Asymmetric hydrogenation catalyzed by transition metal complexes has been comprehensively studied. To reveal the mechanism of inducing the asymmetry, the complexes of his (dimethylglyoximato) cobalt and asymmetric amine are the most interesting because the intermediate complexes are easily isolated and crystallized. On the basis of the structure analyses of such complexes, we proposed that the asymmetry of the amine is transferred to the products at a transition state through the distortion of the his (dimethylglyoximato) cobalt moiety. This hypothesis was supported by the calculation of the potential energy at the transition state of which the structure was derived from the analysed ones.
The α-helix is one of the most typical conformations of the synthetic polypeptide in the solid state. In most cases, the deviation from the 18 residues 5 turns α-helix which was first proposed by Pauling and Corely has been reported. Several reflections unexpected from a regular α-helix appear on the meridian in diffraction diagrams of many polypeptides. Two different explanations have been presented, one is due to a regular distortion of the backbone α-helix, and the other due to a regular side-chain structure which is independent of the backbone structure. In a mixture of equimoles of poly (γ-benzyl L-glutamate) and poly (γ-benzyl D-glutα-mate) regular stacks of benzyl groups occur. This mixture shows the first order phase transition in the vicinity of 90°C characterized by a sudden increase in inter-helix distance and a disappearance of the 10.6A meridional reflection, suggesting the disruption of the regular stacks of benzyl groups. Poly (β-benzyl L-aspartate) can exist in a helix with 4 residues in a turn (ω-helix) as well as the left-handed α-helix. Poly [β- (p-chlorobenzyl) L-aspartate] is, however, the right-handed α-helix, which transforms into the ω-helix by heat treatment at 190°C. Poly (γ- (p-chlorobenzyl) L-glutamate) is found to be a helix with 7 residues in 2 turns which slightly deviates from the α-helix. The variation of the backbone conformation and side-chain structure are discussed in terms of intra- and inter-molecular side chain interactions.