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The Zr‐based Metal Organic Framework (MOF) UiO‐66(Zr) is widely employed owing to its good thermal and chemical stabilities. Although the long‐range structure of this MOF is preserved in the presence of water during several days, little is known about the formation of defects, which cannot be detected using diffraction techniques. We apply here 17O solid‐state NMR spectroscopy at 18.8 T to investigate the reactivity of UiO‐66, through the exchange of oxygen atoms between the different sites of the MOF and water. For that purpose, we have selectively enriched in 17O isotope the carboxylate groups of UiO‐66(Zr) by using it with 17O‐labeled terephthalic acid prepared using mechanochemistry. In the presence of water at 50 °C and a following dehydration at 150 °C, we observe an overall exchange of O atoms between COO− and μ3‐O2− sites. Furthermore, we demonstrate that the three distinct oxygen sites, μ3‐OH, μ3‐O2− and COO−, of UiO‐66(Zr) MOF can be enriched in 17O isotope by post‐synthetic hydrothermal treatment in the presence of 17O‐enriched water. These results demonstrate the lability of Zr−O bonds and the reactivity of UiO‐66(Zr) with water. [ABSTRACT FROM AUTHOR]

While ball-milling is becoming one of the common tools used by synthetic chemists, an increasing number of studies highlight that it is possible to further expand the nature and number of products which can be synthesized, by heating the reaction media during mechanochemical reactions. Hence, developing set-ups enabling heating and milling to be combined is an important target, which has been looked into in both academic and industrial laboratories. Here, we report a new approach for heating up reaction media during ball-milling reactions, using induction heating (referred to as i-BM). Our set-up is attractive not only because it enables a very fast heating of the milling medium (reaching ≈80 °C in just 15 s), and that it is directly adaptable to commercially-available milling equipment, but also because it enables heating either the walls of the milling jars or the beads themselves, depending on the choice of the materials which compose them. Importantly, the possibility to heat a milling medium "from the inside" (when using for example a PMMA jar and stainless steel beads) is a unique feature compared to previously proposed systems. Through numerical simulations, we then show that it is possible to finely tune the properties of this heating system (e.g. heating rate and maximum temperature reached), by playing with the characteristics of the milling system and/or the induction heating conditions used. Lastly, examples of applications of i-BM are given, showing how it can be used to help elucidate reaction mechanisms in ball-milling, to synthesize new molecules, and to control the physical nature of milling media. [ABSTRACT FROM AUTHOR]

17O NMR spectroscopy is a powerful technique, which can provide unique information regarding the structure and reactivity of biomolecules. However, the low natural abundance of 17O (0.04 %) generally requires working with enriched samples, which are not easily accessible. Here, we present simple, fast and cost‐efficient 17O‐enrichment strategies for amino acids and peptides by using mechanochemistry. First, five unprotected amino acids were enriched under ambient conditions, consuming only microliter amounts of costly labeled water, and producing pure molecules with enrichment levels up to ∼40 %, yields ∼60‐85 %, and no loss of optical purity. Subsequently, 17O‐enriched Fmoc/tBu‐protected amino acids were produced on a 1 g/day scale with high enrichment levels. Lastly, a site‐selective 17O‐labeling of carboxylic functions in peptide side‐chains was achieved for RGD and GRGDS peptides, with ∼28 % enrichment level. For all molecules, 17O ssNMR spectra were recorded at 14.1 T in reasonable times, making this an important step forward for future NMR studies of biomolecules. [ABSTRACT FROM AUTHOR]

The possibility of enriching in 17O the water molecules within hydrated biominerals belonging to the Ca-pyrophosphate family was investigated, using liquid assisted grinding (LAG) in the presence of 17O-labelled water. Two phases with different hydration levels, namely triclinic calcium pyrophosphate dihydrate (Ca2P2O7·2H2O, denoted t-CPPD) and monoclinic calcium pyrophosphate tetrahydrate (Ca2P2O7·4H2O, denoted m-CPPT β) were enriched in 17O using a "post-enrichment" strategy, in which the non-labelled precursors were ground under gentle milling conditions in the presence of stoichiometric quantities of 17O-enriched water (introduced here in very small volumes ∼10 μL). Using high-resolution 17O solid-state NMR (ssNMR) analyses at multiple magnetic fields, and dynamic nuclear polarisation (DNP)-enhanced 17O NMR, it was possible to show that the labelled water molecules are mainly located at the core of the crystal structures, but that they can enter the lattice in different ways, namely by dissolution/recrystallisation or by diffusion. Overall, this work sheds light on the importance of high-resolution 17O NMR to help decipher the different roles that water can play as a liquid-assisted grinding agent and as a reagent for 17O-isotopic enrichment. [ABSTRACT FROM AUTHOR]

