Weak Chirality in Ordered Dna Phases

Recent experimentsl on aligned DNA show hexatic order with no sign of macroscopic chirality. I make the analogy between smectic liquid crystals and chiral hexatics and show how the absence of chirality cannot occur in a thermodynamic phase of chiral molecules. In addition, I discuss the microscopic origin of chiral mesophases in liquid crystals and show that within the context of central forces between “atoms” on “molecules”, ciral interactions can occur only there are biaxial correlations between the mesogens. Weak biaxial correlations can therefore lead to small cholesteric pitches.