A. Berman et al., CRYSTAL PROTEIN INTERACTIONS - CONTROLLED ANISOTROPIC CHANGES IN CRYSTAL MICROTEXTURE, Journal of physical chemistry, 97(19), 1993, pp. 5162-5170
A unique set of proteins extracted from a variety of invertebrate calc
itic mineralized tissues is able to selectively interact in vitro with
certain crystal faces and not others. This was previously demonstrate
d by observing changes in morphology of crystals grown in the presence
of proteins as compared to those grown in the absence of proteins. Fo
llowing interaction, the proteins are overgrown by the crystal and are
subsequently occluded within the crystal itself. Here we address the
fundamental question of whether or not the proteins also alter the cry
stal texture in an anisotropic manner. For this purpose we used high-r
esolution synchrotron X-ray diffraction to monitor changes in coherenc
e length and angular spread. We studied the interactions of proteins e
xtracted from the mineralized skeletal hard parts of sea urchins and m
ollusks, with crystals of two calcium dicarboxylic acids, calcium fuma
rate and calcium malonate, as well as the polymorph of CaCO3 calcite.
For the calcium dicarboxylate crystals, we did demonstrate that the co
herence lengths are reduced in the directions perpendicular to the pla
nes onto which the proteins preferentially adsorb. In contrast the cal
cite crystals grown in the presence of the proteins exhibited an incre
ase in angular spread compared to the controls, but no anisotropic eff
ect in coherence length was detected. A biologically produced calcite
crystal, on the other hand, showed a preferential reduction in coheren
ce length in the direction of the c axis. Clearly in the case of calci
te, the processes controlling crystal texture in the biological enviro
nment are more sophisticated than those in vitro. The detection of a r
eduction in coherence length in the directions perpendicular to the pl
anes onto which the proteins preferentially adsorbed represents one of
very few direct demonstrations that an additive that is able to selec
tively alter crystal morphology also affects crystal texture in an ani
sotropically specific manner. An understanding of this phenomenon may,
in the future, improve our ability to control crystal texture in synt
hetic materials.