The picture shows two low energy conformations of monomeric units of [4.3.0]-bicyclo-DNA, a conformationally restricted DNA analogue. As part of her PhD, Andrea Stauffiger realized the synthesis of the modified DNA-building block, investigated the nucleoside structure by X-ray crystallography and determined the thermal melting properties of oligonucleotides.
This picture is shown on the title page of the March 2009 issue of Eur. J. Org. Chem. (doi:10.1002/ejoc.200990015).

This work was carried out in the group of Prof. Christian Leumann.

References:

• A. Stauffiger and C. J. Leumann;
  "Screening the Structural Space of Bicyclo-DNA: Synthesis and Thermal Melting Properties of bc^4,3-DNA"
  Eur. J. Org. Chem., 2009, 1153-1162, (2009); doi:10.1002/ejoc.200801034.