title: In situ ATR-IR investigation of L-lysine adsorption on montmorillonite.
abstract: The adsorption behavior of lysine on montmorillonite in aqueous solution was investigated by in situ attenuated total reflectance infrared (ATR-IR) spectroscopy. To distinguish the protonation states of alpha-amino group, side-chain amino group and carboxyl group in lysine structure using ATR-IR spectra (i.e., NH2 versus NH3+ and COO- versus COOH), pH-induced spectral changes of dissolved lysine were firstly measured and correlated with the thermodynamically calculated dissociation states of lysine (di-cationic, cationic, zwitterionic and anionic states). The obtained result was applied to interpret the ATR-IR spectra of lysine adsorbed on montmorillonite. We found that the adsorbed lysine was dominantly present as cationic state over the whole range of tested pH (pH=4.9-9.7). This indicates that the adsorption is mainly driven by electrostatic interaction between the negatively charged montmorillonite surface and positively charged cationic lysine. We also found that lysine interacts with montmorillonite surface through the protonated side-chain amino group. This result suggests that lysine has a preferred vertical orientation, with the side-chain amino group pointing toward the surface.
authors.affiliation: Department of Earth and Space Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan. nkitadai@ess.sci.osaka-u.ac.jp
authors.forename: Norio
authors.initials: N
authors.lastname: Kitadai
authors.forename: Tadashi
authors.initials: T
authors.lastname: Yokoyama
authors.forename: Satoru
authors.initials: S
authors.lastname: Nakashima
mesh_terms: D000327:Adsorption; D001546:Bentonite / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008239:Lysine / Q000737:chemistry*; D013055:Spectrophotometry, Infrared / Q000379:methods; D013499:Surface Properties
chemical_list: D001546:Bentonite; D008239:Lysine