Solid-state Carbon-13 Nuclear Magnetic Resonance Research Articles

Wheat bran biodegradation by Pleurotus ostreatus: A solid-state Carbon-13 NMR study

Solid-state 13C nuclear magnetic resonance (NMR) and elemental analysis techniques were used to monitor the degradation of wheat bran by the white-rot fungus Pleurotus ostreatus during a 62-day cultivation period. The weight loss and in vitro organic matter digestibility of the substrate were also evaluated after fungal treatment. The 13C NMR spectra of degraded wheat bran samples showed a lower content in carbohydrates and a higher content in aliphatic and carboxylic groups than the untreated control sample. In parallel, changes in the wheat bran elemental composition evidenced a decrease in carbon content and a concomitant increase in nitrogen and oxygen content during mycelium growth. These results clearly indicate the occurrence of progressive changes in the composition of wheat bran during fungal treatment and are interpreted in terms of preferential degradation of amorphous vs. crystalline polysaccharides by the fungal mycelium and accumulation of proteins in the substrate. At the end of the cultivation period, the treated samples experienced an average weight loss of 20% and an increase in organic matter digestibility of 17%.

Deactivation patterns of Mo/Al 2O 3, Ni–Mo/Al 2O 3 and Ni–MoP/Al 2O 3 catalysts in atmospheric residue hydrodesulphurization

In the present work, a comparative study on the deactivation behavior of three types of industrial hydrotreating catalysts, namely, Mo/Al 2O 3, Ni–Mo/Al 2O 3 and Ni–MoP/Al 2O 3, that are used to promote primarily hydrodemetallization (HDM), hydrodesulphurization (HDS) and hydrodesulphurization + hydrodenitrogenation (HDS/HDN) reactions, respectively, in the first, second and third reactor of commercial atmospheric residue desulfurization (ARDS) units was carried out. The main objective of the study was to contribute to a better understanding of the relationship between catalyst type and catalyst deactivation patterns. The used catalysts from these experiments were fully characterized to determine the extent and the cause of deactivation. Special emphasis was paid to understanding the nature of the coke and metal deposition on the used catalysts by applying chemical analysis and various advanced analytical techniques, such as solid-state carbon-13 nuclear magnetic resonance spectroscopy ( 13C NMR), temperature-programmed oxidation (TPO), electron probe micro-analysis (EPMA), and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The results are discussed scientifically based on the physico–chemical properties of the three catalysts.

13C-NMR analysis of decomposing litter and fine roots in the semi-arid Mulga Lands of southern Queensland

Plant litter and fine roots are important carbon (C) inputs to soil and a direct source of CO 2 to the atmosphere. Solid-state carbon-13 nuclear magnetic resonance ( 13C-NMR) spectroscopy was used to investigate the nature of C changes during decomposition of plant litter and fine roots of mulga ( Acacia aneura F. Muell. Ex. Benth.), wheat ( Triticum aestivum L.), lucerne ( Medicago sativa) and buffel grass ( Cenchrus ciliaris) over an 18-month period. Alkyl C was closely associated with total N concentrations in all litter materials during decay and as alkyl C increased so did total N, indicating an increase in refractory biomacromolecules. Mulga phyllodes had the greatest alkyl C concentration of all litter and fine root materials, and also exhibited the NMR peaks assigned to tannins that may slow or hinder decomposition rates and nitrification. Mulga litter and fine roots decomposed slower than all other litter materials and the soil under mulga had the highest soil C concentration, indicating slower CO 2 release. The alkyl C-to- O-alkyl C ratio is generally used as an index of the extent of decomposition, but is not useful for the decay of woody components. Of all the NMR ratios studied that may indicate the extent of decomposition, the carbohydrate C-to-methoxyl C ratio proved to have the strongest and most consistent relationship with decay time, fraction of mass remaining and total C, even though increases in alkyl C were observed with decreases in carbohydrate C.

Phase behaviors and supra-molecular structures of a series of symmetrically tapered bisamides.

