Four stranded aggregates of oligodeoxy- guanilates forming lyotropic liquid crystals: a study by circular dichroism, optical microscopy and X-ray diffraction

The guanosine derivatives d(pG), d(GpG), d(GpGpG), d(GpGpGpG), and d(GpGpGpGpGpG), dissolved in water, give rise to cholesteric and hexagonal mesophases. These phases were investigated by X-ray diffraction, optical microscopy, and circular dichroism. The building block of these phases is a chiral rod-shaped aggregate composed of a stacked array of Hoogsteen-bonded guanosine tetramers. The ability of the different derivatives to originate the liquid-crystalline phases is discussed. Circular dichroism measurements show that the chirality of the rod-shaped aggregates is not the same for the five derivatives as is reflected also by the different handedness and pitches of the relative cholesteric phases. This seems to depend on the ratio between covalent and noncovalent bonds holding together the oligodeoxyguanylates in the chiral rod-shaped aggregates.