Cross polarisation/magic angle spinning 13C-NMR spectroscopic studies of cellulose structural changes in hardwood dissolving pulp process

Holzforschung ◽  
2007 ◽  
Vol 61 (6) ◽  
pp. 675-679 ◽  
Author(s):  
Xolani Nocanda ◽  
Per Tomas Larsson ◽  
Andrew Spark ◽  
Tamara Bush ◽  
Ann Olsson ◽  
...  
Keyword(s):  
Surface Area ◽  
Structural Changes ◽  
Magic Angle Spinning ◽  
Dissolving Pulp ◽  
Magic Angle ◽  
Cellulose Fibril ◽  
Dissolving Pulps ◽  
Angle Spinning ◽  
Fibril Aggregates ◽  
Pulp Process

Abstract Cross polarisation/magic angle spinning 13C NMR spectroscopy has been used to study structural changes in cellulose induced by the dissolving pulp process. The cellulose structure in several dissolving pulps was investigated for commercial and laboratory cooked Eucalyptus 92α and 96α. The average lateral dimension, or average thickness, of the cellulose fibril aggregates is related to the amount of surface area exposed and could be one controlling factor for the chemical reactivity of commercial dissolving pulps during modification reactions. The thickness of the cellulose fibril aggregates governs the amount of surface area present in the fibre wall, and cellulose surface material constitutes the part of the cellulose that is directly accessible to reagents. In all sample series investigated, the raw pulp was found to be less aggregated than the corresponding bleached final pulp. Furthermore, an irreversible increase in fibril aggregate width was observed on free drying for both laboratory cooked and commercial pulps. Upon rewetting with water, the freely dried 96α pulp was found to be more aggregated than the freely dried 92α pulp, although sugar analysis showed very similar carbohydrate compositions. As indicated by the molecular mass distribution, the commercial 92α pulp contained larger amounts of degraded cellulose; this may be a plausible explanation for the different behaviour of the 92α and 96α pulps during free drying.

Solid State 13C NMR Applied to Styrene-Butadiene Rubbers Study of the Rubber Vulcanized Network Structures

2002 ◽  
Vol 75 (1) ◽  
pp. 65-76 ◽  
Author(s):  
L. Pellicioli ◽  
S. K. Mowdood ◽  
F. Negroni ◽  
D. D. Parker ◽  
J. L. Koenig
Keyword(s):  
13C Nmr ◽  
Structural Changes ◽  
Magic Angle Spinning ◽  
Magic Angle ◽  
Nmr Spectrum ◽  
Polymer Microstructure ◽  
Polybutadiene Rubber ◽  
Angle Spinning ◽  
Styrene Butadiene

Abstract This paper discusses the structural changes that occur during the accelerated sulfur vulcanization of styrene-butadiene rubbers (SBR) through characterization of the network sulfide structures influenced by the curing agent concentration, the polymer microstructure, and the nature of the filler. Magic angle spinning (MAS) 13C FT - NMR spectroscopy was used to investigate the chemical crosslink properties of unfilled vulcanized SBR in addition to carbon black and silica filled polybutadiene rubber (BR), SBR, and 1:1 BR / SBR blends. New resonances in the 13C NMR spectrum are assigned to the various sulfide crosslink structures in SBR. Structural changes during vulcanization are also discussed.

scholarly journals Synthesis of Nitrogen-Rich Polymers by Click Polymerization Reaction and Gas Sorption Property

Molecules ◽  
2018 ◽  
Vol 23 (7) ◽  
pp. 1732 ◽  
Author(s):  
Jing-Ru Song ◽  
Wen-Gui Duan ◽  
Dian-Peng Li
Keyword(s):  
Surface Area ◽  
Sorption Property ◽  
Sorption Isotherms ◽  
Magic Angle Spinning ◽  
Polymerization Reaction ◽  
Magic Angle ◽  
Gas Sorption ◽  
Click Polymerization ◽  
Sorption Ability ◽  
Angle Spinning

Microporous organic polymers (MOPs) are promising materials for gas sorption because of their intrinsic and permanent porosity, designable framework, and low density. The introduction of nitrogen-rich building block in MOPs will greatly enhance the gas sorption capacity. Here, we report the synthesis of MOPs from the 2,4,6-tris(4-ethynylphenyl)-1,3,5-triazine unit and aromatic azides linkers by click polymerization reaction. Fourier transform infrared (FTIR) and solid-state 13C CP-MAS (Cross Polarization-Magic Angle Spinning) NMR confirm the formation of the polymers. CMOP-1 and CMOP-2 exhibit microporous networks with a BET (Brunauer–Emmett–Teller) surface area of 431 m2·g−1 and 406 m2·g−1 and a narrow pore size distribution under 1.2 nm. Gas sorption isotherms including CO2 and H2 were measured. CMOP-1 stores a superior CO2 level of 1.85 mmol·g−1 at 273 K/1.0 bar, and an H2 uptake of up to 2.94 mmol·g−1 at 77 K/1.0 bar, while CMOP-2, with its smaller surface area, shows a lower CO2 adsorption capacity of 1.64 mmol·g−1 and an H2 uptake of 2.48 mmol·g−1. In addition, I2 vapor adsorption was tested at 353 K. CMOP-1 shows a higher gravimetric load of 160 wt%. Despite the moderate surface area, the CMOPs display excellent sorption ability for CO2 and I2 due to the nitrogen-rich content in the polymers.

