From crystalline to amorphous calcium pyrophosphates: A solid state Nuclear Magnetic Resonance perspective

Abstract

The general concept of NMR crystallography is applied to the detailed study of calcium pyrophosphates (CPP), whether hydrated or not, and whether crystalline or amorphous. CPP are a fundamental family of materials among osteoarticular pathologic calcifications. Their prevalence increases with age, impacting on 17.5% of the population after the age of 80. They are frequently involved or associated with acute articular arthritis such as pseudogout. Current treatments are mainly directed at relieving the symptoms of joint inflammation but not at inhibiting CPP formation nor at dissolving these crystals. The combination of advanced NMR techniques, modeling and DFT based calculation of NMR parameters allows new original insights in the detailed structural description of this important class of biomaterials.

Non-linear dissolution mechanisms of sodium calcium phosphate glasses as a function of pH in various aqueous media

“…These spectra and their deconvolutions are shown in Fig. S3, with fitted peaks assigned to specific chemical shifts with reference to literature [29][30][31]. Q 1 and Q 2 phosphate tetrahedra were observed, with the proportion of Q 1 tetrahedra increasing as more Ca was added to the glass.…”

Structural variations of bioactive glasses obtained by different synthesis routes

“…The Raman spectroscopy confirms the presence of both orthophosphate and pyrophosphate units (Fig.2). [58,59], depending on the synthesis route.…”

Recent directions in the solid-state NMR study of synthetic and natural calcium phosphates

“…In such investigations, high resolution NMR analyses are combined to powder X-ray and neutron diffraction data, and often complemented by ab initio calculations of NMR parameters (in the so-called « SMARTER crystallography » strategy), [40] in order to refine the atomic positions. Over the past 5 years, these approaches have clearly enabled to gain deeper insight into the bulk structure of monetite, [41,42] hydrated calcium pyrophosphates, [43] and carbonated hydroxyapatite [44], as detailed below.…”

“…[15] Most of the early magic angle spinning (MAS) NMR work concerned 1 H and 31 P NMR analyses, [16][17][18] as both of these spin-1/2 isotopes have a very good receptivity (Table 1). [19][20][21] One of the highlights of these investigations was the study by Ackermann et al in 2003, who provided direct evidence of the presence of apatite-like hydroxyl groups in bone mineral using 2D 1 H- 31 [23,24] the first 2D NMR studies of substituted apatites aiming at locating precisely the position of ionic substituents, [25][26][27] and the first complete natural-abundance 43 Ca MAS NMR experiments of synthetic calcium phosphates and bone. [27][28][29] In the latter case, the main challenge was due to the very poor receptivity of calcium-43, which has a natural abundance of only 0.14% and a very low resonance frequency (Table 1).…”