A series of symmetrically tapered 1,4-bis[3,4,5-tris(alkan-1-yloxy)benzamido] benzene bisamides (CPhBA, where is the number of carbon atoms in the alkyl chains, = 10, 12 and 16), was synthesized in order to investigate the effect of alkyl chain length on supra-molecular ordered structures induced by hydrogen (H)-bonding and micro-phase separation. These bisamides consist of a rigid aromatic bisamide core with three flexible alkyl chains at each end of the core. Major phase transitions and their origins in CPhBA bisamides were studied with differential scanning calorimetry, one-dimensional (1D) wide angle X-ray diffraction (WAXD), infrared spectroscopy, and solid-state carbon-13 nuclear magnetic resonance experiments. The structures of these compounds in different phases were identified using 2D WAXD from oriented samples and were also confirmed by selected area electron diffractions in transmission electron microscopy from stacked single crystals and by computer simulations. All of the CPhBA bisamides in this series formed a highly ordered oblique columnar () phase and a low-ordered oblique columnar () phase, similar to a recent report on C14PhBA. The two main driving forces in the formation of these two supra-molecular columnar structures were identified: One was the H-bond formation between N-H and C[double bond, length as m-dash]O groups, and the other was the micro-phase separation between the bisamide cores and the alkyl chains. With increasing the length of alkyl tails, the isotropization temperature decreased, while the disordering temperature of the alkyl tails increased. The 2D lattice structures perpendicular to the columnar axis also increasingly deviated from the pseudo-hexagonal packing with increasing the alkyl tail length. However, the alkyl tail length did not have a significant influence on the packing along the columnar axis direction. Utilizing polarized optical microscopy, the phase identifications were also supported by the observation of texture changes and molecular arrangements inside of the micro-sized domains.

Phase Structures and Self-assembled Helical Suprastructures via Hydrogen Bonding in a Series of Achiral 4-Biphenyl Carboxylic Acid Compounds

A series of achiral 4-biphenyl carboxylic acid compounds (BPCA-Cn-PmOH) connected with alkoxyl chains having various carbon numbers (n = 6−10) and terminated by phenyl groups with meta-positioned hydroxyl groups was synthesized. Different phase structures including nematic, smectic A (SmA), smectic C (SmC), and highly ordered smectic liquid-crystalline phases along with crystalline phases were identified based on wide-angle X-ray diffraction and electron diffraction experiments. It was found via infrared spectroscopy that the hydrogen (H)-bonds were formed between the carboxylic acids to construct head-to-head dimers as the building blocks for these ordered structural formations. H-bonds formed via the meta-positioned hydroxyl groups also played an important role in forming ordered layers in these structures. The morphology of this series of BPCA-Cn-PmOH as observed under polarized light microscopy showed an oily streak (cylinder) texture with Myelin-figure in the SmA phase. When temperature cools to enter the SmC phase, these streaks (cylinders) started to twist into helical suprastructures, which were not only by the birefringence changes but also by the three-dimensional helical geometry observed in other microscopic techniques. The dynamic conformational changes of the aromatic and aliphatic parts in this series of BPCA-Cn-PmOH at different temperatures correspond well with the thermal transitions via solid-state carbon-13 nuclear magnetic resonance experiments. Computer simulation indicated that the head-to-head dimers possess a twisted rather than a bent conformation. It was deduced that the twisted conformation of the dimers and the terminal meta-substituted phenyl groups at both ends of the dimers are critically important in forming the helical suprastructures.

Taxonomic and Chemical Relationships Revealed by Nuclear Magnetic Resonance Spectra of Plant Exudates

Exudates collected from 65 species of gymnosperms and angiosperms were examined by solid-state carbon-13 (13C) nuclear magnetic resonance (NMR) spectroscopy. Diagnostic criteria were developed to distinguish resins, gums, and gum resins. The typology generated from the exudate spectra generally follows current taxonomic classifications, suggesting that 13C NMR spectroscopy may have applications in exudate identification, at least at the familial level, and in some cases at the generic or specific levels.

