Quantitative study of crystallization kinetics of hen egg-white lysozyme using magnetic orientation

Magnetic stabilization energy of a lysozyme crystal is a function of both magnetic strength and the number of molecules in a crystal. We therefore used magnetic orientation to clarify the process under normal gravity where crystals grow in solution and then sediment to the bottom of the vessel, where they continue to grow. When a magnetic field of 1.6 T was applied immediately after the solution preparation (t = 0) and was continued for various duration times, photomicrographs taken after completion of the crystallization process showed that magnetically oriented crystals sediment before the field was switched off (t = t). The ratio of the number of magnetically orientated crystals to the total number of crystals could be approximated by Ratio = 1 - exp(- kt), where k is a rate constant of the crystal growth and sedimentation. When the supersaturation ratio beta was 5.3, 6.7, and 8.0, the approximated value of k was 0.016, 0.15, and 0.48h, respectively, k significantly increases with increasing beta. This equation explains quantitatively the transient behavior of the growth and sedimentation of crystals. We also analyzed Ratio by growing crystals under various magnetic-field strengths (0-1.6 T), and found that most crystals sediment to the bottom, when their size is 2-6 mu m Numerical simulation also showed that the process of sedimentation is determined by the size of crystals. In conclusion, a rate constant k that we determined in this study characterizes the process where crystals grow to 2-6 mu m and then sediment to the bottom of the vessel, and that crystallization growth strongly depends on the supersaturation ratio beta. (C) 1998 Elsevier Science B.V. All rights reserved.