The crystal structure of the conformationally constrained peptide Z-(Aib)6-OBut


The structure of the synthetic, protected peptide Z-(Aib)6-OBut (C36H58O9N6, Mw = 718.89) which contains the conformationally constrained residue α-aminoisobutyric acid (Aib) has been determined by X-ray crystallography. The title compound crystallizes in P21/c with a = 8.992(4) Å, b = 19.382(4) Å, c = 27.451(10) Å, β = 115.63(4)°, V = 4360.5(8) Å3, Z = 4, Dx = 1.14(2) gcm−3. The final R after refinement is 0.088 for 5221 observed reflections. The hexapeptide adopts a 310 helical conformation with a reversal of the sense of the helix at the C-terminal Aib residue. The helix consists of three β-turns of type III and one β-turn of type I. Both senses of the helix occur in the crystal. The sequence – (Aib)6 – possesses a remarkable conformational flexibility. In the crystal the molecules are hydrogen-bonded head-to-tail, forming infinitely long, parallel, helical columns along [001].

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Zeitschrift für Kristallographie – Crystalline Materials offers a place for researchers to present results of their crystallographic studies. The journal includes theoretical as well as experimental research. It publishes Original Papers, Letters and Review Articles in manifold areas of crystallography.