13C CPMAS NMR Research Articles

Chemical and Molecular Composition of the Chrysalis Reveals Common Chitin-Rich Structural Framework for Monarchs and Swallowtails

The metamorphosis of a caterpillar into a butterfly is an awe-inspiring example of how extraordinary functions are made possible through specific chemistry in nature’s complex systems. The chrysalis exoskeleton is revealed and shed as a caterpillar transitions to butterfly form. We employed solid-state NMR to evaluate the chemical composition and types of biomolecules in the chrysalides from which Monarch and Swallowtail butterflies emerged. The chrysalis composition was remarkably similar between Monarch and Swallowtail. Chitin is the major polysaccharide component, present together with proteins and catechols or catechol-type linkages in each chrysalis. The high chitin content is comparable to the highest chitin-containing insect exoskeletons. Proteomics analyses indicated the presence of chitinases that could be involved in synthesis and remodeling of the chrysalis as well as cuticular proteins which play a role in the structural integrity of the chrysalis. The nearly identical 13C CPMAS NMR spectra of each chrysalis and similar structural proteins supports the presence of underlying design principles integrating chitin and protein partners to elaborate the chrysalis.

Single-pot tandem oxidative/C-H modification amidation process using ultrasmall PdNP-encapsulated porous organosilica nanotubes.

Herein, we studied a single-pot method with a dual catalysis process towards the conversion of primary aromatic alcohols to amides using ultrasmall PdNPs of controlled uniform size (1.8 nm) inside hybrid mesoporous organosilica nanotubes (MO-NTs). The catalyst exhibited excellent performance in water under mild conditions and showed high stability. The catalytic activity towards the tandem oxidation of alcohols in the presence of amine salts and H2O2 to their corresponding amides without producing byproducts was evaluated, and high yields were obtained for all products. The structure of the organosilica nanotubes containing palladium nanoparticles was investigated using various characterization techniques such as XRD, TEM, BET, solid-state 29Si NMR and solid-state 13C CP MAS NMR. Catalyst recycling tests showed that the catalytic power of PdNPs@B-SNTs was preserved after 8 cycles and a slight decrease in catalyst activity was observed.

Effects of fire on soil organic matter in northern Amazonian forest fragments

ABSTRACT Forest fires incorporate pyrogenic organic matter into the soil, affecting the characteristics of soil organic matter (SOM) due to its high aromaticity, increasing its renewal time. However, the factors that control the concentration of pyrogenic organic matter and its chemical composition and structure are still little known. Forest fragments dispersed in a savanna matrix of the northern Brazilian Amazon are frequently impacted by fires, which can affect the composition of SOM within the fragments. The aim of this study was to analyse the chemical composition of SOM in the border and interior of six forest fragments in the Roraima savanna, in the northern Brazilian Amazon. Soil samples were collected at 10-cm intervals up to 1 m in depth at the border and in the interior of each fragment. Soil organic material concentration was determined with 10% HF solution and its elemental composition, thermogravimetric index, and 13C CPMAS NMR spectroscopic analysis were determined. There was no significant difference in the aromaticity index between border and interior. The concentration of alkyl C structures between border (22 to 25%) and interior (19 to 29%) indicated the occurrence of medium-intensity fires in the study area. The thermogravimetric analysis showed no significant difference in the thermal stability of SOM between border and interior. Our results showed no pronounced difference in SOM quality up to 1 m depth between the border and the interior of the evaluated forest fragments, indicating that this compartment is stable throughout the fragments.

