Jay X Tang — Page 2 | Search PubMed

PubMed2003

Continuous isotropic-nematic liquid crystalline transition of F-actin solutions.

The phase transition from the isotropic (I) to nematic (N) liquid crystalline suspension of F-actin of average length ł> or =3 microm was studied by local measurements of optical birefringence and protein concentration. Both parameters were detected to be continuous in the transition region, suggesting that the I-N transition is higher than first order. Thus we report experimental evidence for a continuous I-N transition for a suspension of rodlike macromolecules. Our findings are consistent with a recent theory by Lammert, Rokhsar, and Toner [Phys. Rev. Lett. 70, 1650 (1993)], predicting that the I-N transition may become continuous due to suppression of disclinations.

Actins↗

PubMed2002

Metal ion-induced lateral aggregation of filamentous viruses fd and M13.

We report a detailed comparison between calculations of inter-filament interactions based on Monte-Carlo simulations and experimental features of lateral aggregation of bacteriophages fd and M13 induced by a number of divalent metal ions. The general findings are consistent with the polyelectrolyte nature of the virus filaments and confirm that the solution electrostatics account for most of the experimental features observed. One particularly interesting discovery is resolubilization for bundles of either fd or M13 viruses when the concentration of the bundle-inducing metal ion Mg(2+) or Ca(2+) is increased to large (>100 mM) values. In the range of Mg(2+) or Ca(2+) concentrations where large bundles of the virus filaments are formed, the optimal attractive interaction energy between the virus filaments is estimated to be on the order of 0.01 kT per net charge on the virus surface when a recent analytical prediction to the experimentally defined conditions of resolubilization is applied. We also observed qualitatively distinct behavior between the alkali-earth metal ions and the divalent transition metal ions in their action on the charged viruses. The understanding of metal ions-induced reversible aggregation based on solution electrostatics may lead to potential applications in molecular biology and medicine.

Bacteriophage M13↗