Double helical conformation and extreme rigidity in a rodlike polyelectrolyte

Ying Wang,Curt J Zanelotti,Jianwei Gao,Robert B Moore,Bernd Ensing,Maruti Hegde,Stephanie Ten Brinck,Theo J Dingemans,Carla Slebodnick,Louis A Madsen,Yadong He,Zhou Yu,Rui Qiao,Gregory B Fahs

doi:10.1038/s41467-019-08756-3

Abstract

The ubiquitous biomacromolecule DNA has an axial rigidity persistence length of ~50 nm, driven by its elegant double helical structure. While double and multiple helix structures appear widely in nature, only rarely are these found in synthetic non-chiral macromolecules. Here we report a double helical conformation in the densely charged aromatic polyamide poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) or PBDT. This double helix macromolecule represents one of the most rigid simple molecular structures known, exhibiting an extremely high axial persistence length (~1 micrometer). We present X-ray diffraction, NMR spectroscopy, and molecular dynamics (MD) simulations that reveal and confirm the double helical conformation. The discovery of this extreme rigidity in combination with high charge density gives insight into the self-assembly of molecular ionic composites with high mechanical modulus (~ 1 GPa) yet with liquid-like ion motions inside, and provides fodder for formation of other 1D-reinforced composites.

Highlights

The ubiquitous biomacromolecule DNA has an axial rigidity persistence length of ~50 nm, driven by its elegant double helical structure
The strong monodomain orientational order maintained after removal of the sample from the B field indicates the extremely long persistence length of the PBDT chain[34], which we attribute to the rigid PBDT backbone and more importantly to the double helical structure
Future studies will further unravel the specific interactions at play in order to provide additional insights for informed molecular design for tailored self-assemblies. In this communication, we describe the molecular configuration of the sulfonated aramid PBDT in aqueous solutions

Summary

Introduction

The ubiquitous biomacromolecule DNA has an axial rigidity persistence length of ~50 nm, driven by its elegant double helical structure. We report a double helical conformation in the densely charged aromatic polyamide poly (2,2′-disulfonyl-4,4′-benzidine terephthalamide) or PBDT This double helix macromolecule represents one of the most rigid simple molecular structures known, exhibiting an extremely high axial persistence length (~1 micrometer). As far as we know, this is the only instance of a synthetic polymer that can form a double helix in aqueous solution This all-para, all-aromaticbackbone macromolecule is obtained using a simple, single-step interfacial polycondensation reaction. We verify formation of this double helix via complementary investigations utilizing X-ray diffraction (XRD), 23Na NMR spectroscopy, and molecular dynamics simulations This synthetic sulfonated aramid polyanion, poly-2,2'disulfonyl-4,4'-benzidine terephthalamide (PBDT), can be used to form a unique series of hydrogels[30,31] and ion gels[32,33], which have displayed great potential as next-generation functional materials for batteries, fuel cells, and optical sensors. We demonstrate that the all-para linkage is essential to form the double helix structure

Methods

Results

Conclusion