Solid-state 13C Nuclear Magnetic Resonance Spectroscopy Research Articles

Characterization of natural organic matter in Wyoming-type bentonites irradiated at varied moisture levels

Wyoming-type bentonite clay (MX-80; Wyoming, USA) will be used in a deep geological repository (DGR) for the long-term storage of used nuclear fuel in Canada. The natural organic matter (NOM) found in bentonite may serve as a microbial nutrient source and potentially compromise the performance of the used fuel containers. Previous investigations indicate that NOM is present in low concentrations in MX-80 and has undergone extensive diagenetic alteration, though limited knowledge is available regarding NOM chemistry under simulated DGR conditions. Of particular concern is the possibility for gamma-radiation to alter NOM dissolution and reactivity due to the presence of reactive species generated by water radiolysis in Wyoming-type bentonites. In this study, NOM chemistry was investigated using complementary molecular-level techniques following exposure to a total gamma-radiation dose of 100 kGy (1.08 kGy/h for 93 h) at varied moisture levels (20%, 40%, 60% and 80%) and room temperature. Treated samples exhibited relatively low total organic carbon concentrations (0.074–0.232%), with no evidence of any major changes in total, organic, and inorganic carbon concentrations. Solid-state 13C NMR spectroscopy detected no changes in solid-phase NOM chemistry after irradiation. Solubilization of NOM increased significantly with radiation exposure at 80% moisture, suggesting higher levels of water saturation may enhance dissolved organic matter (DOM) production. Solution-state 1H nuclear magnetic resonance (NMR), and UV–Vis analyses did not identify any significant differences in DOM composition. More sensitive, targeted compound analysis revealed significant decreases in total n-alkanol concentration at lower moisture content levels (20% and 40%). Several individual compound concentrations also differed significantly at the nanogram-level, including n-octacosanol and several n-alkanoic acids at elevated moisture levels (60% and 80%). These findings suggest the majority of NOM in MX-80 remains chemically stable under the anticipated initial conditions of the proposed DGR.

Characterization of grafting properties of ABS latexes: ATR-FTIR vs NMR spectroscopy

Acrylonitrile–Butadiene–Styrene (ABS) polymers have a complex microstructure which is formed during the grafting reaction of a polybutadiene seed latex. During the reaction, some styrene-acrylonitrile (SAN) chains are grafted onto the polybutadiene (PB) backbone chains, and this grafting is critical to achieve effective dispersion and compatibility of both phases. Therefore, accurate characterization of grafting properties helps understanding the polymerization mechanism as well as the final properties of the ABS polymer and its applications properties. In this work, the grafting properties of ABS latexes were determined by separation of the soluble and insoluble phase of the polymer, followed by the characterization of these phases using analytical techniques. Phase separation was carried out dispersing the latex in acetone followed by ultracentrifugation. The soluble and insoluble polymer phases were for the first time analysed by NMR spectroscopy to obtain the corresponding fractions of SAN and PB in each phase. The soluble fraction was analysed by liquid-state 1H Nuclear Magnetic Resonance (NMR) spectroscopy, whereas the insoluble fraction was analysed by solid-state 13C NMR spectroscopy. Moreover, both phases were analysed by Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR), and the results obtained are compared and discussed in this article. We found that the most accurate grafting properties are achieved by analysing the composition of the soluble and insoluble fraction by NMR spectroscopy.

Influence of chain length of prepolymers in permanent memory effect of PDLC assessed by solid-state NMR

ABSTRACTThe relationship between linear chain (ethylene oxide units) length of polymerisable monomers with morphology, electro-optical properties and 13C nuclear magnetic resonance (NMR) spectroscopy of the corresponding polymer-dispersed liquid crystal (PDLC) films was investigated. The preferred liquid crystal molecule alignment and permanent memory effect of PDLC were greatly influenced by the length of the molecular chain of prepolymers to be incorporated as a polymer matrix. By increasing the number of ethylene oxide in prepolymer chain and maintaining the number of functionalities (polymerisable groups in each monomer molecule), the permanent memory effect of PDLC increased, as proved by solid-state 13C NMR spectroscopy.

