6MIK:
reference: Hachimoji DNA and RNA: A genetic system with eight building blocks., Hoshika S, Leal NA, Kim MJ, Kim MS, Karalkar NB, Kim HJ, Bates AM, Watkins NE Jr, SantaLucia HA, Meyer AJ, DasGupta S, Piccirilli JA, Ellington AD, SantaLucia J Jr, Georgiadis MM, Benner SA, Science. 2019 Feb 22;363(6429):884-887. doi: 10.1126/science.aat0971. PMID: 30792304

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