Intercalation of amino acids and oligopeptides into Zn–Al layered double hydroxide by coprecipitation reaction

The coprecipitation of amino acids and oligopeptides with the Zn–Al LDH was investigated using phenylalanine (Phe), phenylalanyl-phenylalanine (Phe-Phe), glycyl-phenylalanine (Gly–Phe), glycine (Gly), glycyl-glycine (Gly–Gly), glycyl-glycyl-glycine (Gly–Gly–Gly) and N-(N-γ-glutamyl-cysteinyl)-glycine (GSH) as guest species. The coprecipitation behavior of amino acids and oligopeptides was found to be influenced by the solution pH and the kind of their side chain groups, and reached the maximum at pH 8 or 9. The basal spacing, d003, of the Phe, Phe-Phe and GSH/LDH was 1.81, 2.41 and 1.64 nm, supporting that guests were arranged vertical to the LDH basal layer. Acceding to the basal spacing of the Gly, Gly–Gly and Gly–Gly–Gly/LDH (d003=0.84–0.88 nm), these guests were oriented horizontal to the LDH basal layer with the co-intercalated NO3−. Moreover, the amount of Phe-Phe, Gly–Gly and Gly–Gly–Gly intercalated was almost the same as that of Phe and Gly despite increasing the number peptide bond and the molecular size. GSH was intercalated into the LDH interlayer space as GSH oxidized form with bridged LDH layers by their carboxylate groups.