Spherulitic
growth of hen egg-white lysozyme crystals
Heijna MCR (Heijna, Maurits C. R.),
Theelen MJ (Theelen, Mirjam J.), van Enckevort WJP (van Enckevort,
Willem J. P.), Vlieg E (Vlieg, Elias)
JOURNAL OF PHYSICAL CHEMISTRY B 111
(7): 1567-1573 FEB 22 2007
Abstract:
In protein crystallography, spherulites are considered the result of a
failed crystallization experiment. Understanding the formation of these
structures may contribute to finding methods to prevent their
formation. Here, we present an in situ study on lysozyme spherulites
grown from sodium nitrate and sodium thiocyanate solutions,
investigating their morphology and growth kinetics using optical
microscopy. In a morphodrom, we indicate the conditions at which
spherulites form for the lysozyme-nitrate system, showing that
liquid-liquid phase separation is not a prerequisite to form sheaflike
spherulites and that supersaturation is not the only factor determining
their creation. Despite their sheaflike morphology, the spherulites all
appear to be formed through heterogeneous nucleation. The spherulites
are of a new polymorphic form and are less stable than the monoclinic
form. For a single needle, growth kinetics indicate surface processes
to be the rate-limiting step during growth, but for an entire
spherulite volume, diffusion still plays a role. Spherulites simulated
by using a time-dependent, tip-splitting model are found to compare
well to experimentally observed spherulites.