scholarly journals Structural changes of TasA in biofilm formation ofBacillus subtilis

2018 ◽  
Vol 115 (13) ◽  
pp. 3237-3242 ◽  
Author(s):  
Anne Diehl ◽  
Yvette Roske ◽  
Linda Ball ◽  
Anup Chowdhury ◽  
Matthias Hiller ◽  
...  
Keyword(s):  
Structural Change ◽  
Structural Changes ◽  
Analytical Ultracentrifugation ◽  
Magic Angle Spinning ◽  
Magic Angle ◽  
X Ray ◽  
X Ray Crystallography ◽  
Angle Spinning

Microorganisms form surface-attached communities, termed biofilms, which can serve as protection against host immune reactions or antibiotics.Bacillus subtilisbiofilms contain TasA as major proteinaceous component in addition to exopolysaccharides. In stark contrast to the initially unfolded biofilm proteins of other bacteria, TasA is a soluble, stably folded monomer, whose structure we have determined by X-ray crystallography. Subsequently, we characterized in vitro different oligomeric forms of TasA by NMR, EM, X-ray diffraction, and analytical ultracentrifugation (AUC) experiments. However, by magic-angle spinning (MAS) NMR on live biofilms, a swift structural change toward only one of these forms, consisting of homogeneous and protease-resistant, β-sheet–rich fibrils, was observed in vivo. Thereby, we characterize a structural change from a globular state to a fibrillar form in a functional prokaryotic system on the molecular level.

scholarly journals The influence of thermal treatments on the secondary structure of silk fibroin scaffolds and their interaction with fibroblasts

2020 ◽  
Vol 2 ◽  
pp. e8
Author(s):  
Tomoko Hashimoto ◽  
Yuka Nakamura ◽  
Yasushi Tamada ◽  
Hiromichi Kurosu ◽  
Tsunenori Kameda
Keyword(s):  
Secondary Structure ◽  
Silk Fibroin ◽  
Structural Changes ◽  
Magic Angle Spinning ◽  
Magic Angle ◽  
Dry Heat ◽  
Dry Heating ◽  
Heat Method ◽  
Angle Spinning ◽  
The Stability

Background Recently, silk fibroin-based biomaterials have received attention for application in tissue engineering and drug delivery systems. The usefulness of heat sterilization methods for silk fibroin-based biomaterials was investigated in this study as all biomaterials are required to undergo a sterilization process when they are used in medical devices. Methods The influence of wet and dry heating on the properties of fibroin molecules in silk fibroin sponges was investigated by measurements of solid-state 13C cross-polarization/magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analyses, strength tests, and cell proliferation/migration assays. Results 13C CP/MAS NMR spectra of wet-heated sponges revealed no changes in the molecular structure below 50 °C. However, above 60 °C, the crystalline structure of the silk proteins transitioned from silk I to silk II; the silk II:silk I ratio increased with temperature. In contrast, dry heating (below 190 °C for up to 180 min) induced no structural changes in the fibroin molecules. These results indicate that, although autoclave sterilization (121 °C for 20 min) induces structural changes in silk fibroin sponges, no such changes are observed with the dry-heat sterilization (180 °C for 30 min). Sterilized sponges with a silk I structure can be obtained using dry-heat method during sterilization. Moreover, the structural differences between the wet- and dry-heated silk fibroin sponges did not influence their interaction with fibroblasts. Discussion This study indicates that both autoclaving and dry heating are acceptable sterilization methods for silk fibroin-based sponges as the scaffold. In particular, dry heating maintains the stability of the secondary structure of the sterilized silk fibroin-based biomaterials.

A MAS NMR investigation of aluminosilicate, silicophosphate, and aluminosilicophosphate gels and the evolution of crystalline structures on heating the gels

1991 ◽  
Vol 6 (3) ◽  
pp. 592-601 ◽  
Author(s):  
S. Prabakar ◽  
K.J. Rao ◽  
C.N.R. Rao
Keyword(s):  
Nmr Spectroscopy ◽  
Nmr Spectra ◽  
Structural Changes ◽  
Orthophosphoric Acid ◽  
Magic Angle Spinning ◽  
Hydroxyl Groups ◽  
Magic Angle ◽  
Major Phase ◽  
Higher Temperature ◽  
Angle Spinning