Assessment of clay mineral selectivity for adsorption of aliphatic/aromatic humic acid fraction

Understanding the interactions of humic acids with clay minerals is important for modeling the geochemical fate and transport of nutrients and pollutants in soils and natural waters. This study assesses the selectivity of the clay minerals kaolinite and montmorillonite for the adsorption of the leonardite humic acid (LHA) fractions. The whole LHA was fractionated by ultrafiltration into five fractions of different molecular size (F1, >0.2 μm; F2, 0.2 μm–300,000 Da; F3, 300,000–50,000 Da; F4, 50,000–10,000 Da; F5, 10,000–1000 Da). Characterization by solid-state 13C nuclear magnetic resonance spectroscopy (NMR) indicated that the fraction >0.2 μm contains primarily aliphatic carbon, while the smaller molecules of the fraction <10,000 Da consists of predominantly aromatic carbon species. The adsorption characteristics of humic acid fractions onto kaolinite and montmorillonite at pH = 6 and 0.01 mol dm−3 NaCl ionic strength, were also evaluated by solid-state 13C NMR and UV–visible spectroscopy.UV–visible and 13C NMR spectra demonstrated preferential sorption by the clay minerals for different carbon types; kaolinite preferentially sorbed the aromatic carbon types, while montmorillonite preferentially sorbed the aliphatic carbon at the first point of LHA adsorption (low coverage). However, this preferential effect wasn't pronounced at the complete surface coverage (high coverage).

Humic acid composition and soil fertility of soils near an ancient charcoal kiln: are they similar to Terra Preta de Índios soils?

Charcoal production during the nineteenth century transformed landscapes in the Brazilian Atlantic Forests in Rio de Janeiro city. These paleo-territories were studied to improve our understanding of how this activity altered soil properties. By comparing their humic acids (HA) with those extracted from a Terra Preta de Indios (TPI) site, we showed that the aging of charcoal in soils alone is sufficient to generate recalcitrant organic material with high cation exchange capacity (CEC). The soils were sampled: at the center of the area affected by the ancient charcoal kiln (center of the kiln—CK), at the dump site (D—local deposition of charcoal residues not used for marketing, downstream of the ancient charcoal kiln), and from the surrounding soil, upstream of the kiln, as a control (natural soil—NS). Elemental analysis and fertility characterization of the soil samples were performed. Solid-state 13C nuclear magnetic resonance (NMR) spectra were obtained from their humic acids (HA). These spectra were compared against HA data on TPI. As shown by solid-state 13C NMR spectroscopy, the soil organic matter (SOM) fraction which is high in charged functional groups (the so-called humic acids—HA) was extracted from areas rich in ancient charcoal and dominated by recalcitrant carboxylated aromatic structures (aged charcoal). This peculiar SOM explains the observed high cation exchange capacity (CEC). It yields a fertile soil with a high resistance against degradation by potential intensive use. Comparable results are described in the literature for SOM of TPI. The high structural similarity between the HA from the soils under the paleo-charcoal kilns and from TPI supports the hypothesis that just the natural weathering and biochemical reworking of charcoal in soils, together with ash input, is sufficient to generate fertile and resilient soils with peculiar SOM and properties commonly associated with the high fertility and C sequestration potential of TPI.

Solid state 13C NMR spectroscopy provides direct evidence for reaction between ethinyl estradiol and a silicone elastomer vaginal ring drug delivery system

