Into the polymer brush regime through the "grafting-to" method: densely polymer-grafted rodlike viruses with an unusual nematic liquid crystal behavior.

The current work reports an intriguing discovery of how the force exerted on protein complexes like filamentous viruses by the strong interchain repulsion of polymer brushes can induce subtle changes of the constituent subunits at the molecular scale. Such changes transform into the macroscopic rearrangement of the chiral ordering of the rodlike virus in three dimensions. For this, a straightforward "grafting-to" PEGylation method has been developed to densely graft a filamentous virus with poly(ethylene glycol) (PEG). The grafting density is so high that PEG is in the polymer brush regime, resulting in straight and thick rodlike particles with a thin viral backbone. Scission of the densely PEGylated viruses into fragments was observed due to the steric repulsion of the PEG brush, as facilitated by adsorption onto a mica surface. The high grafting density of PEG endows the virus with an isotropic-nematic (I-N) liquid crystal (LC) phase transition that is independent of the ionic strength and the densely PEGylated viruses enter into the nematic LC phase at much lower virus concentrations. Most importantly, while the intact virus and the one grafted with PEG of low grafting density can form a chiral nematic LC phase, the densely PEGylated viruses only form a pure nematic LC phase. This can be traced back to the secondary to tertiary structural change of the major coat protein of the virus, driven by the steric repulsion of the PEG brush. Quantitative parameters characterising the conformation of the grafted PEG derived from the grafting density or the I-N LC transition are elegantly consistent with the theoretical prediction.

Thermoresponsive Chiral to Nonchiral Ordering Transformation in the Nematic Liquid-Crystal Phase of Rodlike Viruses: Turning the Survival Strategy of a Virus into Valuable Material Properties.

The current work investigates the thermoresponsive in situ chiral to nonchiral ordering transformation of a rodlike virus in the naturally assembled state-the chiral nematic liquid crystal (CLC) phase. We take this as an elegant example of reconfigurable self-assembly, through which it is possible to realize in situ transformation from one assembled state to another without disrupting the preformed assembly in general or going through a secondary assembling procedure of the disassembled building blocks. The detailed investigation presented here reveals many unique characteristics of the thermoresponsive 3D chiral ordering of rodlike viruses induced by heat stress. The chiral to nonchiral ordering transformation is highly reversible in the temperature range of up to 60 °C and can be repeated many times. There exists a critical temperature around 40 °C which is independent of the ionic strength and virus concentration. Such reconfigurable ordering in the CLC phase stems from the intrinsic structure change of constituent coat proteins without disrupting the structural integrity of the virus, as revealed by three analytical techniques targeting levels ranging from the molecular, secondary conformation of the constituent proteins to the whole single virus, respectively. Such structural flexibility, also termed polymorphism, is relative to the survival strategies of a biological organism such as the virus and can be transformed into very precious material properties. The potential of the virus-based CLC phase as the chiral matrix to regulate chiro-optical properties of gold nanorods is also presented.

Pure Anisotropic Hydrogel with an Inherent Chiral Internal Structure Based on the Chiral Nematic Liquid Crystal Phase of Rodlike Viruses.

Imparting ordered structures into otherwise amorphous hydrogels is expected to endow these popular materials with novel multiple-stimuli responsiveness that promises many applications. The current contribution reports a method to fabricate pure polymeric hydrogels with an inherent chiral internal structure by templating on the chiral nematic liquid crystal phase of a rodlike virus. A method was developed to form macroscopically homogeneous chiral templates by confinement induced self-assembly in the presence of monomers, cross-linkers and initiators. Polymerization induced gelation was performed without perturbing the elegant 3D chiral organization of the rodlike virus bearing double bonds. Furthermore, a suitable method was found to remove the organic virus template while keeping the desired polymeric replica intact, resulting in a pure polymeric hydrogel with a unique internal chiral feature that originates from the 3D chiral ordering of the cylindrical pores left by the virus. Multiple-stimuli responsiveness has been demonstrated and can be quantified by the change of the pitch of the chiral feature. The chiral structure endows the otherwise featureless hydrogel with a unique material property that might be used as a readout signal for sensing and acts as the basis for responsive, biomimetic nanostructured materials.