Determining the geometry of strongly hydrogen-bonded silanols in a layered hydrous silicate by solid-state nuclear magnetic resonance

Gardiennet, Carole; Marica, Florea; Fyfe, C. A.; Tékély, Piotr

doi:10.1063/1.1839551

Cited by 11 publications

(6 citation statements)

References 43 publications

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“…The general behavior is also very similar to that reported for the different Si sites in silica gel by Sindorf and Maciel (1980) and examined in detail by Klur et al (2000) who showed that the C P dynamics could be characterized as being in the "slow exchange regime." A similar situation was also found for layered silicates by Gardiennet et al (2005) and appears to be characteristic of Q 3 Si-OH based polarization transfer from the hydroxyl protons, providing further support for this interpretation. It is not possible to provide more specific structural information on these sites from the present experiments, but it is worthwhile noting that the degree of substitution at the Al1 site is substantial, the three resonances accounting for approximately 22-27% of the total intensity of the quantitatively reliable single pulse silicon spectrum (Fig.…”

Section: Nmr Experimentssupporting

confidence: 73%

MAS NMR measurements and ab initio calculations of the 29Si chemical shifts in dumortierite and holtite

Evans

Fyfe

Groat

et al. 2012

American Mineralogist

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Three samples from the dumortierite group of minerals were examined with magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR): a dumortierite [c. (Al,)Al 6 (BO 3 ) Si 3 O 13 (O,OH) 2 ] consisting of dark blue euhedral crystals from Madagascar (D34); a fine-grained pale blue dumortierite from Island Copper mine, British Columbia, Canada (D12); and a creamy white holtite [c. (Ta,Nb,,Al)Al 6 (BO 3 )(Si,Sb,As) 3 O 12 (O,OH,) 3 ] from Szklary, Lower Silesia, Poland (WPH). Restricted Hartree-Fock ab initio electronic structure calculations were performed on model clusters with the goal of matching local environments of Si atoms to peaks in the 29 Si MAS NMR spectra. The spectrum of D34 showed five resolved peaks at -95.2, -92.6, -91.3, -89.1, and -86.5 ppm with deconvoluted peak area contributions of 57, 19, 7, 10, and 7%. Electronic structure calculations, cross-polarization MAS NMR measurements and relative intensities support assigning the peaks at -95.2 and -92.6 ppm to Si2 and Si1 sites, respectively, adjacent to fully occupied Al1 sites (i.e., Q 4 Si sites), and assigning the three remaining peaks to Si sites adjacent to vacant Al1 sites (i.e., Q 3 Si sites). Due to the complexity of the dumortierite structure, clusters composed of at least the first four shells of nearest neighbor atoms to the target Si atom are necessary to model Q 4 sites. The spectrum of D12 showed two main peaks at -93 and -95 ppm, with minor peaks below -90 ppm and above -100 ppm. The spectrum of WPH showed one broad peak at -93 ppm, likely containing both Si1 and Si2 signals, and two minor peaks below -90 ppm.Single-crystal X-ray diffraction and structure refinement on D34 shows orthorhombic symmetry, Pnma, Z = 4, a = 4.6882(1), b = 11.7924(2), c = 20.1856(3) Å, and V = 1115.97(4) Å 3 with R 1 = 0.0124. Three distinct sub-sites of the face-sharing octahedral chain site Al1 were distinguished corresponding to sites with one vacancy above, with one vacancy below, and between two occupied sites; the vacancy-adjacent sites have the cation displaced to increase the Al 3+ -Al 3+ distance. Each sub-site is approximately ¼ occupied, suggesting that Al 3+ cations in individual face-sharing octahedral chains are ordered as -Al-Al-Al, although cations from chain to chain are disordered, preserving Pnma symmetry.Powder X-ray diffraction measurements were performed on both D34 and D12. The unit cell of D12 was found to be a = 4.7001(7), b = 11.785(2), c = 20.277(3) Å.

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Section: Nmr Experimentssupporting

confidence: 73%

MAS NMR measurements and ab initio calculations of the 29Si chemical shifts in dumortierite and holtite

Evans

Fyfe

Groat

et al. 2012

American Mineralogist

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“…Solid-state NMR spectroscopy provides important structural information and constraints that open new opportunities for determining the structures of molecularly ordered silicate frameworks. − In particular, solid-state 29 Si NMR yields: (i) the numbers and relative populations of distinct 29 Si sites in the structure; (ii) the chemical natures of such sites (e.g., the degree of condensation Q n of four-coordinate 29 Si moieties, where n represents the number of next-nearest-neighbor Si atoms that are covalently bonded via bridging oxygen atoms); (iii) 29 Si–O– 29 Si connectivities among the different resolved sites; ,− (iv) internuclear 29 Si–O– 29 Si distances; , and (v) additional local composition and bonding details derived from NMR interactions of 29 Si nuclei (e.g., chemical shift anisotropies , or scalar couplings , ), including with other nuclei potentially present, e.g., 17 O, − 27 Al, or 23 Na . Such detailed information provides stringent local structural constraints that can subsequently be combined to determine framework topologies (i–iii), to construct model candidate structures in conjunction with the space groups and unit cell shapes and sizes obtained from XRD data (iv), , to probe the accuracy of different candidate structures, , and/or to refine these structures by comparing NMR interactions measured experimentally and calculated from first principles (v). , Complete structure determination, however, remains a major challenge in non-, semi-, or nanocrystalline solids, where XRD provides little or insufficient information.…”