43Ca nuclear magnetic resonance (NMR) spectroscopy has been extensively applied to the detailed study of octacalcium phosphate (OCP), Ca8(HPO4)2(PO4)4.5H2O, 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 43Ca magic angle spinning (MAS) experiments, including double‐rotation (DOR) 43Ca NMR, as well as 43Ca{1H} rotational echo DOR (REDOR) and 31P{43Ca} REAPDOR NMR spectra, were recorded on a 43Ca‐labeled 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 Ca2+ sites of OCP. Natural‐abundance 43Ca MAS NMR spectra were then recorded for the hybrid organic–inorganic derivatives, revealing changes in the 43Ca 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 43Ca NMR experiments and computational modeling for studying complex hybrid biomaterials. [ABSTRACT FROM AUTHOR]

Oxygen‐17 and deuterium are two quadrupolar nuclei that are of interest for studying the structure and dynamics of materials by solid‐state nuclear magnetic resonance (NMR). Here, 17O and 2H NMR analyses of crystalline ibuprofen and terephthalic acid are reported. First, improved 17O‐labelling protocols of these molecules are described using mechanochemistry. Then, dynamics occurring around the carboxylic groups of ibuprofen are studied considering variable temperature 17O and 2H NMR data, as well as computational modelling (including molecular dynamics simulations). More specifically, motions related to the concerted double proton jump and the 180° flip of the H‐bonded (–COOH)2 unit in the crystal structure were looked into, and it was found that the merging of the C=O and C–OH 17O resonances at high temperatures cannot be explained by the sole presence of one of these motions. Lastly, preliminary experiments were performed with a 2H–17O diplexer connected to the probe. Such configurations can allow, among others, 2H and 17O NMR spectra to be recorded at different temperatures without needing to tune or to change probe configurations. Overall, this work offers a few leads which could be of use in future studies of other materials using 17O and 2H NMR. [ABSTRACT FROM AUTHOR]

In recent years, there has been increasing interest in developing cost‐efficient, fast, and user‐friendly 17O enrichment protocols to help to understand the structure and reactivity of materials by using 17O NMR spectroscopy. Here, we show for the first time how ball milling (BM) can be used to selectively and efficiently enrich the surface of fumed silica, which is widely used at industrial scale. Short milling times (up to 15 min) allowed modulation of the enrichment level (up to ca. 5 %) without significantly changing the nature of the material. High‐precision 17O compositions were measured at different milling times by using large‐geometry secondary‐ion mass spectrometry (LG‐SIMS). High‐resolution 17O NMR analyses (including at 35.2 T) allowed clear identification of the signals from siloxane (Si−O−Si) and silanols (Si−OH), while DNP analyses, performed by using direct 17O polarization and indirect 17O{1H} CP excitation, agreed with selective labeling of the surface. Information on the distribution of Si−OH environments at the surface was obtained from 2D 1H−17O D‐HMQC correlations. Finally, the surface‐labeled silica was reacted with titania and using 17O DNP, their common interface was probed and Si−O−Ti bonds identified. [ABSTRACT FROM AUTHOR]

Two mechanochemical procedures for 17O/18O-isotope labeling of fatty acids are reported: a carboxylic acid activation/hydrolysis approach and a saponification approach. The latter route allowed first-time enrichment of important polyunsaturated fatty acids (PUFAs) including docosahexaenoic acid (DHA). Overall, a total of 9 pure labeled products were isolated in high yields (≥80%) and with high enrichment levels (≥37% average labeling of C=O and C-OH carboxylic oxygen atoms), under mild conditions, and in short time (

The spectroscopic study of pathological calcifications (including kidney stones) is extremely rich and helps to improve the understanding of the physical and chemical processes associated with their formation. While Fourier transform infrared (FTIR) imaging and optical/electron microscopies are routine techniques in hospitals, there has been a dearth of solid-state NMR studies introduced into this area of medical research, probably due to the scarcity of this analytical technique in hospital facilities. This work introduces effective multinuclear and multidimensional solid-state NMR methodologies to study the complex chemical and structural properties characterizing kidney stone composition. As a basis for comparison, three hydrates (n D 1, 2 and 3) of calcium oxalate are examined along with nine representative kidney stones. The multinuclear magic angle spinning (MAS) NMR approach adopted investigates the ¹H, 13C, 31P and 31P nuclei, with the 1H and 13C MAS NMR data able to be readily deconvoluted into the constituent elements associated with the different oxalates and organics present. For the first time, the full interpretation of highly resolved 1H NMR spectra is presented for the three hydrates, based on the structure and local dynamics. The corresponding 31P MAS NMR data indicates the presence of low-level inorganic phosphate species; however, the complexity of these data make the precise identification of the phases difficult to assign. This work provides physicians, urologists and nephrologists with additional avenues of spectroscopic investigation to interrogate this complex medical dilemma that requires real, multitechnique approaches to generate effective outcomes. [ABSTRACT FROM AUTHOR]

Janus bis(N-heterocyclic carbenes) composed of a porphyrin core with two N-heterocyclic carbene (NHC) heads fused to opposite pyrroles were used as bridging ligands for the preparation of metal complexes. We first focused our attention on the synthesis of gold(I) chloride complexes [(NHC)AuCl] and investigated the substitution of the chloride ligand by acetylides to obtain the corresponding [(NHC)AuC≡CR] complexes. Polyacetylides were then used to obtain molecular multiporphyrinic systems with porphyrins fused to only one NHC ligand, while main-chain organometallic polymers (MCOPs) were obtained when using Janus porphyrin bis(NHCs). Interestingly, MCOPs incorporating zinc(II) porphyrins proved to be efficient as heterogeneous photocatalysts for the generation of singlet oxygen upon visible light irradiation. [ABSTRACT FROM AUTHOR]

