- Structure of calcium phosphate
- Amorphous calcium phosphate
- The rest of the family
- Physical and chemical properties
- Names
- Molecular weight
- Physical description
- Taste
- Melting point
- Solubility
- Density
- Refractive index
- Standard enthalpy of formation
- Storage temperature
- pH
- Training
- Calcium nitrate and ammonium hydrogen phosphate
- Calcium hydroxide and phosphoric acid
- Applications
- In bone tissue
- Bioceramic cements
- Doctors
- Others
- References
The calcium phosphate is an inorganic salt and tertiary whose chemical formula is Ca 3 (PO 4) 2. The formula states that the composition of this salt is 3: 2 for calcium and phosphate, respectively. This can be seen directly in the image below, where the Ca 2+ cation and the PO 4 3- anion are shown. For every three Ca 2+ there are two PO 4 3- interacting with them.
On the other hand, calcium phosphate refers to a series of salts that vary depending on the Ca / P ratio, as well as the degree of hydration and pH. In fact, there are many types of calcium phosphates that exist and can be synthesized. However, following the nomenclature to the letter, calcium phosphate refers only to tricalcium, the one already mentioned.
Proportion and ions in tricalcium phosphate. Source: RicHard-59, from Wikimedia Commons
All calcium phosphates, including Ca 3 (PO 4) 2, are white solids with slight grayish tones. They can be granular, fine, crystalline, and have particle sizes of around microns; and even nanoparticles of these phosphates have been prepared, with which biocompatible materials for bones are designed.
This biocompatibility is due to the fact that these salts are found in the teeth and, in short, in the bone tissues of mammals. For example, hydroxyapatite is a crystalline calcium phosphate, which in turn interacts with an amorphous phase of the same salt.
This means that there are amorphous and crystalline calcium phosphates. For that reason it is not surprising the diversity and multiple options when synthesizing materials based on calcium phosphates; materials in whose properties every day researchers are more interested worldwide to focus on the restoration of bones.
Structure of calcium phosphate
Calcium phosphate in the mineral whitlockite. Source: Smokefoot, from Wikimedia Commons
The upper image shows the structure of tribasic calico phosphate in the strange mineral whitlockite, which can contain magnesium and iron as impurities.
Although at first glance it may seem complex, it is necessary to clarify that the model assumes covalent interactions between the oxygen atoms of phosphates and the metal centers of calcium.
As a representation, it is valid, however, the interactions are electrostatic; that is, Ca 2+ cations are attracted to PO 4 3- (Ca 2+ - O-PO 3 3-) anions. With this in mind, it is understood why in the image the calcium (green spheres) are surrounded by the negatively charged oxygen atoms (red spheres).
Since there are so many ions, it does not leave a symmetrical arrangement or pattern visible. Ca 3 (PO 4) 2 adopts at low temperatures (T <1000 ° C) a unit cell corresponding to a rhombohedral crystalline system; This polymorph is known by the name of β-Ca 3 (PO 4) 2 (β-TCP, for its acronym in English).
At high temperatures, on the other hand, it transforms into the polymorph α-Ca 3 (PO 4) 2 (α-TCP), whose unit cell corresponds to a monoclinic crystalline system. At even higher temperatures, the polymorph α'-Ca 3 (PO 4) 2, which has a hexagonal crystalline structure, can also form.
Amorphous calcium phosphate
Crystal structures have been mentioned for calcium phosphate, which is to be expected from a salt. However, it is capable of exhibiting disordered and asymmetric structures, linked more to a type of “calcium phosphate glass” than to crystals in the strict sense of its definition.
When this occurs, calcium phosphate is said to have an amorphous structure (ACP, amorphous calcium phosphate). Several authors point to this type of structure as responsible for the biological properties of Ca 3 (PO 4) 2 in bone tissues, its repair and biomimetization being possible.