Steroid molecules have a long history of incorporation into silicone elastomer materials for controlled release drug delivery applications. Previously, based on in vitro release testing and drug content analysis, we demonstrated indirectly that the contraceptive progestin levonorgestrel (LNG) chemically and irreversibly binds to addition cure silicone elastomers, presumably via a hydrosilylation reaction between the levonorgestrel ethynyl group and the hydrosilane groups in the poly(dimethylsiloxane-co-methylhydrosiloxane) crosslinker of the silicone elastomer. Here, for the first time, we report that solid state 13C nuclear magnetic resonance (NMR) spectroscopy provides direct evidence for the irreversible binding of ethinyl estradiol (EE) – an estrogenic steroid molecule also containing an ethynyl functional group – to an addition cure silicone elastomer. By preparing silicone elastomer samples containing 13C-labelled EE, signals in the NMR spectra could readily be assigned to both the free and bound EE. Additional depolymerisation studies, performed on an addition cure silicone elastomer system from which the unbound EE fraction was completely extracted, further confirmed the presence of bound EE through the formation of coloured reaction mixtures resulting from the reaction of bound EE and trifluoroacetic acid (TFA). These methods will be particularly useful in the ongoing development of new steroid-releasing silicone drug delivery devices, including various vaginal ring devices for contraception, HIV prevention and multipurpose prevention technology applications.

Long-term litter manipulation alters soil organic matter turnover in a temperate deciduous forest

Understanding soil organic matter (OM) biogeochemistry at the molecular-level is essential for assessing potential impacts from management practices and climate change on shifts in soil carbon storage. Biomarker analyses and nuclear magnetic resonance (NMR) spectroscopy were used in an ongoing detrital input and removal treatment experiment in a temperate deciduous forest in Pennsylvania, USA, to examine how above- and below-ground plant inputs control soil OM quantity and quality at the molecular-level. From plant material to surface soils, the free acyclic lipids and cutin, suberin, and lignin biomarkers were preferentially retained over free sugars and free cyclic lipids. After 20years of above-ground litter addition (Double Litter) or exclusion (No Litter) treatments, soil OM composition was relatively more degraded, as revealed by solid-state 13C NMR spectroscopy. Under Doubled Litter inputs, soil carbon and phospholipid fatty acid (PLFA) concentrations were unchanged, suggesting that the current OM degradation status is a reflection of microbial-mediated degradation that occurred prior to the 20-year sampling campaign. Soil OM degradation was higher in the No Litter treatments, likely due to the decline in fresh, above-ground litter inputs over time. Furthermore, root and root and litter exclusion treatments (No Roots and No Inputs, respectively) both significantly reduced free sugars and PLFAs and increased preservation of suberin-derived compounds. PLFA stress ratios and the low N-acetyl resonances from diffusion edited 1H NMR also indicate substrate limitations and reduced microbial biomass with these treatments. Overall, we highlight that storage of soil carbon and its biochemical composition do not linearly increase with plant inputs because the microbial processing of soil OM is also likely altered in the studied forest.

Tannin-Based Copolymer Resins: Synthesis and Characterization by Solid State 13C NMR and FT-IR Spectroscopy.

In recent years, the interest for bio-sources is rising exponentially and tannins extracts are one of the most interesting, easily-available, phenolic building blocks. The condensed tannins or proanthocyanidins are already known for their polymerization chemistry, which is the basis for several natural-based materials (e.g., adhesives, foams). In the present work we aim to observe the behavior of the extract of Acacia Mimosa (Acacia mearnsii) when reacted with several possible co-monomers at different relative amount, pH and temperature conditions. The more insoluble copolymers obtained with formaldehyde, hexamine, glyoxal, maleic anhydride, furfural and furfuryl alcohol were analyzed through solid state 13C NMR (Nuclear magnetic resonance) and FT-IR (Fourier Transform-Infrared) spectroscopy. The 13C NMR afforded the opportunity to detect: (i) aromatic substitutions and consequent poly-condensations for the majority of the hardeners studied; (ii) acylation for the maleic anhydride and also some; (iii) Diels–Alder arrangements for the furanic co-monomers; the FT-IR spectroscopy suggested that the formaldehyde and hexamine copolymers present a higher cross-linking degree.

