High-Resolution Magic Angle Spinning Nmr-Studies Of P-31 And B-11 In Fast Ion Conducting Agi-Ag2o-P2o5 And Agi-Ag2o-B2o3 Glasses

Silver iodide-based fast ion conducting glasses containing silver phosphate and silver borate have been studied. An attempt is made to identify the interaction between anions by studying the chemical shifts of31P and11B atoms in high resolution (HR) magic angle spinning (MAS) NMR spectra. Variation in the chemical shifts of31P or11B has been observed which is attributed to the change in the partial charge on the31P or11B. This is indicative of the change in the electronegativity of the anion matrix as a whole. This in turn is interpreted as due to significant interaction among anions. The significance of such interaction to the concept of structural unpinning of silver ions in fast ion conducting glasses is discussed.

The use of simultaneous H-1 & P-31 magic angle spinning nuclear magnetic resonance measurements to characterize energy metabolism during the conversion of muscle to meat

In order to investigate the potential of magic angle spinning nuclear magnetic resonance (MAS NMR) in the elucidation of post-mortem metabolism in muscle biopsies, simultaneous H-1 and (31)p MAS NMR measurements were made continuously on postmortem (20 min to 24 h) muscle longissimus samples from rabbits. The animals had either been or not been given adrenaline (0.5 mg kg(-1) 4 h pre-slaughter) to deplete stores of muscle glycogen. The intracellular pH was calculated from H-1 spectra, and the post-mortem rate of formation of lactate was followed and quantified. Comparison of measurements made on muscle samples from rabbits treated with adrenaline with measurements made on muscle samples from untreated' rabbits revealed significant effects of adrenaline treatment on both pH (pH24 h = 6.42 vs. pH24 It = 5.60) and formation of lactate (16 mmol g(-1) vs. 65 mmol g(-1)). The P-31 NMR spectra were used to follow the rate of degradation of ATP and phosphocreatine. The present study clearly shows that MAS NMR has potential for the study of post-mortem energy metabolism.

Solid-state MAS NMR studies on the hydrothermal stability of the zeolite catalysts for residual oil selective catalytic cracking

By using the solid-state MAS NMR technique, the hydrothermal stabilities (under 100% steam at 1073 K) of HZSM-5 zeolites modified by lanthanum and phosphorus have been studied. They are excellent zeolite catalysts for residual oil selective catalytic cracking (RSCC) processes. It was indicated that the introduction of phosphorus to the zeolite via impregnation with orthophosphoric acid led to dealumination as well as formation of different Al species, which were well distinguished by Al-27 3Q MAS NMR. Meanwhile, the hydrothermal stabilities of the zeolites (P/HZSM-5, La-P/HZSM-5) were enhanced even after the samples were treated under severe conditions for a prolonged time. It was found that the Si-O-Al bonds were broken under hydrothermal conditions, while at the same time the phosphorous compounds would occupy the silicon sites to form (SiO)(x)Al(OP)(4 - x) species. With increasing time, more silicon sites around the tetrahedral coordinated Al in the lattice can be replaced till the aluminum is completely expelled from the framework. The existence of lanthanum can partially restrict the breaking of the Si-O-Al bonds and the replacement of the silicon sites by phosphorus, thus preventing dealumination under hydrothermal conditions. This was also proved by P-31 MAS NMR spectra. (C) 2004 Elsevier Inc. All rights reserved.

NMR study on the acidity of TS-1 zeolite

The acidic properties of TS-1 and Silicalite-I zeolites have been investigated by the solid-state MAS NMR technique capable of in situ sample pretreatment. As shown by a combination of the P-31 MAS NMR and H-1 MAS NMR techniques with trimethylphosphine, not only Bronsted acid sites but also Lewis acid sites exist in the TS-1 zeolites. Moreover, TS-1 zeolite is more acidic compared with Silicalite-1. The H-1, Si-29 MAS NMR spectra and the resonance related to Bronsted acid species in the P-31 MAS NMR spectra demonstrate clearly that the presence of titanium in the framework results in the formation of a new hydroxy group, titanols, which is more acidic than silanols of Silicalite-1. The P-31 MAS NMR measurements also illustrate convincingly the existence of at least two different Lewis acid species on the TS-1 zeolites. The conversion of propylene oxide into methoxypropanol catalyzed by TS-1 or Silicalite-I zeolite in methanol solution as a test reaction has also been described. With the increase of titanium in zeolite, TS-1 appears to have a higher activity during the reaction of propylene oxide to methoxypropanol.

