Cross Polarization With Magic Angle Spinning Research Articles

Polysaccharide compositions of collenchyma cell walls from celery (Apium graveolens L.) petioles

BackgroundCollenchyma serves as a mechanical support tissue for many herbaceous plants. Previous work based on solid-state NMR and immunomicroscopy suggested collenchyma cell walls (CWs) may have similar polysaccharide compositions to those commonly found in eudicotyledon parenchyma walls, but no detailed chemical analysis was available. In this study, compositions and structures of cell wall polysaccharides of peripheral collenchyma from celery petioles were investigated.ResultsThis is the first detailed investigation of the cell wall composition of collenchyma from any plant. Celery petioles were found to elongate throughout their length during early growth, but as they matured elongation was increasingly confined to the upper region, until elongation ceased. Mature, fully elongated, petioles were divided into three equal segments, upper, middle and lower, and peripheral collenchyma strands isolated from each. Cell walls (CWs) were prepared from the strands, which also yielded a HEPES buffer soluble fraction. The CWs were sequentially extracted with CDTA, Na2CO3, 1 M KOH and 4 M KOH. Monosaccharide compositions of the CWs showed that pectin was the most abundant polysaccharide [with homogalacturonan (HG) more abundant than rhamnogalacturonan I (RG-I) and rhamnogalacturonan II (RG-II)], followed by cellulose, and other polysaccharides, mainly xyloglucans, with smaller amounts of heteroxylans and heteromannans. CWs from different segments had similar compositions, but those from the upper segments had slightly more pectin than those from the lower two segments. Further, the pectin in the CWs of the upper segment had a higher degree of methyl esterification than the other segments. In addition to the anticipated water-soluble pectins, the HEPES-soluble fractions surprisingly contained large amounts of heteroxylans. The CDTA and Na2CO3 fractions were rich in HG and RG-I, the 1 M KOH fraction had abundant heteroxylans, the 4 M KOH fraction was rich in xyloglucan and heteromannans, and cellulose was predominant in the final residue. The structures of the xyloglucans, heteroxylans and heteromannans were deduced from the linkage analysis and were similar to those present in most eudicotyledon parenchyma CWs. Cross polarization with magic angle spinning (CP/MAS) NMR spectroscopy showed no apparent difference in the rigid and semi-rigid polysaccharides in the CWs of the three segments. Single-pulse excitation with magic-angle spinning (SPE/MAS) NMR spectroscopy, which detects highly mobile polysaccharides, showed the presence of arabinan, the detailed structure of which varied among the cell walls from the three segments.ConclusionsCelery collenchyma CWs have similar polysaccharide compositions to most eudicotyledon parenchyma CWs. However, celery collenchyma CWs have much higher XG content than celery parenchyma CWs. The degree of methyl esterification of pectin and the structures of the arabinan side chains of RG-I show some variation in the collenchyma CWs from the different segments. Unexpectedly, the HEPES-soluble fraction contained a large amount of heteroxylans.

Monometallic Ni(0) and Heterobimetallic Ni(0) /Au(I) Complexes of Tripodal Phosphine Ligands: Characterization in Solution and in the Solid State and Catalysis.

The tridentate chelate nickel complexes [(CO)Ni{(PPh2 CH2 )3 CMe}] (2), [(CO)Ni{(PPh2 CH2 CH2 )3 SiMe}] (6), and [Ph3 PNi{(PPh2 CH2 CH2 )3 SiMe}] (7), as well as the bidentate complex [(CO)2 Ni{(PPh2 CH2 )2 CMeCH2 PPh2 }] (3) and the heterobimetallic complex [(CO)2 Ni{(PPh2 CH2 )2 CMeCH2 Ph2 PAuCl}] (4), have been synthesized and fully characterized in solution. All (1) H and (13) C NMR signal assignments are based on 2D-NMR methods. Single crystal X-ray structures have been obtained for all complexes. Their (31) P CP/MAS (cross polarization with magic angle spinning) NMR spectra have been recorded and the isotropic lines identified. The signals were assigned with the help of their chemical shift anisotropy (CSA) data. All complexes have been tested regarding their catalytic activity for the cyclotrimerization of phenylacetylene. Whereas complexes 2-4 display low catalytic activity, complex 7 leads to quantitative conversion of the substrate within four hours and is highly selective throughout the catalytic reaction.