α-Canaphite (CaNa2P2O7·4H2O) is a layered calcium disodium pyrophosphate tetrahydrate phase of significant geological and potential biological interest. This study overcomes the lack of a reliable protocol to synthesize pure α-canaphite by using a novel simple and reproducible approach of double decomposition in solution at room temperature. The pure α-canaphite is then characterized from the atomic to the macroscopic level using a multitool and multiscale advanced characterization strategy, providing for the first time full resolution of the α-canaphite monoclinic structure, including the hydrogen bonding network. Synchrotron X-ray diffraction and neutron diffraction are combined with multinuclear solid state NMR experimental data and computational modeling via DFT/GIPAW calculations. Among the main characteristics of the α-canaphite structure are some strong hydrogen bonds and one of the four water molecules showing a different coordination scheme. This peculiar water molecule could be the last to leave the collapsed structure on heating, leading eventually to anhydrous α-CaNa2P2O7 and could also be involved in the internal hydrolysis of pyrophosphate ions as it is the closest water molecule to the pyrophosphate ions. Relating such detailed structural data on α-canaphite to its physico-chemical properties is of major interest considering the possible roles of canaphite for biomedical applications. The vibrational spectra of α-canaphite (deuterated or not) are analyzed and Raman spectroscopy appears to be a promising tool for the identification/diagnosis of such microcrystals in vitro, in vivo or ex vivo. [ABSTRACT FROM AUTHOR]

The development of amorphous phosphate-based materials is of major interest in the field of biomaterials science, and especially for bone substitution applications. In this context, we herein report the synthesis of gel-derived hydrated amorphous calcium/sodium ortho/pyrophosphate materials at ambient temperature and in water. For the first time, such materials have been obtained in a large range of tunable orthophosphate/pyrophosphate molar ratios. Multi-scale characterization was carried out thanks to various techniques, including advanced multinuclear solid state NMR. It allowed the quantification of each ionic/molecular species leading to a general formula for these materials: [(Ca2+ y Na+ z H+ 3+ x -2y-z)(PO 4 3−) 1-x (P 2 O 7 4−) x ](H 2 O) u. Beyond this formula, the analyses suggest that these amorphous solids are formed by the aggregation of colloids and that surface water and sodium could play a role in the cohesion of the whole material. Although the full comprehension of mechanisms of formation and structure is still to be investigated in detail, the straightforward synthesis of these new amorphous materials opens up many perspectives in the field of materials for bone substitution and regeneration. The metastability of amorphous phosphate-based materials with various chain length often improves their (bio)chemical reactivity. However, the control of the ratio of the different phosphate entities has not been yet described especially for small ions (pyrophosphate/orthophosphate) and using soft chemistry, whereas it opens the way for the tuning of enzyme- and/or pH-driven degradation and biological properties. Our study focuses on elaboration of amorphous gel-derived hydrated calcium/sodium ortho/pyrophosphate solids at 70 °C with a large range of orthophosphate/pyrophosphate ratios. Multi-scale characterization was carried out using various techniques such as advanced multinuclear SSNMR (31P, 23Na, 1H, 43Ca). Analyses suggest that these solids are formed by colloids aggregation and that the location of mobile water and sodium could play a role in the material cohesion. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Calcium benzoate trihydrate (Ca[([C.sub.6][H.sub.5]COO).sub.2].3[H.sub.2]O) is used as a model for the NMR analysis of calcium sites in biological materials, because of the similarity of its calcium coordination, to water and carboxylate ligands, to that in many calcium-proteins. The studies have shown that despite the weakness of [super 13]C-[super 43]Ca interactions, it is possible to discriminate carbon atoms according to their calcium environment.

A systematic study is carried out on cationic and anionic substitution in hydroxyapatite structures in order to understand the impact of the ion exchange on the crystalline structure and properties of these materials. The existence of a wide variety of environments for OH in substituted apatites is shown by [super 1]H NMR and the mobility of the water molecules has changed upon introduction of lead into the structure.

A computational study of the relative stability of the monolacunary Keggin polyoxotungstates [alpha] and [[beta].sub.3]-[[X[W.sub.11][O.sub.39]].sup.m-] (X = P, m = 7; X = Si, m = 8) and the effect of the nature of different grafted cations and of the central anion X[O.sub.4.sup.n-] on the relative stabilities of the lacunary isomers are described. The studies have shown how to favor the formation of [[beta].sub.3] derivatives in future synthesis.

The investigation of the bidentate coordination of ruthenium and osmium fragments toward the lacunary heteropolyoxoanion, [[alpha-P[W.sub.11][O.sub.39]].sub.7-] was performed. The findings underscores the versatility of the [[alpha-P[W.sub.11][O.sub.39]].sub.7-] ligand, which experimentally allows both bi and pentadentate coordination modes.