ATR-IR spectroscopic study of L-lysine adsorption on amorphous silica

Attenuated total reflectance infrared (ATR-IR) spectroscopy was employed to quantitatively evaluate the dissociation states (di-cationic, cationic, zwitterionic, and anionic) of lysine adsorbed on amorphous silica. To determine the relationship between the ATR-IR spectra and each dissociation state, we first measured pH-induced spectral changes of dissolved lysine and correlated these changes with the thermodynamically calculated dissociation states of lysine. This procedure yielded calibration curves with good linearity; we used these curves for the quantitative analysis of adsorbed lysine. Our analysis revealed that 81±5%81±5% of the lysine adsorbed on amorphous silica was present in a cationic state and 19±5%19±5% was in a zwitterionic state; these percentages remained mostly unchanged over the whole range of pH values tested (pH = 7.1–9.8). We interpret the values obtained to indicate that lysine adsorption is mainly driven by electrostatic interaction with the negatively charged silica surface (SiO−⋯Lys+, SiO−⋯Lys±).

Graphical abstractAttenuated total reflectance infrared (ATR-IR) spectroscopy was employed to quantitatively evaluate the dissociation states (di-cationic, cationic, zwitterionic, and anionic) of lysine adsorbed on amorphous silica.Figure optionsDownload full-size imageDownload as PowerPoint slide