Humic acid composition and humification processes in wetland soils of a Mediterranean semiarid wetland

The present study focuses on a compositional characterization of the humic acid (HA) fraction of several wetland soils using solid-state 13C NMR spectroscopy. The data were analysed using the molecular mixing model (MMM), based on an empirical approach by Nelson and Baldock. The compositional data from HAs obtained with this model were used to obtain a wider assessment of the process of humification from comparison of total soil wetland organic matter composition and HA composition. Twenty samples of humic acids (HAs) isolated from a Mediterranean semiarid wetland (‘Tablas de Daimiel’, central Spain) were studied using elemental analysis and cross polarization magic angle spinning (CPMAS)13C nuclear magnetic resonance (NMR) spectroscopy. The NMR data were analysed with the molecular mixing model (MMM) considering up to six generic components (carbohydrate, protein, lignin, lipid, char and ‘carbonyl’). HAs are considered a conceptual mixture of these model components, and the MMM determines the proportions of the characteristic biomolecules contributing to HA composition. The composition of the HAs under study depends on local factors such as site vegetation and occurrence of fire. Correlations between the proportions of the six generic components and further comparison with those determined for the unfractionated OM (whole sample, WS), gave information on HA origin and humification mechanisms. In particular, the proportions of char and carbohydrate (R 2 0.637) and contents of lignin and protein (R 2 0.471) in the HAs were negatively correlated (P < 0.05). Significant correlations (R 2 0.439) also existed for char contents in whole sample (WS) compared to HA, and for carbohydrates in WS compared to HA (R 2 0.558). Char proportion grew in HA with respect to the WS, and carbohydrates dropped to a half on average in HA compared to WS. Two different humification mechanisms could be identified for no-fire and fire areas. In the former, HA-char was preserved selectively from char in the sample, whereas in the latter, char was newly formed by fire effect.

Modelling the transformation of organic materials in soil with nuclear magnetic resonance spectra

Changes in the carbon (C) and nitrogen (N) compartments that result from the addition of organic material (OM) to the soil are predicted by the transformation of added OM (TAO) model with three parameters: very labile (P′L) and stable (PS) fractions of the OM and the rate of remineralization (kremin) of nitrogen immobilized by microorganisms. We propose relations between P′L, PS, kremin and various chemical groups in the OM identified by their 13C nuclear magnetic resonance (NMR) spectra. The aromatic content increased the predicted PS in accordance with published results. The O‐aromatic content also increased PS, but much less so than the aromatic content. The carboxyl content decreased PS and increased P′L as in the TAO model based on infrared spectrometry. The carbonyl content decreased P′L, whereas di‐O‐alkyl increased P′L. The chemical composition of the population of decomposer organisms did not appear to be homeostatic, but was related rather to the composition of the substrate: kremin was positively correlated with the carboxyl and di‐O‐alkyl content and negatively correlated with the alkyl content. Solid state 13C NMR spectroscopy gave better predictions of the transformations that resulted from adding OM than biochemical fractionation and near infrared reflectance spectrometry (NIRS). It is fast and non‐destructive and provides new insights into the processes that control decomposition for research into waste recycling, agro‐ecology and climate change.Highlights Linking decomposition of organic materials in soil to NMR measurements. First mathematical model of decomposition based on NMR spectra. Stability of the OM depends on the chemical groups and the inorganic N supply. NMR is a promising tool for monitoring ecosystem changes and soil–air exchanges. RésuméLes transformations des compartiments carbone (C) et azote (N) résultant de l'addition de matériaux organiques (MO) au sol sont prédites par le modèle Transformation des Apports Organiques (TAO) utilisant trois paramètres: fractions très labile (P'′L) et stable (PS) de MO et taux de reminéralisation de N immobilisé par les microorganismes (kremin). Nous proposons des relations liant P'L, PS et kremin à plusieurs groupes chimiques identifiés par les spectres de résonance magnétique nucléaire (RMN) 13C des MO. Le contenu aromatique accroit la prédiction de PS en accord avec les données publiées. Le contenu O‐aromatique augmente aussi PS mais beaucoup moins que le groupe aromatique. Le contenu carboxyle diminue PS et augmente P'L en accord avec de précédentes prédictions par spectrométrie proche infrarouge (SPIR). Le contenu carbonyle diminue P'L alors que di‐O‐alkyle augmente P'L. La composition des organismes décomposeurs n'apparaît pas homéostatique mais reliée à la composition de leur substrat : kremin est lié positivement aux contenus carboxyl et di‐Oalkyl de la MO et négativement à son contenu alkyl. La spectrométrie RMN 13C de l'état solide prédit mieux les transformations liées à l'addition de MO que la mesure des fibres et la SPIR. C'est une méthode rapide et non destructive qui améliore la connaissance des processus contrôlant la décomposition dans les domaines du recyclage des déchets, de l'agro écologie et du changement climatique.Points clé Liaison entre décomposition des matériaux organiques dans le sol et mesures RMN. Premier modèle mathématique de décomposition basé sur les spectres RMN. Stabilité des MO liée à leurs groupes chimiques et leur fourniture azote inorganique. RMN, un outil prometteur pour piloter l'évolution des écosystèmes et les échanges sol/air.

