CPMAS Nuclear Magnetic Resonance Spectroscopy Research Articles

Aqueous adsorption of bisphenol A over a porphyrinic porous organic polymer

A new porphyrinic porous organic polymer (PPOP) with high stability and excellent textural properties (929 m2/g surface area with 0.73 cm3/g pore volume) was made via the Friedel-Crafts reaction and applied for bisphenol A (BPA) adsorption in water. The material was examined by X-ray diffraction, N2 adsorption-desorption isotherms, scanning electron microscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, and solid-state 13C CP-MAS nuclear magnetic resonance spectroscopy. PPOP was proven highly effective for capturing BPA among the many adsorbent materials investigated. The Langmuir model could closely match the adsorption isotherm data with a high adsorption amount of ca. 653 mg/g at 25 °C. Approximately 95% of BPA was adsorbed in 50 min, and the pseudo-second-order kinetic model satisfactorily described the adsorption behavior. This adsorption process was exothermic (ΔH° = −39.10 kJ/mol), and the capacity gradually decreased with increasing pH. Spectroscopic analyses indicated that the BPA adsorption on PPOP was affected by (1) π-π interaction between BPA and the aromatic constituents of PPOP, (2) hydrogen bonding between the N sites of porphyrin units in PPOP and the hydroxyl group of BPA and, and (3) hydrophobic interactions. PPOP was easily regenerated after acetone washing, and >98% efficiency was observed throughout the five repeated adsorption-desorption cycles.

A comprehensive investigation into the structure-property relationship of wax and how it influences the properties of hot melt adhesives

A detailed study was conducted on seven different waxes used in hot melt adhesive formulations together with conventional resins and tackifiers, to characterize the waxes and investigate the effects of wax structure and morphology on the thermal behaviour and basic properties of the resultant hot melt adhesive formulations (HMAs). The waxes selected included representatives of each of the following types: Fischer-Tropsch wax (FT), fully refined paraffin wax (FRP), by-product polyethylene wax (BPPE), microcrystalline wax (microwax), alpha-olefin wax (AO), carnauba wax and first intention polyethylene wax (FIPE). Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), high temperature size exclusion chromatography (HT-SEC), nuclear magnetic resonance spectroscopy (NMR) and confocal laser scanning microscopy (CLSM) were used as analytical tools to characterize the waxes. Molecular chain architecture as determined by solution 13C NMR highlighted the superior chain linearity of FT wax. Methyl, ethyl and butyl short chain branching were detected in other waxes. Solid-state 13C CP-MAS NMR provided information on the semi-crystalline nature of the waxes. FIPE, AO and Microwax showed significant structural mobility at room temperature as observed by 1H Wideline NMR and was attributed to chain branching and mobile crystalline domains respectively. This was supported by CLSM micrographs. All waxes enhanced crystallinity in both metallocene catalysed polyethylene (mPE) and ethylene-vinyl acetate (EVA) based HMAs. This was confirmed by the characteristic splitting in FTIR bands and increased DSC enthalpies observed for the HMA relative to the neat polymers. Of the formulations containing high melting waxes, FT wax resulted in HMAs with narrower crystallization profiles, an important factor in determining HMA set times. HMA viscosities were found to be dependent on the molecular weight of the wax while the HMA melting temperatures and enthalpies were more dependent on the crystalline morphology of the waxes.

The concentration of polysaccharides and proteins in EPS of Pseudomonas putida and Aureobasidum pullulans as revealed by 13C CPMAS NMR spectroscopy

