The chirality of the cholesteric phases of DNA and G-wires: Its connectionto their molecular structures

While the handedness of the cholesteric phases formed by assembled guanosin e derivatives (G-wires) follow the correlation right-handed helices --> rig ht-handed cholesterics (left-handed --> left-handed), the cholesteric phase formed by B-DNA (right-handed helix) is left-handed. This apparent discrep ancy is overcome by considering pitch (p) variations with temperature. Plot s of p(-1) versus T-1 have, in fact, the same trend (positive intercept and negative slope) in the case of right-handed G-wires and B-DNA, while for t he left-handed G-wire of deoxyguanosine monophosphate (dGMP), the opposite behavior is observed (negative intercept and positive slope). Therefore, th e relation between molecular handedness and cholesteric helicity cannot, in general, be assessed by using measurements based on a single temperature; hence the temperature variation of the cholesteric parameters should be inv estigated. In all cases there is no remarkable salt effect on the cholester ic parameters.