Olga Gliko

Diffusion-limited kinetics of the solution–solid phase transition of molecular substances

For critical tests of whether diffusion-limited kinetics is an option for the solution–solid phase transition of molecular substances or whether they are determined exclusively by a transition state, we performed crystallization experiments with ferritin and apoferritin, a unique pair of proteins with identical shells but different molecular masses. We find that the kinetic coefficient for crystallization is identical (accuracy ≤7%) for the pair, indicating diffusion-limited kinetics of crystallization. Data on the kinetics of this phase transition in systems ranging from small-molecule ionic to protein and viri suggest that the kinetics of solution-phase transitions for broad classes of small-molecule and protein materials are diffusion-limited.

Molecular mechanisms of microheterogeneity‐induced defect formation in ferritin crystallization

We apply in situ atomic force microscopy to the crystallization of ferritins from solutions containing ≈5% (w/w) of their inherent molecular dimers. Molecular resolution imaging shows that the dimers consist of two bound monomers. The constituent monomers are likely partially denatured, resulting in increased hydrophobicity of the dimer surface. Correspondingly, the dimers strongly adsorb on the crystal surface. The adsorbed dimers hinder step growth and on incorporation by the crystal initiate stacks of up to 10 triple and single vacancies in the subsequent crystal layers. The molecules around the vacancies are shifted by ≈0.1 molecular dimensions from their crystallographic positions. The shifts strain the lattice and, as a consequence, at crystal sizes > 200 μm, the accumulated strain is resolved by a plastic deformation whereupon the crystal breaks into mosaic blocks 20–50 μm in size. The critical size for the onset of mosaicity is similar for ferritin and apoferritin and close to the value for a third protein, lysozyme; it also agrees with theoretical predictions. Trapped microcrystals in ferritin and apoferritin induce strain with a characteristic length scale equal to that of a single point defect, and, as a consequence, trapping does not contribute to the mosaicity. The sequence of undesired phenomena that include heterogeneity generation, adsorption, incorporation, and the resulting lattice strain and mosaicity in this and other proteins systems, could be avoided by improved methods to separate similar proteins species (microheterogeneity) or by increasing the biochemical stability of the macromolecules against oligomerization. Proteins 2001;43:343–352.

Step bunching in a diffusion-controlled system: phase-shifting interferometry investigation of ferritin.

We present a novel phase-shifting interferometry technique for investigations of the unsteady kinetics and the formation of spatio-temporal patterns during the protein crystallization. We applied this technique to the ferritin crystal growth, which is controlled by the rate of supply of material. We find strong fluctuations of growth rate, step density and step velocity due to passage of step bunches. The fluctuation amplitudes decrease with higher supersaturation and larger crystal size, as well as with increasing distance from the step sources. Since these are parameters affecting the solute supply field, we conclude that fluctuations are rooted in the coupling of the interfacial processes of growth to the bulk transport in the solution. Analysis of the step velocity dependence on local slope indicates a very weak interaction between the steps. Hence, in diffusion-controlled systems with non-interacting or weakly interacting steps the stable growth mode is that via equidistant step trains, and randomly arising step bunches decay.

Spatio-Temporal Patterns in Ferritin Crystal Growth

Abstract : We investigate the unsteady kinetics and the formation of spatio-temporal patterns during the ferritin crystal growth, which is controlled by the rate of supply of material. For this we apply a novel phase-shifting interferometry technique. We find that the growth rate and local slope fluctuate by up to 100% of their average values as a result of step bunching. The fluctuation amplitudes decrease with higher supersaturation and larger crystal size, as well as with increasing distance from the step sources. Since these are parameters that govern the protein supply field, we conclude that fluctuations are rooted in the coupling of the interfacial processes of growth to the bulk transport in the solution. Analysis of the step velocity dependence on local slope indicates a very weak interaction between the steps. Hence, in transport-controlled systems with non-interacting or weakly interacting steps the step bunches decay and step train tends towards its stable, equidistant state.