By elucidating its structure by nuclear magnetic resonance (NMR), the presence of OH - and HPO 4 2- ions has been found in ACP. These ions are formed by the hydrolysis of one of the phosphates:
PO 4 3- + H 2 O <=> HPO 4 2- + OH -
As a result, the true structure of ACP becomes more complex, whose composition of its ions is represented by the formula: Ca 9 (PO 4) 6-x (HPO 4) x (OH) x. The 'x' indicates the degree of hydration, since if x = 1, then the formula would be: Ca 9 (PO 4) 5 (HPO 4) (OH).
The different structures that ACP may have depend on the Ca / P molar ratios; that is, of the relative amounts of calcium and phosphate, which change all its resulting composition.
The rest of the family
Calcium phosphates are in fact a family of inorganic compounds, which in turn can interact with an organic matrix.
The other phosphates are obtained "simply" by changing the anions that accompany calcium (PO 4 3-, HPO 4 2-, H 2 PO 4 -, OH -), as well as the type of impurities in the solid. Thus, up to eleven or more calcium phosphates, each with its own structure and properties, can be naturally or artificially originated.
Some phosphates and their respective chemical structures and formulas will be mentioned below:
-Calcium hydrogen phosphate dihydrate, CaHPO 4 ∙ 2H 2 O: monoclinic.
-Calcium dihydrogen phosphate monohydrate, Ca (H 2 PO 4) 2 ∙ H 2 O: triclinic.
-Anhydrous diacid phosphate, Ca (H 2 PO 4) 2: triclinic.
-Octacalcium hydrogen phosphate (OCP), Ca 8 H 2 (PO 4) 6: triclinic. It is a precursor in the synthesis of hydroxyapatite.
-Hydroxyapatite, Ca 5 (PO 4) 3 OH: hexagonal.
Physical and chemical properties
Names
-Calcium phosphate
-Tricalcium phosphate
-Ticalcium diphosphate
Molecular weight
310.74 g / mol.
Physical description
It is an odorless white solid.
Taste
Tasteless.
Melting point
1670 ° K (1391 ° C).
Solubility
-Practically insoluble in water.
-Insoluble in ethanol.
-Soluble in dilute hydrochloric acid and nitric acid.
Density
3.14 g / cm 3.
Refractive index
1,629
Standard enthalpy of formation
4126 kcal / mol.
Storage temperature
2-8 ° C.
pH
6-8 in an aqueous suspension of 50 g / L of calcium phosphate.
Training
Calcium nitrate and ammonium hydrogen phosphate
There are numerous methods to be able to produce or form calcium phosphate. One of them consists of a mixture of two salts, Ca (NO 3) 2 ∙ 4H 2 O, and (NH 4) 2 HPO 4, previously dissolved in absolute alcohol and water, respectively. One salt provides the calcium, and the other the phosphate.
From this mixture the ACP precipitates, which is then subjected to heating in an oven at 800 ° C for 2 hours. As a result of this procedure, β-Ca 3 (PO 4) 2 is obtained. By carefully controlling temperatures, agitation, and contact times, nanocrystal formation can occur.
To form the α-Ca 3 (PO 4) 2 polymorph it is necessary to heat the phosphate above 1000 ° C. This heating is carried out in the presence of other metal ions, which stabilize this polymorph sufficiently so that it can be used at room temperature; that is, it remains in a stable meta state.
Calcium hydroxide and phosphoric acid
Calcium phosphate can also be formed by mixing the solutions of calcium hydroxide and phosphoric acid, producing an acid-base neutralization. After half a day of maturation in the mother liquors, and their due filtration, washing, drying and sieving, a granular amorphous phosphate powder, ACP, is obtained.