High‐temperature steam‐treatment of PBI, PEKK, and a PEKK‐PBI Blend: A solid‐state NMR and IR spectroscopic study

AbstractBlends of polyaryletherketones (PAEK) with polybenzimidazole (PBI) are of commercial interest due to their improved upper service temperatures and wear properties when compared with the PAEK analogs examined to date. The retention of properties of the PBI component generally thought to be disadvantageous in more thermally or chemically aggressive environments is not well understood, nor are the specifics of interactions between the PBI and PAEK components in a melt or dry blend systems. In this initial investigation, focus is placed on the behavior and mechanism of polyetherketoneketone (PEKK)/PBI systems in contact with steam or condensed phase water. The goal is to understand the chemistry of the reaction, if any, upon exposure to steam as well as to examine the reversibility of moisture uptake of this material when exposed to liquid water or saturated steam. In this contribution, the pure polymer components and the PEKK‐PBI (60 : 40 wt %) blend are steam‐treated at 149°C (300°F) and 316°C (600°F). IR and solid‐state NMR spectroscopy are used to study chemical or morphological transformations of the polymers. All changes detectable by 13C cross‐polarization with magic angle spinning (CP/MAS) upon steam‐treatment are reversible, and not of a chemical nature, indicating that under the conditions of exposure used here no detectable chemical degradation occurs during steam exposure and with moisture uptake. The temporary water uptake of the samples, as studied by 1H wideline NMR and 13C T1 time measurements, leads to a change in the ratio of rigid versus mobile domains of the materials. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Crystallinity and Miscibility of Poly(vinyl isobutyl ether)/Poly(ε-L-lysine) Blends by Solid State 13C NMR Study

The relation between crystallinity and miscibility of semicrystalline polymer blends of poly(vinyl isobutyl ether) (PVIBE) and poly(e-L-lysine) (e-PL) is investigated by 13C cross-polarization with magic-angle-spinning (CPMAS) NMR (nuclear magnetic resonance) and DSC measurements. Analysis of the 1H spin-lattice relaxation curves observed from both PVIBE and e-PL signals, which are indirectly obtained from well-resolved 13C CPMAS NMR spectra, suggested that the domains of e-PL in the blends are in the range of 50–100 nm scale. Two-spin or three-spin models were used to simulate the 1H relaxation curves taking into account the contribution of a 1H spin-diffusion rate between PVIBE and e-PL. Furthermore, it was found that blending e-PL largely influences the crystallinity of PVIBE but that of e-PL is little affected by blending PVIBE except for 10/1 composition. The observed melting point of e-PL shifted towards lower temperature accompanied by PVIBE content. This shift was explained by the Gibbs-Thomson effect that the decrease of thickness of crystalline phase causes the depression of the melting point.

Cooperativity between the Hydrophobic and Cross-linking Domains of Elastin

The principal protein component of the elastic fiber found in elastic tissues is elastin, an amorphous, cross-linked biopolymer that is assembled from a high molecular weight monomer. The hydrophobic and cross-linking domains of elastin have been considered separate and independent, such that changes to one region are not thought to affect the other. However, results from these solid-state 13C NMR experiments demonstrate that cooperativity in protein folding exists between the two domain types. The sequence of the EP20-24-24 polypeptide has three hydrophobic sequences from exons 20 and 24 of the soluble monomer tropoelastin, interspersed with cross-linking domains constructed from exons 21 and 23. In the middle of each cross-linking domain is a "hinge" sequence. When this pentapeptide is replaced with alanines, as in EP20-24-24[23U], its properties are changed. In addition to the expected increase in alpha-helical content and the resulting increase in rigidity of the cross-linking domains, changes to the organization of the hydrophobic regions are also observed. Using one-dimensional CPMAS (cross-polarization with magic angle spinning) techniques, including spectral editing and relaxation measurements, evidence for a change in dynamics to both domain types is observed. Furthermore, it is likely that the methyl groups of the leucines of the hydrophobic domains are also affected by the substitution to the hinge region of the cross-linking sequences. This cooperativity between the two domain types brings new questions to the phenomenon of coacervation in elastin polypeptides and strongly suggests that functional models for the protein must include a role for the cross-linking regions.

Enzymatically Synthesized Conducting Polyaniline Nanocomposites: A Solid‐State NMR Study

The chiral conducting polyaniline (PANI) nanocomposites [polyacrylic acid/polyaniline/(−) camphorsulphonic acid (CSA)] were synthesized using enzyme, horseradish peroxidase (HRP) in the aqueous buffer solution at pH 4.3. It appears that the enzyme HRP apart being a biocatalyst, plays an important role during the polymerization, which allows PANI to prefer a specific helical conformation whether the induced chirality in the monomer‐CSA complex is either by (+)CSA or (−)CSA. In this paper, we report, the structural characterization of these nanocomposites by solid‐state 13C cross‐polarization with magic angle spinning (CP/MAS) NMR techniques. The structural features of PANI in the conducting form of nanocomposite (as‐synthesized) are similar to that of enzymatically and chemically synthesized PANI. Preliminary data also suggest that some portion of nanocomposite samples are not completely doped. Dedoping of as‐synthesized PANI nanocomposite with aqueous NH4OH shows the spectral features that of the emeraldine base form. Solid‐state 13C NMR data suggest that it is possible to detach PAA and CSA from PANI in the nanocomposite material.