Comparing microfiltration-reverse osmosis and soil-aquifer treatment for indirect potable reuse of water

Microfiltration (MF) followed by reverse osmosis (RO) and soil-aquifer treatment (SAT) are the two principal technologies considered for indirect potable reuse of wastewater. This study, conducted at the Northwest Water Reclamation Plant, Mesa (Arizona), evaluated MF/RO and SAT (>6 months residence time) treated tertiary effluent with respect to organics removal. Effluent organic matter was characterized as total organic carbon (TOC), by UV absorbance (UVA), solid-state carbon-13 nuclear magnetic resonance spectroscopy, and size exclusion chromatography. Several trace organic micropollutants, including EDTA, NTA, and alkylphenolethoxylate residues, were analyzed by GC/MS. The study revealed that final TOC concentrations of MF/RO and SAT are 0.3 and 1.0 mg l −1, respectively. Based on the characterization techniques used, the character of bulk organics present in final SAT water resembles the character of natural organic matter present in drinking water. Depending on the molecular weight cut-off, RO membranes can efficiently reject high molecular weight organic matter (characterized as humic and fulvic acids). However, approximately 40–50 percent of the remaining TOC in permeates consists of low molecular weight acids and neutrals representing a molecular weight range of ∼500 Da and less. In the SAT treated effluent, EDTA and APECs were removed to approximately 4.3 and 0.54 μg/l, respectively, but were below the detection limit in the MF/RO treated effluent.

X-ray absorption and NMR spectroscopic investigations of zinc glutarates prepared from various zinc sources and their catalytic activities in the copolymerization of carbon dioxide and propylene oxide

The local and microstructures of zinc glutarates synthesized from various zinc sources were investigated by X-ray absorption and solid-state carbon-13 nuclear magnetic resonance spectroscopy, and related to their catalytic activities in the copolymerization of carbon dioxide and propylene oxide. It was found that the local structure around the Zn atoms of the zinc glutarate catalysts consists basically of tetrahedrally coordinated carboxyl oxygen atoms with a ZnO bond distance in the range 1.95–1.96 Å, and that the nearest neighbor Zn atom distance is 3.19–3.23 Å. These results suggest that the catalysts have a network structure composed of layers interconnected by glutarate ligands. However, the first-shell structures of the catalysts tested are somewhat different, which might originate from differences in the catalysts' overall crystallinity and crystal quality (crystal size and perfection) produced by their different synthetic routes. The surface areas of the catalysts also varied with synthetic route. In the copolymerization, one catalyst with low surface area but the highest crystallinity and best crystal quality shows the highest catalytic activity, which is contrary to the usual expectation of increased catalytic activity with increased catalyst surface area. Therefore, the catalytic activities of zinc glutarates in the copolymerization seem to depend primarily on their morphological structures rather than on their surface areas. The surface areas of zinc glutarates may play a crucial role in improving the catalytic activity in the copolymerization when they first meet the morphological requirements (i.e., high crystallinity and crystal quality).

Preparation and solid-state nuclear magnetic resonance characterization a styrene/butadiene/acrylonitrile (ABS)/poly(vinyl chloride) (PVC)/gypsum ternary system

Polymer blends were prepared to obtain a new material with specific characteristics. To prepare a miscible polymer blend, it is necessary to evaluate the chemical structure and molecular dynamics of all polymers involved and to thereby establish a structure–property relationship for these materials. In this work, ternary blends for application in plates chromatography were formed with styrene/butadiene/acrylinotrile (ABS), poly(vinyl chloride) (PVC), and gypsum, and were studied by solid-state carbon-13 nuclear magnetic resonance (13C NMR). Magic-angle spinning (MAS), cross-polarization magic-angle spinning (CPMAS), variable contact time (VCT), and proton spin-lattice relation time in the rotating frame (Tρ) were the techniques used to evaluate the miscibility, homogeneity, and compatibility of polymer blends at the molecular level. From the values of Tρ, it was verified that ABS/PVC/gypsum formed good polymer blends with some specific physical interaction at the molecular level. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 293–296, 2003

