NMR spectroscopy of citrate in solids: cross‐polarization kinetics in weakly coupled systems

Feng, Jian; Lee, Young Jong; Kubicki, James D.; Reeder, Richard J.; Phillips, Brian L.

doi:10.1002/mrc.2191

Cited by 10 publications

(16 citation statements)

References 49 publications

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“…Although the results of these previous studies are generally accepted as indicating structural incorporation, NMR spectroscopy remains one of the few methods by which a direct atomic-scale spatial interaction between occluded molecules and calcite structural components can be detected. The present results, along with our previous study of citrate/calcite coprecipitates (Feng et al, 2008), are in agreement with and amplify the results of these previous studies, by demonstrating direct, atomic scale proximity between the phosphate group of coprecipitated organic molecules and carbonate carbon in the calcite structure, even for large molecules containing more than sixty carbon atoms.…”

Section: Intracrystalline Organic Matter In Calcitesupporting

confidence: 93%

NMR spectroscopic study of organic phosphate esters coprecipitated with calcite

Phillips

Zhang

Kubista

et al. 2016

Geochimica et Cosmochimica Acta

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Organic phosphorus incorporated in calcite during laboratory precipitation experiments and in natural cave deposits was investigated by solid-state NMR spectroscopy. For calcite precipitated in the presence of organic phosphoesters of varying size and functionality, solid-state 31 P{ 1 H} CP/MAS NMR shows that the phosphoesters were incorporated intact into the solid. Systematic changes in the 31 P NMR chemical shift of the phosphate group were observed between the solid phosphoester and that incorporated in the solid precipitate, yielding 31 P NMR chemical shifts of the coprecipitates in the range of +1.8 to -2.2 ppm.These chemical shifts are distinct from that of similarly prepared calcite coprecipitated with inorganic phosphate, 3.5 ppm. Only minor changes were noted in the phosphoester 31 P chemical shift anisotropy (CSA) which suggests no significant change in the local structure of the phosphate group, which is dominated by C-O-P bonding. Close spatial proximity of the organic phosphate group to calcite structural components was revealed by 31 P/ 13 C rotational echo double resonance (REDOR) experiments for coprecipitates prepared with 13 C-labeled carbonate. All coprecipitates showed significant 31 P dephasing effects upon 13 C-irradiation, signaling atomic-scale proximity to carbonate carbon. The dephasing rate for smaller organophosphate molecules is similar to that observed for inorganic phosphate, whereas much slower dephasing was observed for larger molecules having long and/or bulky side-chains. This result suggests that small organic molecules can be tightly enclosed within the calcite structure, whereas significant structural disruption required to accommodate the larger organic molecules leads to longer phosphate-carbonate distances. Comparison of 31 P NMR spectroscopic data from the synthetic coprecipitates with those from calcite moonmilk speleothems indicates that phosphorus occurs mainly as inorganic orthophosphate in the natural deposits, although small signals occur with characteristics consistent with phosphate monoesters. The results of this study indicate that trace-to minor concentrations of dissolved organic molecules can be effectively taken up during calcite precipitation and incorporated in the structure, leaving a resilient record of materials present during crystallization.

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Section: Intracrystalline Organic Matter In Calcitesupporting

confidence: 93%

NMR spectroscopic study of organic phosphate esters coprecipitated with calcite

Phillips

Zhang

Kubista

et al. 2016

Geochimica et Cosmochimica Acta

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“…The CP MAS signal observed from a calcite sample prepared by the precipitation protocol described, except that no amino acids were added (SI, Figure S6), is significantly weaker. This demonstrates that the majority of the CP MAS peak in our carbonate/Asp samples reflects only those carbonates found within the CP-able “sphere of influence” of the amino acids and their associated water molecules …”

Section: Resultsmentioning

confidence: 79%

“…We selectively access the interfacial region where carbonates are in proximity to the amino acids via 13 C CP MAS NMR − where the detected 13 C magnetization is transferred from nearby hydrogen ( 1 H) sites. Magnetization transfer during the cross-polarization period falls off rapidly with increasing 1 H··· 13 C distance, and thus, the CP MAS spectra of the coprecipitates (Figure d–f) represent exclusively the fraction of carbonates that are sufficiently close (≤1 nm) to hydrogen atoms–which are found only in the amino acids and/or water molecules.…”

