Cross Polarization Magic Angle Spinning 13C Nuclear Magnetic Resonance Research Articles

Multi-Parameter Characterization of Disease-Suppressive Bio-composts from Aromatic Plant Residues Evaluated for Garden Cress (Lepidium sativum L.) Cultivation

Garden cress is a vegetable crop in the Brassicaceae family that is appreciated for its nutraceutical and taste-giving components in minimally processed food chains. Due to its very short cycle, which depends on the range of production from microgreens to baby-leaf vegetables, this crop is threatened by soil-borne pathologies developing within the initial stages of germination and emergence. This study aims to evaluate the suppressive bio-compost as an innovative means to counteract the main telluric diseases of garden cress and reduce the risks of yield loss by adopting sustainable remedies and decreasing the dependence on synthetic fungicides. Therefore, eleven green composts obtained using both previously distilled and raw aromatic plant residues were analyzed for suppressive properties against Rhizoctonia solani and Sclerotinia sclerotiorum on sown garden cress. The biological active component of the composts, detected by CO2-release, FDA-hydrolysis and microbial counts, proved to be indispensable for pathogen control in vitro and in vivo, as demonstrated by the loss of suppressiveness after sterilization. Cross-polarization magic angle spinning 13C-nuclear magnetic resonance (CP-MAS-13C-NMR) was used to analyze the molecular distribution of organic C in composts. The results indicated the suitability of the feedstock used to make quality compost. The suppression levels shown by composts P1 (40% wood chips, 30% escarole and 30% a mixture of sage, basil, mint and parsley) and P2 (40% wood chips, 30% escarole and 30% a mixture of essential oil-free sage, basil and rosemary) are promising for the sustainable, non-chemical production of garden cress vegetables.

Investigating the water-soluble organic functionality of urban aerosols using two-dimensional correlation of solid-state 13C NMR and FTIR spectral data

Two-dimensional (2D) correlation spectroscopy, applied to one-dimensional solid-state cross polarization magic angle spinning (CP-MAS) 13C nuclear magnetic resonance (NMR), Fourier transform infrared coupled to attenuated total reflectance (FTIR-ATR), and the combination of CP-MAS 13C NMR and FTIR-ATR data, has been used to glean new structural information on the most hydrophobic water-soluble organic matter (WSOM) from fine urban air particles collected during different seasons. CP-MAS 13C NMR analysis confirmed that unsubstituted saturated aliphatics, aromatics, oxygenated aliphatics, and carboxylic acids accounted for most (84–92%) of the characterized carbon functional groups. Applying 2D correlation spectroscopy to CP-MAS 13C NMR and FTIR-ATR spectra indicates an increase in the contribution of hydroxyl and carboxylic groups to the aliphatic component with increasing air temperature, suggesting the photo-chemical origin of these WSOM structures. Urban samples from colder periods are clearly impacted by biomass combustion sources, although the presence of aged and processed organic aerosols cannot be ruled out. Using 2D FTIR-13C NMR hetero-spectral correlation spectroscopy, it has been demonstrated that the studied WSOM samples consists of at least two different classes of compounds: (i) an aliphatic component rich in both carboxylic and hydroxyl functional groups, and (ii) lignin-derived structures.

Investigation of the chemical and morphological structure of thermally rearranged polymers

Reacting ortho-functional poly(hydroxyimide)s via a high-temperature (i.e., 350 °C–450 °C) solid-state reaction produces polymers with exceptional gas separation properties for separations such as CO2/CH4, CO2/N2, and H2/CH4. However, these reactions render these so-called thermally rearranged (TR) polymers insoluble in common solvents, which prevent the use of certain experimental characterization techniques such as solution-state nuclear magnetic resonance (NMR) from identifying their chemical structure. In this work, we seek to identify the chemical structure of TR polymers by synthesizing a partially soluble TR polymer from an ortho-functional poly(hydroxyamide). The chemical structure of this TR polymer was characterized using 1-D and 2-D NMR. By use of cross-polarization magic-angle spinning 13C NMR, the structure of the polyamide-based TR polymer was compared to that of a polyimide-based TR polymer with a nearly identical proposed structure. The NMR spectra suggest that oxazole functionality is formed for both of these TR polymers. Furthermore, gas permeation results are provided for the precursor polymers and their corresponding TR polymer. The differences in transport properties for these polymers result from differences in the isomeric nature of oxazole-aromatic linkages and morphological differences related to free volume and free volume distribution.