Observation of the glycines in elastin using (13)C and (15)N solid-state NMR spectroscopy and isotopic labeling.

We report the solid-state 13C and 15N NMR of insoluble elastin which has been synthesized in vitro with isotopically enriched glycine. Most of the glycines reside in a domain with good cross-polarization (CP) efficiencies, although surprisingly, a portion resides in an environment that is not detectable using CP. Our data indicate that much of the 13C population resides in regions of significant conformational flexibility. To support these conclusions, we present 13C and 15N cross-polarization with magic-angle-spinning (CPMAS) data in conjunction with "direct-polarization", nonspinning CP, and T1 measurements.

Analysis of Potentially Mobile Phosphorus in Arable Soils Using Solid State Nuclear Magnetic Resonance

In many intensive agroecosystems continued inputs of phosphorus (P) over many years can significantly increase soil P concentrations and the risk of P loss to surface waters. For this study we used solid-state 31P nuclear magnetic resonance (NMR) spectroscopy, high-power decoupling with magic angle spinning (HPDec-MAS) NMR, and cross polarization with magic angle spinning (CP-MAS) NMR to determine the chemical nature of potentially mobile P associated with aluminum (Al) and calcium (Ca) in selected arable soils. Three soils with a range of bicarbonate-extractable Olsen P concentrations (40-102 mg P kg(-1)) were obtained from a long-term field experiment on continuous root crops at Rothamsted, UK, established in 1843 (sampled 1958). This soil has a threshold or change point at 59 mg Olsen P kg(-1), above which potentially mobile P (as determined by extraction with water or 0.01 M CaCl2) increases much more per unit increase in Olsen P than below this point. Results showed that CaCl2 and water preferentially extracted Al-P and Ca-P forms, respectively, from the soils. Comparison among the different soils also indicated that potentially mobile P above the threshold was largely present as a combination of soluble and loosely adsorbed (protonated-cross polarized) P forms largely associated with Ca, such as monetite (CaHPO4) and dicalcium phosphate dihydrate (CaHPO4-2H2O), and some Al-associated P as wavellite. The findings of this study demonstrate that solid-state NMR has the potential to provide accurate information on the chemical nature of soil P species and their potential mobility.

13C NMR spectral editing of humic material

The spectral-editing method introduced by Wu, Burns and Zilm (J. Magn. Reson. A, 111 (1994) 29) based on a prescribed combination of 13C CP-MAS (cross-polarization with magic-angle spinning) experiments that include suitably chosen depolarization periods, polarization inversion periods and either short or long CP periods, has been applied to a humic acid that was isolated from the Uncompahgre National Forest. The separate spectra derived on the basis of CHn multiplicity (n=0,1,2,3) for CH groups, CH2 groups and CH3+C (no directly attached hydrogen) groups confirm and advance previous structural interpretations based on chemical shift arguments. This work demonstrates that, while very time consuming, these spectral-editing techniques based on 13C CP-MAS techniques, are practicable for complex soil-derived samples.

97/00834 Coal liquefaction method

Catalysts of the CoMo type were prepared on four different surface-modified alumina supports: (1) TiO2-coated by impregnation, (2) ZrO2-coated by impregnation, (3) TiO2-coated by deposition, and (4) carbon-coated by pyrolysis. These catalysts were used in a catalytic coal liquefaction microreactor. The coke deposits on the spent catalysts were investigated using 13C solid-state nuclear magnetic resonance techniques of cross polarization with magic angle spinning (CP-MAS) and dipolar dephasing (DD). CP-MAS 13C spectral data of the coke deposits were used to quantify the aromatic and aliphatic carbon types, and 13C DD spectral data of the same samples to quantify the aromatic quaternary carbon types, from which the aromatic cluster size of the coke deposits was determined. Catalysts which promote the most coke deposition were found to perform poorly in terms of coal liquefaction conversion. The aromatic cluster size of the coke deposited on the spent catalysts appears to depend on the initial pore volume of the fresh catalyst and on the percentage of surface coating of the alumina support.

97/00828 Characterization and activity of ferric-sulfide-based catalyst in model reactions of direct coal liquefaction: effect of preparation conditions

Catalysts of the CoMo type were prepared on four different surface-modified alumina supports: (1) TiO2-coated by impregnation, (2) ZrO2-coated by impregnation, (3) TiO2-coated by deposition, and (4) carbon-coated by pyrolysis. These catalysts were used in a catalytic coal liquefaction microreactor. The coke deposits on the spent catalysts were investigated using 13C solid-state nuclear magnetic resonance techniques of cross polarization with magic angle spinning (CP-MAS) and dipolar dephasing (DD). CP-MAS 13C spectral data of the coke deposits were used to quantify the aromatic and aliphatic carbon types, and 13C DD spectral data of the same samples to quantify the aromatic quaternary carbon types, from which the aromatic cluster size of the coke deposits was determined. Catalysts which promote the most coke deposition were found to perform poorly in terms of coal liquefaction conversion. The aromatic cluster size of the coke deposited on the spent catalysts appears to depend on the initial pore volume of the fresh catalyst and on the percentage of surface coating of the alumina support.

