Rod-like Virus Research Articles

Chiral Nematic Phase of Suspensions of Rodlike Viruses: Left-Handed Phase Helicity from a Right-Handed Molecular Helix

We report a study on charged, filamentous virus called M13, whose suspensions in water exhibit a chiral nematic (cholesteric) phase. In spite of the right-handed helicity of the virus, a left-handed phase helicity is found, with a cholesteric pitch which increases with temperature and ionic strength. Several sources of chirality can be devised in the system, ranging from the subnanometer to the micrometer length scale. Here an explanation is proposed for the microscopic origin of the cholesteric organization, which arises from the helical arrangement of coat proteins on the virus surface. The phase organization is explained as the result of the competition between contributions of opposite handedness, deriving from best packing of viral particles and electrostatic interparticle repulsions. This hypothesis is supported by calculations based on a coarse-grained representation of the virus.

Nematic-isotropic spinodal decomposition kinetics of rodlike viruses

We investigate spinodal decomposition kinetics of an initially nematic dispersion of rodlike viruses. Quench experiments are performed from a flow-stabilized homogeneous nematic state at a high shear rate into the two-phase isotropic-nematic coexistence region at a zero shear rate. We present experimental evidence that spinodal decomposition is driven by orientational diffusion, in accordance with a very recent theory.

Study and characterization of tobacco mosaic virus head-to-tail assembly assisted by aniline polymerization

One-dimensional composite nanofibres with narrow dispersity, high aspect ratio and high processibility have been fabricated by head-to-tail self-assembly of rod-like tobacco mosaic virus assisted by aniline polymerization, which can promote many potential applications including electronics, optics, sensing and biomedical engineering.

Kinetic pathways of the nematic–isotropic phase transition as studied by confocalmicroscopy on rod-like viruses

We investigate the kinetics of phase separation for a mixture of rod-like viruses (fd) andpolymer (dextran), which effectively constitutes a system of attractive rods. This dispersionis quenched from a flow-induced fully nematic state into the region where thenematic and the isotropic phase coexist. We show experimental evidence thatthe kinetic pathway depends on the overall concentration. When the quench ismade at high concentrations, the system is meta-stable and we observe typicalnucleation-and-growth. For quenches at low concentration the system is unstable and thesystem undergoes a spinodal decomposition. At intermediate concentrations we see thetransition between both demixing processes, where we locate the spinodal point.

DNA Cholesteric Pitch as a Function of Density and Ionic Strength

The nature of chiral interactions among chiral biopolymers, such as DNA, protein α-helices, and rodlike virus particles, remains elusive. In particular, a satisfactory model connecting molecular chiral interactions and the pitch of the resulting chiral mesophases is lacking. We report the measurement of short-fragment (146-bp) DNA cholesteric spherulite pitch as a function of osmotic pressure, average DNA interaxial spacing, and salt concentration. We determined cholesteric pitch and interaxial spacing by polarizing optical microscopy and x-ray scattering, respectively, from which the twist-angle between DNA molecules can be calculated. Surprisingly, we found that decreasing ionic strength resulted in weaker chiral interactions between DNA chains, as evidenced by the decrease in the twist-angle, and consequent increase in the cholesteric pitch, for a fixed interaxial spacing. We propose that this behavior can be explained by increased smearing-out of the helical charge pattern along DNA as the Debye screening length is increased.

Flow Behavior of Colloidal Rodlike Viruses in the Nematic Phase

The behavior of a colloidal suspension of rodlike fd viruses in the nematic phase, subjected to steady state and transient shear flows, is studied. The monodisperse nature of these rods combined with relatively small textural contribution to the overall stress make this a suitable model system to investigate the effects of flow on the nonequilibrium phase diagram. Transient rheological experiments are used to determine the critical shear rates at which director tumbling, wagging, and flow-aligning occurs. The present model system enables us to study the effect of rod concentration on these transitions. The results are in quantitatively agreement with the Doi-Edwards-Hess model. Moreover, we observe that there is a strong connection between the dynamic transitions and structure formation, which is not incorporated in theory.

