Amorphous calcium carbonate
Amorphous calcium carbonate (ACC) is the
ACC is an example of crystallization by particle attachment (CPA), where crystals form via the addition of particles ranging from multi-ion complexes to fully formed nanocrystals.[5] Research of such systems have diverse application; however, the current lack of unambiguous answers to fundamental questions (i.e. solubility product, interfacial forces, structure, etc.) causes them to be topics of study in fields ranging from chemistry, geology, biology, physics, and materials science engineering.[6][5]
Stability
ACC is the sixth and least stable
In biology
Several organisms have developed methods to stabilize ACC by using specialized
Synthetic ACC
Many methods,[9][7][11] have been devised for synthetically producing ACC since its discovery at 1989, however, only few syntheses successfully stabilized ACC for more than several weeks. The best effective method to stabilize ACC lifetime is by forming it in the presence of magnesium and/or phosphorus.[12][13] Also, ACC crystallisation pathways have been observed to depend on its Mg/Ca ratio, transforming to aragonite,[14] Mg-calcite,[15] monohydrocalcite[16] or dolomite[17] with increasing Mg content. Huang et al. managed to stabilize ACC using polyacrylic acid for several months,[18] while Loste et al. showed that magnesium ions can increase ACC stability as well.[19] But only the discovery that aspartic acid, glycine,[20] citrate,[21] and phosphorylated amino acids can produce long term stable ACC[22] have opened the door for production commercialization.
Highly porous ACC
Highly porous ACC has been synthesized using a surfactant-free method.[23] In this method CaO is dispersed in methanol under a pressure of carbon dioxide in a sealed reaction vessel. ACC with surface area over 350 m2/g was synthesized using this method. Highly porous ACC appeared to be made up aggregated nanoparticles with dimensions less than 10 nm in size. Highly porous ACC was also found to be stable in ambient conditions for up to 3 weeks with most of its porosity retained.
Applications and uses
Bioavailability: Since 2013 a company named Amorphical Ltd. sells an ACC dietary supplement.[24][25] Calcium carbonate is used as a calcium supplement worldwide, however, it is known that its bioavailability is very low, only around 20–30%. ACC is roughly 40% more bioavailable than crystalline calcium carbonate.[26]
Drug delivery: Due to the ability to tune the size and morphology of the amorphous calcium carbonate particles (as well as other calcium carbonate particles), they have huge applications in drug delivery systems.[citation needed] Highly porous ACC showed the ability to stabilize poorly soluble drug molecules in its extensive pore system and could also enhance the drug release rates of these drugs.[23]
Paleoclimate reconstruction: A better understanding of the transformation process from amorphous to crystalline calcium carbonate will improve reconstructions of past climates that use chemical and biological proxies. For example, the calibrations of the clumped 13C-18O carbonate paleothermometer and understanding the origins and evolution of skeletal structures.[6][5]
Environmental remediation: Improving environmental remediation efforts through gaining insight into the roles of earth materials in biogeochemical cycling of nutrients and metals through better understandings of the properties of environmental mineral phases involved in elemental uptake and release[27][28]
Material science: Improving nanomaterials design and synthesis such as improving photovoltaic, photocatalytic, and thermoelectric materials for energy applications or improving biomedical cementations. Also improving framework material development for CO2 capture, H2 storage, emissions control, biomass conversion, molecular separations, and biofuel purification.[5]
References
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- ^ US patent 603225, Sturcke, Herman E., "Process of preparing amorphous carbonate of lime from residues", issued April 26, 1898
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- ^ The dietary supplement "DENSITY" homepage Archived March 11, 2015, at the Wayback Machine
- ^ סידן, הדור הבא: התוסף שמצליח לבנות עצם מחדש Hebrew article on Ynet about the new calcium dietary supplement, December 2013
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