Insights into Novel Supramolecular Complexes of Two Solid Forms of Norfloxacin and β-Cyclodextrin

The solid-state properties of novel complexes of β-cyclodextrin and two different solid forms of norfloxacin were investigated at the molecular level, in an attempt to obtain promising candidates for the preparation of alternative matrices used in pharmaceutical oral formulations. In order to evaluate the physical properties inherited from the different polymorphs, these supramolecular systems were characterized using a variety of spectroscopic techniques including natural-abundance (13) C cross-polarization magic-angle-spinning (CP-MAS) nuclear magnetic resonance (NMR), powder X-ray diffraction, and Fourier transform infrared spectroscopy. The intrinsic proton spin-lattice relaxation times detected in (13) C CP-MAS NMR spectra are used to confirm and distinguish the complex formation, as well as to provide better insights into the molecular fragments that are involved in the interaction with β-cyclodextrin.

HEAT-INDUCED CHEMICAL AND COLOR CHANGES OF EXTRACTIVE-FREE BLACK LOCUST (ROBINIA PSEUDOACACIA) WOOD

To investigate chemical and color changes of the polymeric constituents of black locust (Robinia pseudoacacia) wood during heat treatment, extractive-free wood flour was conditioned to 30% initial moisture content (MC) and heated for 24 h at 120 °C in either an oxygen or nitrogen atmosphere. The color change was measured using the CIELAB color system. Chemical changes of the wood components were determined by means of solid state cross-polarization/magic angle spinning 13C-nuclear magnetic resonance (CPMAS-13C-NMR), Fourier transform infrared (FTIR), diffuse reflectance UV-Vis (DRUV) spectroscopy, and elemental (CHN) analysis. The results showed that lightness (L*) decreased, while chromaticity indexes (a* and b*) and chroma (C*) increased after heat treatment. There was greater color difference (ΔE*) in the samples heated in the presence of oxygen compared to nitrogen. CHN analysis showed an increase in hydrogen and oxygen and a decrease in carbon content. NMR spectra confirmed the cleavage of the β-O-4 structure in the lignin, resulting in a decrease in etherified lignin units and an increase in phenolic structures. DRUV and FTIR spectra confirmed the formation of extensive conjugated structures, such as unsaturated ketones and quinones due to the cleavage of the lignin units. Formation of quinones can be attributed to heat treatment in the presence of oxygen.

Interactions between 2‐Aminobenzothiazole and Natural Organic Matter as Evidenced by CPMAS Nitrogen‐15 NMR Spectroscopy

Cross‐polarization magic angle spinning (CPMAS) 15N nuclear magnetic resonance (NMR) spectroscopy was used to study the interactions between 2‐aminobenzothiazole (ABT) and natural organic matter in the presence of the natural enzyme laccase and synthetic air. Through the use of synthesized model compounds, we were able to confirm previous findings by CPMAS 13C NMR spectroscopy that showed the formation of covalent amide bonds. We also provide evidence of the presence of two additional H bonds between ABT and the natural organic matter. Both H bonds involved the amino and thiazole groups of ABT.

Metal Ion Uptake from Aqueous Solution by Olive Stones: A Carbon‐13 Solid‐State Nuclear Magnetic Resonance and Potentiometric Study

The use of biomasses that result from the agriculture and food industries in removing heavy metals from wastewaters is attracting increasing interest. We present a joined potentiometric and cross polarization magic angle spinning (CP-MAS) carbon-13 (13C) nuclear magnetic resonance (NMR) study on the interaction of olive stones with copper(II), nickel(II), and cadmium(II). The potentiometric measurements allow both to distinguish two kind of basic sites in the olive stones and to postulate the coordination models for the three studied metals. The NMR spectral analysis allows the attribution of the different signals to the components of the olive stone matrix. A comparison of CP-MAS 13C NMR spectra of the samples after metal treatment suggests a specific complexation between metal ions and hydroxyl groups on guaiacyl and syringyl moieties.