Urea-based covalent organic crown polymers and KI electrostatic synergy in CO2 fixation reaction: A combined experimental and theoretical study

Multifunctional organic polymer materials are supposed to be the most promising catalysts in the utilization of carbon dioxide (CO2) to five-membered cyclic carbonates (5CCs). Herein, functional one dimensional (1D) organic polymer materials (1D-UCP and 1D-UP) were successfully synthesized and their structural features were thoroughly characterized by FT-IR, 13C CP MAS NMR, SEM, TGA and XPS spectroscopy. These materials showed excellent reaction performance in the CO2 cycloaddition reaction. Notably, the 1D-UCP decorated by crown ether group and urea unit simultaneously showed excellent yields of 5CCs under solvent-free conditions and low pressure of CO2. The outstanding performance was attributable to the synergistic effect of activated KI by coordinating with crown ether fragment and urea unit as hydrogen bonding donor facilitating implementation of speed-determined step of this reaction. In combination with density functional theory (DFT) calculations including intermediates structure optimization and transition states free energy profile, a possible catalytic mechanism was proposed that the urea group accelerated the reaction by vicinal dual hydrogen bonding and increasing nucleophilicity of I anion.

Metal-Free Pyrene-Based Conjugated Microporous Polymer Catalyst Bearing N- and S-Sites for Photoelectrochemical Oxygen Evolution Reaction.

The development of an efficient, sustainable, and inexpensive metal-free catalyst for oxygen evolution reaction (OER) via photoelectrochemical water splitting is very demanding for energy conversion processes such as green fuel generators, fuel cells, and metal-air batteries. Herein, we have developed a metal-free pyrene-based nitrogen and sulfur containing conjugated microporous polymer having a high Brunauer-Emmett-Teller surface area (761 m2 g−1) and a low bandgap of 2.09 eV for oxygen evolution reaction (OER) in alkaline solution. The π-conjugated as-synthesized porous organic material (PBTDZ) has been characterized by Fourier transform infrared spectroscopy (FT-IR), solid-state 13C (cross-polarization magic angle spinning-nuclear magnetic resonance) CP-MAS NMR, N2 adsorption/desorption analysis, field-emission scanning electron microscope (FESEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) experiments. The material acts as an efficient catalyst for photoelectrochemical OER with a current density of 80 mA/cm2 at 0.8 V vs. Ag/AgCl and delivered 104 µmol of oxygen in a 2 h run. The presence of low bandgap energy, π-conjugated conducting polymeric skeleton bearing donor heteroatoms (N and S), and higher specific surface area associated with inherent microporosity are responsible for this admirable photoelectrocatalytic activity of PBTDZ catalyst.

Silica Chemisorbed Bis(Hydrogensulphato)Benzene (SiO2-BHSB) as a New, Environmentally Benign and Recyclable Catalyst for an Efficient Synthesis of Biscoumarin Scaffolds in Water Based Solvent

The immobilization of homogeneous catalytic material over the inert heterogeneous support is a recent strategy to overcome the drawbacks and unite the merits associated with the homogeneous as well as heterogeneous catalysts. However the physisorption-induced immobilization does not serve the purpose because of its sensitive reversible nature, a tiny change in reaction parameters may revert the physisorption and so the immobilization. In this work, a new catalytic material silica chemisorbed bis(hydrogensulphato)benzene (SiO2-BHSB) was achieved through the chemisorption of bis(hydrogensulphato)benzene as an active catalytic part on the surface of porous silica. Structural features, purity, thermal stability, and acid strength of the synthesized SiO2-BHSB material were established by adequate analytical techniques, such as FT-IR, solid-state CP-MAS 13C NMR, solid-state CP-MAS 29Si NMR, EDX, DTG, TGA, and acid–base volumetric studies. An environmentally benign catalytic protocol for the synthesis of biscoumarin scaffolds through a tandem reaction between 4-Hydroxycoumarin and structurally diverse aldehydes was developed in which the synthesized material SiO2-BHSB was observed to work as an efficient and reusable catalyst. The structures of the synthesized biscoumarin derivatives were established from their physical and spectrometric data. The synthesized catalytic material was observed to show sustained catalytic activity even after five cycles of its recovery and reuse. In comparison with the earlier reported methods, a tiny amount (2.5 mol%) of catalyst is sufficient to bring out the transformation smoothly in an aqueous-based solvent, ease of recovery, and reusability of the catalyst are additional salient features of the present protocol.

