From vermiculite saturated with 1-ornithine cations, three crystalline phases with basal spacings of 20.3 Å, 16.3 Å, and 14.63 Å were obtained, giving rational 001 X-ray reflections up to 20 values of 140°. The structures have been determined by monodimensional Fourier syntheses normal to (001).

The first two phases contain monovalent ornithine cations and water molecules in the interlayer space (ten and six water molecules per cation, respectively). The third phase is dehydrated, and contains divalent peptide cations of the diketopiperazine type.

In the 20.3 Å phase the interlayer material (Fig. 3) is arranged in three layers. Ornithine cations lie flat on the vermiculite surfaces, with the plane of the zig-zag chain perpendicular to the layer and with the —COO- and —NH+3 groups directed toward the center of the structure, away from the silicate surface. None of the —NH+3 groups are keyed into the ditrigonal cavities of the tetrahedral sheet, due probably to intermolecular association with neighboring —COO- groups. Five water molecules per each ornithine cation cover the silicate surface. The rest of the water forms a bimolecular layer at the center of the structure.

The 16.3 Å phase has the interlayer material (Fig. 2) arranged in two layers. Organic cations and water molecules are adsorbed on each surface with the same disposition as before, but the crystal has lost the intermediate water layer.

The 14.63 Å phase has the peptide cations arranged in one layer. The plane of the cyclic ring is inclined 60° to the vermiculite layers, with the >C = O groups at the center of the structure and the >N-H groups each directed to one surface. Both lateral chains are on planes normal to the layers, resulting from a 60° rotation around the >CH-CH2— bonds.

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