Uptake of amino-acids by zirconium phosphate. Part 3. Intercalation of L-histidine, L-lysine, and L-aginine by γ-zirconium phosphate

Abstract

The uptake of L-histidine (His), L-lysine, and L-arginine by γ-zirconium phosphate has been studied. The intercalation of His is initiated by the partial replacement of interlayer water by a monolayer of the guest molecules oriented horizontally to the sheet of the host crystal to form a phase Zr(HPO₄)₂(His)_0.2·1.9H₂O with an interlayer spacing of 14.1 Å. This is followed by the formation of a phase Zr(HPO₄)₂(His)_0.4·0.8H₂O without any appreciable change in interlayer spacing, which is finally converted into a phase Zr(HPO₄)₂(His)_0.9·3H₂O with an interlayer spacing of 22.9 Å in which the guest molecules are intercalated as a bilayer. Lysine and arginine also form one or two monolayered phases at low uptakes, while at higher loadings the intercalates formed are highly disordered, but with a certain degree of order in the host lattice. The different behaviour of α- and γ-zirconium phosphates in intercalating amino acid molecules is discussed in terms of the structural or functional characteristics of the individual acids and phosphates. A supplementary discussion of the amino acid arrangement in α-zirconium phosphate is also made.