Membrane crystallization of lysozyme: kinetic aspects

The relevant kinetic aspects related to an innovative method of biological macromolecules crystallization based on microporous hydrophobic membranes, used both as active surfaces to promote heterogeneous nucleation and as a mass-transfer apparatus to concentrate macromolecular solutions by solvent removal in vapour phase, have been evaluated. Polypropylene membranes, supplied in the form of hollow fibres, have been aligned in a versatile system, designed for an on-line spectrophotometric monitoring of hen egg white lysozyme crystallizing solutions (experimental conditions: 0.1 M NaAc/HAc Buffer pH 4.6, 0.5–5.8% wt/vol NaCl, 20°C). The turbidity measurements have been exploited in order to follow: (i) the induction time of crystallization, (ii) the early stage nucleation kinetics based on the Rayleigh scattering theory, and the crystal growth rate (coupled with data evaluated from image-analysis carried out by optical microscopy) under a model hypothesis of exponential growth of clusters. The crystals have been qualitatively assessed by an X-ray crystallographic analysis carried out at the synchrotron light laboratory ELETTRA.