Rate of Lyotropic Nematic Phase Formation: Derivation and Application of Time–Concentration–Temperature–Transformation Diagrams

The effect of both temperature and composition on the rate of transformation of a nematic phase from an isotropic solution is examined from a theoretical standpoint. The kinetics of the transformation are presented as a time–concentration–temperature–transformation (TCTT) diagram, analogous to the time–temperature–transformation (TTT) diagrams commonly used in metallurgical process design. The transformation is regarded as a nucleated process in which the transformation rate is proportional to the number of stable nuclei, and this in turn depends on a balance between the energy gained by nematic ordering and the energy expended in forming the nematic–isotropic interface. The nematic ordering term is estimated as a function of both concentration and temperature via two different approaches: (i) the lattice theory as described by Flory and Warner and (ii) the Maier–Saupe theory of nematic ordering. Although there are differences in detail, both approaches yield the same qualitative result. The present work provides the details necessary for developing a specific example application of our recently reported generalized system-independent model of nucleation and growth. The TCTT diagram is in essence a phase diagram augmented by kinetic information for nematic ordering, and thus is expected to be a powerful graphical tool in liquid crystal process engineering and other applications

Acute emergence and reversion of influenza A virus quasispecies within CD8+ T cell antigenic peptides

Influenza A virus-specific CD8 + cytotoxic T lymphocytes (CTLs) provide a degree of cross-strain protection that is potentially subverted by mutation. Here we describe the sequential emergence of such variants within CTL epitopes for a persistently infected, immunocompromised infant. Further analysis in immunodeficient and wild-type mice supports the view that CTL escape variants arise frequently in influenza, accumulate with time and revert in the absence of immune pressure under MHCI-mismatched conditions. Viral fitness, the abundance of endogenous CD8 + T cell responses and T cell receptor repertoire diversity influence the nature of these de novo mutants. Structural characterization of dominant escape variants shows how the peptide-MHCI interaction is modified to affect variant-MHCI stability. The mechanism of influenza virus escape thus looks comparable to that recognized for chronic RNA viruses like HIV and HCV, suggesting that immunocompromised patients with prolonged viral infection could have an important part in the emergence of influenza quasispecies