13.4.4.2 “Nonclassical Effects” of Acidic Proteins of P. nobilis: Effects
at the Crystal Lattice Level
Besides these effects, which can be measured at the micrometric scale (interference
tests), or at the macroscopic levels on gels (calcium-binding) or with an electrode
(inhibition), far less classical effects have been recorded few years ago. These
remarkable findings, which have been generated by our colleagues B. Pokroy and
E. Zolotoyabko, both from the Technion in Haı ¨fa, Israel, require high-precision
diffraction equipment, such as the one of the ESRF, in Grenoble. The goal of their
study was to evidence or not whether intracrystalline proteins had an effect on the
crystallographic properties of biogenic calcite.
In a first set of experiments, Pokroy and Zolotoyabko measured the lattice
parameters of five calcitic molluscan shells microstructures, namely, Pinna nobilis
(prisms), Atrina rigida (prisms), Ostrea edulis (foliated), Crassostrea gigas (foliated), and Haliotis rufescens (prisms). By applying corrections dues to the
incorporation of magnesium and of sulfur in the crystalline lattice, they calculated
the theoretical a, b, c, parameters of these biogenic calcitic crystals. Without any
exception, they observed higher lattice parameter values than that of chemical
calcite. This clearly suggests a slight distortion of the crystal lattice, the maximal
distorsion being according to the c axis (0.2%).
In a second set of experiments, they heated the biogenic calcitic structures, in
order to burn the intracrystalline matrix. They observed a relaxation of the crystal
lattice, i.e., a reduction of the crystal lattice parameters. This indirectly proved that
the intracrystalline molecules induce the lattice distorsion.
To demonstrate without any ambiguity the effect of intracrystalline proteins on
calcite, Pokroy crystallized in vitro pure calcite and also calcite in the presence of
caspartin, via the ammonium bicarbonate diffusion technique. A comparison of the
lattice parameters of both calcites shows again a slight distorsion for the calcite
grown with caspartin. These remarkable results were published in 2006 (Pokroy
et al. 2006). Recently, Zolotoyabko et al. (2010), by using high-resolution neutron
powder diffraction, demonstrated that some of the atomic bonds of biogenic calcite
have significantly different lengths as compared to those of geological calcite. Of
course, in their measurements, they took in account the incorporation of magnesium
ions in the calcite crystal lattice.
Not less remarkable was the following finding of Pokroy and Zolotoyabko.
This time they focused on the phenomenon of twinning. In crystallography, twinning is a well-known phenomenon. It is the oriented association of two or more
crystals of the same chemical nature. These crystals are linked together via a
symmetry operation, according to a plan (twinning plan, twinning by reflection),
to an axis (twinning axis, twinning by rotation), or to a center (twinning center,
twinning by inversion). In more than 150 years of research in crystallography, the
different twinning patterns of calcite had been identified. They are four,
corresponding to the following twinning plans: (001), (012), (104), (018).
13 Acidic Shell Proteins of the Mediterranean Fan Mussel Pinna nobilis
381
at the Crystal Lattice Level
Besides these effects, which can be measured at the micrometric scale (interference
tests), or at the macroscopic levels on gels (calcium-binding) or with an electrode
(inhibition), far less classical effects have been recorded few years ago. These
remarkable findings, which have been generated by our colleagues B. Pokroy and
E. Zolotoyabko, both from the Technion in Haı ¨fa, Israel, require high-precision
diffraction equipment, such as the one of the ESRF, in Grenoble. The goal of their
study was to evidence or not whether intracrystalline proteins had an effect on the
crystallographic properties of biogenic calcite.
In a first set of experiments, Pokroy and Zolotoyabko measured the lattice
parameters of five calcitic molluscan shells microstructures, namely, Pinna nobilis
(prisms), Atrina rigida (prisms), Ostrea edulis (foliated), Crassostrea gigas (foliated), and Haliotis rufescens (prisms). By applying corrections dues to the
incorporation of magnesium and of sulfur in the crystalline lattice, they calculated
the theoretical a, b, c, parameters of these biogenic calcitic crystals. Without any
exception, they observed higher lattice parameter values than that of chemical
calcite. This clearly suggests a slight distortion of the crystal lattice, the maximal
distorsion being according to the c axis (0.2%).
In a second set of experiments, they heated the biogenic calcitic structures, in
order to burn the intracrystalline matrix. They observed a relaxation of the crystal
lattice, i.e., a reduction of the crystal lattice parameters. This indirectly proved that
the intracrystalline molecules induce the lattice distorsion.
To demonstrate without any ambiguity the effect of intracrystalline proteins on
calcite, Pokroy crystallized in vitro pure calcite and also calcite in the presence of
caspartin, via the ammonium bicarbonate diffusion technique. A comparison of the
lattice parameters of both calcites shows again a slight distorsion for the calcite
grown with caspartin. These remarkable results were published in 2006 (Pokroy
et al. 2006). Recently, Zolotoyabko et al. (2010), by using high-resolution neutron
powder diffraction, demonstrated that some of the atomic bonds of biogenic calcite
have significantly different lengths as compared to those of geological calcite. Of
course, in their measurements, they took in account the incorporation of magnesium
ions in the calcite crystal lattice.
Not less remarkable was the following finding of Pokroy and Zolotoyabko.
This time they focused on the phenomenon of twinning. In crystallography, twinning is a well-known phenomenon. It is the oriented association of two or more
crystals of the same chemical nature. These crystals are linked together via a
symmetry operation, according to a plan (twinning plan, twinning by reflection),
to an axis (twinning axis, twinning by rotation), or to a center (twinning center,
twinning by inversion). In more than 150 years of research in crystallography, the
different twinning patterns of calcite had been identified. They are four,
corresponding to the following twinning plans: (001), (012), (104), (018).
13 Acidic Shell Proteins of the Mediterranean Fan Mussel Pinna nobilis
381