Here is the NMR strucure of an interstrand crosslink formed between thymines on opposite strands and the intercalating crosslinker 4'-hydroxymethyl-4,5',8-trimethylpsoralen (a synthetic derivative of psoralen). The two cyclobutane bridges between the drug and the Ts are in magenta.The two base pairs shown here are extracted from the middle of the 8 bp duplex characterized in the original work. From PDB file 204D, obtained by Spielmann et al., 1995. The top image is a representative structure, the bottom is a superposition of the 40 structures in the PDB file. The 40 structures represent 40 independent refinements obtained by restrained molecular dynamics using NMR experimental observations as constraints. Images made using Pymol. If you load the PDB into Pymol, you can shuffle through the structures as a movie.