Functionalization strategy influences the porosity of amino-containing porous aromatic frameworks and the hydrogenation activity of palladium catalysts synthesized on their basis

We investigated the influence of functionalization strategy (post- or pre-) on the structure of amino-modified porous aromatic frameworks (PAF-NH2). Different techniques, such as low-temperature N2 adsorption-desorption, IR spectroscopy and solid-state CP-MAS 13C NMR spectroscopy, were used to characterize the synthesized materials. Palladium catalysts were prepared based on obtained PAF-NH2 supports, characterized by TEM, XPS and elemental analysis and studied in the semihydrogenation of C8-acetylenes and dienes. The results show that the modification approach influences structure of PAF and, therefore, the morphology and distribution of palladium nanoparticles. Post-modified catalysts proved to be more active, while pre-modified ones exhibited enhanced selectivity towards desired olefins and improved stability.

Physicochemical and conductivity studies of chitosan-tapioca flour-LiBF4 gel polymer electrolytes

The present study emphasizes the isolation of chitin and chitosan from the exoskeleton of white shrimp, Fenneropenaeus indicus. Demineralization and deproteination were used to extract chitin, followed by deacetylation of the extracted chitin to yield chitosan. Chitin and chitosan were characterized by FT-IR, TGA, SEM, XRD and CP-MAS 13C NMR analyses. FT-IR spectra presented characteristic peaks at 1655 cm−1 (amide) and 3441 cm−1 (hydroxyl). XRD analysis outlined two peaks at 9.41⁰ and 19.29⁰. Different compositions of CS-TF-LiBF4 gel polymer electrolytes were fabricated successfully using chitosan (CS), tapioca flour (TF), and lithium tetrafluoroborate (LiBF4) as organic filler, polymer host, and primary ions carrier to the polymer matrix, respectively. Gel polymer electrolytes were investigated through electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) to infer their ionic conductivity. It was revealed that electrical conductivity improved with increasing LiBF4 concentration from 0% to 10%. The maximum ionic conductivity was found to be 2.699 ± 0.28 mS cm−1 for CS-TF-10% LiBF4 biopolymer electrolyte with an electrochemical stability window potential of 2.34 V. EIS analysis showed that LiBF4 facilitated to enhance the amount of charge carried along with providing free ions for conduction.

Grafting of amine functions on cellulose acetate fibers by branched polyethylenimine coating

The aim of this study is to functionalize cellulose acetate (CA) fibers with an amine function by the adsorption of branched polyethyleneimine (bPEI) into the fiber surface. The adsorption was carried out by immersing CA tow in branched bPEI solution and washing off with water to remove any non-adsorbed bPEI. The mass increase and X-ray Photoelectron Spectroscopy (XPS) quantified the amount of bPEI adsorbed on the surface of the CA fibers. The effects of the coating duration, bPEI molecular mass, bPEI concentration, bPEI solvent and plasma treatment on the amount of the bPEI adsorbed and the amine density on the surface of the CA fibers have been investigated and reported here. The surface morphology of bPEI-treated CA fibers, compared to one of native CA fibers, was investigated by both Electron Probe Micro-Analyzer (EPMA) coupled with X-ray mapping, which is an important tool to analyze surface chemical composition, and Scanning Electron Microscopy (SEM), in order to illustrate the morphology of the CA fibers after bPEI adsorption as well as the plasma effect on adsorption process. The evaluation of bPEI coated-CA fibers for the adsorption aldehydes was carried out by exposing them to formaldehyde vapor generated from a formaldehyde solution. The adsorption mechanism was investigated by Cross Polarization - Magic Angle Spinning 13Carbon Nuclear Magnetic Resonance (CP-MAS 13C NMR) which proved that the aldehydes are chemically attached to the surface of CA fibers in the form of hemiaminals. Finally, the shelf life of plasma-treated CA fibers coated with bPEI was studied and reported.

Investigation of Adsorption Behavior of Anticancer Drug on Zinc Oxide Nanoparticles: A Solid State NMR and Cyclic Voltammetry (CV) Analysis.

