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A fundamental step in the replication of a viral particle is the self-assembly of its rigid shell (capsid) from its constituent proteins. Capsids play a vital role in genome replication and intercellular movement of viruses, and as such, understanding viral assembly has great potential in the development of new antiviral therapies and a systematic treatment of viral infection. In this article, we assume that nucleation is the underlying mechanism for self-assembly and combine the theoretical methods of the physics of equilibrium polymerization with those of the classical nucleation to develop a theory for the kinetics of virus self-assembly. We find expressions for the size of the critical capsid, the lag time, and the steady-state nucleation rate of capsids, and how they depend on both protein concentration and binding energy. The latter is a function of the acidity of the solution, the ionic strength, and the temperature, explaining why capsid nucleation is a sensitive function of the ambient conditions.

Impurities affect the nucleation, growth, and structure of crystals. Here we report the effect of large, spherical, polymethylmethacrylate impurities on the crystal growth of monodisperse, hard, polymethylmethacrylate colloids in a density- and optically matching apolar solvent mixture. Crystal growth, initiated at the bottom of the sample, was studied by imaging sequences of two-dimensional xy slices in the plane of the impurity's center with a laser scanning confocal microscope. Impurities form the center of grain boundaries, and a single fluid particle layer around the impurity persists in all cases. The growth rate sensitively depends on the impurity's size. Crystal growth is inhibited to a greater extent near smaller impurities, pointing to local crystal frustration induced by the curvature of the impurity.

Thermodynamically stable AgI clusters were studied in the presence of high- and low-molecular-weight additives: polyethyleneimine (PEI) and dimethylformamide (DMF), respectively. Clusters containing up to 20 silver iodide pairs, roughly twice as many as in the system without PEI or DMF, have been observed. We show that the mechanism stabilizing these clusters is mixed adsorption with iodide ions at the AgI-electrolyte interface. We make it plausible that more strongly adsorbing additives give rise to ultralow interfacial tensions of the AgI-electrolyte interface, with perspectives for "reversible colloids."

Recent experiments show that, in the range from approximately 15 to 45 degrees C, an increase in the temperature promotes the spontaneous assembly into capsids of the Escherichia coli-expressed coat proteins of hepatitis B virus. Within that temperature interval, an increase in ionic strength up to five times that of standard physiological conditions also acts to promote capsid assembly. To explain both observations we propose an interaction of mean force between the protein subunits that is the sum of an attractive hydrophobic interaction, driving the self-assembly, and a repulsive electrostatic interaction, opposing the self-assembly. We find that the binding strength of the capsid subunits increases with temperature virtually independently of the ionic strength, and that, at fixed temperature, the binding strength increases with the square root of ionic strength. Both predictions are in quantitative agreement with experiment. We point out the similarities of capsid assembly in general and the micellization of surfactants. Finally we make plausible that electrostatic repulsion between the native core subunits of a large class of virus suppresses the formation in vivo of empty virus capsids, that is, without the presence of the charge-neutralizing nucleic acid.

In concentrated suspensions of fluorescent colloidal hard spheres (close to and above the glass transition density), we bleached part of the system in cube shaped regions using high intensity laser light. Recovery of these bleached cubes was followed in real space using confocal scanning laser microscopy (CSLM). This method provides mean squared particle displacements up to timescales that are three orders of magnitude beyond those available by present experimental techniques. We show that, above the (hard sphere) glass transition density, particles move over distances of the order of their own diameter on timescales of 10(6) to 10(8) Brownian times. Moreover, the mean squared displacement, (x2), shows powerlaw behavior over seven time (tau) decades: (x2) alpha tau(0.30 +/- 0.05). This behavior is different from earlier observations by dynamic light scattering. It is argued that these differences are caused by gravity effects, as the only difference between the systems is the buoyant mass of the colloids.

We report a single step procedure to prepare monodisperse colloidal poly(methyl)methacrylate (PMMA) particles where fluorescent dyes are incorporated into the polymer network. The particles are sterically stabilized against flocculation by poly(12-hydroxystearic acid). The fluorescent dyes are RITC (rhodamine isothiocyanate)-aminostyrene (RAS) and 4-methylaminoethylmethacrylate-7-nitrobenzo-2-oxa-1,3-diazol (NBD-MAEM), which are prepared from (commercially available) RITC and 4-chloro-7-nitrobenzo-2-oxa-1,3-diazol (NBD-Cl), respectively, as starting materials. The particles can be grown larger with nonfluorescent PMMA. Examples of the usefulness of these model particles in colloid science are given.