11/28/2023 0 Comments Ionic charge of calcium carbonateResearchers had long suspected that organic scaffolds caused calcium carbonate to mineralize and find its most stable form, calcite, by creating low energy surfaces where the ions could easily arrange themselves in rows side-by-side. One is by providing an environment where the atoms assemble in the crystal in the least energetic way possible, sort of like organizing a classroom full of schoolchildren by having them sit in seats arranged neatly in rows side-by-side in the corner of the room.Īnother is via chemical binding - negatively or positively charged atoms or molecules called ions attract one another, sort of like waving popsicles in front of those kids to gather them in one spot. There are two main ways that calcium carbonate molecules might be persuaded to come together to form a mineral. The team realized that controlling crystallization by attracting calcium ions to the macromolecules was not the way researchers had long thought it happened. The researchers concluded that calcium binding to the polymer is the key to forming the ACC and controlling where it forms. The ACC grew in size until the supply of calcium ran out. When the researchers then added carbonate to the experimental chamber, ACC formed instead and it only appeared within these globules. ![]() They determined that the polymer had soaked up more than half of the calcium to form the globules. When they mixed the polymer with the calcium first before introducing carbonate, they found globules of the polymer forming in the solution. With the polymer, however, ACC always appeared first and vaterite formed much later.īecause the polymer interfered with vaterite formation, the team looked a little closer at what the polymer was doing. Without the polymer, they saw crystals of vaterite and a little calcite forming randomly under the microscope. Collaborators also hailed from Eindhoven University of Technology in The Netherlands.īut this time they added a negatively charged macromolecule, a polymer called polystyrene sulfonate. To find out, De Yoreo and team allowed calcium carbonate to mineralize under a specialized transmission electron microscope at the Molecular Foundry, a DOE Office of Science User Facility at DOE's Lawrence Berkeley National Laboratory. De Yoreo and his colleagues wondered what role macromolecules - carbs, proteins or other large molecules with a negative charge - play. In addition, biologically built minerals often start out as ACC. For example, pearls develop in the presence of negatively charged carbohydrates and proteins from the oyster. Those experiments, however, lacked a crucial element found in the biological world, where minerals form within an organic scaffold. But in some cases, droplet-like particles of uncrystallized material known as amorphous calcium carbonate, or ACC, formed first and then transformed into either aragonite or vaterite. All of the common crystal forms, including calcite (found in limestone), aragonite (found in mother-of-pearl), and vaterite (found in gallstones), crystallized from solution, often at the same time. Previous work showed that calcium carbonate takes multiple routes to becoming a mineral. And it is one that should provide us with considerable control." Missing Piece "Ion binding defines a completely different mechanism for controlling crystallization than does making a perfect interface between the crystal and the scaffold. "This whole story is different from what we had believed to be the case," said lead researcher Jim De Yoreo at PNNL. ![]() ![]() Rather than these chemical interactions, researchers had previously thought the scaffold guides crystallization by providing the best energetic environment for the crystal. The negative charge on the macromolecules attract the positively charged calcium ions, placing them in the scaffold through so-called ion binding. These large macromolecules do so by directing where calcium ions bind in the scaffold. Using a powerful microscope that lets researchers see the formation of crystals in real time, a team led by the Department of Energy's Pacific Northwest National Laboratory found that negatively charged molecules - such as carbohydrates found in the shells of mollusks - control where, when, and how calcium carbonate forms. Understanding the process better may help researchers develop advanced materials for energy and environmental uses, such as for removing carbon dioxide from the atmosphere. Now, research suggests that the soft, organic scaffolds in which such crystals form guide crystallization by soaking up the calcium like an "ion sponge," according to new work in Nature Materials. ![]() Nature packs away carbon in chalk, shells and rocks made by marine organisms that crystallize calcium carbonate.
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