Forest-floor chemical properties are altered by clear-cutting in boreal mixedwood forest stands dominated by trembling aspen and white spruce

Alterations in the chemical properties of the forest floor following clear-cut harvesting may have implications for forest productivity in boreal stands. We used proximate analysis, carbon-13 (13C) isotopic determination, and cross-polarization, magic-angle spinning (CPMAS) 13C nuclear magnetic resonance (NMR) spectroscopy to examine differences in the characteristics of the forest floors from uncut stands and clear-cut stands dominated by white spruce (Picea glauca (Moench) Voss; SPRUCE) and trembling aspen (Populus tremuloides Michx.; ASPEN) in northern Alberta. Proximate analysis revealed no difference in the chemical properties of forest floors from clear-cut and uncut stands in either stand type, but the acid-insoluble residue of forest floors from clear-cut ASPEN stands was enriched in 13C compared with those from uncut ASPEN stands. CPMAS 13C NMR spectroscopy revealed that forest floors from clearcuts were enriched in total aromatic C, particularly in ASPEN stands, and depleted in phenolic C, particularly in SPRUCE stands. These patterns indicate that forest floors from the clearcuts have become more humified, which may reflect stand-type differences in the amount of labile C available to the forest-floor microbial community and reductions in above- and below-ground inputs to the forest floor following clear-cutting in both stand types. Changes in the chemical properties of forest floors from clear-cut SPRUCE and ASPEN stands could exacerbate C limitation in these soils and alter patterns of nutrient cycling.

Organic N forms of a subtropical Acrisol under no-till cropping systems as assessed by acid hydrolysis and solid-state NMR spectroscopy

This study was conducted to investigate the influence of land-use systems (grassland and cropland) and of long-term no-till cropping systems [bare soil, oat/maize (O/M), pigeon pea+maize (P+M)] on the composition of organic N forms in a subtropical Acrisol. Soil samples collected from the 0- to 2.5-cm layer in the study area (Eldorado do Sul RS, Brazil) were submitted to acid hydrolysis and cross-polarization magic angle spinning (CPMAS) 15N and 13C nuclear magnetic resonance (NMR) spectroscopies. The legume-based cropping system P+M contained the highest contents of non-hydrolysable C and N, hydrolysable C and N, amino acid N and hydrolysed unknown N. The relative proportion of non-hydrolysable N was higher in bare soil (30.0%) and decreased incrementally in other treatments based on the total C and N contents. The amino acid N corresponded to an average of 37.2% of total N, and was not affected by land use and no-till cropping systems. The non-hydrolysable residue contained lower O-alkyl and higher aromatic C concentrations, as revealed by CPMAS 13C NMR spectroscopy, and higher C:N ratio than the bulk soil. No differences in the bulk soil organic matter composition could be detected among treatments, according to CPMAS 13C and 15N NMR spectra. In the non-hydrolysable fraction, grassland showed a lower concentration of aromatic and a higher concentration of alkyl C than other treatments. From CPMAS 15N NMR spectra, it could be concluded that amide N from peptide structures are the main organic N constituent. Amide structures are possibly protected through encapsulation into hydrophobic sites of organic matter and through organomineral interaction.

The effect of 10% HF treatment on the resolution of CPMAS 13C NMR spectra and on the quality of organic matter in Ferralsols

The investigation of the chemical composition of soil organic matter (SOM) in Ferralsols by means of solid-state cross-polarization magic angle spinning (CPMAS) 13C nuclear magnetic resonance (NMR) spectroscopy is limited by their high iron oxide concentration and their low organic carbon content. In order to circumvent those limitations, such samples are often treated with hydrofluoric acid (HF) to remove paramagnetic material and to concentrate the amount of SOM. The main objectives of this study were to elucidate the impact of this approach on the resolution of the CPMAS 13C NMR spectra and on the chemical composition of the SOM in the A and B horizons of four Brazilian Ferralsols. Therefore, those soils were subjected to up to eight successive treatments with 10% (w/w) HF. Each of those extractions resulted in an enhancement of the C content of the samples. A relationship between mass loss caused by the treatment and texture and mineralogy was observed. However, high losses of carbon occurred during the HF treatments, particularly in the B horizons, but no consistent alterations in the distribution of carbon functional groups were determined by CPMAS 13C NMR, suggesting that preferential loss of specific carbon groups was not induced. The concentration of total and dithionite extractable Fe increased after two treatments for most of the samples. This may be best explained by the preferential dissolution of silicate leading to a selective enrichment of iron containing minerals. After four treatments, the Fe concentration declined considerably. After the second treatment, the spectral resolution improved. Considering the obtained results, it can be confirmed that the efficiency of the HF treatment is rather controlled by the number than by the duration of the extraction. We suggest that, for A horizons of Ferralsols, four repetitions of HF treatment are sufficient to yield well-defined spectra. For their B horizons, on the other hand, the CPMAS 13C NMR spectra obtained after four HF extractions were of poor quality, indicating that for these soils at least eight HF treatments have to be performed to acquire reasonable spectra.