Carbon-13 solid-state n.m.r. investigation of coke deposits on spent catalysts used in coal liquefaction

Catalysts of the CoMo type were prepared on four different surface-modified alumina supports: (1) TiO 2-coated by impregnation, (2) ZrO 2-coated by impregnation, (3) TiO 2-coated by deposition, and (4) carbon-coated by pyrolysis. These catalysts were used in a catalytic coal liquefaction microreactor. The coke deposits on the spent catalysts were investigated using 13C solid-state nuclear magnetic resonance techniques of cross polarization with magic angle spinning (CP-MAS) and dipolar dephasing (DD). CP-MAS 13C spectral data of the coke deposits were used to quantify the aromatic and aliphatic carbon types, and 13C DD spectral data of the same samples to quantify the aromatic quaternary carbon types, from which the aromatic cluster size of the coke deposits was determined. Catalysts which promote the most coke deposition were found to perform poorly in terms of coal liquefaction conversion. The aromatic cluster size of the coke deposited on the spent catalysts appears to depend on the initial pore volume of the fresh catalyst and on the percentage of surface coating of the alumina support.

Formation of Coke in the Disproportionation of n-Propylbenzene on Zeolites

Abstract We investigated the formation of coke on zeolitic catalysts in the disproportionation of n -propylbenzene by means of 129 Xe, 27 Al, and 13 C NMR spectroscopy. According to 13 C CP-MAS (proton cross polarization with magic angle spinning) spectra, the coke formed in USY and ZSM-5 zeolites was classified into aliphatics and aromatics. It was found that aliphatic coke could be removed by a simple evacuation procedure. The location of the coke determined from 129 Xe NMR spectra and xenon adsorption isotherms varied with the zeolite catalysts. For zeolite USY, the coke was formed inside the supercages and is mainly polyaromatic. For zeolite ZSM-5. the coke is alkykaromatic and tended to deposit at the openings of the channels rather than at their intersections. In regard to the mechanism, the reaction on USY followed bimolecular kinetics, whereas on ZSM-5 the reaction was monomolecular.

Quantitative solid-state 13C nuclear magnetic resonance spectrometric analyses of wood xylen: effect of increasing carbohydrate content

Isolated lignin with a low carbohydrate content was spiked with increasing amounts of alpha-cellulose, and then analysed by solid-state 13C nuclear magnetic resonance (NMR) using cross-polarization with magic angle spinning (CPMAS) and dipolar dephasing methods in order to assess the quantitative reliability of CPMAS measurement of carbohydrate content and to determine how increasingly intense resonances for carbohydrate carbons affect calculations of the degree of lignin's aromatic ring substitution and methoxyl carbon content. Comparisons were made of the carbohydrate content calculated by NMR with carbohydrate concentrations obtained by phenol-sulfuric acid assay and by the calculation from the known amounts of cellulose added. The NMR methods used in this study yield overestimates for carbohydrate carbons due to resonance area overlap from the aliphatic side chain carbons of lignin. When corrections are made for these overlapping resonance areas, the NMR results agree very well with results obtained by other methods. Neither the calculated methoxyl carbon content nor the degree of aromatic ring substitution in lignin, both calculated from dipolar dephasing spectra, change with cellulose content. Likewise, lignin methoxyl content does not correlate with cellulose abundance when measured by integration of CPMAS spectra.

CRAMPS determined proton aromaticities of Australian coals: a comparison with dipolar dephasing

The proton (H ar ) and carbon aromaticities (f a ) of a range of Australian coals and a few coals from other sources have been measured by high-resolution solid-state nuclear magnetic resonance spectroscopy. Combined rotation and multiple pulse spectroscopy (CRAMPS) was used to measure proton aromaticities while cross polarization with magic angle spinning (CPMAS) was used in carbon aromaticity measurement. Whereas reasonable correlations (correlation coefficient r=0.85) were found between f a and atomic hydrogen to carbon ratios (H/C), proton aromaticities exhibited a greatly smaller dependence upon H/C which predominantly grouped around H ar =0.3 (r=0.62). It is proposed that, for the coal suite studied here, dealkylation with subsequent protonation of the aromatic rings competes with aryl-aryl ring cross-linking involving loss of aromatic hydrogen without loss of alkyl groups