A Helical Polymer with a Cooperative Response to Chiral Information

TLDR

Polyisocyanates, unlike biological helices, lack a predetermined helical sense yet exhibit unusual sensitivity to chiral effects due to alternating right‑ and left‑handed helical blocks separated by rare mobile reversals. The study aims to use the polymer’s chiral response to test theories of cholesteric liquid crystals, particularly the assignment of helical sense. Statistical thermodynamic analysis provides an exact description of the polymer and its cooperative chiral behavior. Even minute energy biases favoring one helical sense produce easily measurable conformational changes, despite being difficult to predict from structural theory.

Abstract

Polyisocyanates, long studied as theoretical models for wormlike chains in dilute solution and liquid crystals, differ from their biological helical analogs in the absence of a pre-determined helical sense. These polymers have an unusual sensitivity to chiral effects that arises from a structure in which alternating right- and left-handed long helical blocks are separated by infrequent and mobile helical reversals. Statistical thermodynamic methods yield an exact description of the polymer and the cooperative nature of its chiral properties. Minute energies that favor one of the helical senses drive easily measurable conformational changes, even though such energies may be extremely difficult to calculate from structural theory. In addition, the chiral nature of the polymer can be used to test theoretical ideas concerned with cholesteric liquid crystals, one of which solves the problem of assigning the helical sense.