Fates of 13 C from enriched glucose and glycine in an organic soil determined by solid-state NMR

The transformations of the indigenous 13C and the 13C from either uniformly enriched 13C-D-glucose or 13C-glycine added to an organic soil were followed during a 28-day incubation using cross polarization (CP) magic angle spinning (MAS) 13C nuclear magnetic resonance (NMR) spectroscopy and dipolar dephased (DDP) MAS 13C NMR. The C mineralization was determined from 13C remaining by mass spectrometry and from CO2 evolution by gas chromatography. DDP MAS 13C NMR of the unamended soil indicated a transient increase in molecularly mobile 13C in the alkyl- and methyl-C over 5 days, which may be due to redistribution of 13C in the microbial biomass in response to perturbation. The added glucose-13C remaining declined to 43% after 7 days and 34% after 28 days. After 28 days the amount of added glucose-13C remaining was 6 times greater than the biomass C at the outset, while the microbial activity (CO2 production) was 38% greater, indicating that a significant proportion of added glucose-13C was not in microorganisms. Added glycine-13C declined faster, such that 29% and 8% remained after 7 and 28 days, respectively. After 28 days’ incubation with 13C-glucose, the O-alkyl-C, the acetal- and ketal-C, and the methyl- and alkyl-C resonances in CP MAS 13C NMR spectra were all enhanced compared with the unamended soil. The calculated T1ρH values of the O-alkyl-C and the acetal- and ketal-C resonances were less than those of crystalline glucose, indicating that there was no substantial reservoir of unreacted glucose. After 7 days’ incubation with 13C-glycine, none of the signals in the CP MAS 13C NMR spectra were enhanced when compared with the unamended soil, indicating that the added 13C remaining was distributed in undetectable quantities in a range of functionalities. The calculated T1ρH values indicated that glycine 13C was in O-alkyl-C, acetal- and ketal-C and carbonyl-C. T1ρH values may be more sensitive to changes in the distribution of 13C when 13C content is low. The DDP MAS 13C NMR spectra of both the 13C-glucose- and the 13C-glycine-amended soil showed that the molecularly mobile alkyl- and methyl-C increased compared with the unamended soil.

Analysis of Humic Acids by Solution and Solid‐state Carbon‐13 Nuclear Magnetic Resonance

AbstractEighteen humic acids (HA's) were characterized by chemical analyses, infrared (IR) and electron spin resonance spectra, and by solution and solid‐state cross polarization magic‐angle spinning (CPMAS) 13C nuclear magnetic resonance (NMR). The main objectives of this investigation were: (i) to compare the solution and solid‐state 13C NMR spectra of the HA's; (ii) to examine effects of different delay times (D1) on the solution spectra; and (iii) to find reasons for the failure of 13C NMR to detect the presence of significant concentrations of phenolic C in unmethylated HA's. Compared to solution spectra, CPMAS spectra consisted of relatively few, broad bands, indicative of considerable overlapping of individual signals, especially in the aliphatic regions. Proportions of aliphatic C determined by solution 13C NMR at D1 = 0.74 s were greater than those obtained at D1 = 1.90 s and by CPMAS 13C NMR (where D1 = relaxation delay). By contrast, proportions of aromatic C and aromaticities were greatest at D1 = 1.90 s. The highest values for CO2H groups were obtained by CPMAS 13C NMR and approached total acidities; values measured by solution 13C NMR at D1 = 1.90 s were intermediate, while those determined by solution 13C NMR with D1 = 0.74 s were the lowest and closest to CO2H concentrations determined chemically. Because the presence in HA's of significant concentrations of phenolic OH groups has been confirmed by several independent methods, it is possible that in 13C NMR spectra of HA's, signals arising from phenolic C are shifted downfield so that they overlap with resonances of C in CO2H groups. The net result is that CO2H groups are overestimated and phenolic OH groups underestimated.