Growth Modes and Energetics of (101) Face Lysozyme Crystal Growth

Abstract

From analyses of lysozyme (101) face growth rate data using a 2D nucleation model for layer-by-layer growth, we find the effective barrier for crystal growth to be γ = 1.0 ± 0.2 × 10-13 erg/molecule. The magnitude of the effective barrier is (2.4 ± 0.5)kBT, at 22 °C. We also find that beyond a critical solution supersaturation, σc, crystal growth rates are more accurately described by a kinetic roughening hypothesis. Beyond σc, crystals grow by the continuous addition of molecules anywhere on the crystal surface rather than layer-by-layer. The magnitude of the critical supersaturation (σc = 1.7 ± 0.2) for a crossover from a layer-by-layer to continuous growth is found to be statistically independent of the solution conditions that vary with buffer pH, temperature, or precipitant concentration. Using the experimentally determined values for γ and σc, we find the crystal growth unit to be comprised of 7 ± 3 molecules. The energy barrier, Ec, for the continuous addition of the growth units is 6.2 ± 0.3 × 10-13 erg/molecule or (15 ± 1)kBT at 22 °C.