The present study aims to comprehend the adsorption behavior of a set of anticancer drugs namely 5-fluorouracil (5-FU), doxorubicin and daunorubicin on ZnO nanoparticles (ZnO NPs) proposed as drug delivery systems employing solid state (ss) NMR, FTIR and Cyclic Voltammetry (CV) analysis. FTIR and 1H MAS ssNMR data recorded for bare ZnO nanoparticle confirmed the presence of adsorbed -OH groups on the surface. 13C CP-MAS NMR spectra recorded for free and ZnO surface adsorbed drug samples exhibited considerable line broadening and chemical shift changes that complemented our earlier report on UV-DRS and XRD data of surface adsorption in case of 5-FU. Moreover, a remarkable enhancement of 13C signal intensity in case of loaded 5-FU was observed. This clearly indicated rigid nature of the drug on the surface allowing efficient transfer of 1H polarization from the hetero nitrogen of 5-FU to ZnO to form surface hydroxyl (-OH) groups and the same has been observed in the quantum chemical calculations. To further analyze the motional dynamics of the surface adsorbed 5-FU, longitudinal relaxation times (T1) were quantified employing Torchia method that revealed significant enhancement of 13C relaxation rate of adsorbed 5-FU. The enhanced rate suggested an effective role of quadrupolar contribution from 67Zn to the 13C relaxation mechanism of ZnO_5-FU. The heterogeneous rate constant (khet), average free energy of activation (∆G≠) and point of zero charge (PZC) measured for free and drug loaded ZnO NPs samples using CV further support the SS-NMR results.

Neutral Sugar Content and Composition as a Sensitive Indicator of Fire Severity in the Andisols of an Araucaria–Nothofagus Forest in Southern Chile

Wildfire induces soil alterations that have a long-term impact on soil organic matter (SOM) quality. We postulated that after different fire severities, the neutral sugars in soils can be used as an indicator of soil organic matter quality after fire. The aim of this study was to determine the contribution of neutral sugar, bulk and occluded particulate organic matter (oPOM) affected by wildfire, at different soil depths in an Araucaria–Nothofagus Forest, four years post-after fire. The concentration and composition of the neutral sugars in the soils clearly comprised the major fraction in the unburned soil. Medium- and high-severity fires caused a drastic reduction in soil sugars in the bulk soil as well as in the oPOM fractions. The 13C-CPMAS NMR spectroscopy analysis revealed a high contribution of recalcitrant carbon to the decomposition such as aryl–C and aryl–O derived from charred material, whereas the abundance of O–alkyl C and alkyl C functional groups were decreased. The neutral sugars (Galactose+Mannose/Xilose+Arabinose) revealed a major microbial origin in fire affected areas as the ratio was >2. Therefore. Therefore, we suggest that the neutral sugar content of soil should be used for monitoring both short- and long-term changes in SOM altered by fires.

Phenoloxidase activity and organic carbon dynamics in historic Anthrosols in Scotland, UK.

Phenolic compounds are chemical precursor building blocks of soil organic matter. Their occurrence can be inhibitory to certain enzymes present in soil, thereby influencing the rate of decomposition of soil organic matter. Microbe-derived phenoloxidases (laccases) are extracellular enzymes capable of degrading recalcitrant polyphenolic compounds. In this study, our aim was to investigate the relationships between phenoloxidase enzyme activity, organic carbon content and microbial abundance in the context of long-term anthropogenically amended soils. To achieve this, we used a series of complementary biochemical analytical methods including gas chromatography, enzyme assays and solid-state Carbon-13 Cross Polarisation Magic-Angle Spinning Nuclear Magnetic Resonance Spectroscopy (13C CPMAS NMR). Using several anthrosols found in St Andrews (Scotland, UK) that had been subjected to intense anthropogenic modification since the medieval period (11th century AD) to present-day, we were able to scope the impact of past waste disposal on soils. The long-term anthropogenic impact led to organic matter-rich soils. Overall, phenoloxidase activity increased by up to 2-fold with soil depth (up to 100 cm) and was inversely correlated with microbial biomass. Solid-state 13C NMR characterisation of carbon species revealed that the observed decline in soil organic matter with depth corresponded to decreases in the labile organic carbon fractions as evidenced by changes in the O/N-alkyl C region of the spectra. The increase in phenoloxidase activity with depth would appear to be a compensatory mechanism for the reduced quantities of organic carbon and lower overall nutrient environment in subsoils. By enzymatically targeting phenolic compounds, microbes can better utilise recalcitrant carbon when other labile soil carbon sources become limited, thereby maintaining metabolic processes.

