Figure 23.

(a) A right-handed α-helix with the vectors s [Eq. 15], viewed along the C^α⋯C^β axis. (b) Two consecutive vectors s [Eq. 15] along the right-handed α-helix, viewed along the tangent vector t_i that connects the successive C^α atoms. The angle of their projection onto the plane, which is normal to the vector t_i is given by Eq. 23. The top of the vector ${\mathbf{s}}_{\mathbf{i}+\mathbf{1}}$ is colored blue in (b) to distinguish it from the top of the vector ${\mathbf{s}}_{\mathbf{i}}$.