Extracellular polymeric substances were extracted from the bacterial strain Pseudomonas putida and the fungal species Aureobasidium pullulans using three different methods (formaldehyde-NaOH, ethylenediaminetetraacetic acid (EDTA) and cation-exchange-resin). The composition of the extracellular polymeric substances (EPS) was analysed by biochemical and high-resolution solid state 13C nuclear magnetic resonance (NMR) spectroscopic methods. The EPS yield was strongly dependent on the extraction method, with the formaldehyde-NaOH method showing the best extraction efficiency. The NMR method revealed that when using the EDTA extraction method, about 40% of the EDTA accumulated in the EPS and that was responsible for the apparent high extraction yields. EPS protein content determined by the NMR method was up to 30% higher than the protein content determined using the biochemical (Lowry) method for P. putida and for A. pullulans. The average protein carbon content determined by the NMR method was approximately 70% of the total carbon content. NMR results could be supported by elemental analysis, which showed a high nitrogen content (approximately 10%) in the EPS. The carbohydrate carbon content detected with both methods in the cell aggregates and the EPS was approximately 20% in each. In this study, quantitative 13C cross-polarisation magic angle spinning NMR spectroscopy was conducted on unlabeled cell strains, and EPS and could be used to quantify protein and carbohydrate of different samples.

Search for basic relationships between “molecular size” and “chemical structure” of aquatic natural organic matter—Answers from 13C and 15N CPMAS NMR spectroscopy

To investigate the structural composition of natural organic matter (NOM), a 3-step micro- and ultrafiltration procedure was applied to 3 surface waters from southern Germany, and fractions from all filtration steps were collected. The NOM was characterized using solid-state 13C and 15N nuclear magnetic resonance (NMR) techniques. Routine integration of the 13C NMR spectra and extended data analysis procedures were carried out for a quantitative comparison of the structural components as well as for the elucidation of structural fractionation patterns. A common feature of the large molecular size fractions was the predominance of polysaccharide material, with the dissolved high molecular weight organics being mostly enriched in N-acetylated polysaccharides derived from microbial leftovers. Aromatic structures like lignin and tannin derivatives were most abundant in the intermediate size fraction. All membranes were found to be highly permeable for branched aliphatics, i.e. isoprenoids. Fouling layers of the ultrafiltration membrane were significantly enriched in long-chain aliphatics (lipids). Biofouling was not observed on any of the membranes. Overall, a strong interdependence between the chemical structural characteristics of NOM components and their size, shape, or interaction characteristics could be shown. The results provide the basis for a better understanding of water process technologies as treatment effectiveness is strongly dependent on the chemical composition and the “size” distribution of NOM.

Use of Chitosan-Alginate as Alternative Pelletization Aid to mMicrocrystalline Cellulose in Extrusion/Spheronization

Two types of different molecular weight chitosan were investigated as a pelletization aid in extrusion/spheronization using water as granulation liquid. Spherical pellets with a maximum fraction of 60% w/w chitosan could be produced when 1.25-2.5% w/w sodium alginate was included in the formulations with no microcrystalline cellulose (MCC). Chitosan with lower molecular weight of 190 kDa showed a better pellet forming property. The pellets obtained had acceptable physical characteristics and a fast drug release. The results from Fourier transform infrared spectroscopy, differential scanning calorimetry and (13)C CP-MAS nuclear magnetic resonance spectroscopy confirmed the formation of polyelectrolyte complex (PEC) between chitosan and sodium alginate, which might be a reason for successful pelletization by extrusion/spheronization. Moreover, the presence of PEC might influence the physical characteristics and dissolution behavior of chitosan-alginate pellets. The results indicated an achievement in production of pellets by extrusion/spheronization without using MCC. Moreover, chitosan combined with sodium alginate could be used as a promising alternative pelletization aid to MCC in extrusion/spheronization.

Adducts of rhodium(II) tetraacetate with some nitrogenous organic ligands: Application of natural abundance 15N and 13C CPMAS NMR spectroscopy

