Solid-state MAS NMR Spectra Research Articles

Unexpected structural/motional mode of water intercalated into an α-crystalline zirconium phosphate deduced by 31 P and 2 H solid-state MAS NMR spectra.

In developing the approach to understanding dynamics of intercalates in layered materials, crystalline-layered zirconium phosphate Zr (HPO4 )2 ·0.35D2 O has been prepared and characterized by the 1 H, 31 P, and 2 H solid-state MAS NMR spectra, including 31 P and 2 H T1 measurements. At temperatures >253 K, the intercalated water shows two spectrally-distinguished deuterons unprecedentedly with different DQCC's and 2 H T1 times, one of which is hydrogen bonded. The collected data allowed to identify an unexpected bonding/dynamic mode of water molecules, which experience fast rotation around the hydrogen bond, formed with a zirconium-coordinated oxygen. The low-temperature 2 H MAS NMR experiments have demonstrated the presence of additional hydrogen bond P(H)O˙˙˙ DO, population of which grows on cooling to 195 K corresponding to the doubly hydrogen-bonded immobile water molecule.

Synthesis and characterization of a single phase zeolite A using coal fly ash.

Zeolitization of coal fly ash (CFA) provides a potential alternative for creating high-added-value products from this hazardous solid waste. In this work, a single phase zeolite A with high crystallinity was successfully synthesized from CFA via the alkali fusion hydrothermal method. X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence (XRF), Fourier transform infrared (FT-IR) spectroscopy, N2 physisorption, and solid-state MAS NMR spectra were applied to characterize as-synthesized zeolites. Results indicated that the type and purity of zeolite were closely related to the synthesis conditions and parameters. A well-defined cubic shape of zeolite A with a specific surface area of 43.7 m2 g−1 was obtained at a low temperature of 75 °C during hydrothermal treatment for 18 h. The ammonium cation exchange capacity (CEC) test showed an impressive value of 232.2 mmol 100 g−1 over prepared zeolite A, which was about 22 times that of the original CFA and close to commercial zeolite A. These results pave the way for the exploitation and utilization of the CFA.

CryoEM Structure Refinement by Integrating NMR Chemical Shifts with Molecular Dynamics Simulations.

Single particle cryoEM has emerged as a powerful method for structure determination of proteins and complexes, complementing X-ray crystallography and NMR spectroscopy. Yet, for many systems, the resolution of cryoEM density map has been limited to 4-6 Å, which only allows for resolving bulky amino acids side chains, thus hindering accurate model building from the density map. On the other hand, experimental chemical shifts (CS) from solution and solid state MAS NMR spectra provide atomic level data for each amino acid within a molecule or a complex; however, structure determination of large complexes and assemblies based on NMR data alone remains challenging. Here, we present a novel integrated strategy to combine the highly complementary experimental data from cryoEM and NMR computationally by molecular dynamics simulations to derive an atomistic model, which is not attainable by either approach alone. We use the HIV-1 capsid protein (CA) C-terminal domain as well as the large capsid assembly to demonstrate the feasibility of this approach, termed NMR CS-biased cryoEM structure refinement.

Structural and luminescent characteristics of two-step processed BaAl2−xSixO4−xNx:Eu2+ phosphors

Green emitting BaAl2−xSixO4−xNx:Eu2+ phosphors were synthesized using high temperature solid state reaction via two step process for white LED applications. The effect of (SiN)+ incorporation on structural and luminescent properties of BaAl2O4:Eu was studied. XRD analysis shows that solid solution is obtained upto x=0.50 beyond which phase segregates. The lattice parameters are found to decrease and cell volume shrinks with (SiN)+ incorporation due to the reduction in bond length of Si–N compared to Al–O in host lattice. The peak wavelength of PL emission from the samples, when excited using 450nm light, was found to red shift with SiN incorporation upto x=0.50 beyond which no shift was observed. The PL emission intensity was found to be maximum for x=0.80 (SiN)+ incorporation in to the host lattice. The chemical shift of 27Al solid state MAS NMR spectra shows the presence of AlO4−xNx tetrahedra at higher SiN concentrations. From the XPS and FTIR analysis of the samples, the presence of SiO, SiN, SiON, AlO, AlN and AlON bondings were detected and even though phase segregates at x=0.50, nitrogen is incorporated in the host lattice which resulted in the enhanced absorption at 450nm.