Structural studies of AgPO3-MoO3 glasses using solid state NMR and vibrational spectroscopies

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Quantification of Short and Medium Range Order in Mixed Network Former Glasses of the System GeO2-NaPO3: A Combined NMR and X-ray Photoelectron Spectroscopy Study

Glasses in the system xGeO(2)-(1-x)NaPO3 (0 <= x <= 0.50) were prepared by conventional melting quenching and characterized by thermal analysis, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and P-31 nuclear magnetic resonance (MAS NMR) techniques. The deconvolution of the latter spectra was aided by homonuclear J-resolved and refocused INADEQUATE techniques. The combined analyses of P-31 MAS NMR and O-1s XPS lineshapes, taking charge and mass balance considerations into account, yield the detailed quantitative speciations of the phosphorus, germanium, and oxygen atoms and their respective connectivities. An internally consistent description is possible without invoking the formation of higher-coordinated germanium species in these glasses, in agreement with experimental evidence in the literature. The structure can be regarded, to a first approximation, as a network consisting of P-(2) and P-(3) tetrahedra linked via four-coordinate germanium. As implied by the appearance of P-(3) units, there is a moderate extent of network modifier sharing between phosphate and germanate network formers, as expressed by the formal melt reaction P-(2) + Ge-(4) -> P-(3) + Ge-(3). The equilibrium constant of this reaction is estimated as K = 0.52 +/- 0.11, indicating a preferential attraction of network modifier by the phosphorus component. These conclusions are qualitatively supported by Raman spectroscopy as well as P-31{Na-23} and P-31{Na-23} rotational echo double resonance (REDOR) NMR results. The combined interpretation of O-1s XPS and P-31 MAS NMR spectra shows further that there are clear deviations from a random connectivity scenario: heteroatomic P-O-Ge linkages are favored over homoatomic P-O-P and Ge-O-Ge linkages.

Influence of composition of heteropolyphosphatotungstate catalyst on epoxidation of propylene

A series of heteropolyphosphatotungstate catalysts with different W/P ratio were prepared by different means. P-31 MAS NMR spectra show every heteropolyphosphatotungstate contains several species with different W/P ratio. Combined with propylene epoxidation results, it is shown that the band at chemical shift ca. delta = 5 ppm maybe corresponds to a catalyst precursor which can be the most efficiently converted to the structure {PO4 [WO(O-2)(2)](4)}(3-). Characterization results of ICP show, the catalysts with low W/P ratio show a good reactivity for propylene epoxidation. (C) 2004 Elsevier B.V. All rights reserved.

Characterization of the acid sites in dealuminated nanosized HZSM-5 zeolite with the probe molecule trimethylphosphine

The acid sites in dealuminated HZSM-5 zeolite with crystal sizes down to the nanoscale were firstly characterized by the probe molecule trimethylphosphine (TMP). As evidenced by the combination of P-31 CP/MAS NMR, Al-27 MAS and H-1 --> Al-27 CP/MAS NMR measurements, the Bronsted acid sites of both microsized and nanosized HZSM-5 could be decreased upon the dealumination of zeolitic framework after hydrothermal treatment. At the same time, the appearance of Lewis acid sites was observed. The dealuminated nanosized HZSM-5 is easier to form Lewis acid sites than microsized HZSM-5, and the type of Lewis acid sites in nanosized HSM-5 is more than one. In addition, the origin of Lewis acid sites is mainly associated with the aluminum at ca. 30 ppm, in the Al-27 MAS NMR spectra, and only a part of which in the dealuminated HZSM-5 zeolite acts as Lewis acid sites. (C) 2002 Elsevier Science B.V. All rights reserved.

Grafting polymerization of L-lactide on the surface of hydroxyapatite nano-crystals

A novel method of grafting ring-opening polymerization of L-lactide (LLA) onto the surface of hydroxyapatite nano-particles (n-HAP) was developed. PLLA was directly connected onto the HAP surface through a chemical linkage. The PLLA-g-HAP particles could be stably dispersed in organic solvent such as chloroform for several weeks. The n-HAP particles still retained the original dimension and shape after the grafting of PLLA. Compared with the P-31 MAS-NMR spectrum of pure HAP powders, there appeared a downfield displacement of 1.2 ppm in the spectrum of PLLA-g-HAP. Fourier transformation infrared (FT-IR) spectra further confirmed the existence of PLLA on the surface of PLLA-g-HAP. The amount of grafted polymer determined by thermal gravimetric analysis (TGA) was about 6% in weight. The tensile strength and elongation at break of the PLLA/PLLA-g-HAP composite containing 8 wt% of PLLA-g-HAP were 55 MPa and about 10-13%, respectively, while those of the PLLA/n-HAP composites were 40 MPa and 3-5%, respectively.

