Fig. 1. Superimposition of benzylfentanyl (compound 2, colour: purple blue) and 4-IBP (N-(1-benzyl-4-piperidyl)-4-iodo-benzamide, colour: aquamarine). The binding mode of compound 2 is taken from simulation II, t = 300.0 ns. The binding mode of 4-IBP is taken from chain A of crystallographic structure ; 5HK2.15 Only several residues of the binding site are shown for clarity. The receptor structures are given as ribbons representing the secondary structure. Heteroatoms are coloured according to the convention: red – oxygen, dark blue – nitrogen, dark pink – iodine.