Figure 4

Distribution of Cα···O distances in the Cambridge Structural Database structures (July 2003 release), containing the motif depicted in Figure 2. Three cases are considered: single Cα-H···O hydrogen bond (light grey), bifurcated hydrogen bond (dark grey), and no hydrogen bond (white). The single hydrogen bonded case clearly dominates with 1688 hits overall, for 218 of the bifurcated case and 166 hits for the no hydrogen bond case. The maximum in the single hydrogen bond distribution around 3.4 Å suggests that value as the Cα···O hydrogen bonding distance, although a significantly large number of interactions can be still classified as hydrogen bonds at the longer Cα···O distances.