Due to its layered nature and structural water content, advantageous properties for applications within the biomedical field are anticipated. In this work, we introduce another crystalline form of CaP: dicalcium phosphate monohydrate (DCPM, CaHPO 4 Metastable CaPs with structural water are thus promising for advancing biomedical applications. However, DCPD seems to provide generally better performance in real uses, as it exists in the majority of setting products 36, 37. DCP and DCPD are both useful in biomedical applications, especially for the curing of calcium phosphate cements in clinical orthopedics. These differences give rise to rather distinct chemical and physical properties for the two forms 34, 35. In DCPD, structural water molecules link layers composed of CaHPO 4 via hydrogen bonds, whereas DCP is anhydrous and the structure is not layered 32, 33 (see below). Until now, two different forms of crystalline CaPs with a Ca/P atomic ratio of 1:1 have been documented: CaHPO 4♲H 2O (brushite dicalcium phosphate dihydrate, DCPD) and CaHPO 4 (monetite dicalcium phosphate, DCP), both playing important roles in geology 4, 5 and biology 30, 31. Despite their structural and chemical variability, however, no further crystalline form of CaP has been found lately. Since X-ray crystallography was developed in the early 20th century 28, 29, the structures of all known CaPs were resolved in the course of that century, while some CaPs were discovered for the first time even earlier 7. CaPs are involved in hard tissue formation and the metabolism of humans and animals, whereas they can also form pathologically 13, 26.ĭue to their chemical composition being similar to that of hard tissues, high biocompatibility and bioactivity, synthetic CaPs have been extensively studied for uses in biomedicine, for example, as coatings of metallic implants and synthetic substitutes for bone repair 27. However, the role of ACPs in biomineralization has been debated 21, 22, 23, 24, 25. Amorphous calcium phosphates (ACPs) have different chemical formulae, and can be the precursors of various crystalline CaPs 8, 9, 10, 11, 12, 13, including hydroxyapatite, in vivo 14, 15, 16, 17, 18, 19, 20. Important members are hydroxyapatite (Ca 10(PO 4) 6(OH) 2) 2, octacalcium phosphate (Ca 8H 2(PO 4) 6♵H 2O) 3, brushite (CaHPO 4♲H 2O) 4, monetite (CaHPO 4) 5, and tricalcium phosphate (Ca 3(PO 4) 2) 6, 7. This study serves as an inspiration for the future exploration of DCPM’s potential role in biomineralization, or biomedical applications.Ĭalcium orthophosphates (CaPs) are common and important in geological and biological systems 1, constituting a family of compounds with varying Ca/P atomic ratios and structural water contents. DCPM is metastable in water, but can be stabilized by organics, and has a higher alkalinity than DCP and DCPD. The crystal structure of DCPM is determined to show a layered structure with a monoclinic symmetry. This form of CaP is found to crystallize from amorphous calcium hydrogen phosphate (ACHP) in water-poor environments. Here, we report the synthesis and crystal structure determination of DCPM. H 2O (dicalcium phosphate monohydrate, DCPM) has remained elusive.In the case of dicalcium phosphates, ever since brushite (CaHPO 4♲H 2O, dicalcium phosphate dihydrate, DCPD) and monetite (CaHPO 4, dicalcium phosphate, DCP) were first described in 19 th century, the form with intermediary chemical formula CaHPO 4 Calcium orthophosphates (CaPs) are important in geology, biomineralization, animal metabolism and biomedicine, and constitute a structurally and chemically diverse class of minerals.
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