The crystal structure of DL-acetylleucine N-methylamide, C9H18O2N2

Beta-pleated sheets in oligopeptide crystals

Many oligopeptide crystals show the beta-pleated sheet structures. Both parallel and antiparallel chain pleated sheets are found, and also both ideal (flat) and heavily twisted sheets are found. The structural parameters, such as the T (NC alpha C') angles, the torsion angles (phi and psi), the fiber axis periods, the hydrogen bond lengths, and the interchain spacings, are studied. Some of them deviate significantly from those proposed by Pauling & Corey ()Proc. Natl. Acad. Sci. US (1953), 39, 253-256). In the heavily twisted sheets, the twists are large than those in the globular proteins, and each two neighboring chains are almost perpendicular with each other, preserving the beta-sheet type hydrogen bond system. The torsion angles in the twisted sheets are rather close to those of the poly (L-proline) II helix. It also is discussed that the T (NA alpha C') angles sometimes deviate by almost 5 degrees from the standard value depending on the structures of the main and side chains.

Interaction between asymmetric solutes and solvents. Diamides derived from L-valine as stationary phases in gas-liquid partition chromatography

The resolution of enantiomers of (+/-)-a-amino acid derivatives on optically active diamides derived from L-valine, R1CONHCH[CH(CH3)2]CONHR2, as gas chromatographic stationary phases was studied. The effects of the structure of R1 and R2 in the stationary phases, the structure of the racemic a-amino acid derivatives, temperature, etc., on the separation factors are reported. In the light of these and related results, a more probable mechanism of resolution is presented.