Adducts of rhodium(II) tetraacetate with some nitrogenous organic ligands: 1-azabicyclo[2,2,2]octane 1, 1,2-diazabicyclo[2,2,2]octane 2, pyrazine 3, pyrimidine 4, [1,3,5]triazine 5 and 1,3,5,7-tetraazatricyclo[3,3,1,1 3,7]decane 6 have been investigated by means of natural abundance 13C and 15N CPMAS nuclear magnetic resonance (NMR) spectroscopy. 1-Azabicyclo[2,2,2]octane 1 having one nitrogen atom in the molecule produces either the 1:1 or 1:2-adduct depending on the reagent molar ratio; some features of its 13C CPMAS NMR spectra suggest the dimeric structure of the 1:1-adduct. Multifunctional ligands having more than one nitrogen atom in a molecule yield the adducts insoluble in common organic solvents. Elemental analysis and NMR experiments have revealed that 1,2-diazabicyclo[2,2,2]octane, pyrazine, pyrimidine and [1,3,5]triazine produced adducts in the form of 1:1 polymeric chains. 1,3,5,7-tetraazatricyclo[3,3,1,1 3,7]decane yields the adduct containing ligand and metal salt in the molar ratio of 3:4. The 15N chemical shift change caused by the Rh–N bond formation (Δ δ parameter) varies from ca. −9 ppm for aliphatic ligands to ca. −40 ppm for heteroaromatic species. The NMR findings have been supported by theoretical calculation (density functional calculation (DFT), LanLD2Z//B3LYB level) of molecular geometry, energy and chemical shieldings.

Effect of N content and soil texture on the decomposition of organic matter in forest soils as revealed by solid-state CPMAS NMR spectroscopy

N has a controlling effect on litter biodegradation in the forest floor, while stabilization of organic matter in the mineral soil may be influenced by physical parameters related to soil texture. In this study, in order to understand the processes involved in soil organic matter (SOM) formation, the chemical composition of SOM was followed and evaluated with regards to N contents and soil texture. Samples were taken on sites covered with Norway spruce and displaying contrasting values of C/N ratios in the forest floor. The chemical structure of OM was characterized using solid-state CPMAS 13C and 15N nuclear magnetic resonance (NMR) spectroscopy, along with Proton Spin Relaxation Editing (PSRE) sequences. Four groups of sampling sites were defined based on the NMR spectra of Oh and A horizons. In each group displaying similar NMR characteristics, N content and soil texture could be highly different among sites. Some Oh horizons with similar NMR spectra had very different N contents. Highly humified OM in Oh horizons were observed mainly on sites with low N contents. Some A horizons with different soil texture displayed similar OM chemical structure. High contents of O-alkyl C in some A horizons could originate from higher fresh root material input.

Characterization and comparison of hydrophobic neutral and hydrophobic acid dissolved organic carbon isolated from three municipal landfill leachates

The acid-precipitated (AP) and acid-soluble (AS) fractions of the combined hydrophobic neutral and hydrophobic acid dissolved organic carbon (DOC) were isolated from leachate collected from three municipal landfills of different age and redox conditions. The AP and the AS combined hydrophobic neutral and hydrophobic acid DOC comprised 6–15% and 51–66%, respectively, of the leachate nonpurgable organic carbon. Elemental analysis, infra-red spectroscopy, 13C CP-MAS nuclear magnetic resonance spectroscopy and dipolar dephasing experiments, and thermochemolysis gas chromatography/mass spectrometry results showed that the AP and AS fractions of hydrophobic neutral and hydrophobic acid DOC are highly aliphatic, with linear and branching moieties, and less oxidized than most terrestrial and aquatic humic substances. Very little, if any, polysaccharide or cellulose, lignin, or cutin components comprise these fractions. It is hypothesized that a majority of the organic carbon in these fractions originates highly branched, cyclic aliphatic organic compounds.

Detection of charred organic matter in soils from a Neolithic settlement in Southern Bavaria, Germany

The amount and chemical structure of the aromatic carbon fraction in archaeological soil materials was investigated. Samples from several Neolithic pits and a ditch from a settlement in southern Germany were analysed together with the surrounding loamy soil. A suite of complementary methods including 13C CPMAS nuclear magnetic resonance (NMR) spectroscopy, dipolar dephasing NMR, combined fractionation/high-energy ultraviolet (UV) photo-oxidation/ 13C CPMAS NMR spectroscopy and analysis of benzenepolycarboxylic acids (BPCA) were used to investigate the aromatic organic matter composition of the pits. Most of the Neolithic samples gave the highest proportion of NMR spectral intensity in the aryl carbon region with a dominant peak at 130 ppm with very low, if any, signals for substituted aromatic carbons, such as in lignin or other phenols. Between 29% and 77% of soil organic carbon survived UV photo-oxidation, mostly present as aromatic structures. Dipolar dephasing NMR spectroscopy indicated a high degree of condensation for the aromatic rings while scanning electron microscopy showed that the material had a plant-like morphology. The analysis of BPCAs as specific markers provided further evidence for the presence of highly condensed aromatic structures in the organic matter of the Neolithic pits. The evidence therefore that the aromatic carbon is derived from charcoal is strong. This material either originated from soil material that has undergone vegetation fires or from other charred organic material, e.g., residues from Neolithic fire places.

