the crystal structure of an 8-mer ( s)-gna duplex is presented . as a tool for phasing , the anomalous diffraction of two copper(ii ) ions within two artificial metallo - base pairs was employed . 
 the duplex structure confirms a canonical watsoncrick base pairing scheme of gna with antiparallel strands . 
 the duplex secondary structure is distinct from canonical a- and b - form nucleic acids and can be described as a right - handed helical ribbon wrapped around the helix axis , resulting in a large hollow core . 
 most intriguingly , neighboring base pairs slide strongly against each other , resulting in extensive interstrand basebase hydrophobic interactions along with unusual hydrophobic intrastrand interactions of nucleobases with their backbone . 
 these results reveal how a minimal nucleic acid backbone can support highly stable watsoncrick - like duplex formation .