Section: Introductionmentioning

confidence: 99%

A General Protocol for Determining the Structures of Molecularly Ordered but Noncrystalline Silicate Frameworks

et al. 2013

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A general protocol is demonstrated for determining the structures of molecularly ordered but noncrystalline solids, which combines constraints provided by X-ray diffraction (XRD), one- and two-dimensional solid-state nuclear magnetic resonance (NMR) spectroscopy, and first-principles quantum chemical calculations. The approach is used to determine the structure(s) of a surfactant-directed layered silicate with short-range order in two dimensions but without long-range periodicity in three-dimensions (3D). The absence of long-range 3D molecular order and corresponding indexable XRD reflections precludes determination of a space group for this layered silicate. Nevertheless, by combining structural constraints obtained from solid-state (29)Si NMR analyses, including the types and relative populations of distinct (29)Si sites, their respective (29)Si-O-(29)Si connectivities and separation distances, with unit cell parameters (though not space group symmetry) provided by XRD, a comprehensive search of candidate framework structures leads to the identification of a small number of candidate structures that are each compatible with all of the experimental data. Subsequent refinement of the candidate structures using density functional theory calculations allows their evaluation and identification of "best" framework representations, based on their respective lattice energies and quantitative comparisons between experimental and calculated (29)Si isotropic chemical shifts and (2)J((29)Si-O-(29)Si) scalar couplings. The comprehensive analysis identifies three closely related and topologically equivalent framework configurations that are in close agreement with all experimental and theoretical structural constraints. The subtle differences among such similar structural models embody the complexity of the actual framework(s), which likely contain coexisting or subtle distributions of structural order that are intrinsic to the material.

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“…The initial oscillations are characteristic of the largely coherent nature of the polarization transfer in spin systems with moderate proton–proton couplings. Consequently, the Fourier transform of the time dependence leads to dipolar spectra (Figure , right) featuring modified Pake doublets due to the oscillating heteronuclear polarization transfer, while proton spin-diffusion leads to an isolated central peak. ,, …”

Section: Resultsmentioning

confidence: 99%

“…The dipolar coupling constants D CH exp and D NH exp were extracted from the splittings multiplied by a factor of √2 to account for the n = −1 CP matching condition. Simulated build-up curves and corresponding dipolar spectra were obtained with the SPINEVOLUTION program for isolated pairs of spins (in red), while the fitting of the experimental build-up curves and corresponding dipolar spectra (in blue) were obtained using the exact analytical treatment for isolated pairs of spins that includes spin diffusion effects and implemented using the Scilab software.…”

Section: Resultsmentioning

confidence: 99%

“…Heteronuclear PISSARRO decoupling, a supercycled version of the phase-alternated (XiX) decoupling scheme, was applied during both evolution and detection intervals in all experiments. Numerical simulations were carried out with SPINEVOLUTION or by using an exact analytical treatment of isolated spin pairs under MAS including spin diffusion effects …”

Section: Methodsmentioning

confidence: 99%

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Probing Structural and Motional Features of the C-Terminal Part of the Human Centrin 2/P17-XPC Microcrystalline Complex by Solid-State NMR Spectroscopy

et al. 2012

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Insight into structural and motional features of the Cterminal part of the Human Centrin 2 in complex with the peptide P17-XPC was obtained by using complementary solid-state NMR methods. We demonstrate that the experimental conditions and procedures of sample crystallization determine the quality of solid-state NMR spectra and the internal mobility of the protein. 13 C− 13 C and 15 N− 15 N correlation spectra reveal intra-and inter-residue dipolar connectivities and provide partial, site-specific assignments of 13 C and 15 N resonance signals. The secondary structure of the C-ter HsCen2/P17-XPC complex in a microcrystalline state appears similar to that found in solution. Conformational flexibility is probed through relaxation-compensated measurements of dipolar order parameters that exploit the dynamics of cross-polarization in multidimensional experiments. The extracted dipolar coupling constants and relevant order parameters reveal increased backbone flexibility of the loops except for residues involved in coordination with the Ca 2+ cation that stabilizes the hydrophobic pocket containing the peptide P17-XPC.

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Determining the geometry of strongly hydrogen-bonded silanols in a layered hydrous silicate by solid-state nuclear magnetic resonance

Cited by 11 publications

References 43 publications

MAS NMR measurements and ab initio calculations of the 29Si chemical shifts in dumortierite and holtite

MAS NMR measurements and ab initio calculations of the 29Si chemical shifts in dumortierite and holtite

A General Protocol for Determining the Structures of Molecularly Ordered but Noncrystalline Silicate Frameworks

Probing Structural and Motional Features of the C-Terminal Part of the Human Centrin 2/P17-XPC Microcrystalline Complex by Solid-State NMR Spectroscopy

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