This ACP reactions product of high temperatures, transforming according to the following chemical equations:
2Ca 9 (HPO 4) (PO 4) 5 (OH) => 2Ca 9 (P 2 O 7) 0.5 (PO 4) 5 (OH) + H 2 O (at T = 446.60 ° C)
2Ca 9 (P 2 O 7) 0.5 (PO 4) 5 (OH) => 3Ca 3 (PO 4) 2 + 0.5H 2 O (at T = 748.56 ° C)
In this way, β-Ca 3 (PO 4) 2, its most common and stable polymorph, is obtained.
Applications
In bone tissue
Ca 3 (PO 4) 2 is the main inorganic constituent of bone ash. It is a component of bone replacement transplants, this being explained by its chemical similarity with the minerals present in bone.
Calcium phosphate biomaterials are used to correct bone defects and in the coating of titanium metal prostheses. Calcium phosphate is deposited on them, isolating them from the environment and slowing down the titanium corrosion process.
Calcium phosphates, including Ca 3 (PO 4) 2, are used to make ceramic materials. These materials are biocompatible, and are currently used to restore alveolar bone loss resulting from periodontal disease, endodontic infections, and other conditions.
However, they should only be used to accelerate periapical bone repair, in areas where there is no chronic bacterial infection.
Calcium phosphate can be used to repair bone defects when an autogenous bone graft cannot be used. It can be used alone or in combination with a biodegradable and resorbable polymer, such as polyglycolic acid.
Bioceramic cements
Calcium phosphate cement (CPC) is another bioceramic used in the repair of bone tissue. It is made by mixing the powder of different types of calcium phosphates with water, forming a paste. The paste can be injected or fitted to the bone defect or cavity.
Cements are molded, gradually resorbed, and replaced by newly formed bone.
Doctors
-Ca 3 (PO 4) 2 is a basic salt, which is why it is used as an antacid to neutralize excess stomach acid and increase the pH. In toothpastes, it provides a source of calcium and phosphate to facilitate the remineralization process of the teeth and bone hemostasis.
-It is also used as a nutritional supplement, although the cheapest way to supply calcium is by using its carbonate and citrate.
-Calcium phosphate can be used in the treatment of tetany, latent hypocalcemia and maintenance therapy. Also, it is useful in calcium supplementation during pregnancy and lactation.
-It is used in the treatment of contamination with radioactive isotopes radio (Ra-226) and strontium (Sr-90). Calcium phosphate blocks the absorption of radioactive isotopes in the digestive tract, thus limiting the damage caused by them.
Others
-Calcium phosphate is used as feed for birds. In addition, it is used in toothpastes to control tartar.
-It is used as an anti-caking agent, for example to prevent table salt from compacting.
-It works as a flour bleaching agent. Meanwhile, in lard, it prevents unwanted coloration and improves the frying condition.
References
- Tung MS (1998) Calcium Phosphates: Structure, Composition, Solubility, and Stability. In: Amjad Z. (eds) Calcium Phosphates in Biological and Industrial Systems. Springer, Boston, MA.
- Langlang Liu, Yanzeng Wu, Chao Xu, Suchun Yu, Xiaopei Wu, and Honglian Dai. (2018). "Synthesis, Characterization of Nano-β-Tricalcium Phosphate and the Inhibition on Hepatocellular Carcinoma Cells," Journal of Nanomaterials, vol. 2018, Article ID 7083416, 7 pages, 2018.
- Combes, Christ and Rey, Christian. (2010). Amorphous calcium phosphates: synthesis, properties and uses in biomaterials. Acta Biomaterialia, vol. 6 (n ° 9). pp. 3362-3378. ISSN 1742-7061
- Wikipedia. (2019). Tricalcium phosphate. Recovered from: en.wikipedia.org
- Abida et al. (2017). Tricalcium phosphate powder: Preparation, characterization and compaction abilities. Mediterranean Journal of Chemistry 2017, 6 (3), 71-76.
- PubChem. (2019). Calcium phosphate. Recovered from: pubchem.ncbi.nlm.nih.gov
- Elsevier. (2019). Calcium phosphate. Science Direct. Recovered from: sciencedirect.com