Synthesis of hierarchical ZSM-5 by silanization and alkoxylation of protozeolitic units

Hierarchical ZSM-5 zeolite has been synthesized by means of a method involving a precrystallization stage to form the protozeolitic units, the addition and subsequent grafting of both silanization and alkoxylation agents, and a final hydrothermal crystallization. The influence of the alkoxylation with different alcohols (methanol, ethanol, 2-propanol and n-butanol) on the properties of the final hierarchical ZSM-5 samples has been investigated. In every case, the alcohol addition increased the incorporation of the seed silanization agent as it decreases the gel viscosity. In addition, the presence of alcohols deeply affects the physicochemical properties of the final materials. The samples prepared with 2-propanol and methanol were highly crystalline and presented improved textural properties with regard to the reference h-ZSM-5 and n-ZSM-5. In contrast, the samples obtained with ethanol and n-butanol were partially and totally X-ray amorphous, respectively. 1H and 13C-CP solid state MAS NMR spectra proved the alkoxylation of the external surface of the protozeolitic units. Catalytic cracking of LDPE pointed out the higher TOF values obtained over the hierarchical samples prepared with methanol and 2-propanol due to a right combination of accessibility and crystallinity in these materials. The differences observed among the samples prepared with alcohols were ascribed to the strong interaction produced between the silanization agent and the linear alcohols on the surface of the protozeolitic nanounits, which form a very stable protective layer, hindering their aggregation and subsequent crystallization.

Crystal structure, vibrational spectra and thermal decomposition study of a new, dicationic, acidic pyrophosphate: KHMgP2O7⋅2H2O

Colourless crystals of a new, dicationic, hydropyrophosphate dihydrate salt, KHMgP2O7⋅ 2H2O, are formed, when a mixture of aqueous equimolar solutions of MgCl2⋅4H2O and K4P2O7, at pH 2.12, are left to stand at ambient temperature for 4 days. The new pyrophosphate salt has been characterized by single-crystal X-ray diffraction, IR and Raman spectra, and DSC-TG thermal analysis. The structure consists of alternating layers of [HP2O7]3− groups and MgO6 octahedra, joined by K+ ions and bridging hydrogen bonds. The [P2O7]4− anions exhibit a bent eclipsed conformation. The absence of coincidences for the majority of the IR and Raman bands is in accord with the centrosymmetric structure of the material. The 31P chemical shift tensor components have been determined from the solid-state MAS NMR spectra. The structural changes occurring during thermal decomposition have been examined by TG-DSC, X-ray powder diffraction (XRD) and IR spectroscopy. When the new pyrophosphate salt is heated gradually, it first becomes amorphous and then condenses to chain metaphosphates.

Synthesis, solid‐state NMR, and magnetic characterization of h‐GaN containing magnetic ions

GaN crystals doped with Mn ions were synthesized by the alkali metal flux method. Mixtures of metals were premelted to form an alloy and the alloy was mixed with Na/K and heated to ∼800 °C under ∼1400 psi N2 in an alumina crucible. Up to 2 mol% Mn could be incorporated into the h-GaN lattice, and the products were characterized by solid state NMR, magnetometry, Raman spectroscopy, and powder X-ray diffraction. The solid state MAS NMR spectra (71Ga, 69Ga, 14N) of the most heavily doped material, which is a normal paramagnet, have broad peaks that are shifted appreciably to higher frequency from the hexagonal GaN chemical shift position, probably due to Knight shifts. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Survival of Dipolar Splittings between Equivalent Nuclei in High-Speed MAS-NMR—Interpretation of the31P Coupling Patterns for Tetraphosphorus Decaoxide

Unexpected splittings in solid-state MAS-NMR spectra can indicate high rather than low local symmetry. A quantitative analysis of the resulting lineshapes provides information about geometry from a different range of space and time averaging than that of X-ray crystallography, as is demonstrated here for tetraphosphorus decaoxide (spectra on the right).

High-Resolution Solid State 19F and 15N MAS NMR Spectra of Fluoroaromatics and Aromatic Nitrogen Heterocycles Physisorbed on Silica and Alumina

High-resolution 19F and 15N solid state MAS NMR spectra have been obtained for fluoro-substituted aromatics and for aromatic nitrogen heterocycles, respectively, adsorbed on silica and alumina, where line narrowing is due to the high mobility of these systems on the surface of the porous materials. 19F,19F COSY, 19F,13C HETCOR, and 19F → 13C INEPT experiments were successfully performed, and 15N NMR was measured in natural abundance.

Refinement of solid-state MAS NMR spectra of quadrupolar nuclei: Application to the analysis of some 51V compounds

Magic angle solid-state 51V NMR spectra of several vanadium powder compounds have been recorded. A refinement of these spectra using theoretical simulations of the powder spectra have been performed assuming the simultaneous anisotropic effects of electric field gradients (EFG) and of electronic shielding. It is shown that the relative orientation of the principal axes of the two tensors have to be considered.

13C solid State MAS NMR spectra of [M 3(CO) 12] complexes (M = Ru and Os). Evidence for motional effects in [Ru 3(CO) 12

13C solid State MAS NMR spectra of [M 3(CO) 12] complexes (M = Ru and Os). Evidence for motional effects in [Ru 3(CO) 12