A ⁴³Ca nuclear magnetic resonance perspective on octacalcium phosphate and its hybrid derivatives

Abstract

Ca nuclear magnetic resonance (NMR) spectroscopy has been extensively applied to the detailed study of octacalcium phosphate (OCP), Ca 8 (HPO 4 ) 2 (PO 4 ) 4 .5H 2 O, and hybrid derivatives involving intercalated metabolic acids (viz., citrate, succinate, formate, and adipate). Such phases are of importance in the development of a better understanding of bone structure. High-resolution 43 Ca magic angle spinning (MAS) experiments, including double-rotation (DOR) 43 Ca NMR, as well as 43 Ca{ 1 H} rotational echo DOR (REDOR) and 31 P{ 43 Ca} REAPDOR NMR spectra, were recorded on a 43 Calabeled OCP phase at very high magnetic field (20 T), and complemented by ab initio calculations of NMR parameters using the Gauge-Including Projector Augmented Wave-density functional theory (GIPAW-DFT) method. This enabled a partial assignment of the eight inequivalent Ca 2+ sites of OCP.Natural-abundance 43 Ca MAS NMR spectra were then recorded for the hybrid organic-inorganic derivatives, revealing changes in the 43 Ca lineshape. In the case of the citrate derivative, these could be interpreted on the basis of computational models of the structure. Overall, this study highlights the advantages of combining high-resolution 43 Ca NMR experiments and computational modeling for studying complex hybrid biomaterials.

Metabolic acids impact bone mineral maturation

“…43 Ca chemical shifts are highly sensitive to Ca local environments, including for bone mineral and OCP-derived phases and so are a good monitor of the mineral structures present in our materials. 33,[46][47][48] The 43 Ca NMR spectrum of the lactate-only material is more similar to the one of pure OCP (Fig 1B), while those of the citrate-only and mixed citrate/lactate materials have more similarities with that of HAp (Fig 1B ), in line with the conclusions made from the 1D 31 P NMR data (Fig 1A). Interestingly, the 43 Ca spectrum for the mixed citrate-lactate material is highly similar to that for bone, in contrast to the 43 Ca NMR spectra nanocrystalline carbonatesubstituted HAp.…”

“…To generate nanocrystalline HAp domains in a restricted space rich in citrate and lactate anions, we exploit the well-known transformation of OCP to HAp [25][26][27][28][29][30][31] and the ability of OCP to incorporate carboxylic acid anions into its structure. 14,[32][33][34][35][36][37][38][39][40][41][42][43][44] Carboxylic acid anions locate to the hydrated layer of OCP 14,34,42,44,45 where they bind to the apatitic-like structures either side of the OCP hydrated layers. Nucleation of HAp within an OCP lattice is hypothesized to begin in the apatitic layers of OCP and we reasoned that the presence of citrate and/ or lactate in the OCP hydrated layers would mimic the close presence of those anions around forming apatitic crystals in in vivo bone mineral formation.…”

A novel multinuclear solid-state NMR approach for the characterization of kidney stones

“…For better accuracy, a longer experimental time will be necessary. Moreover, NMR experiments will be combined with denoising techniques developed recently by Laurent and Bonhomme (2020).…”

17O solid state NMR as a valuable tool for deciphering reaction mechanisms in mechanochemistry: the case study on the 17O-enrichment of hydrated Ca-pyrophosphate biominerals

“…More generally speaking, similar analyses could help understand in detail how liquid-grinding agents like water can interact or react with other crystal structures. From a more practical perspective, the possibility to enrich in 17 O biominerals using only microlitre amounts of expensive 17 O-enriched water makes LAG a highly attractive approach for future studies on other hydrated biominerals, for which the local environment of water molecules still deserves investigation, as it is the case for canaphite (CaNa 2 P 2 O 7 ·4H 2 O), 23 octacalcium phosphate (OCP, Ca 8 (HPO 4 ) 2 (PO 4 ) 4 ·5H 2 O), 24 and calcium carbonate hemihydrate (CaCO 3 ·0.5H 2 O). 25 Further work in the case of canaphite has been initiated, which will be reported in due course.…”