Solid-State Carbon-13 Nuclear Magnetic Resonance of Humic Acids at High Magnetic Field Strengths

Solid-State Carbon-13 Nuclear Magnetic Resonance of Humic Acids at High Magnetic Field Strengths

The influence of hemicellulose on fibril aggregation of kraft pulp fibres as revealed by FE-SEM and CP/MAS 13C-NMR

Three Norway spruce pulps were produced using different kraft pulping methods, in order to obtain large differences in cellulose and hemicellulose proportions at a similar lignin content. The hemicellulose content in the three pulps varied between 10% and 22%. The aim of the study was to evaluate the influence of cellulose and hemicellulose on fibre ultrastructure and correlate this with the differences observed in the mechanical properties between the pulps. The ultrastructure of the pulp fibres were studied using Field Emission Scanning Electron Microscopy (FE-SEM) and Solid-State Cross Polarisation Magic Angle Spinning Carbon-13 Nuclear Magnetic Resonance (CP/MAS 13C-NMR) in combination with spectral fitting. CP/MAS 13C-NMR measured the average bulk properties of the pulp fibres, while FE-SEM allowed for observations on the ultrastructure of fibre surfaces. The ultrastructure of the fibres varied with varying hemicellulose content. The pulp with a high hemicellulose content had a porous surface structure. In fibres with a low hemicellulose content, the fibril aggregates (macrofibrils) formed a much more compact surface structure. With CP/MAS 13C-NMR this change was reflected by an increase in average fibril aggregate width with decreasing hemicellulose content. Results from FE-SEM and CP/MAS 13C-NMR correlated well. The changes recorded in ultrastructure may explain the very different mechanical properties reported previously for pulps with different hemicellulose content.

13C-NMR study on cure-accelerated phenol-formaldehyde resins with carbonates

Both liquid- and solid-state carbon-13–nuclear magnetic resonance (13C-NMR) spectroscopies were used to investigate the cure acceleration effects of three carbonates (propylene carbonate, sodium carbonate, and potassium carbonate) on liquid and cured phenol-formaldehyde (PF) resins. The liquid-phase 13C-NMR spectra showed that the cure acceleration mechanism in the propylene carbonate-added PF resin seemed to be involved in increasing reactivity of the phenol rings, whereas the addition of both sodium carbonate and potassium carbonate into PF resin apparently resulted in the presence of ortho–ortho methylene linkages. Proton spin-lattice rotating frame relaxation time (T1ρH) measured by solid-state 13C cross polarization/magic-angle spinning NMR spectroscopy was smaller for the cure-accelerated PF resins than that of the control PF resin. The result indicated that the cure-accelerated PF resins are less rigid than the control PF resin. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1284–1293, 2000

Characterization of tolbutamide polymorphs (burger's forms II and IV) and polymorphic transition behavior

Burger's two polymorphs of tolbutamide (TB), an oral hypoglycemic agent, were obtained by spray-drying the drug dissolved in a mixed solvent of ethanol/dichloromethane (Form IV) and allowing Form IV to stand at constant temperatures and humidities (Form II). These polymorphs were characterized by various physical methods [e.g., powder X-ray diffractometry, differential scanning calorimetry, infrared spectrometry, and solid-state carbon-13 nuclear magnetic resonance (13C NMR) spectroscopy] and compared with two other TB polymorphs Forms I and III. The 13C NMR spectra showed that the chemical shift and the peak shape of resonance associated with the toluene and n-butyl moieties of TB were different for each of the four polymorphs, whereas the carbonyl carbon was unchanged, indicating different conformations and molecular motions of the toluene and n-butyl moieties in the solid states. Form IV converted itself to Form II within 3 h when it was stored at 45 °C and 75% relative humidity (RH) and, in turn, Form II transformed to Form I at higher temperatures. The conversion of Form IV to Form II proceeded according to a zero-order equation (Polany–Winger equation), and that of Form II to Form I according to a first-order equation. The increase in RH accelerated the polymorphic transition of Form IV. Both the apparent dissolution rate and the solubility of Form IV were nearly identical with those of Form II, because the former changed to the latter during the dissolution, but their dissolution rates and solubility were higher than those of Forms I and III. These dissolution characteristics of TB polymorphs were reflected in the oral absorption behavior in dogs; that is, the bioavailability increased in the order Form I < Form III < Form II ≈ Form IV.