Absence of charge inversion on rodlike polyelectrolytes with excess divalent counterions

Filamentous viruses such as fd and M13 are highly charged rodlike polyelectrolytes. In this study, we employ fd virus to test the recent prediction of charge inversion [Nguyen, Rouzina, and Shklovskii, J. Chem. Phys. 112, 2562 (2000)]. Light scattering measurements show bundle formation and resolubilization of fd viruses when MgCl(2) was added from 0 to 600 mM. The effective charge of fd was studied by measuring their electrophoretic mobility using a filament tracking method uniquely suited for the system. Monte Carlo simulations were performed under canonical ensemble to predict the charge distribution around the rodlike virus. Charge inversion, which has been suggested theoretically to accompany with bundle resolubilization, was not observed in either experiments or simulations. A modified analysis of force balance is called upon to account for these new findings.

Non-equilibrium phase behaviour of rod-like viruses under shear flow

We present the non-equilibrium phase diagram of rod-like colloids (fd-viruses) under shearflow. The shear-induced displacement of the isotropic–nematic binodal is obtained fromtime resolved rheology measurements. Vorticity banding is observed within thebiphasic region, as bounded by the binodal. Here, in the stationary state, regular,millimetre sized bands with mutually differing orientational order are stacked alongthe vorticity direction. For the fully nematic phase we determine the location oftransition lines from tumbling to either wagging or flow aligning, depending on theconcentration. The location of these dynamical transition lines agree with theoryfor hard rods, when scaling to the orientational order parameter in equilibrium.

Elongation and fluctuations of semiflexible polymers in a nematic solvent.

We directly visualize single polymers with persistence lengths l(p), ranging from 0.05 to 16 microm, dissolved in the nematic phase of rodlike fd virus. Polymers with a sufficiently large persistence length undergo a coil-rod transition at the isotropic-nematic transition of the background solvent. We quantitatively analyze the transverse fluctuations of the semiflexible polymers and show that at long wavelengths they are driven by the fluctuating nematic background. We extract the Odijk deflection length and the elastic constant of the background nematic phase from the data.

What is the origin of chirality in the cholesteric phase of virus suspensions?

We report a study of the cholesteric phase in monodisperse suspensions of the rodlike virus fd sterically stabilized with the polymer polyethylene glycol (PEG). After coating the virus with neutral polymers, the phase diagram and nematic order parameter of the fd-PEG system then become independent of ionic strength. Surprisingly, the fd-PEG suspensions not only continue to exhibit a cholesteric phase, which means that the grafted polymer does not screen all chiral interactions between rods, but paradoxically the cholesteric pitch of this sterically stabilized fd-PEG system varies with ionic strength. Furthermore, we observe that the cholesteric pitch decreases with increasing viral contour length, in contrast to theories which predict the opposite trend. Different models of the origin of chirality in colloidal liquid crystals are discussed.

Measuring the nematic order of suspensions of colloidal fd virus by x-ray diffraction and optical birefringence.