27Al Mas NMR and Aluminum X-Ray Absorption Near Edge Structure Study of Imogolite and Allophanes

AbstractThis paper compares the results of 27Al nuclear magnetic resonance spectroscopy (NMR) and Al-K-edge X-ray Absorption Near Edge Structure (XANES) of natural imogolite and allophanes and some crystalline reference minerals. All soil allophanes studied contain 4-coordinated Al (AlIV). The highest relative proportion of AlIV, 21% of the total Al, was found in Si-rich allophane. This value is close to that found in spring allophanes, which were previously considered to be different from soil allophanes. For a quantitative determination of the AlIV/Altotal ratio, NMR is more reliable than XANES, because of the sensitivity of the chemical shift to low AlIV concentrations, but XANES may be used even if paramagnetic impurities (mostly Fe) are present. Al-K XANES also yields more information than NMR on the local environment of AlVI and especially site multiplicity. AlVI XANES of imogolite and allophanes are similar regardless of the Al/Si ratio. They yield two well-resolved resonances with maxima near 1568 and 1570 eV, which indicates the presence of a unique AlVI site by comparison with crystalline references. The presence of only one AlVI site indicates that imogolite and allophanes have an octahedral sheet with a structure similar to 2/1 dioctahedral phyllosilicates but different from gibbsite or kaolinite, previously considered as structural analogues. The 27AlIV MAS NMR peak maxima of allophanes are between 58.6 and 59.8 ppm, in the range observed for crystalline and amorphous framework alumino-silicates, and less positive than those of sheet silicates, which are typically in the range 65–75 ppm. 27Al-H1 CPMAS NMR spectra suggest that both AlIV and AlVI have Al-O-H linkages.

Comparison of humus horizons from two ecosystem phases on northern Vancouver Island using 13C CPMAS NMR spectroscopy and CuO oxidation

Much forested land in the wetter zones of northern Vancouver Island is characterized by thick humus layers, with two distinct ecosystem phases: the younger "HA" phase arising from disturbance is productive after clearcutting, but in the old-growth "CH" phase, seedlings suffer growth check after 5–8 yr, with reinvasion of the ericaceous shrub salal (Gaultheria shallon Pursh.). We used solid-state 13C nuclear magnetic resonance (NMR) spectroscopy and CuO oxidation to examine whether chemical differences in the humus might be associated with difference in forest productivity after clearcutting. NMR spectra of woody horizons, which were similar for CH and HA sites, were dominated by signals from lignin of decomposed wood. Non-woody humus types were typical of forest litter layers, and were dominated by signals in the O-alkyl region. The differences between CH and HA sites were: (i) higher tannin content in the CH sites, most likely from salal inputs and (ii) higher ratio of carbohydrate to lignin C, indicating less effective decomposition in CH sites. Oxidation with CuO also showed more advanced decomposition in the non-woody horizons of HA than of CH sites. Less effective decomposition possibly due in part to tannin accumulation could contribute to the lower forest productivity on salal-dominated CH sites in this region. Key words: 13C NMR, CuO oxidation, decomposition, humus, tannin, salal

Solid phase stereochemical dynamics of 18-crown-6 ether and its KNCS complex as studied by low temperature carbon-13 nuclear magnetic resonance

We report resolution of individual carbon environments of 18-crown-6 ether and its KNCS complex using 13C CPMAS nuclear magnetic resonance spectroscopy at low temperature. The importance of torsional angle effects in determining chemical shifts in these solids is discussed.