Weak Chirality in Ordered DNA Phases

TL;DR

This paper explores the absence of macroscopic chirality in aligned DNA phases and explains how weak chiral interactions can arise from microscopic biaxial correlations in liquid crystal models.

Contribution

It demonstrates that macroscopic chirality cannot occur in thermodynamic phases of chiral molecules without biaxial correlations and links microscopic interactions to cholesteric pitch.

Findings

Aligned DNA shows hexatic order without macroscopic chirality

Chiral interactions require biaxial correlations in the model

Weak biaxial correlations can produce small cholesteric pitches

Abstract

Recent experiments 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", chiral interactions can occur only if there are biaxial correlations between the mesogens. Weak biaxial correlations can therefore lead to small cholesteric pitches.