Section: Resultsmentioning

confidence: 99%

Resilient Intracrystalline Occlusions: A Solid-State NMR View of Local Structure as It Tunes Bulk Lattice Properties

et al. 2020

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In many marine organisms, biomineralization—the crystallization of calcium-based ionic lattices—demonstrates how regulated processes optimize for diverse functions, often via incorporation of agents from the precipitation medium. We study a model system consisting of l -aspartic acid (Asp) which when added to the precipitation solution of calcium carbonate crystallizes the thermodynamically disfavored polymorph vaterite. Though vaterite is at best only kinetically stable, that stability is tunable, as vaterite grown with Asp at high concentration is both thermally and temporally stable, while vaterite grown at 10-fold lower Asp concentration, yet 2-fold less in the crystal, spontaneously transforms to calcite. Solid-state NMR shows that Asp is sparsely occluded within vaterite and calcite. CP-REDOR NMR reveals that each Asp is embedded in a perturbed occlusion shell of ∼8 disordered carbonates which bridge to the bulk. In both the as-deposited vaterites and the evolved calcite, the perturbed shell contains two sets of carbonate species distinguished by their proximity to the amine and identifiable based on 13 C chemical shifts. The embedding shell and the occluded Asp act as an integral until which minimally rearranges even as the bulk undergoes extensive reorganization. The resilience of these occlusion units suggests that large Asp-free domains drive the vaterite to calcite transformation—which are retarded by the occlusion units, resulting in concentration-dependent lattice stability. Understanding the structure and properties of the occlusion unit, uniquely amenable to ssNMR, thus appears to be a key to explaining other macroscopic properties, such as hardness.

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“…To calculate a maximum possible 207 Pb{ 1 H}CP enhancement for HPm, we estimated the CP rate (T PbH −1 ) by scaling the apparent T PH −1 value (0.2 ms −1 ) by the ratio of second moments for 31 P-1 H and 207 Pb-1 H dipolar coupling (calculated from crystal structure data [45] ), yielding T PbH ≈ 12.3 ms. [46] This value is longer than the observed T 1ρ,Pb value for most of the 207 Pb in the sample and intimates that magnetization transferred from 1 H to 207 Pb decays rapidly, preventing buildup of large 207 Pb{ 1 H} CP signal.…”

Section: Pb{ 1 H} Cp/masmentioning

confidence: 90%

Solid‐state NMR spectroscopy of Pb‐rich apatite

Mason

Hirner

et al. 2009

Magnetic Reson in Chemistry

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Pb-containing hydroxylapatite phases synthesized under aqueous conditions were investigated by X-ray diffraction and solid-state nuclear magnetic resonance (NMR) techniques to determine the Pb, Ca distribution. 31P and 1H magic-angle spinning (MAS) NMR results indicate slight shifts of the isotropic chemical shift with increased Ca content and complex lineshapes at compositions with near equal amounts of Ca and Pb. 31P{207Pb} and 1H{207Pb} rotational-echo double resonance (REDOR) results for intermediate compositions show that resolved spectral features cannot be assigned simply in terms of local Ca, Pb configurations or coexisting phases. 207Pb MAS NMR spectra are easily obtained for these materials and contain well-resolved resonances for crystallographically unique A1 and A2 Pb sites. Splitting of the A1 and A2 207Pb resonances for pure hydroxyl-pyromorphite (Pb10(PO4)6(OH)2) compared to natural pyromorphite (Pb5(PO4)3Cl) suggests symmetry reduced from hexagonal. We find that 207Pb{1H} CP/MAS NMR is impractical in Pb-rich hydroxylapatites due to fast 207Pb relaxation.

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NMR spectroscopy of citrate in solids: cross‐polarization kinetics in weakly coupled systems

Cited by 10 publications

References 49 publications

NMR spectroscopic study of organic phosphate esters coprecipitated with calcite

NMR spectroscopic study of organic phosphate esters coprecipitated with calcite

Resilient Intracrystalline Occlusions: A Solid-State NMR View of Local Structure as It Tunes Bulk Lattice Properties

Solid‐state NMR spectroscopy of Pb‐rich apatite

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