Dipolar dephasing between quadrupolar and spin-12 nuclei. REDOR and TEDOR NMR experiments on VPI-5

Fyfe, C. A.; Mueller, Karl T.; Grondey, H.; Wong-Moon, K. C.

doi:10.1016/0009-2614(92)80069-n

Cited by 101 publications

(99 citation statements)

References 12 publications

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“…Having the molecular agents within the gastrolith identified, the next step is to gain insight into how they are chemically and physically organized to stabilize the bioavailable calcium. To probe for spatial proximity (<6 Å) between the ACC carbonates and either Pi or PEP, we used a 2D NMR experiment, 31 P → 13 C 2D-HETCOR (heteronuclear correlation) (24 × 24T R TEDOR (transferred-echo double-resonance) mixing, SI Text) (43)(44)(45). The 2D-HETCOR NMR spectrum (Fig.…”

Section: Resultsmentioning

confidence: 99%

In situ molecular NMR picture of bioavailable calcium stabilized as amorphous CaCO₃biomineral in crayfish gastroliths

Akiva

Kababya

Balazs

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

120

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Bioavailable calcium is maintained by some crustaceans, in particular freshwater crayfish, by stabilizing amorphous calcium carbonate (ACC) within reservoir organs—gastroliths, readily providing the Ca 2+ needed to build a new exoskeleton. Despite the key scientific and biomedical importance of the in situ molecular-level picture of biogenic ACC and its stabilization in a bioavailable form, its description has eluded efforts to date. Herein, using multinuclear NMR, we accomplish in situ molecular-level characterization of ACC within intact gastroliths of the crayfish Cherax quadricarinatus . In addition to the known CaCO 3 , chitin scaffold and inorganic phosphate (Pi), we identify within the gastrolith two primary metabolites, citrate and phosphoenolpyruvate (PEP) and quantify their abundance by applying solution NMR techniques to the gastrolith “soluble matrix.” The long-standing question on the physico-chemical state of ACC stabilizing, P-bearing moieties within the gastrolith is answered directly by the application of solid state rotational-echo double-resonance (REDOR) and transferred-echo double-resonance (TEDOR) NMR to the intact gastroliths: Pi and PEP are found molecularly dispersed throughout the ACC as a solid solution. Citrate carboxylates are found < 5 Å from a phosphate (intermolecular C⋯P distance), an interaction that must be mediated by Ca 2+ . The high abundance and extensive interactions of these molecules with the ACC matrix identify them as the central constituents stabilizing the bioavailable form of calcium. This study further emphasizes that it is imperative to characterize the intact biogenic CaCO 3 . Solid state NMR spectroscopy is shown to be a robust and accessible means of determining composition, internal structure, and molecular functionality in situ.

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Section: Resultsmentioning

confidence: 99%

In situ molecular NMR picture of bioavailable calcium stabilized as amorphous CaCO₃biomineral in crayfish gastroliths

Akiva

Kababya

Balazs

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

120

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“…The TEDOR pulse sequence is useful for transferring polarization from one type of nucleus to another type via relatively weak dipolar couplings [43,44]. The two-dimensional version, which has been developed and applied to polarization transfer from quadrupolar nuclei to spin-1/2 nuclei [45][46][47][48][49], yields a 2D spectrum showing correlated signal intensity from spatially-proximate nuclear spin pairs that are dipole-dipole coupled. In our case the result is a 2D contour plot with 71 Ga and 15 N shift axes, and a 1D projection spectrum for 15 N. The relative intensity at each 15 N shift position reflects the number of 15 N nuclei at a given 15 N shift that are dipolecoupled (through space, <1 nm) to 71 Ga nuclei having the range of 71 Ga shifts depicted in the 2D contour plot.…”

