Dependence of nucleation kinetics and crystal morphology of a model protein system on ionic strength

Abstract

Nucleation rate data for hen egg-white lysozyme crystallization were obtained using a particle counter. Tetragonal lysozyme crystals were expected to form at the temperature and solution conditions of these experiments: 48C, pH 4.5 with 0.1 M sodium acetate buffer and 2-6% NaCl (w/v). The rates varied as expected, as smooth monotonic functions of supersaturation at 2%, 3% and 6% NaCl. However, at 5% NaCl, a great deal of scatter in the data was observed. At 2% and 3% NaCl, all the batches contained crystals with tetragonal morphology. At 6% NaCl, almost all of the vials contained the white powder with few or no tetragonal crystals. At 5% NaCl concentration, a mixture of tetragonal crystals and powder formed in varying proportions in all the vials as observed by visual inspection. The powdery material was examined using optical microscopy and was seen to consist of needles with regular structure and sharp, faceted edges. Powder diffraction data from these needles was inconsistent with experimental powder diffraction data from tetragonal lysozyme crystals. It is possible that at high salt and protein concentrations liquid-liquid separation occurred and yielded a crystal polymorph. #

Study on nucleation kinetics of lysozyme crystallization

“…At a high salt concentration, i.e. above 5%, the relationship between nucleation rates and protein concentration was absent in the data because crystals with needle shape were formed along with the expected tetragonal crystals reported by Bhamidi et al [8]. Galkin and Vekilov [6,7] reported similar deviations in nucleation rates at high salt concentration.…”

“…From the values of B, the surface free energyγ 8 shown in Table 1 can be estimated. Figure 9 shows the classical nucleation theory model fit to the data.…”

“…It was also based on counting the number of crystals appearing, but the number was again not continuously measured. Bhamidi [8,9] studied Hen egg-white lysozyme (HEWL) nucleation and did use a particle counter (PC2000, from Spectrex Corporation ), but the technique was not intuitive and could have errors. Bhamidi modeled the data using an empirical kinetic expression based on the classical nucleation theory.…”

“…But it was agreed that detecting crystals during the early stages of growth allows one to obtain nucleation rates [9]. So assuming that every critical nucleus can grow into a crystal, one can obtain the nucleation rate by counting crystals as they are formed [8].…”

pH-Driven synthesis of collagen-silica nanohybrids

“…The details of the thermodynamics involved in inorganic-protein crystallization have been studied from a theoretical standpoint [6]. Also, the encapsulation of biological molecules, such as protein or enzymes, into host porous inorganic matrices has received considerable attention [7,8]. The biomolecules encapsulated retain enough level of activity and functionality of the native-state species [9].…”