For insight into the structure and dynamics of phases emerging upon crossing the metastability/instability boundary we monitor with optical microscopy, in real time and in real space, the generation of a dense liquid phase in high-concentration solutions of the protein lysozyme after temperature quenches into thermodynamically defined metastable and unstable regions. We show with this system, which is a poor fit to mean-field assumptions, that the evolution of the structure factor during nucleation is similar to that during spinodal decomposition and reveals no singularity predicted upon crossing the metastability boundary. We introduce two kinetic definitions of the metastability/instability boundary that yield values within approximately 1.5 K, i.e., the boundary appears as an area rather than a line, which is near and above the thermodynamic prediction. Delay times for the appearance of the new phase in the unstable regime are significant, i.e., new-phase growth is hindered by kinetic barriers. While our results agree with predictions of the non-mean-field theories of phase transformations, the experimentally observed behavior is richer than the one envisioned by theory.

The simultaneous binding of multiple ligands on one entity to multiple receptors on another can result in an affinity that is significantly greater than that for the binding of a single ligand to a single receptor. This concept of ''polyvalency'' can be used to design molecules that are potent inhibitors of toxins and pathogens. We describe the design of potent polyvalent inhibitors that neutralize anthrax toxin in vivo as well as our attempts to elucidate the relationship between inhibitor structure and activity. We also highlight promising future avenues for research in polyvalent drug design.

We present an exact expression of spin operators in terms of magnons and quasielectrons in ferromagnetism.Its relation to the Holstein-Primakoff expression is discussed. The result shows that the spin rotation of electrons is induced by a transformation of magnons and quasielectrons which is different from rotation.

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