Preparation of [C60]Fullerene Nanowhisker-gold Nanoparticle Composites and Reduction of 4-Nitrophenol through Catalysis

A gold nanoparticle solution was prepared by adding sodium borohydride (NaBH4), trisodium citrate dihydrate (C6H5Na3O7·2H2O), cetyltrimethyl ammonium bromide (CTAB,(C16H33)N(CH3)3Br), ascorbic acid (C6H8O6), and potassium tetrachloroaurate(III)(KAuCl4) to distilled water and stirring the solution for 15 min. [C60]fullerene nanowhisker-gold nanoparticle composites were synthesized using C60-saturated toluene, the gold nanoparticle solution, and isopropyl alcohol by liquid-liquid interfacial precipitation (LLIP). The product of the nanocomposites was characterized by X-ray diffraction, scanning electron microscopy, Raman spectroscopy, transmission electron microscopy, and solid-state 13C-nuclear magnetic resonance spectroscopy. The catalytic activity of the [C60]fullerene nanowhisker-gold nanoparticle composites was confirmed in 4-nitrophenol reduction by UV-vis spectroscopy.

Aluminum resistance and cell‐wall characteristics of pineapple root apices

AbstractPineapple (Ananas comosus [L.] Merrill) is one of the economically cultivated crops in Taiwan, which is grown mostly on acid soil. Aluminum (Al) is phytotoxic and sometimes inhibits root growth of crops in strongly acid soils. This study was conducted to evaluate the role in Al resistance of root‐apex cell walls of four important pineapple cultivars (Cayenne, Tainung No. 6, Tainung No. 13, and Tainung No. 17). The cell‐wall characteristics of root apices were determined using Fourier transform infrared spectroscopy (FTIR) and solid‐state 13C‐nuclear–magnetic resonance spectroscopy (13C‐NMR). The results show that the carboxylic and phenolic groups were highest in the cell wall of Tainung No.17 and lowest in that of Cayenne. Aluminum adsorption by cell wall could be described by Freundlich equation. The adsorption of Al by the cell wall of root apices was highest in Tainung No.17 and lowest in Cayenne. Tainung No.17 contained more carboxylic and phenolic groups in its cell wall of the root apices, causing more Al adsorption and so more damage to its root apices than that of the other three pineapple cultivars.

Humic acids as proxies for assessing different Mediterranean forest soils signatures using solid-state CPMAS 13C NMR spectroscopy

Humic acids (HAs) of four representative forest soils profiles from Central Spain (two with different vegetation – pine and oak – but same parent material – granitie, and two with same vegetation – holm oak – but different parent material – granite and limestone) were investigated by solid-state cross polarization with magic angle spinning 13C nuclear magnetic resonance (NMR) spectroscopy. The objectives included the investigation of the impact of different forest properties on HA composition, assessing how the structural characteristics of the HA vary with soil depth, and evaluating the role of HA as surrogates for mapping the different forest soils signatures using structural data derived from 13C NMR spectroscopy. On average, alkyl C is the dominant C constituent (38–48% of the total NMR peak area) in all HA samples, followed by aromatic (12–22%) and O-alkyl C (12–19%), and finally carboxyl C (7.0–10%). The NMR data also indicated that HA composition is likely to be differently affected by the soil physico-chemical properties and type of forest vegetation. The structural characteristics of the HA from soil under oak did not differ broadly downward in the profile, whereas soil HA under pine forest exhibits a somewhat higher recalcitrant nature as a consequence of a higher degree of decomposition. The soil HA from holm oak forests differed from the other two forest soils, exhibiting a progressive decomposition of the alkyl C structures with increasing depth, while the carbohydrate-like indicator (O-alkyl C) is apparently being protected from mineralization in the horizons below the ground level. Overall, these differences in soil HA NMR signatures are an important diagnostic tool for understanding the role of different soil environmental factors on the structural composition of HA from Mediterranean forest soils.

