1N4B:
reference: Solution structure of a DNA duplex containing mispair-aligned N4C-ethyl-N4C interstrand cross-linked cytosines., Webba da Silva M, Noronha AM, Noll DM, Miller PS, Colvin OM, Gamcsik MP, Biochemistry 2002 Dec 24;41(51):15181-8. PMID: 12484755

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