Study on Chirality Transfer in Liquid Crystal Viruses

Chirality is a phenomenon commonly found in nature and holds significant influence in various fields such as biology, chemistry, physics, and materials science. However, the mechanism of chirality transfer from nanoscale building blocks to macroscopic helical structures remains an unsolved mystery. In this study, the authors investigate the self-assembly of filamentous viruses in chiral liquid crystal phases, uncovering the key mechanisms of chirality transfer. They delve into how surface charge patterns and the helical deformation of the viral backbone work together to form the helical structures of the viral liquid crystal phase.

Research Background

Chirality transfer in liquid crystal phases is crucial in many areas. For example, understanding and controlling the propagation of chirality from chiral molecules with asymmetric carbon atoms to ordered helical superstructures and chiral bulk devices is essential in biology, chemistry, physics, nanotechnology, and materials science. The chiral liquid crystalline phase known as the “cholesteric phase” is a typical example of chiral assembly. This structure is prevalent in biological materials and has a wide range of technological applications, from display industries to smart windows.

Despite significant efforts over the past decades, the propagation mechanism of chirality in the hierarchical structure, especially the causal relationship from the microscopic properties of molecular building blocks to the macroscopic helical structures they form, remains unresolved. This challenge stems from the inherently weak nature of chiral interactions. When two adjacent particles achieve the optimal twist angle in standard cholesteric arrangements, this angle is often less than one degree.

Paper Source

This research paper was completed by Eric Grelet (Centre de Recherche Paul Pascal, Univ. Bordeaux, CNRS, France) and Maxime M. C. Tortora (Laboratoire de Biologie et Modélisation de la Cellule, INSERM 1293, Univ. Claude Bernard Lyon 1, ENS de Lyon, and currently affiliated with the Department of Computational Biology, University of Southern California). The paper was published in the 2024 issue of the journal Nature Materials.

Research Methods

In this study, the authors utilized experimental and theoretical methods to investigate the cholesteric liquid crystal phases formed by filamentous viruses. Using classic rod-like particles as the model system, they explored the mechanisms of chirality transfer during the self-assembly process. The subjects of the study were two bacteriophages, m13 and y21m, which are long rod-shaped single-stranded DNA viruses widely used as model systems in genetic engineering and soft condensed matter physics.

The research methods included:

1. Characterization of Virus Structure: Using high-resolution X-ray diffraction to characterize the three-dimensional structures of the two viruses, stored in the Protein Data Bank (PDB) with accession numbers 1IFI and 2C0W.
2. Establishment of Chirality Transfer Models: The study employed an all-atom electrostatic model to analyze the transmission of chirality of the viruses to the fluid, quantifying the helical pitch (p) and twist elastic constant (K22).
3. Investigation of Transfer Mechanisms by Regulating Ionic Environment and Chemical Modification: By adjusting the pH and ionic strength of the virus solution, as well as PEG (polyethylene glycol) surface modification, the authors explored the chirality transfer mechanisms under different conditions.

Research Results

1. Relationship Between Charge and Electrostatic Interactions: The m13 and y21m viruses exhibited different chiral liquid crystal phases due to the helical charge patterns on their viral shells—left-handed for m13 and right-handed for y21m. Increasing the solution ionic strength resulted in an increase in the cholesteric pitch (|p|) for both viruses, highlighting the crucial role of electrostatic interactions in chiral liquid crystal structures.
2. Behavior of PEG-Modified Viruses: Upon PEG modification of the viral surface, the behavior of the liquid crystal phase no longer depended on ionic strength but was driven by the elasticity of the viral backbone. The m13-PEG system showed a left-handed cholesteric phase at the isoelectric point (PIE), whereas the y21m-PEG system did not exhibit observable chirality propagation in the liquid crystal phase.
3. Two Main Pathways of Chirality Transfer Mechanism: The study demonstrated that for the rigid y21m virus, the chirality of the cholesteric phase primarily resulted from local electrostatic interactions, while for the more flexible m13 virus, chirality propagation mainly occurred through long-wavelength helical deformations (i.e., superhelical modes).

Conclusions and Significance

The study further showed that chirality transfer in viral liquid crystal phases is a result of the combined effects of electrostatic interactions and backbone elasticity. Different viruses exhibited distinctly different chirality transfer mechanisms. This not only deepens our understanding of the mechanism of chirality transfer in liquid crystal phases but also provides new ideas for designing chiral materials with specific optical, electrical, or biological functions. The study offers a detailed framework from the atomic scale to the macroscopic scale, helping to reveal the process and mechanism of chirality transfer in liquid crystal structures.

Through this research, scientists can better understand and control the propagation of chirality from microscopic molecules to macroscopic structures, which has significant application value in nanotechnology, materials science, and biomedical fields. The quantitative models and experimental results in this study also provide important data and references for similar future research.

Research Highlights

1. Revealed the main mechanisms of chirality transfer of viruses in liquid crystal phases.
2. Demonstrated the combined role of electrostatic interactions and long-wavelength helical deformations.
3. Provided a quantitative framework from the atomic level to the macroscopic scale.
4. Offered guidance for the future design of novel chiral materials.

Future Prospects

Understanding and controlling the propagation of chirality in helical superstructures can reveal various self-assembly processes and mechanisms, offering new possibilities for designing chiral materials with specific functions. Future research can further explore more types of viral liquid crystal systems to investigate their chirality transfer mechanisms, expanding the range of applications of the research results.