The orientational distribution function of the nematic phase of suspensions of the semiflexible rodlike virus fd is measured by x-ray diffraction as a function of concentration and ionic strength. X-ray diffraction from a single-domain nematic phase of fd is influenced by interparticle correlations at low angle, while only intraparticle scatter contributes at high angle. Consequently, the angular distribution of the scattered intensity arises from only the single-particle orientational distribution function at high angle but it also includes spatial and orientational correlations at low angle. Experimental measurements of the orientational distribution function from both the interparticle (structure factor) and intraparticle (form factor) scattering were made to test whether the correlations present in interparticle scatter influence the measurement of the single-particle orientational distribution function. It was found that the two types of scatter yield consistent values for the nematic order parameter. It was also found that x-ray diffraction is insensitive to the orientational distribution function's precise form, and the measured angular intensity distribution is described equally well by both Onsager's trial function and a Gaussian. At high ionic strength, the order parameter S of the nematic phase coexisting with the isotropic phase approaches theoretical predictions for long semiflexible rods S=0.55, but deviations from theory increase with decreasing ionic strength. The concentration dependence of the nematic order parameter also better agrees with theoretical predictions at high ionic strength indicating that electrostatic interactions have a measurable effect on the nematic order parameter. The x-ray order parameters are shown to be proportional to the measured birefringence, and the saturation birefringence of fd is determined enabling a simple, inexpensive way to measure the order parameter. Additionally, the spatial ordering of nematic fd was probed. Measurements of the nematic structure factor revealed a single large peak in contrast to nematics of rigid rods.

Electrophoretic Mobility of Rigid Rodlike Particles in Dilute Aqueous and Glycerol Suspensions: Comparison between Theory and Experiment

The electrophoretic mobilities of rigid rodlike tobacco mosaic virus (TMV) particles solvated in water and in 80% glycerol/20% water solutions with a wide range of electrical double-layer thicknesses have been measured by Deggelmann et al. (Deggelmann, M., Graf, C., Hagenbuchle, M., Hoss, U., Johner, C., Kramer, H., Martin, C., and Weber, R., J. Phys. Chem.98, 364–368 (1994)) and the present authors, respectively. The measured mobilities have a dependence on the electrical double-layer thickness much weaker than that predicted by theories for the mobility of cylinders of infinite length. To interpret the experiments, we develop an approximate theory for the mobility of finite aspect ratio particles with arbitrary ratios of the double-layer thickness to the rod length and diameter. This uniformly valid approximation interpolates between previous theories for infinite rod length and for infinitesimal rod thickness. A comparison of the uniformly valid theory with the experimentally measured mobilities indicates that TMV has a negative charge of 1000e in water and 400e in the glycerol solution.

Development of model colloidal liquid crystals and the kinetics of the isotropic–smectic transition

We have prepared a homologous series of › lamentous viruses with varying contour length using molecular cloning techniques. These viruses are monodisperse enough to form a stable smectic phase. Two systems are studied. The › rst system consists of viruses to the surfaces of which the polymers are covalently bound. Through studies of the isotropic{cholesteric phase transition we demonstrate that covalently attached polymers alter the e¬ective diameter of the virus. Additionally, we have produced mixtures of viruses whose ratio of e¬ective diameters varies by a factor of › ve. The second system is composed of mixtures of rod-like viruses and non-absorbing Gaussian polymers. With this system we study the kinetics of the isotropic{smectic phase transition and describe observations of a number of novel metastable structures of unexpected complexity.

Cholesteric Phase in Virus Suspensions

We report measurements of the cholesteric pitch and twist elastic constant $(K_{22})$ in monodisperse suspensions of the rod-like virus filamentous bacteriophage {\it fd}. Measurements were taken for concentrations spanning the entire cholesteric region at several ionic strengths and temperatures. In the limit of high ionic strength the cholesteric pitch $(P_0)$ scales with concentration (c) as $P_0 \propto c^{-1.66}$. As the ionic strength decreases the scaling exponent systematically changes to lower values.

Phase diagram of tobacco mosaic virus solutions

The phase behavior of an aqueous suspension of rodlike tobacco mosaic viruses is investigated theoretically as a function of the virus density and the concentration of added salt. The total free energy involves ``volume terms'' from the microscopic counter- and co-ions and an effective pair interaction between the colloidal rods described by a Yukawa-segment model according to linear screening theory. Within a thermodynamic perturbation approach, the short-range repulsion between the rods is mapped onto a reference system of effective hard spherocylinders. The free energy of the spherocylinder system is gained from combining a cell model with scaled particle theory, which yields a reasonable phase diagram. The remaining long-range interaction is treated within a mean-field approximation. As a result we find stable fluid, nematic, and smectic phases as well as $\mathrm{AAA}$- and $\mathrm{ABC}$-stacked crystals. For increasing salt concentration at fixed rod concentration, there is a nematic reentrant transition. We finally discuss our results in view of experimental data.

