Nucleation and Growth of Mg-Calcite Spherulites Induced by the Bacterium Curvibacter lanceolatus Strain HJ-1
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Abstract Calcite spherulites have been observed in many laboratory experiments with different bacteria, and spherulitic growth has received much interest in mineralogy research. However, the nucleation and growth mechanism, as well as geological significance of calcite spherulites in solution with bacteria is still unclear. Herein, spherulites composed of an amorphous core, a Mg-calcite body and an organic film were precipitated by the Curvibacter lanceolatus HJ-1 bacterial strain in a solution with a molar Mg/Ca ratio of 3. Based on the results, we provide a possible mechanism for the biomineralization of Mg-calcite spherulites. First, amorphous calcium carbonate particles are deposited and aggregated into a stable sphere-like core in combination with organic molecules. The core then acts as the nucleus of spherulitic radial growth. Finally, the organic film grows on the surface of Mg-calcite spherulites as a result of bacterial metabolism and calcification. These findings provide insight into the growth mode and crystallization of biogenic spherulites during biomineralization, and are of significance in the application of novel biological materials.Keywords:
Amorphous calcium carbonate
Spherulite (polymer physics)
Morphology
The effect of organic molecules on CaCO3 crystallization, in particular on the formation of the initial amorphous calcium carbonate (ACC) phase, is poorly understood despite this knowledge being crucial for designing biomimetic compounds with specific function, strength and stability. We monitored ACC crystallization in the presence of varying concentrations of aspartic acid (ASP) and glycine (GLY). We observed an increase in ACC lifetime with increasing amino acid concentrations and showed that the amino acid molecules sorbed onto the ACC particles. However, little if any difference in composition and atomic structure or the so formed ACC was observed. Similarly, the crystallization pathway of ACC via vaterite and calcite although delayed, was only slightly affected by the added amino acids. The only exemption was at the highest tested ASP concentration where ACC formation was inhibited, The calcite crystals that formed in the presence of ASP had rounded edges and rough surfaces, features that are not observed for the pure, inorganic calcite or calcite formed in the presence of GLY. Overall, the results suggest that the amino acids affected ACC lifetime through the inhibition of crystal nucleation and growth, more so in the presence of ASP than GLY.
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A new and simple method for preparing large-area and continuous calcium carbonate films under mild conditions is described. Amorphous calcium carbonate (ACC) films have been formed both in the presence and absence of a poly(acrylic acid) inhibitor. The transformation from ACC to crystalline vaterite/calcite has been observed by optical microscopy and confirmed by external reflection infrared spectroscopy. We have shown that the inhibiting effects of substrates and inhibitors on the transformation of ACC result in the formation of good CaCO3 films. From our results, we suggested that ACC precipitates are initially formed from highly supersaturated solutions, which then deposit as films through the cooperation between an insoluble matrix and a soluble inhibitor. The matrix and inhibitor were also found to affect the growth, morphology, and structure of CaCO3 crystal by influencing the phase transformation of ACC into crystalline forms. It has been shown that ACC plays an important role in the biomineralization and crystallization of calcium carbonate.
Vaterite
Amorphous calcium carbonate
Supersaturation
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Abstract The use of amorphous calcium carbonate (ACC) as a precursor phase affords organisms with outstanding control over the formation of calcite and aragonite biominerals. Essential to this strategy is that the ACC is maintained within confined volumes in the absence of bulk water. This ensures that the ACC undergoes a pseudomorphic transformation and that the organism can independently control nucleation and growth. However, comparable control has proven hard to achieve in synthetic systems. Here, a straightforward method is demonstrated for controlling the crystallization of ACC thin films in which nucleation is first triggered using a heated probe, and then growth is sustained by incubating the film at a lower temperature. By independently controlling nucleation and growth, sub‐millimeter calcite single crystals can be generated when and where it is desired, morphologies ranging from discs to squares to serpentine strips can be created, and arrays of crystals formed. The mechanism and energetics of crystallization of the ACC are studied using in situ transmission electron microscopy and continuity between the ACC and calcite at the growth front is demonstrated. It is envisaged that this method can be applied to the formation of large single crystals of alternative functional materials that form via amorphous precursor phases.
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Abstract Calcite spherulites have been observed in many laboratory experiments with different bacteria, and spherulitic growth has received much interest in mineralogy research. However, the nucleation and growth mechanism, as well as geological significance of calcite spherulites in solution with bacteria is still unclear. Herein, spherulites composed of an amorphous core, a Mg-calcite body and an organic film were precipitated by the Curvibacter lanceolatus HJ-1 bacterial strain in a solution with a molar Mg/Ca ratio of 3. Based on the results, we provide a possible mechanism for the biomineralization of Mg-calcite spherulites. First, amorphous calcium carbonate particles are deposited and aggregated into a stable sphere-like core in combination with organic molecules. The core then acts as the nucleus of spherulitic radial growth. Finally, the organic film grows on the surface of Mg-calcite spherulites as a result of bacterial metabolism and calcification. These findings provide insight into the growth mode and crystallization of biogenic spherulites during biomineralization, and are of significance in the application of novel biological materials.
Amorphous calcium carbonate
Spherulite (polymer physics)
Morphology
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Watching nucleation pathways in calcite The initial stage of crystallization, the formation of nuclei, is a critical process, but because of the length and time scales involved, is hard to observe. Nielsen et al. explored the crystallization of calcium carbonate, a well-studied material but one with multiple nucleation theories. Different calcium and carbonate solutions were mixed inside a fluid cell and imaged using a liquid cell inside a transmission electron microscope. Competing pathways operated during nucleation, with both the direct association of ions into nuclei from solution and the transformation of amorphous calcium carbonate into and between different crystalline polymorphs. Science , this issue p. 1158
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An ugly duckling grows into a swan: Many organisms grow their crystalline mineral phases through the secondary nucleation of nanospheres made of an amorphous precursor phase. Stable amorphous calcium carbonate biominerals were used to induce a similar transformation in vitro. The amorphous nanospheres underwent a solid-phase transformation that resulted in highly ordered calcite crystals composed of aggregated particles (see SEM image). As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.
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Amorphous calcium carbonate
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Based on the basic principles of biomineralization,the effects of lignin concentration and system temperature on the growth of CaCO3 crystals were studied.Moreover,the structure,appearance and thermal decomposition properties of CaCO3 were characterized by FT-IR,SEM,XRD and TG.The results demonstrated that CaCO3 formed in lignin solution was calcite,displaying dumbbell-shaped,spherical,oval or football-shaped appearance,which was different from that formed in pure water.Lignin concentration and system temperature had significant impact on the crystal morphology.During the course of crystallization,CaCO3 and lignin had mutual interaction,and the possible mechanism had been discussed.
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Amorphous calcium carbonate
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