F faces of apatite and its morphology: Theory and observation

Terpstra, R.A.; Bennema, P.; Hartman, P.; Woensdregt, C. F.; Perdok, W. G.; Senechal, M.

doi:10.1016/0022-0248(86)90149-1

Cited by 30 publications

(19 citation statements)

References 25 publications

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“…Apatite is represented as ideal hydroxyapatite, Ca 10 ðPO 4 Þ 6 ðOHÞ 2 (hexagonal unit cell with a ¼ b ¼ 0.944 nm, c ¼ 0.688 nm). Calcium ions in two planes of highest morphological importance (27) are shown on the top left and right. In the ð1010Þ 1 plane, Ca 2þ is spaced by c∕2 ¼ 0.34 nm, which matches the 0.32 nm spacing between the centers of the three COO − groups of citrate.…”

Section: Resultsmentioning

confidence: 99%

Strongly bound citrate stabilizes the apatite nanocrystals in bone

Rawal

Schmidt‐Rohr

2010

Proc. Natl. Acad. Sci. U.S.A.

463

495

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Nanocrystals of apatitic calcium phosphate impart the organicinorganic nanocomposite in bone with favorable mechanical properties. So far, the factors preventing crystal growth beyond the favorable thickness of ca. 3 nm have not been identified. Here we show that the apatite surfaces are studded with strongly bound citrate molecules, whose signals have been identified unambiguously by multinuclear magnetic resonance (NMR) analysis. NMR reveals that bound citrate accounts for 5.5 wt% of the organic matter in bone and covers apatite at a density of about 1 molecule per ð2 nmÞ 2 , with its three carboxylate groups at distances of 0.3 to 0.45 nm from the apatite surface. Bound citrate is highly conserved, being found in fish, avian, and mammalian bone, which indicates its critical role in interfering with crystal thickening and stabilizing the apatite nanocrystals in bone.T he load-bearing material in bone is a fascinating organicinorganic nanocomposite whose stiffness is provided by thin nanocrystals of carbonated apatite, a calcium phosphate, imbedded in an organic matrix consisting mostly of collagen, a fibrous protein (1-5). The small (ca. 3-nm) thickness of the apatite nanocrystals is favorable for mechanical properties, likely preventing crack propagation (6). While the size and shape of the nanocrystals have been studied extensively (4, 5), the mechanism stabilizing them at a thickness corresponding to only about four unit cells has not been elucidated. A better understanding of the factors controlling the nanocrystals in bone is desirable for prevention and treatment of bone diseases such as osteoporosis, which causes millions of fractures each year (7), and for more efficient synthesis of biomimetic nanocomposites (8, 9). In vitro experiments have shown that carboxylate-rich proteins such as osteocalcin and osteopontin (7) can affect hydroxyapatite crystal formation and growth (10, 11). These observations might suggest that such proteins limit nanocrystal thickening (12); however, these proteins are not sufficiently abundant in vivo to bind to all the nanocrystal surfaces at high enough area concentration; possibly, they control the length of the nanocrystals (7).Here we show instead that the surfaces of the apatite crystals in bone are studded with strongly bound citrate molecules, at a density of ca. 1∕ð2 nmÞ 2 , using advanced solid-state nuclear magnetic resonance (NMR) as a unique tool for probing buried interfaces. Citrate is quite abundant in bone (ca. 1 wt%, or 5 wt% of the organic components) (13,14). Before 1975, citrate in bone was studied by simple wet-chemical methods and thought to regulate bone demineralization (14). However, citrate is no longer even mentioned in most of the prominent literature on the bone nanocomposite published during the last thirty years (1)(2)(3)(4)(5)(15)(16)(17)(18). We now highlight the importance of citrate in bone by demonstrating that it is not a dissolved calcium-solubilizing agent but a strongly bound, integral part of the nanocomposite. Structurally, citrate s...

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Section: Resultsmentioning

confidence: 99%

Strongly bound citrate stabilizes the apatite nanocrystals in bone

Rawal

Schmidt‐Rohr

2010

Proc. Natl. Acad. Sci. U.S.A.

