Figure 2
From: Theoretical study on the polar hydrogen-π (Hp-π) interactions between protein side chains
The Hp-π interaction energies of CH 3 OH-C 2 H 4 (blue diamond) and CH 3 OH-C 6 H 6 (green square) pairs as the function of interaction distance (R). For comparison the curve of NMA-NMA hydrogen bond interaction is also shown (orange triangles), which is the most frequent hydrogen bond in proteins. The bong lengths (~2.5 Å) of Hp-π interactions are longer than that of the hydrogen bonds (~2.0 Å). The force constants (k) of two Hp-π interaction pairs CH3OH-C2H4 and CH3OH-C6H6 are 0.0035 and 0.0055 Hartree/Bohr, smaller that (0.0071 Hartree/Bohr) of the NMA-NMA hydrogen bond interaction. The Hp-π interactions are more soften than the common hydrogen bond interactions in the minimum and short interaction distances.