Calcium Orthophosphates: Applications in Nature, Biology, and Medicine Sergey Dorozhkin Copyright © 2012 Pan Stanford Publishing Pte. Ltd. ISBN 978-981-4316-62-0 (Hardcover), 978-981-4364-17-1 (eBook) www.panstanford.com

C. Glaser in 1885 [10]. In 1880s, occurrence of a calcium apatite [11] and calcium orthophosphate [12-14] in a metallurgical slag was discovered. Chemical reactions between calcium orthophosphates and other chemicals were investigated as early as in 1891 [15]. Research papers on bone repairing are known since, at least, 1892 [16], while the earliest well-documented systematic studies of calcium orthophosphates were performed at the beginning of the twentieth century by F. K. Cameron with co-workers [17-21] and H. Bassett [22-25]. The majority of the aforementioned researchers already operated with individual chemical compounds. Further, historical details might be found in Chapter 8. By definition, all calcium orthophosphates consist of three major chemical elements: calcium (oxidation state +2), phosphorus (oxidation state +5) and oxygen (reduction state −2), as a part of orthophosphate anions. These three chemical elements are present in abundance on the surface of our planet: oxygen is the most widespread chemical element of the earth’s surface (~47 mass%), calcium occupies the fifth place (~3.3-3.4 mass%) and phosphorus (~0.08-0.12 mass%) is among the first twenty of the chemical elements most widespread on our planet [26]. In addition, the chemical composition of many calcium orthophosphates includes hydrogen, as an acidic orthophosphate anion (for example, HPO42− or H2PO4−), hydroxide (for example, Ca10(PO4)6(OH)2) and/or incorporated water (for example, CaHPO4·2H2O). Diverse combinations of CaO and P2O5 (both in the presence of water and without it) provide a large variety of calcium phosphates, which are distinguished by the type of the phosphate anion: ortho-(PO43−), meta-(PO3−), pyro-(P2O74−), and poly-((PO3)nn−). In the case of multi-charged anions (orthophosphates and pyrophosphates), calcium phosphates are also differentiated by the number of hydrogen ions attached to the anion. Examples include mono-(Ca(H2PO4)2), di-(CaHPO4), tri-(Ca3(PO4)2) and tetra-(Ca2P2O7) calcium phosphates [27-29] (here, prefixes “mono”, “di”, “tri” and “tetra” are related to the amount of hydrogen ions replaced by calcium). However, only calcium orthophosphates are considered and discussed in this book. They are listed in Table 1.1 [30, 31]. Since all of them belong to calcium orthophosphates, strictly speaking, all abbreviations in Table 1.1 are incorrect; however, they are extensively used in literature and there is no need to modify them.