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The crystal structure and molecular conformation of the synthetic oligopeptide (Z-Pro-Ala-Thr (But)_2) have been determined by X-ray analysis. The crystal is orthorhombic, spacegroup P2_12_12_1, with four molecules per unit cell of dimensions: a = 29.557, b = 11.583 andc = 8.830A. The diffraction data were collected using a PW-1100 four-circle diffractometer.The strueture was solved by direct methods, using the MULTAN-80 system of computerprograms and refined by the block-diagonal least-squares method. 7he final R value is 0.088(for non-hydrogen atoms). The Ala residue in this peptide is nearly in an eclipsed conformation. The peptide bondbetween Z and Pro is cis. The two atoms, C~β aud C~γ, are displaced on opposite sides of thepyrrolidine ring plane. The dihedral augles between the neighbouring peptide or carboxylgroups are all close to 90°. Hydrogen bonds link the peptides forming a chain in the zdireetion. The stacking of the peptides in the x and y directions is the result of the van derWaals fo
The crystal structure and molecular conformation of the synthetic oligopeptide (Z-Pro-Ala-Thr (But) _2) have been determined by X-ray analysis. The crystal is orthorhombic, space group P2_12_12_1, with four molecules per unit cell of dimensions: a = 29.557, b = 11.583 and c = 8.830 A. The diffraction data were collected using a PW-1100 four-circle diffractometer. The strueture solved by direct methods, using the MULTAN-80 system of computer programs and refined by the block-diagonal least The Ala residue in this peptide is nearly in an eclipsed conformation. The peptide bond between Z and Pro is cis. The two atoms, C ~ beta aud C ~ γ, are displaced on the opposite sides of the pyrrolidine ring plane. The dihedral augles between the neighbor peptide or carboxyl groups are all close to 90 °. Hydrogen bonds link the peptides forming a chain in the zdireetion. The stacking of the peptides in the x and y directions is the result of t he van derWaals fo