463

495

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“…Furthermore, this space group has been experimentally determined in crystal obtained by hydrothermal synthesis [9][10][11] and in natural samples [12] where the OH dipoles are partially replaced by simple cations such as F and Cl. As concerns the theoretical investigation on the surface properties, the P6 3 /m setting has been preferentially adopted to predict the theoretical growth morphology [13], to determine the surface relaxation [14], to simulate the molecular adsorption on the most important HAp surfaces [15][16][17][18] and to evaluate the formation energies of Na and K replacing the Ca ions of HAp [19].…”

Section: The Hexagonal Settingmentioning

confidence: 99%

“…Terpstra et al [13] applied the "connected net" method, based on the morphological theory by Hartman-Perdok [63] platelet morphologies even when these are inconsistent with the symmetry of the crystal" [14,64]. However, the Authors are conscious that platelet growth morphology does not occur when HAp is precipitated in vitro.…”

Section: Solved and Unsolved Problems About The Relationship Between mentioning

confidence: 99%

About the Genetic Mechanisms of Apatites: A Survey on the Methodological Approaches

2017

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Apatites are properly considered as a strategic material owing to the broad range of their practical uses, primarily biomedical but chemical, pharmaceutical, environmental and geological as well. The apatite group of minerals has been the subject of a huge number of papers, mainly devoted to the mass crystallization of nanosized hydroxyapatite (or carboapatite) as a scaffold for osteoinduction purposes. Many wet and dry methods of synthesis have been proposed. The products have been characterized using various techniques, from the transmission electron microscopy to many spectroscopic methods like IR and Raman. The experimental approach usually found in literature allows getting tailor made micro-and nano-crystals ready to be used in a wide variety of fields. Despite the wide interest in synthesis and characterization, little attention has been paid to the relationships between bulk structure and corresponding surfaces and to the role plaid by surfaces on the mechanisms involved during the early stages of growth of apatites. In order to improve the understanding of their structure and chemical variability, close attention will be focused on the structural complexity of hydroxyapatite (HAp), on the richness of its surfaces and their role in the interaction with the precursor phases, and in growth kinetics and morphology.

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“…In that research, apatite is represented as ideal hexagonal hydroxyapatite, Ca10(PO4)6(OH)2 (a0 = b0 = 9.44 Å, c0 = 6.88 Å). As drawn in Figure 1, calcium ions in two planes of highest morphological importance [8] are shown on the top left and right. In the (101 0)1 surface, Ca 2+ is spaced by c/2 = 3.4 Å, which matches the 3.2 Å spacing between the centres of the three COO − groups of citrate.…”

Section: Introductionmentioning

confidence: 98%

Habit Change of Monoclinic Hydroxyapatite Crystals Growing from Aqueous Solution in the Presence of Citrate Ions: The Role of 2D Epitaxy

2018

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Calcium hydroxyapatite (HAp) has been crystallized from aqueous solutions in the presence of citrate ions, in two temperature intervals. At lower temperature, where citrate could form the stable 3D-ordered phase Ca-citrate-tetrahydrate (Ca-Cit-TH), only the monoclinic (P2 1 /c) HAp polymorph occurs and assumes the shape of fence-like aggregates, built by sharply [010] elongated lamellae dominated by the pinacoid {001}. This pronounced anisotropic growth habit is compared with the usually considered rod-like pseudo-hexagonal occurring in pure aqueous solution growth. The habit change is interpreted by assuming that 2D islands of Ca-citrate-tetrahydrate can be adsorbed as epimonolayers of thickness d 001 onto the different growth forms: {001}, {100}, 102 , {010}, and 101 of HAp. A comparison is made among the corresponding coincidence lattices, in order to explain on reticular basis the selective adsorption of citrate on the {001} HAp form. The role exerted by the 2D-epitaxially adsorbed Ca-Cit-TH as a "mortar" in the monoclinic HAp "brick" assembly is outlined as well.

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F faces of apatite and its morphology: Theory and observation

Cited by 30 publications

References 25 publications

Strongly bound citrate stabilizes the apatite nanocrystals in bone

Strongly bound citrate stabilizes the apatite nanocrystals in bone

About the Genetic Mechanisms of Apatites: A Survey on the Methodological Approaches

Habit Change of Monoclinic Hydroxyapatite Crystals Growing from Aqueous Solution in the Presence of Citrate Ions: The Role of 2D Epitaxy

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