Fast and Selective Aqueous-Phase Oxidation of Styrene to Acetophenone Using a Mesoporous Janus-Type Palladium Catalyst.

A heterogeneous Janus-type palladium interphase catalyst was obtained by selective surface modification of a hollow mesoporous silica material. The catalyst comprises hydrophobic octyl groups on one side of the silica nanosheets and single-site bis-imidazoline dichlorido palladium(II) complexes on the other. The structure of this composite material has been analyzed by means of elemental analysis, atomic absorption spectroscopy, BET surface analysis, TGA, SEM and solid-state CP-MAS 13C and 29Si NMR spectroscopy. The catalyst showed extraordinary activity for the aqueous-phase oxidation of styrene to acetophenone using 30% hydrogen peroxide as the oxidant. An 88% yield of acetophenone could be achieved after 60 min.

Crystal growth of PPS nanofibers during annealing studied by solid‐state 13C CPMAS NMR

AbstractInitial crystalline phase growth property for poly(p‐phenylene sulfide) (PPS) nanofibers during annealing are studied by means of the 13C high‐resolution solid‐state cross‐polarization/magic‐angle‐spinning NMR (13C CPMAS NMR) with spectral editing procedure using the difference in 1H spin‐lattice relaxation time in the rotating frame (T1ρH) between the crystalline and non‐crystalline phases. The PPS nanofibers are prepared by drawing the solid microfibers melted by a high‐power carbon dioxide (CO2) laser with supersonic jet velocity of 300–600 ms−1 in a vacuum chamber (CLSD method). The crystallinity and molecular orientation of the pristine drawn PPS nanofibers increase with decrease of the chamber pressure (pch). The growing process and the ordered chain packing of the crystalline phase during annealing depend on the initial chain orientation. The low pressures at pch = 30 and 10 kPa significantly relate to the initial nucleation growth of the PPS nanofibers. In the initial crystal growth of PPS nanofibers obtained at pch = 30 kPa for the low temperature annealing, the rearrangement of chains occurs, but for those at pch = 10 kPa the rearrangement does not occur. This is because the highly ordered chain alignments and packing are already achieved for PPS nanofibers obtained at pch = 10 kPa.

Contribution of Tamarix aphylla to soil organic matter evolution in a natural semi-desert area in Tunisia

A soil, classified as Arenosol (Eutri-Aridic Arenosol (Calcaric)), located in Neffatia (Tunisia) and populated by the shrub tamarisk (Tamarix aphylla), was studied to assess how the litter deriving from tamarisk can affect its characteristics. Several parameters were considered: particle size distributions (PSD), pH, cation exchange capacity (CEC), total CaCO3 content, total nitrogen (TKN), phosphorus and total organic carbon (TOC). Down the soil profile the pH increased from 7.83 to 8.32 as a probable consequence of salts accumulation deriving from the mineralization of the organic matter and the limited leaching due to low rainfall. As expected, TOC and TKN decreased, from the top downwards, and the two parameters were well correlated (TOC vs TKN: R2 = 0.98; p < 0.05; n = 3). CEC assumed progressively lower values reflecting the decreasing organic matter content (CEC vs TOC: R2 = 0.93; p < 0.05; n = 3). PSD showed that the presence of roots influenced the quantity of fine particles down the profile and the PSD cumulative curves were indicative of an aeolian origin for the soil parent material, confirming the hypothesis that tamarisk interacts with the environment, trapping sediment and forming the so-called phytogenic dunes. By chemical and spectroscopic analyses, it was possible to assess that tamarisk plant residues directly contributed to the soil organic matter (SOM) accumulation and characteristics. Stable SOM (ligno-humic fraction) closely resembles that of the plant (leaves and stems) and is chemically lacking in the more easily degradable organic components such as fats, hemicellulose, cellulose and proteins. 13C CPMAS NMR spectroscopy showed that the so-called soil ligno-humic fraction consists of aromatic molecules such as tannins, and aliphatic carbon (i.e. cutins and suberins) already present in the plant and preserved by mineralization processes because they are the most resistant to biological degradation.

