Calcium monohydrogen phosphate

Fig. 5. Presentation of molecular structure of a sheet composed of phosphate-cation chains cross-linked in a planar pattern. Such structures are known from calcium monohydrogen phosphate dihydrate CaHPC>4 2 H2O and from monohydrate CaHP04 H2O (after MacLennan and Beevers65) Beevers64 )...

It was stated that hydrated calcium monohydrogen phosphate in amorphous or cryptocrystalline form is a potential precursor in the formation of hydroxyapatite because the structural position of Ca2+ on (010) and (110) crystal planes of both minerals essentially correspond to one another492. These planes of calcium ions could easily serve as transition boundaries with little distortion of crystal structure the same holds true for octacalcium phosphate or defect apatites. Thus apatite may form from amorphous or microcrystalline calcium monohydrogen phosphate possible via octacalcium phosphate or defect apatites. This process may already start inside the matrix vesicles and continue during extravesicular activities. 

Francis, M. D., and Webb, N. C. Hydroxyapatite formation from a hydrated calcium monohydrogen phosphate precursor. Calc. Tiss. Res. 6, 335-342 (1971). 

Methods for the synthesis of calcium hydroxyapatite have been reported in the past,1,2 but all of them produced either poorly crystallized or somewhat impure products. The following procedure produces a very well-crystallized compound which has a high degree of purity. The reaction is simply the hydrolysis of calcium monohydrogen phosphate to hydroxyapatite in a closed system. The major disadvantage is the small amount of material obtained from each hydrolysis because of the small capacity of the bombs used. Larger reaction vessels would minimize this objection. 

A-TAB calcium monohydrogen phosphate calcium orthophosphate Di-Cafos AN dicalcium orthophosphate E341 Emcompress Anhydrous Fujicalin phosphoric acid calcium salt (1 1) secondary calcium phosphate. 

The presence of even one fluoride ion in the crystal slows the transformation to amorphous calcium monohydrogen phosphate. Thus, in the presence of fluoride (e.g., after using fluoridated toothpastes), fluoroapatite forms at the tooth surface and reduces the rate of caries development. The increased fluoride concentration at the tooth surface also inhibits lactate production. These observations explain why cleaning the teeth with fluoridated toothpaste prevent caries. Cleaning the teeth exposes the apatite at the enamel surface. In the absence of fluoride, there is no protection because the biofilm forms within a few... 

Fig. 16.6 Hydroxyapatite and fluoroapatite formation and dissolution, (a) Hydroxyapatite is transformed to fluoroapatite by isomorphous replacement. Fluoride ions diffuse into a hydroxyapatite crystal where they replace the hydroxide ions, (b) Fluoroapatite cannot dissolve as easily as hydroxyapatite. Right to left shows the solid-state rearrangement of hydroxyapatite to calcium monohydrogen phosphate, free calcium ions, and monohydrogen phosphate. The latter becomes mostly dihydrogen phosphate above pH 6.2. Arrows between (b) and (a) indicate enhanced apatite formation or slower changes to the amorphous solid if fluoride is present. Left to right shows the precipitation of calcium monohydrogen phosphate and its change to hydroxyapatite if an acid solution is made alkaline.

Apatites must undergo a solid-state transition to amorphous calcium phosphate before they can dissolve and the spontaneous replacement of hydroxide with fluoride ions slows the rate at which this transition occurs (Fig. 16.6b). Conversely, as an acid environment becomes more alkaline, fluoride ions promote the precipitation and crystallization of amorphous calcium monohydrogen phosphate/calcium fluoride into fluoro- and difluoro-apatites faster than amorphous calcium phosphate would crystallize into hydroxyapatite. Thus, fluoride ions have two effects on enamel that protect from caries they slow enamel dissolution in lactic acid and promote its re-precipitation and crystallization when the lactic acid is neutralized. 

Calcium monohydrogen phosphate dihydrate Calcium phosphate, dibasic, dihydrate Dicalcium phosphate dihydrate Phosphoric xid, caicium salt (1 1), dihydrate. Dibasic calcium phosphate dihydrate USP/BP excipient tor production of pharmaceutical tablets by direct compression process. Penwest Pharmaceuticals Co. 

Dibasic calcium phosphate, CaHP04, is also called calcium monohydrogen phosphate, dicalcium orthophosphate, or secondary calcium phosphate. It is usually found in the form of hydrate, such as CaHP04 2H20. It does not melt, instead decomposing when heated to 109°C (228°F). 

Francis MD, Web NC (1971) Hydroxylapatite formation from hydrated calcium monohydrogen phosphate precursor. Calc Tissue Res 6 335-342... 

Calcium monohydrogen phosphate. See Calcium phosphate dibasic Calcium monosilkate. See Calcium silicate... 

Synonyms Bicalcium phosphate Calcium hydrogen orthophosphate Calcium hydrogen phosphate Calcium hydrogen phosphate anhydrous Calcium monohydrogen phosphate DCP-0 Dicalcium orthophosphate Dicalcium orthophosphate anhydrous Dicalcium phosphate Phosphoric acid calcium salt (1 1) Secondary calcium phosphate... 

Calcium monohydrogen phosphate. See Calcium phosphate dibasic Calcium monohydrogen phosphate dihydrate. See Calcium phosphate dibasic dihydrate Calcium monosilicate. See Calcium silicate Calcium monosulfide. See Calcium sulfide Calcium montanate... 

Capsules disintegrate when the capsule shell dissolves and the powder mixmre is wetted. Hydrophilic excipients promote the wetting of the powder bed (Fig. 4.1). Due to the low compaction of the encapsulated powder, and the easy dissolution of most diluents for capsules, the addition of a disintegrating agent is often not needed for pharmacy preparations. However, when excipients compact easily (e.g. calcium monohydrogen phosphate dihydrate) a disintegrant is recommended. 

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