The steric behaviour of the α-Helix has been investigated using an elastic molecule-model made of solid rubber balls and steel pins. Shortening of the hydrogen-bonds, which is possible at least in the range from 2.91 to 2.67 A in real α-Helices, has the following effects:1. The α-Helix contracts proportionally to the length of the hydrogen-bonds (figs. 3, 4).2. A torsional force arises leading in the case of longer α-Helices to torsional revolutions of the free ends of the helix (figs. 3 a. 4 a).3. Tertiary structures (superhelices. flattened superhelices. planar wavy lines, planar arcs) superpose the α-Helix if only specific hydrogen-bonds (e. g. indicated by arrows in fig. 5) will be shortened and if the distance between them is repeated in the sequence of the polypeptide chain (Tab. I). Some of the sequence-distances show similar tertiary structures and the same pitches of the superhelices (Tab. II). A general variation in the length of the hydrogen-bonds causes alterations in the superstructure and can also change the coiling direction of the superhelix.4. The Cα— Cβ; bonds incline slightly to the axis of the helix (fig. 11) through which the α-Helix with side chains becomes a little thinner. Because of the torsion (see item 2) the distance between the side chains changes also (fig. 12). The distances increase between specific positions of the side chains and decrease between others (Tab. III).Possible reasons for the shortening of the hydrogen-bonds are briefly discussed. The importance of the described behaviour for biological movements, enzymatic catalysis (“allosteric effect”) and active transport is emphasized.
Design, Synthesis, and Conformational Analysis of Oligobenzanilides as Multifacial α-Helix Mimetics