Structure and Ionic Conductivity in the Mixed-Network Former Chalcogenide Glass System [Na2S](2/3)[(B2S3)(x)(P2S5)(1-x)](1/3)

Glasses in the system [Na2S](2/3)[(B2S3)(x)(P2S5)(1-x)](1/3) (0.0 <= x <= 1.0) were prepared by the melt quenching technique, and their properties were characterized by thermal analysis and impedance spectroscopy. Their atomic-level structures were comprehensively characterized by Raman spectroscopy and B-11, P-31, and Na-23 high resolution solid state magic-angle spinning (MAS) NMR techniques. P-31 MAS NMR peak assignments were made by the presence or absence of homonuclear indirect P-31-P-31 spin-spin interactions as detected using homonuclear J-resolved and refocused INADEQUATE techniques. The extent of B-S-P connectivity in the glassy network was quantified by P-31{B-11} and B-11{P-31} rotational echo double resonance spectroscopy. The results clearly illustrate that the network modifier alkali sulfide, Na2S, is not proportionally shared between the two network former components, B and P. Rather, the thiophosphate (P) component tends to attract a larger concentration of network modifier species than predicted by the bulk composition, and this results in the conversion of P2S74-, pyrothiophosphate, Na/P = 2:1, units into PS43-, orthothiophosphate, Na/P = 3:1, groups. Charge balance is maintained by increasing the net degree of polymerization of the thioborate (B) units through the formation of covalent bridging sulfur (BS) units, B S B. Detailed inspection of the B-11 MAS NMR spectra reveals that multiple thioborate units are formed, ranging from neutral BS3/2 groups all the way to the fully depolymerized orthothioborate (BS33-) species. On the basis of these results, a comprehensive and quantitative structural model is developed for these glasses, on the basis of which the compositional trends in the glass transition temperatures (T-g) and ionic conductivities can be rationalized. Up to x = 0.4, the dominant process can be described in a simplified way by the net reaction equation P-1 + B-1 reversible arrow P-0 + B-4, where the superscripts denote the number of BS atoms for the respective network former species. Above x = 0.4, all of the thiophosphate units are of the P-0 type and both pyro-(B-1) and orthothioborate (B-0) species make increasing contributions to the network structure with increasing x. In sharp contrast to the situation in sodium borophosphate glasses, four-coordinated thioborate species are generally less abundant and heteroatomic B-S-P linkages appear to not exist. On the basis of this structural information, compositional trends in the ionic conductivities are discussed in relation to the nature of the charge-compensating anionic species and the spatial distribution of the charge carriers.

NMR structural study on the As-P-S glassy system

Glasses having the composition As2S3(1-x)-P2S5(x) with x ranging from 0 to 0.7 have been investigated to determine the compositional effect on properties and local structure. Glass transition temperature (T,) decreases and molar volume (V,,) increases with an increase in P content. Using P-31 NMR, we measured the strength of the P-31-P-31 magnetic dipolar interaction in the glass samples and the AsPS4 crystallized phase. Based on these data, we observed the formation of the As2P2S8 network, which reflects an increase in the average coordination number and a decrease in the degree of rigidity.

1, 2-Bis (diphenylphosphino) etane bridged dinuclear copper (I) complexes: Investigations of solid state and solution structures by CP/MAS31P NMR spectroscopy, X-ray crystallography, IR spectroscopy and solution 31P NMR and 63Cu NMR spectroscopy

Three different complexes of copper (I) with bridging 1, 2-bis(diphenylphosphino)ethane (dppe), namely [Cu2 (mu-dppe) (CH3CN)6] (ClO4)2 (1), [Cu2 (mu-dppe)2 (CH3 CN)2] (ClO4)2 (2), and [Cu2 (mu-dppe) (dppe)2 (CH3CN)2] (ClO4)2 (3) have been prepared. The structure of [Cu2 (mu-dppe) (dPPe)2 (CH3CH)2] (ClO4)2 has been determined by X-ray crystallography. It crystallizes in the space group PT with a=12.984(6) angstrom, b=13.180(6) angstrom, c=14.001(3) angstrom, alpha=105.23(3), beta=105.60(2), gamma=112.53 (4), V=1944 (3) angstrom3, and Z=1. The structure was refined by least-squares method with R=0.0365; R(w)=0.0451 for 6321 reflections with F0 greater-than-or-equal-to 3 sigma (F0). The CP/MAS P-31 and IR spectra of the complexes have been analysed in the light of available crystallographic data. IR spectroscopy is particularly helpful in identifying the presence of chelating dppe. P-31 chemical shifts observed in solid state are very different from those observed in solution, and change significantly with slight changes in structure. In solution, complex 1 remains undissociated but complexes 2 and 3 undergo extensive dissociation. With a combination of room temperature H-1, Cu-63, and variable temperature P-31 NMR spectra, it is possible to understand the various processes occurring in solution.