presence of peptide bonds is clearly highlighted. DFT modelization of poly(alaninate) strand on Pt(001) coupled to spectroscopic measurements are in favor of l-alanine electropolymerization into poly-l-alanine in an irreversible way. Due to its proton receptor behavior, electrosynthesized poly-l-alanine on smooth platinum electrode was tested as a whole solid transducer for pH sensing