Chemical structure changes in kerogen from bituminous coal in response to dike intrusions as investigated by advanced solid-state 13C NMR spectroscopy

Coal maturation due to igneous intrusions offers the ideal opportunity to study the chemical-structural evolution of rapidly heated coal. Variations in the chemical structures of kerogens from high volatile bituminous coal near two igneous dike intrusions in the Illinois Basin were characterized in detail by advanced solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. With decreasing distance to dike contacts and increasing thermal maturity (vitrinite reflectance Ro from 0.62% to 5.03%), the new insights into the chemical structural changes in coal kerogens include (i) the C(CH2)C groups removed faster than CCH3 groups, suggesting that the major cleavage of aliphatics should not occur at aryl rings, (ii) a progressive decrease of the relative abundance of protonated aromatic carbons, possibly due to replacement of aromatic hydrogens by aryl groups via cross-linking, and (iii) an increase in the aromatic cluster size, in addition to the well established changes of the elimination of aliphatics and aromatic C-O groups and an increase in aromaticity. For the first time the growth of aromatic cluster sizes with increasing maturity was quantitatively estimated. Another novel finding is that coal kerogen (kerogen #22) directly at the contact with the large dike retained considerable aliphatic components with olefinic and COO groups. These aliphatic components could have been entrapped and failed to diffuse out rapidly enough because intense and very fast heating rendered this kerogen partially fluidized. Our advanced solid-state NMR techniques provided deep insights into the structural changes in kerogen from bituminous coal in response to dike intrusions which cannot be achievable using routine 13C cross polarization/magic angle spinning technique.

Yellow coloration phenomena of incorporated indomethacin into folded sheet mesoporous materials

Solid-state 13C nuclear magnetic resonance (NMR) spectroscopy that included relaxation time measurement was utilized to evaluate the yellow coloration of evaporated samples (EVPs) of indomethacin (IMC) with commercially available folded sheet mesoporous materials (TMPS). Colorimetric analysis by visible light reflection spectroscopy clarified the color differences in each sample: deep yellow-colored melt-quenched amorphous IMC, a slightly yellow-colored EVP of TMPS-1.5 (pore size: 1.8nm), and a yellow-colored EVP of TMPS-7 (pore size: 7.3nm). The color of EVPs changed from yellow to white after washing with ethanol, indicating the reversible coloration without a chemical reaction. Powder X-ray diffractometry and differential scanning calorimetry demonstrated that the EVPs of TMPS-7 entrapped greater amounts of amorphous IMC into the mesopore than TMPS-1.5. The amount of amorphous IMC in the mesopores could affect the strength of yellow coloration. Solid-state 13C NMR spectroscopy that included spin–lattice relaxation time (T1) measurement revealed that the mobility of the aromatic rings of amorphous IMC in TMPS mesopores was higher than that in melt-quenched amorphous IMC. The difference in color between amorphous IMC in TMPS mesopores and melt-quenched amorphous IMC can be explained by their distinct intramolecular π-conjugation systems.

Biodegradability of organic matter in fire-affected mineral soils of Southern Spain

