The title compounds show a pronounced cation-directed ability to selfassemble in water and to gives columnar structures similar to four-stranded helices; for compound (5Ј→5Ј)-d(GpG), this leads to the formation of cholesteric and hexagonal liquid crystalline phases. Both phases are columnar and the cholesteric phase is lefthanded. This behaviour is a further confirmation of the tendency of guanine derivatives to self-assemble to give stacked columnar structures whenever not impossible for structural reasons. The CD spectra of the aggregates in isotropic solutions are dominated by a negative exciton couplet centred around 250 nm associated to a left-handed columnar chirality. The shapes of the profiles, in the 220-300-nm region, for (5Ј→5Ј)-d(GpG) (in water or in saline solutions) and for (3Ј→3Ј)-d(GpG) (in KCl solution) are quasi-mirror images of those of poly(G) and (3Ј→5Ј)-d(GpG). The appearance of relatively intense CD signals around 280-300 nm in solution of (3Ј→3Ј)-d(GpG) in the presence of NaCl resembles that of (3Ј→5Ј)-d(GpG) in the presence of Rb + or Na + . In the compounds investigated in this work, which present two equivalent ends, one observes the two CD features that have been associated, in the current literature, with the signature of fourstranded parallel and antiparallel structures: hence the origin of these CD bands cannot be found in the polarity of the strands. Self-assembly is favoured by the addition of extra salt and the stabilising effect of K + is greater than that of Na + , in the case of (3Ј→3Ј)d(GpG), an assembled species could be detected by CD only in the presence of extra salt.