A solid-state NMR study of aromatic polyimides based on 4,4?-diaminotriphenylmethane

The effect of different synthesis routes on the chemical and molecular order of polyimides based on 4,4′-diaminotripenylmethane (DA-TPM) and various aromatic dianhydrides (PI-TPM) was studied by solid-state carbon-13 nuclear magnetic resonance (13C-NMR). Polyimides were prepared by three different methods including a two-step procedure with either thermal or chemical imidization of precursor poly(amic acid)s (PAA) and one-step high-temperature polycondensation in phenolic solvents. Model compounds were also obtained and used in the assignment of the NMR signals. The NMR spectra for PI-TPMs obtained by one-step high-temperature polycondensation and—to a lesser extent—by thermal imidization of PAA, show sharper lines than those observed in the spectra of polymers prepared from PAA via chemical imidization. These differences are due mainly to the lower degree of ordering of the latter polyimides. WAXD patterns of polyimide films also indicated a less-ordered structure of the polymers resulting from the chemical imidization of PAA. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1053–1064, 1998

Thermal crosslinking of cis‐1,4‐polybutadiene at ultrahigh pressures

cis-1,4-Polybutadiene (BR) samples, in the absence of crosslinking agents, were simultaneously compressed by ultrahigh pressures (>4.0 GPa) and annealed between 25 and 180°C. The BR samples were crosslinked when the annealing temperatures were above 100°C. The Vickers microhardness of the treated BR increased and the extent of swelling decreased rapidly as the annealing temperature increased, indicating that the crosslinking density increased. Solid-state carbon-13 nuclear magnetic resonance and Fourier transform infrared spectroscopy results showed that some C=C bonds in the BR were opened to form the crosslinking network structures with C—C linkages and that a partial cis–trans isomerization took place during the treatments. Differential scanning calorimetry studies revealed that the glass transition temperature increased and the crystallinity decreased as the annealing temperature increased. When the annealing temperature exceeded 140°C, the treated BR samples lost their rubbery elastic characteristics completely and became brittle materials. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:2131–2140, 1998

Thermal crosslinking ofcis-1,4-polybutadiene at ultrahigh pressures

cis-1,4-Polybutadiene (BR) samples, in the absence of crosslinking agents, were simultaneously compressed by ultrahigh pressures (>4.0 GPa) and annealed between 25 and 180°C. The BR samples were crosslinked when the annealing temperatures were above 100°C. The Vickers microhardness of the treated BR increased and the extent of swelling decreased rapidly as the annealing temperature increased, indicating that the crosslinking density increased. Solid-state carbon-13 nuclear magnetic resonance and Fourier transform infrared spectroscopy results showed that some C=C bonds in the BR were opened to form the crosslinking network structures with C—C linkages and that a partial cis–trans isomerization took place during the treatments. Differential scanning calorimetry studies revealed that the glass transition temperature increased and the crystallinity decreased as the annealing temperature increased. When the annealing temperature exceeded 140°C, the treated BR samples lost their rubbery elastic characteristics completely and became brittle materials. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:2131–2140, 1998

The 3'-keto-diol equilibrium of trospectomycin sulfate bulk drug and freeze-dried formulation: solid-state carbon-13 cross-polarization magic angle spinning (CP/MAS) and high-resolution carbon-13 nuclear magnetic resonance (NMR) spectroscopy studies.

