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The poly(dG-dC) helical duplex forms a modified, B-familoy structure (B*) at very high hydration and a normal B structure at slightly lower hydration. The B* structure is slightly different in sugar-phosphate and base-stacking conformations than the B structure. Increasing the hydration or decreasing the NaC1 content stabilizes B* with respect to B.

Poly(dG-dC) forms the Z structure at low NaC1 contents when the hydration is sufficiently reduced. At moderate NaC1 content, the B to Z transition is sharp and cooperative for hydration with D2O. Hydration with H2O broadens the transition which occurs at lower hydration. This suggests that hydrogen bonding is stronger in the Z structute and helps stabilize Z over B.

IR spectra may be used to quantitatively estimate the fractions of B and Z structures present in a sample. Some new indicator bands are described.