greater part when WSM from vaterite pearls existed in the solution. The formation
of vaterite appears to be clearly connected to the water-soluble matrices. Such
kind of extraction method could also define different effects of protein matrices
in a more detailed way. Using biochemical methods like reverse-phase highperformance liquid chromatography and SDS-PAGE, scientists have successfully
obtained purified proteins, such as nacrein (Miyamoto et al. 1996), lustrin A (Shen
et al. 1997), MSI60 (Sudo et al. 1997), N16 (Sarikaya et al. 1999), pearlin
(Miyashita et al. 2000), mucoperlin (Marin et al. 2000), N14 (Kono et al. 2000),
N66 (Kono et al. 2000), perlucin (Weiss et al. 2000), perlustrin (Weiss et al. 2000),
p20 (Bedouet et al. 2001), MSI7 (Zhang et al. 2003b), AP7 (Michenfelder et al.
2003), AP24 (Michenfelder et al. 2003), p10 (Zhang et al. 2006), and AP8 (Fu et al.
2005). Some of their effects on mineralization under in vitro conditions were
studied. Almost all these protein matrices were extracted by EDTA or weak acids
(acetic acid normally) dissolving the calcium carbonate crystals, and were classified
by their dissolubility. But, the formation of natural biominerals is a very complicated process, in which a series of proteins were involved, even though initial
researches about how proteins work in the mineralization process in organisms, a
lot of issues were still not figured out clearly, and those proteins with even tiny
content might be extremely in such processes.
6.4.1.2 Amino Acids in the Solution as Additives
Amino acid analysis of SM indicated that the three most important amino acids are
glycine, aspartic acid, and glutamic acid (Lavi et al. 1998).
Hou and Feng (2006b) studied the function of glycine in the mineralization
system; they selected two methods to precipitate CaCO 3 particles: titration method
and diffusion method. In titration method, under stirring condition, with short
depositing time, both calcite and vaterite particles were formed, and the proportion
of vaterite increased with the increase of the glycine concentration. The shape of
calcite and vaterite are normally rhombic and spherical, respectively (Fig. 6.15).
With the extending of deposition time, all calcium carbonate crystals are vaterite
particles with spherical and spindly morphologies, regardless the concentration of
glycine. The results showed that stirring condition itself was sufficient to induce
formation of spindly vaterite when the dripping velocity was slow enough. The
possible reason is that stirring changed the activation energy of nucleation (DG n ) of
calcite and vaterite in the aqueous system and upset their nucleation priorities
(Mann et al. 1993). They also found that rapid titration produced local instantaneous high supersaturation to overcome the nucleation energy barrier of both
calcite and vaterite. On the other hand, slow titration provided a longer time for
nucleation and limited the supersaturation value to induce vaterite. In the diffusion
method with glycine in the solution without stirring, depositions were almost all
spherical vaterite particles without any spindly ones, which implied that the spindly
shape occurring in the titration experiments is directly caused by stirring. And
they supposed that glycine may change the activation energy of nucleation in
6 Principles of Calcium-Based Biomineralization
173
of vaterite appears to be clearly connected to the water-soluble matrices. Such
kind of extraction method could also define different effects of protein matrices
in a more detailed way. Using biochemical methods like reverse-phase highperformance liquid chromatography and SDS-PAGE, scientists have successfully
obtained purified proteins, such as nacrein (Miyamoto et al. 1996), lustrin A (Shen
et al. 1997), MSI60 (Sudo et al. 1997), N16 (Sarikaya et al. 1999), pearlin
(Miyashita et al. 2000), mucoperlin (Marin et al. 2000), N14 (Kono et al. 2000),
N66 (Kono et al. 2000), perlucin (Weiss et al. 2000), perlustrin (Weiss et al. 2000),
p20 (Bedouet et al. 2001), MSI7 (Zhang et al. 2003b), AP7 (Michenfelder et al.
2003), AP24 (Michenfelder et al. 2003), p10 (Zhang et al. 2006), and AP8 (Fu et al.
2005). Some of their effects on mineralization under in vitro conditions were
studied. Almost all these protein matrices were extracted by EDTA or weak acids
(acetic acid normally) dissolving the calcium carbonate crystals, and were classified
by their dissolubility. But, the formation of natural biominerals is a very complicated process, in which a series of proteins were involved, even though initial
researches about how proteins work in the mineralization process in organisms, a
lot of issues were still not figured out clearly, and those proteins with even tiny
content might be extremely in such processes.
6.4.1.2 Amino Acids in the Solution as Additives
Amino acid analysis of SM indicated that the three most important amino acids are
glycine, aspartic acid, and glutamic acid (Lavi et al. 1998).
Hou and Feng (2006b) studied the function of glycine in the mineralization
system; they selected two methods to precipitate CaCO 3 particles: titration method
and diffusion method. In titration method, under stirring condition, with short
depositing time, both calcite and vaterite particles were formed, and the proportion
of vaterite increased with the increase of the glycine concentration. The shape of
calcite and vaterite are normally rhombic and spherical, respectively (Fig. 6.15).
With the extending of deposition time, all calcium carbonate crystals are vaterite
particles with spherical and spindly morphologies, regardless the concentration of
glycine. The results showed that stirring condition itself was sufficient to induce
formation of spindly vaterite when the dripping velocity was slow enough. The
possible reason is that stirring changed the activation energy of nucleation (DG n ) of
calcite and vaterite in the aqueous system and upset their nucleation priorities
(Mann et al. 1993). They also found that rapid titration produced local instantaneous high supersaturation to overcome the nucleation energy barrier of both
calcite and vaterite. On the other hand, slow titration provided a longer time for
nucleation and limited the supersaturation value to induce vaterite. In the diffusion
method with glycine in the solution without stirring, depositions were almost all
spherical vaterite particles without any spindly ones, which implied that the spindly
shape occurring in the titration experiments is directly caused by stirring. And
they supposed that glycine may change the activation energy of nucleation in
6 Principles of Calcium-Based Biomineralization
173