Electrostatically Induced Polyelectrolyte Association of Rodlike Virus Particles

Calculations of the electrostatic osmotic pressure for a closely packed phase of laterally ordered rodlike fd or M13 virus particles at equilibrium with a bulk salt solution have been performed using grand canonical Monte Carlo simulations. With increasing concentration of divalent counterions, the pressure becomes attractive. The attraction is stronger for higher surface charge density (of fd virus as opposed to M13 virus) and smaller counterion radius. The calculations agree with the results from light scattering measurements, which sensitively detect the formation of laterally ordered virus aggregates.

Phase Behavior of Mixtures of Rods (Tobacco Mosaic Virus) and Spheres (Polyethylene Oxide, Bovine Serum Albumin)

Aqueous suspensions of mixtures of the rodlike virus tobacco mosaic virus (TMV) with globular macromolecules such as polyethylene oxide (PEO) or bovine serum albumin (BSA) phase separate and exhibit rich and strikingly similar phase behavior. Isotropic, nematic, lamellar, and crystalline phases are observed as a function of the concentration of the constituents and ionic strength. The observed phase behavior is considered to arise from attractions between the two particles induced by the presence of BSA or PEO. For the TMV/BSA mixtures, the BSA adsorbs to the TMV and bridging of the BSA between TMV produces the attractions. For TMV/PEO mixtures, attractions are entropically driven via excluded volume effects known alternatively as the “depletion interaction” or “macromolecular crowding.”

Rotational and Translational Diffusion of a Rodlike Virus in Random Coil Polymer Solutions

Depolarized dynamic light scattering was used to measure the translational and rotational diffusion of tobacco mosaic virus, TMV, in aqueous solutions of dextran (M ∼505 000). TMV is an electrically charged, nucleoprotein assembly with the shape of a stiff, rigid rod. Dextran is an uncharged, flexible carbohydrate polymer. The TMV was held at a fixed, dilute concentration (0.5 mg/mL), while the concentration of dextran spanned both dilute and semidilute regimes (0−14.5% by weight). There was no evidence of phase separation or strong aggregation of the TMV particles in the presence of the dextran. The TMV particles dominated the depolarized scattering at all dextran concentrations. The angular variation of the decay rates of the autocorrelation functions always followed the form expected for symmetric top molecules in the absence of translational−rotational coupling. Nevertheless, translational and rotational motions are almost surely coupled in most dextran-containing solutions. The apparent translational...

Self-Assembly of Viruses as Models for the Design of new Macromolecular and supramolecular architectures

Abstract This paper reviews the principles of self-assembly of rodlike viruses, such as tobacco mosaic virus (TMV), and discusses with selected examples the strategy used in our laboratory to produce synthetic systems which self-assemble via related principles.

Isotropic-cholesteric phase transition in colloidal suspensions of filamentous bacteriophagefd

Abstract The co-existence concentrations of the isotropic and cholesteric liquid crystalline phases of the semi-flexible rod-like virus fd in aqueous suspension were measured as a function of ionic strength at room temperature. At several ionic strengths the magnetic-field-induced birefringence, which is proportional to the number of particles in a correlation volume N corr, was measured for fd concentrations spanning the entire isotropic region. From this data the limiting concentration of stability (spinodal) of the isotropic phase, ρ*, was obtained. The co-existence concentrations and ρ* versus ionic strength compare well with predictions based on the theory of Khokhlov and Semenov, modified to include the effects of charge. A theoretical expression for the magnetic birefringence of persistent polymers was derived and agreed well with the data with the exception that N corr at the isotropic to liquid crystal transition was smaller than predicted.