Synthesis, capillary crystallization and preliminary joint X-ray and neutron crystallographic study of Z-­DNA without polyamine at low pH

In order to crystallographically study the hydration of the major groove (convex surface) of Z-DNA, the oligonucleotide d(CGCGCG) has been synthesized. Single crystals were grown by vapor diffusion using the hanging-drop and sitting-drop methods for X-ray studies and by batch crystallization and evaporation within silicon tubes for neutron studies. Hexagonal crystals were obtained without the use of duplex-stabilizing polyamines and at an acid pH. X-­ray data collected at room temperature (1.5 Å resolution; unit-cell parameters a = 17.90, b = 30.59, c = 44.61 Å) and at 100 K (1 Å resolution; a = 17.99, b = 30.98, c = 44.07 Å) and neutron data collected at room temperature (1.6 Å resolution; a = 18.00, b = 31.16, c = 44.88 Å) indicate that the DNA is in the Z-form packing in space group P2₁2₁2₁.