Understanding how moisture interacts with a drug or formulation is a critical component of product development. This study demonstrates how water affects the 3'-gem-diol<==>3'-keto equilibrium in trospectomycin sulfate bulk drug and freeze-dried formulation, as probed by solid-state carbon-13 cross-polarization magic angle spinning (CP/MAS) and high-resolution nuclear magnetic resonance (NMR) spectroscopy. Drying the bulk drug or formulation to low water levels dehydrates trospectomycin sulfate from the diol to the keto form. Carbon-13 CP/MAS NMR spectroscopy measures the keto drug concentration in solid samples directly. The bulk drug, which contains approximately 16% water, is more than 90% in the 3'-diol form. Oven drying to < 3% water converts approximately 75% of the drug to the 3'-keto form. The drug is formulated as a freeze-dried, sterile powder that can contain up to 12% water depending on the freeze-drying conditions. These studies show that the 3'-keto concentration rises uniformly (up to 75%) with decreasing residual water in the freeze-dried cake. The keto-diol equilibrium was also studied in solution by high-resolution carbon-13 NMR experiments, and it was found that raising the temperature or using dimethyl sulfoxide (DMSO) as a solvent also dehydrates the drug. For example, in aqueous solution at 25 degrees C, nearly all (> 95%) of the drug is in the 3'-diol form. After equilibration at 60 degrees C, however, the 3'-keto content increases to 7%, and in d6-DMSO solvent at 25 degrees C the drug is mostly (60%) in the 3'-keto form.

Synthesis of methylamines studied by in situ carbon-13 MAS NMR spectroscopy

Solid-state carbon-13 nuclear magnetic resonance (NMR) measurements under magic angle spinning conditions (MAS NMR) have been performed on alumina, NaZSM-5, and various catalysts of mordenite type loaded with ammonia and methanol. The samples were contained in sealed glass ampoules and spectra were measured at room temperature as a function of increasing pretreatment temperature. An analysis of the MAS NMR spectra provides not only information about the activity and deactivation of the catalysts but also quantitative results for the concentration of the reaction products (selectivity of the catalyst). In addition to the well-known fact that the values for the concentration of the reaction products c e calculated under the assumption of thermodynamic equilibrium may be different from the values cf measured under flowing gas conditions due to shape selectivity, it is shown in the present study that they are also different from the values c s derived from MAS NMR measurements performed on sealed samples if adsorption complexes are formed by at least one of the reaction products.

Carbon-13 Solid-state Nuclear Magnetic Resonance of Sporopollenins from Modern and Fossil Plants

13 C solid-state nuclear magnetic resonance (NMR) has been applied to modern pollen and spore exines (Betula, Pinus and Lycopadium) and those of two fossil spores (Lagenicula and Parka) in order to assess the composition of their constituent sporopollenin. While they prove to have broadly similar structural characteristics, there are some significant differences between all types and particularly between the fossil and living material

Isolation and Solid‐State Characteristics of a New Crystal Form of Indomethacin

AbstractA new polymorphic crystal form of indomethacin was precipitated from an aqueous solution of indomethacin and β-clodextrin by titration with a 0.5N HCI aqueous solution. Three polymorphs (α, β, and yforms) and a new crystal form were differentiated with thermal analysis, infrared spectroscopy, powder X-ray diffractometry, thin-layer chromatography, elemental analysis, and Fourier transform infrared (FTIR) spectroscopy with a newly developed FTIR microscope equipped with a thermal analyzer. The new crystal polymorph of indomethacin exhibited endo- and exothermic peaks near 102.8 and 104.1 °C, respectively, because of phase transitions without weight loss, followed by two additional endothermic peaks at 151 and 158.9 °C, because of fusion. The differential scanning calorimetry-FTIR system can be used to examine the correlation between structural change of C=O stretching bands of this new polymorph and its thermal response. The new crystal form contained some y-form crystals, determined with an FTIR microscope equipped with a mapping option. Solid-state carbon-13 nuclear magnetic resonance spectra of the polymorphs of indomethacin were also examined.