Incorporated into the soil, naturally formed pyrogenic organic matter (PyOM) is considered as highly recalcitrant, but direct estimation of PyOM decomposition rates are scarce. With this aim in mind, we subjected organic matter (OM) of fire-affected and unaffected soils to biochemical degradation under laboratory conditions and monitored CO2 production over a period of seven months. The soils derived from the Sierra de Aznalcóllar, Southern Spain, and were sampled 4 weeks and 5 years after a severe fire. Virtual fractionation of the solid-state 13C nuclear magnetic resonance (NMR) spectra of the fire-affected soils into fire-unaffected soil organic matter (SOM) and PyOM yielded charcoal C contributions of 30 to 50% to the total organic C (Corg) of the sample. Fitting the respiration data with a double exponential decay model revealed a fast carbon flush during the first three weeks of the experiment. Solid-state 13C NMR spectroscopy evidenced the contribution of aromatic moieties of the PyOM to this initial carbon release and to the biosynthesis of new microbial biomass. Considering the loss of microbiologically easily available fresh litter by wildfires, this relatively labile PyOM fraction may contribute to a fast recovery of a fire-affected site. The input of PyOM resulted in an increase of the mean residence time (MRT) of the slow OM pool of the soil by a factor of 3–4 to approximately 40 years. Assuming that under field conditions, the microbial activity corresponds to approximately 10% of the value observed under optimal laboratory conditions, MRTs of 500–600 years were estimated for the slow PyOM pool. The fact that these times are only 5–6 times longer than those calculated for fire-unaffected SOM rises doubts about the presumed big influence of PyOM as an additional C-sink in soils. On the other hand, although being small the difference in turnover rates is evident and has some major implication with respect to long-term alteration of the chemical composition of OM in fire-affected soils. In case of a reduced input of fresh litter, the preferential degradation of fire-unaffected SOM yields in a selective preservation of PyOM. To what extent this can alter soil properties, has still to be elucidated. In cultivated soils rarely affected by fire or with low charcoal input after burning of harvest, the impact of PyOM accumulation may be of minor importance. On the other hand, for soils regularly amended with high amounts of biochar or subjected to frequent natural or prescribed burnings, it may be an important factor.

Antimony coordination to humic acid: Nuclear magnetic resonance and X-ray absorption fine structure spectroscopy study

This current study examined the fate of antimony (Sb) in the soil environment and its association with soil humic acid (HA). It is anticipated that a significant proportion of Sb is retained in soil organic layer; therefore, the oxidation state of Sb is controlled by the soil HA to some extent which influences Sb solubility and ecotoxicity. Parent HA material as well as prepared HA–Sb (III) composites was investigated by determining elemental composition and by performing nuclear magnetic resonance (NMR) and X-ray absorption fine structure (XAFS) spectroscopy study in order to study Sb coordination to natural macro organic ligand. The Sb (III) binding to soil derived HA mainly contributed to its open chains through carboxyl and hydroxyl moieties as revealed by the 1H and solid state 13C NMR spectroscopy. The protons in carboxylic and hydroxylic groups (those proton signals are characteristic of HAs with different origins) disappeared in the HA–Sb composite; and relative changes were observed in aliphatic proton distribution between the HA samples with and without Sb. The overall patterns of 13C NMR spectra for the investigated samples were analogous to each other; moreover, it was estimated that the cyclic structure of the HA nucleus remained unchanged during Sb (III) association. Based on the absorption edge energy and coordination numbers, Sb oxidation state in a native soil was interpreted as pentavalent, meanwhile the HA–Sb composite contained both Sb (III) and Sb (V). It was shown that HA catalyzes Sb (III) oxidation to Sb (V) but the process was relatively slow. However, XAFS spectra sensitivity was limited when studying the HA–Sb composite that was prepared from the isolated soil HA fraction, so only data on the first shell Sb–O coordination were interpreted.

Chemical and nanometer-scale structure of kerogen and its change during thermal maturation investigated by advanced solid-state 13C NMR spectroscopy

