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

Abstract

Abstract. 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=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.

First Direct Insight into the Local Environment and Dynamics of Water Molecules in the Whewellite Mineral Phase: Mechanochemical Isotopic Enrichment and High-Resolution 17O and 2H NMR Analyses

“…For COM, using a homonuclear decoupling pulse sequence (DUMBO), the 1 H NMR spectrum was recorded, showing only one signal centered at 5.26 ppm at room temperature, which was attributed to an averaging of the water molecules’ 1 H resonances. 37 Upon lowering the temperature to 100 K, four proton environments could be resolved using a heteronuclear NMR experiment (FSLG-HETCOR 1 H– 13 C), which is consistent with the crystallographic data (i.e., two inequivalent water molecules). 37 Recently, 1 H NMR has also been used to analyze crystalline phases of the calcium oxalate minerals present in kidney stones: 37 it was demonstrated that T 2 * edited 1 H and 1 H– 1 H double-quantum (DQ) NMR experiments can be used to separate the organic and mineral parts within stones, showing them to be more insightful than the routinely used IR spectroscopy.…”

“… 37 Upon lowering the temperature to 100 K, four proton environments could be resolved using a heteronuclear NMR experiment (FSLG-HETCOR 1 H– 13 C), which is consistent with the crystallographic data (i.e., two inequivalent water molecules). 37 Recently, 1 H NMR has also been used to analyze crystalline phases of the calcium oxalate minerals present in kidney stones: 37 it was demonstrated that T 2 * edited 1 H and 1 H– 1 H double-quantum (DQ) NMR experiments can be used to separate the organic and mineral parts within stones, showing them to be more insightful than the routinely used IR spectroscopy. 37 Lastly, 13 C NMR (spin-1/2 nucleus of moderate receptivity, γ = 6.7281 × 10 7 rad s –1 T –1 ) studies on COM have shown that the NMR signature of this nucleus is particularly sensitive to temperature, as attested by the changes in the resolution of the four peaks belonging to the two inequivalent oxalate ions, and 13 C was further used to follow structural transformations from COT to COM.…”

“…Therefore, (ultra-)high fields and large amounts of sample are required to study 43 Ca by NMR at natural abundance, 36,39 which can be an issue especially when it comes to analyzing more complex compositions of minerals of pathological relevance, like renal stones. 37,38 Nevertheless, natural abundance 43 Ca MAS NMR spectra have been recorded for all three crystalline hydrates, where two calcium sites have been observed for the LT-COM phase and one for the COD and COT phases, as expected from their crystal structures. 36−38 In contrast to calcium-43, 1 H is a highly sensitive spin-1/2 nucleus for NMR (γ = 2.6752 × 10 8 rad s −1 T −1 ), but it can suffer from a lack of resolution in the solid state, especially in cases of strong 1 H− 1 H dipolar couplings.…”

“…37 Recently, 1 H NMR has also been used to analyze crystalline phases of the calcium oxalate minerals present in kidney stones: 37 it was demonstrated that T 2 * edited 1 H and 1 H− 1 H double-quantum (DQ) NMR experiments can be used to separate the organic and mineral parts within stones, showing them to be more insightful than the routinely used IR spectroscopy. 37 Lastly, 13 C NMR (spin-1/2 nucleus of moderate receptivity, γ = 6.7281 × 10 7 rad s −1 T −1 ) studies on COM have shown that the NMR signature of this nucleus is particularly sensitive to temperature, as attested by the changes in the resolution of the four peaks belonging to the two inequivalent oxalate ions, and 13 C was further used to follow structural transformations from COT to COM. 36,41 A tentative assignment of all carbon signals was then proposed with the help of density functional theory (DFT) and gauge including projector augmented wave (GIPAW) calculations of NMR parameters.…”

“…O (99.3% 18 O enrichment, CortecNet), D 2 O (≥99% 2 H enrichment, Sigma-Aldrich), and HPLC-grade water (Acros Organics) were used as received. COD was prepared as previously described in the literature 37,41 and stored under vacuum before any further use. 17 O, 18 O, and 2 H Isotopic Enrichment Procedures of COM Using Mechanochemistry.…”