3R6R:
reference: The crystal structure of human telomeric DNA complexed with berberine: an interesting case of stacked ligand to G-tetrad ratio higher than 1:1., Bazzicalupi C, Ferraroni M, Bilia AR, Scheggi F, Gratteri P, Nucleic Acids Res. 2013 Jan 1;41(1):632-8. doi: 10.1093/nar/gks1001. Epub 2012, Oct 26. PMID: 23104378

This OCA Structure page
uses Jmol, developed by the Jmol Development Team (documentation).