Interactions of Aminopropyl–Azithromycin Derivatives, Precursors in the Synthesis of Bioactive Macrozones, with E. coli Ribosome: NMR and Docking Studies

The structure and interactions of several aminopropyl–azithromycin derivatives (1a–c) have been studied by using NMR spectroscopy and docking calculations. Compounds 1a–c are precursors in the synthesis of macrozones, novel bioactive azithromycin–thiosemicarbazone conjugates active against some resistant bacterial strains. Today, bacterial resistance is considered as one of the major threats to human health. Knowledge on drug binding mode and conformations is one of the key factors in the process of designing molecules to fight resistance. In solution state, compounds 1a and 1c exist in the 3-endo-folded-out conformation, while 1b adopts a classical folded-out conformation. 13C and 15N CPMAS NMR spectra pointed towards similar structures in the solid state. The transferred NOESY NMR spectra confirmed binding to the E. coli ribosome and suggest that dominant conformations in the bound state resemble those in the free one. STD experiments identified reactive groups of 1a–c in close contact with the ribosome resembling binding epitopes observed for the related 15-membered macrolides. Docking studies revealed that the studied compounds bind to the same ribosome binding pocket similarly to erythromycin in the crystal state, and that the binding is achieved through H-bonds and van der Waals interactions. The bound conformation is the same as determined by NMR. STD enhancements observed for methylene protons in the aminopropyl side chain indicate additional interactions which contribute to the overall binding energy.

Bifunctional crystalline microporous organic polymers: Efficient heterogeneous catalysts for the synthesis of 5-hydroxymethylfurfural

Developing efficient catalysts for the synthesis of 5-hydroxymethylfurfural (HMF) from biomass resources is very demanding as it is an important renewable platform chemical for the synthesis of biofuels, polymers and fine chemicals. Here, we have designed two new crystalline microporous bi-functional porous organic polymers through the extended aromatic substitution reaction under refluxing conditions. Porous polymers containing sulfonic acid and secondary amine groups are two reactive catalytic centres for carrying out the bi-functional heterogeneously catalysed reactions. Bifunctionalized porous polymers POPDS and POPSDS are synthesized through the reaction of 2,2′-benzidinedisulfonic acid and 4,4′-diaminostilbene-2,2′-disulfonic acid with cyanuric chloride, respectively. The materials were characterized thoroughly using powder X-ray diffraction, N2 sorption, FTIR, solid state 13C CP MAS NMR spectroscopy, FE-SEM, HR-TEM, XPS and TG/DTA analysis. These two crystalline porous polymers possesses good surface acidic and basic sites, and having flower-like and spherical particle morphologies. POPDS and POPSDS exhibited superior catalytic activity for the conversion of different small carbohydrates to 5-hydroxymethylfurfural (HMF) under microwave irradiation. Moreover, the recyclability tests of these catalysts revealed good durability up to sixth consecutive reaction cycles, suggesting the future potential of these catalysts in the sustainable synthesis of HMF.

Chitin Cryogels Prepared by Regeneration from Phosphoric Acid Solutions.