Section: Oretical Line From Eq(3) Similar Distributions Ofmentioning

confidence: 99%

Spatially correlated distributions of local metallic properties in bulk and nanocrystalline GaN

et al. 2017

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We compare local electronic structure at different atom types of a metallic semiconductor in bulk and nanocrystalline form. Multinuclear magic-angle-spinning nuclear magnetic resonance (MAS NMR) establishes that GaN synthesized as an intentionally-doped bulk powder or as annealed nanocrystalline particles exhibits metallic behavior and a wide distribution of differing electronic environments in both forms. Bulk polycrystalline wurtzite GaN doped with 0.13% Ge as a shallow donor exhibits a temperature-independent distribution of 71 Ga Knight shifts over the temperature range 123-473 K. Each Knight shift frequency in the inhomogeneously-broadened spectrum is characterized by a 71 Ga spin-lattice relaxation time T 1 that is in good agreement with the value predicted by the Knight-Korringa relation across the broad range of temperatures. The14 N spectrum shows a slightly smaller Knight shift distribution with spin-lattice relaxation time T 1 values at 295 K across the distribution also in good agreement with the Knight-Korringa relation. Similarly, annealed nanocrystalline wurtzite GaN (50-100 nm, and without Ge) exhibits a 71 Ga Knight shift distribution and T 1values (at 295 K) that follow the same Knight-Korringa behavior. Thus, both bulk and nanocrystalline forms of GaN are n-type and well above the metal-insulator transition (MIT), the nanocrystals most likely as a result of incorporation of shallow donor oxygen atoms during synthesis. Carriers in both forms of sample exhibit the near-ideal characteristics of a degenerate Fermi gas of non-interacting spins. The observation of NMR signals from both atom types, Ga and N, allows for the direct spatial correlation of the local electronic structure at the two sites in the lattice, specifically the s-orbital character of the electronic wavefunction of conduction band electrons at the Fermi edge. The relative values of these carrier wavefunction probabilities (nearly twice as great for the N atom as for the Ga) are in line with theoretical predictions. Analyses of 71 Ga, 14 N, and 15 N NMR results, including double-resonance 2D 15 N{ 71 Ga} measurements, reveal electronic disorder in the form of broad distributions of local metallic properties (Knight shifts) that are shown to be spatially correlated on a sub-nanometer scale.

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“…58 Obviously, this approach will not work in the case of a disordered zeolite surface where a broad distribution of internuclear distances always prevails. 51,52 A certain success has been achieved recently by Grey et al 62 -65 in the study of Lewis acidity of dealuminated zeolite HY with a TRAPDOR technique. 62 This technique is specifically designed to measure QCC values and to estimate internuclear distances by observing a signal from spin- 1 2 nuclei coupled to quadrupolar nuclei ( 27 Al) by heteronuclear dipolar interaction.…”

Section: Sample Preparation and Experimental Strategymentioning

confidence: 96%

Characterization of Brønsted and Lewis acidity in zeolites by solid-state NMR and the recent progress in the REDOR technique

Blumenfeld

Fripiat

1999

Magn. Reson. Chem.

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Dipolar dephasing between quadrupolar and spin-12 nuclei. REDOR and TEDOR NMR experiments on VPI-5

Cited by 101 publications

References 12 publications

In situ molecular NMR picture of bioavailable calcium stabilized as amorphous CaCO₃biomineral in crayfish gastroliths

In situ molecular NMR picture of bioavailable calcium stabilized as amorphous CaCO₃biomineral in crayfish gastroliths

Spatially correlated distributions of local metallic properties in bulk and nanocrystalline GaN

Characterization of Brønsted and Lewis acidity in zeolites by solid-state NMR and the recent progress in the REDOR technique

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Dipolar dephasing between quadrupolar and spin-12 nuclei. REDOR and TEDOR NMR experiments on VPI-5

Cited by 101 publications

References 12 publications

In situ molecular NMR picture of bioavailable calcium stabilized as amorphous CaCO3biomineral in crayfish gastroliths

In situ molecular NMR picture of bioavailable calcium stabilized as amorphous CaCO3biomineral in crayfish gastroliths

Spatially correlated distributions of local metallic properties in bulk and nanocrystalline GaN

Characterization of Brønsted and Lewis acidity in zeolites by solid-state NMR and the recent progress in the REDOR technique

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In situ molecular NMR picture of bioavailable calcium stabilized as amorphous CaCO₃biomineral in crayfish gastroliths

In situ molecular NMR picture of bioavailable calcium stabilized as amorphous CaCO₃biomineral in crayfish gastroliths