We have used advanced and quantitative solid-state nuclear magnetic resonance (NMR) techniques to investigate structural changes in a series of type II kerogen samples from the New Albany Shale across a range of maturity (vitrinite reflectance R0 from 0.29% to 1.27%). Specific functional groups such as CH3, CH2, alkyl CH, aromatic CH, aromatic C–O, and other nonprotonated aromatics, as well as “oil prone” and “gas prone” carbons, have been quantified by 13C NMR; atomic H/C and O/C ratios calculated from the NMR data agree with elemental analysis. Relationships between NMR structural parameters and vitrinite reflectance, a proxy for thermal maturity, were evaluated. The aromatic cluster size is probed in terms of the fraction of aromatic carbons that are protonated (∼30%) and the average distance of aromatic C from the nearest protons in long-range H–C dephasing, both of which do not increase much with maturation, in spite of a great increase in aromaticity. The aromatic clusters in the most mature sample consist of ∼30 carbons, and of ∼20 carbons in the least mature samples. Proof of many links between alkyl chains and aromatic rings is provided by short-range and long-range 1H–13C correlation NMR. The alkyl segments provide most H in the samples; even at a carbon aromaticity of 83%, the fraction of aromatic H is only 38%. While aromaticity increases with thermal maturity, most other NMR structural parameters, including the aromatic C–O fractions, decrease. Aromaticity is confirmed as an excellent NMR structural parameter for assessing thermal maturity. In this series of samples, thermal maturation mostly increases aromaticity by reducing the length of the alkyl chains attached to the aromatic cores, not by pronounced growth of the size of the fused aromatic ring clusters.

Chemical Changes During 6 Years of Decomposition of 11 Litters in Some Canadian Forest Sites. Part 2. 13C Abundance, Solid-State 13C NMR Spectroscopy and the Meaning of “Lignin”

There is still a poor understanding of how changes in the organic composition of litter contribute to slowing or even cessation of decomposition. Using 13C nuclear magnetic resonance (NMR) spectroscopy of samples from the Canadian Intersite Decomposition Experiment (CIDET), we asked whether increasing lignin per se could account for the well-known increase in acid-unhydrolyzable residue (AUR), and secondly, using three litters from four sites with different mean annual temperatures, whether changes in organic composition would follow similar trajectories with C mass loss. At 6 years, there was 16–39% C remaining for 10 foliar litters and wood blocks at a site with rapid initial decomposition, and higher amounts remaining for three species at three colder sites. 13C NMR spectra obtained with rapid cross-polarization (CP) mainly showed increasing similarity among the foliar litters, although wood showed little change in composition. Foliage generally showed loss of O- and di-O-alkyl C, mainly from carbohydrate, and increase in alkyl, aromatic, phenolic and carboxyl C. However, O-alkyl C loss was limited, especially for litters with slow initial decomposition, and many litters showed relatively small changes in intensity distribution. Quantitative 13C (“BD”) spectra showed similar trends, but even smaller changes in C composition, and 6-year CP difference spectra showed that C was lost across the whole range of structures. Changes in δ13C were small and variable, but could be correlated to some extent with loss of carbohydrates versus tannins. Lignin was not selectively preserved, and the increase of resistant structures derived from lignin, tannins, and cutin collectively accounts for increasing AUR. Compositional changes of NMR C fractions across sites with different temperatures were small and inconsistent, likely due to the influence of other site factors; however, changes in their contents did largely follow consistent trajectories with %C remaining.

Study on structural changes of microwave heat-moisture treated resistant Canna edulis Ker starch during digestion in vitro

Microwave heat-moisture treated Canna edulis Ker starch has been applied to study structural changes in vitro using porcine α-amylase, pancreatin and amyloglucosidase. The structures at different digestion stages were characterized using scanning electron microscopy (SEM), polarized optical microscopy (POM), small angle X-ray scattering (SAXS), X-ray diffraction (XRD), Fourier transforms infrared (FT-IR) spectroscopy and solid state 13C nuclear magnetic resonance (NMR) spectroscopy. The increase in molecular order was observed with increasing digestion time and reflected in higher scattering intensity measured by SAXS, higher crystallinity observed by XRD, the increase of the double helix order obtained by solid state 13C NMR spectroscopy, and corresponding changes in the measurement of FT-IR, in favour of increasing resistant starch content. SAXS reveals a single peak around 0.6335 nm −1, suggesting that the enzyme may erode the special site of granule surface and catalyze whole hydrolysis reaction through pitted canals. In the process of digestion, amorphous region of starch granule is susceptible to the attack of enzyme. Moreover, the result also demonstrates that the resistance to enzymatic digestion may mainly depend on specific structure in the treated starches.