Cryogelation is a developing technique for the production of polysaccharide materials for biomedical applications. The formation of a macroporous structure during the freeze-drying of polysaccharide solutions creates biomaterials suitable for tissue engineering. Due to its availability, biocompatibility, biodegradability, and non-toxicity, chitin is a promising natural polysaccharide for the production of porous materials for tissue engineering; however, its use is limited due to the difficulty of dissolving it. This work describes the preparation of cryogels using phosphoric acid as the solvent. Compared to typical chitin solvents phosphoric acid can be easily removed from the product and recovered. The effects of chitin dissolution conditions on the structure and properties of cryogels were studied. Lightweight (ρ 0.025–0.059 g/cm3), highly porous (96–98%) chitin cryogels with various heterogeneous morphology were produced at a dissolution temperature of 20 ± 3 °C, a chitin concentration of 3–15%, and a dissolution time of 6–25 h. The crystallinity of the chitin and chitin cryogels was evaluated by 13C CP-MAS NMR spectroscopy and X-ray diffractometry. Using FTIR spectroscopy, no phosphoric acid esters were found in the chitin cryogels. The cryogels had compressive modulus E values from 118–345 kPa and specific surface areas of 0.3–0.7 m2/g. The results indicate that chitin cryogels can be promising biomaterials for tissue engineering.

Tillage-residues affect mineral-associated organic matter on Vertisols in northern Mexico

Managing croplands for increased storage of soil organic matter (SOM) contributes to the development of resilient farming systems in a changing climate. We examined SOM dynamics in a wheat (Triticum durum L.) – maize (Zea mays L.) irrigated bed planting system established near Ciudad Obregón, Sonora, Mexico. Soil samples (0–15 cm) were collected from conventionally tilled raised beds (CTB) with all crop residues incorporated (CTB-I) and permanent raised beds (PB) with crop residues burned (PB-B), removed (PB-R), partly retained (PB-P) or fully retained (PB-K) receiving 0, 150 or 300 kg N ha−1, and analyzed for organic C (OC), total N (TN) and δ13C in whole-soil, light fraction (LF) and coarse- (sand) and fine- (silt and clay) mineral-associated organic matter (MAOM). Results indicated that PB-K and PB-B increased soil OC (p <0.05) in whole-soil relative to CTB-I, mainly through increases in sand- and silt-size MAOM, respectively. Similarly, N-fertilization increased soil OC and TN contents in whole-soil, coarse-MAOM and fine-MAOM, but not in the LF pool. Soil δ13C was higher (p <0.05) in PB-K (−20.18‰) relative to PB-B (−20.67‰), possibly due to the stabilization of partly decomposed maize-C in silt- and clay-size MAOM. Composition of SOM surveyed by CPMAS 13C NMR was not affected by tillage-residue management, and roughly consisted of 35% O-alkyl-C, 31% alkyl-C, 24% aromatic-C and 10% carboxyl-C. Our results indicate that long-term PB-K and PB-B adoption increased surface soil OC contents relative to CTB-I, even though pathways of SOM stabilization differed between systems. Under PB-K, accumulation of fine-MAOM was mostly related to straw-C inputs, whereas in PB-B it was closely associated to black-C precursors. Fine-MAOM appeared responsive to crop residue management, and should be therefore considered when analyzing mechanisms of SOM stabilization in irrigated croplands.

A highly reusable polydimethylsiloxane sorbents for oil/organic solvent clean-up from water

Frequent oil spills in recent years due to human activities including oil drilling, tanker accidents or industrialization, give rise to an urgent need for the development of sorbent materials with high sorption ability, good selectivity and reusability. In this work, PDMS based hydrophobic sorbents acting as oil removing agents were fabricated via bulk polymerization of tetraethyl orthosilicate (TEOS) and different lengths of polydimethylsiloxane (PDMS), without using any activator, initiator, catalyst or solvent. The PDMS sorbents were characterized by using FTIR, 13C and 29Si CPMAS NMR, SEM, contact angle measurements, and thermal gravimetric analysis. The results show the successful preparation of the crosslinked sorbent structure with water contact angle (WCA) of 123°, indicating its hydrophobic structure. The prepared sorbents have high swelling ability in organic liquids/oils in the range of 9–21 g g−1. They have the ability to quickly absorb the oil from the water surface and float before and after oil sorption, while the capacity of the sorbents did not change in different water types. They can be reusable for at least 10 absorption-desorption cycles without capacity change, and have stability in oils over 300 cycles, demonstrating that the obtained hydrophobic PDMS sorbents can be used as oil removing agents in the field of oil spill applications.