Gels of various composition containing SiO2, Al2O3, and P2O5 have been investigated by employing high resolution magic-angle-spinning (MAS) 27Al, 29Si, and 31P NMR spectroscopy. Changes occurring in the NMR spectra as the gels are progressively heated have been examined to understand the nature of structural changes occurring during the crystallization of the gels. 27Al resonance is sensitive to changes in the coordination number even when the Al concentration is as low as 1 mol%. As the percentage of Al increases, the hydroxyl groups tend to be located on the Al sites while Si remains as SiO4/2 (Q4). Mullite is the major phase formed at higher temperature in the aluminosilicate gels. In the case of the silicophosphate gels, Si is present in the form of Q4 and Q3 species. There is a change in the coordination of Si from four to six as the gel is heated. The formation of six-coordinated Si is facilitated even at lower temperatures (∼673 K) when the P2O5 content is high. The phosphorus atoms present as orthophosphoric acid units in the xerogels change over to metaphosphate-like units as the gel is heated to higher temperatures. In aluminosilicophosphates, Si is present as Q4 and Q3 species while P is present as metaphosphate units; Al in these gels seems to be inducted into the tetrahedral network positions.

scholarly journals Glass formation in the Sb2O3-SbPO4-WO3 system

2017 ◽  
Vol 42 (1) ◽  
pp. 51 ◽  
Author(s):  
Douglas Faza Franco ◽  
Hassen Fares ◽  
Antônio Eduardo De Souza ◽  
Silvia Helena Santagneli ◽  
Marcelo Nalin
Keyword(s):  
Structural Changes ◽  
Antimony Oxide ◽  
Magic Angle Spinning ◽  
Magic Angle ◽  
Scanning Calorimetry ◽  
Edge Structure ◽  
Primary Network ◽  
Angle Spinning ◽  
X Ray Absorption ◽  
Thermal Stability Of

Glasses in the ternary system (Sb2O3)(0.6-x)(SbPO4)(0.4)(WO3)(x), with composition 0.1 £ x £ 0.5 were studied. The structural changes due to the replacement of Sb2O3 by WO3 have been investigated. It was found that the incorporation of WO3 enhances the thermal stability of the glasses against devitrification when compared to the binary Sb2O3(0.6) - SbPO4(0.4) composition. The connectivity of the network increases with WO3 content which is consistent with the high values of the glass transition temperature. Raman studies suggest that WO3 incorporation breaks the primary network, constituted by antimony oxide, while a second network containing WO6 octahedral units is built up. Thermal and structural properties were evaluated by differential scanning calorimetry, infrared and Raman spectroscopies, 31P Magic Angle Spinning NMR and X-ray absorption near edge structure (XANES) at L1 and L3 edges of Sb and L1 edge of W atoms.

scholarly journals Structural changes, thermodynamic properties, 1H magic angle spinning NMR, and 14N NMR of (NH4)2CuCl4·2H2O

RSC Advances ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 6502-6506
Author(s):  
Ae Ran Lim ◽  
Sun Ha Kim
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Differential Scanning Calorimetry ◽  
Magnetic Resonance ◽  
Thermodynamic Properties ◽  
Structural Changes ◽  
Magic Angle Spinning ◽  
Magic Angle ◽  
Scanning Calorimetry ◽  
Angle Spinning ◽  
14N Nmr

The structural changes and thermodynamic properties of (NH4)2CuCl4·2H2O were studied by differential scanning calorimetry (DSC), thermogravimetric (TG) analysis, and nuclear magnetic resonance (NMR).

Pulse Shaped Dynamic Nuclear Polarization Under Magic Angle Spinning

2019 ◽  
Author(s):  
ASIF EQUBAL ◽  
Kan Tagami ◽  
Songi Han
Keyword(s):  
Electron Spin ◽  
Lattice Relaxation ◽  
Magic Angle Spinning ◽  
Spin Lattice Relaxation ◽  
Magic Angle ◽  
Total Electron ◽  
Spin Lattice ◽  
Maximum Benefit ◽  
Selective Saturation ◽  
Angle Spinning

In this paper, we report on an entirely novel way of improving the MAS-DNP efficiency by shaped μw pulse train irradiation for fast and broad-banded (FAB) saturation of the electron spin resonance. FAB-DNP achieved with Arbitrary Wave Generated shaped μw pulse trains facilitates effective and selective saturation of a defined fraction of the total electron spins, and provides superior control over the DNP efficiency under MAS. Experimental and quantum-mechanics based numerically simulated results together demonstrate that FAB-DNP significantly outperforms CW-DNP when the EPR-line of PAs is broadened by conformational distribution and exchange coupling. We demonstrate that the maximum benefit of FAB DNP is achieved when the electron spin-lattice relaxation is fast relative to the MAS frequency, i.e. at higher temperatures and/or when employing metals as PAs. Calculations predict that under short T<sub>1e </sub>conditions AWG-DNP can achieve as much as ~4-fold greater enhancement compared to CW-DNP.

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