Solid-state NMR Spectra Research Articles

Poplar Hot Water Extract Enhances Barrier and Antioxidant Properties of Chitosan/Bentonite Composite Film for Packaging Applications.

Herein, the chitosan-based (CS) composite film was fabricated via a simple and efficient blending approach by adding poplar hot water extract (HWE), bentonite (BT) and chitosan. The addition of HWE largely improved the UV blocking ability and antioxidant properties of the resultant composite film, and simultaneously a tortuous path was constructed within the chitosan matrix to enhance the water vapor and oxygen barriers after the addition of BT. Specially, the content of HWE at 10 wt % gave a greatly decreased UV light transmittance at 280 nm to the CS-BT-HWE composite film that was 99.36% lower than that of CS-BT film, and the oxidation resistance was 9.65 times higher than that of CS-BT. The mechanical properties and surface morphological observation evaluated by scanning electron microscopy (SEM) and scanning probe microscope (SPM) confirmed the film had a denser structure. The internal chemical structure analyzed using solid state NMR, FTIR and X-ray spectra exhibited the resultant Maillard structure and strong hydrogen bonding that contributed to the improved mechanical properties. Overall, the as-prepared composite film has great potential as food packaging materials, and also provides a high-efficient utilization pathway for HWE.

Structural Understanding of MnO–SiO2–Al2O3–Ce2O3 Slag via Raman, 27Al NMR and X-ray Photoelectron Spectroscopies

In order to understand sulfur solubility in the MnO–SiO2–Al2O3–Ce2O3 slag or inclusion system (mol MnO/mol SiO2 = M/S = 2.2 or 0.9, Al2O3 = 14.2[± 1.8] mol%, Ce2O3 = 0–5.6 mol%), the effect of Ce3+ ions on the structure of the Mn–aluminosilicate system with different M/S molar ratios has been studied by micro-Raman spectroscopy, solid-state nuclear magnetic resonance (NMR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Because constant oxygen partial pressure was maintained at p(O2) = 2.8 × 10−7 atm, oxidation state of Mn and Ce would be in Mn2+ and Ce3+ in the MnO–SiO2–Al2O3–Ce2O3 system, which were also confirmed by XPS analysis. Although it was difficult to measure the 27Al solid-state NMR spectra of the quenched MnO–SiO2–Al2O3 system due to the paramagnetic effect, 27Al NMR spectra did show structural changes in aluminate when cerium was added to the Mn–aluminosilicate melts. Addition of Ce2O3 in the high M/S(= 2.2) system caused both an explosive enhancement in the intensity of Raman bands at 600 cm−1 and a peak shift in 27Al NMR spectra, indicating the transition from the [AlO4]–:0.5Mn2+ tetrahedron to a [AlO6]3–:Ce3+ octahedron complex due to a strong attraction between aluminate and the cerium ion. XPS spectra show that the transition of the aluminate structure upon introduction of Ce3+ ions consumes free oxygen in Mn–aluminosilicate melts in high M/S(= 2.2) system. However, the same structural changes were not observed when Ce2O3 was added to lower M/S(= 0.9) system, because Ce3+ ions primarily interact with the pre-existing [AlO6]-octahedron in low M/S system.

Including Protons in Solid-State NMR Resonance Assignment and Secondary Structure Analysis: The Example of RNA Polymerase II Subunits Rpo4/7

1H-detected solid-state NMR experiments feasible at fast magic-angle spinning (MAS) frequencies allow accessing 1H chemical shifts of proteins in solids, which enables their interpretation in terms of secondary structure. Here we present 1H and 13C-detected NMR spectra of the RNA polymerase subunit Rpo7 in complex with unlabeled Rpo4 and use the 13C, 15N, and 1H chemical-shift values deduced from them to study the secondary structure of the protein in comparison to a known crystal structure. We applied the automated resonance assignment approach FLYA including 1H-detected solid-state NMR spectra and show its success in comparison to manual spectral assignment. Our results show that reasonably reliable secondary-structure information can be obtained from 1H secondary chemical shifts (SCS) alone by using the sum of 1Hα and 1HN SCS rather than by TALOS. The confidence, especially at the boundaries of the observed secondary structure elements, is found to increase when evaluating 13C chemical shifts, here either by using TALOS or in terms of 13C SCS.

On the use of frequency-swept pulses and pulses designed with optimal control theory for the acquisition of ultra-wideline NMR spectra.

Frequency-swept (FS) pulses, such as wideband uniform-rate smooth-truncation (WURST) pulses, have found much success for the acquisition of ultra-wideline (UW) solid-state NMR spectra. In this preliminary study, new pulses and pulse sequences are explored in simulation and experimentally for several nuclei exhibiting UWNMR powder patterns under static conditions, including 119Sn (I = 1/2), 195Pt (I = 1/2), 2H (I = 1), and 71Ga (I = 3/2). First, hyperbolic secant (HS) and tanh/tan (THT) pulses are tested and implemented as excitation and refocusing pulses in spin-echo and Carr-Purcell/Meiboom Gill (CPMG)-type sequences, and shown to have comparable performances to analogous WURST pulses. Second, optimal control theory (OCT) is utilized for the design of new Optimal Control Theory Optimized Broadband Excitation and Refocusing (OCTOBER) pulses, using carefully parameterized WURST, THT, and HS pulses as starting points. Some of the new OCTOBER pulses used in spin-echo sequences are capable of efficient broadband excitation and refocusing, in some cases resulting in spectra with increased signal enhancements over those obtained in experiments using conventional FS pulses. Finally, careful consideration of the spin dynamics of several systems, by monitoring of the time evolution of the density matrix via the Liouville-von Neumann equation and analysis of the time-resolved Fourier transforms of the pulses, lends insight into the underlying mechanisms of the FS and OCTOBER pulses. This is crucial for understanding their performance in terms of generating uniformly excited patterns of high signal intensity, and for identifying trends that may offer pathways to generalized parameterization and/or new pulse shapes.

Structure, Topology, and Dynamics of Membrane-Inserted Polypeptides and Lipids by Solid-State NMR Spectroscopy: Investigations of the Transmembrane Domains of the DQ Beta-1 Subunit of the MHC II Receptor and of the COP I Protein p24.

MHC class II receptors carry important function in adaptive immunity and their malfunctioning is associated with diabetes type I, chronic inflammatory diseases and other autoimmune diseases. The protein assembles from the DQ alpha-1 and DQ beta-1 subunits where the transmembrane domains of these type I membrane proteins have been shown to be involved in homo- and heterodimer formation. Furthermore, the DQ alpha 1 chain carries a sequence motif that has been first identified in the context of p24, a protein involved in the formation of COPI vesicles of the intracellular transport machinery, to specifically interact with sphingomyelin-C18 (SM-C18). Here we investigated the membrane interactions and dynamics of DQ beta-1 in liquid crystalline POPC phospholipid bilayers by oriented 15N solid-state NMR spectroscopy. The 15N resonances are indicative of a helical tilt angle of the membrane anchor sequence around 20°. Two populations can be distinguished by their differential dynamics probably corresponding the DQ beta-1 mono- and homodimer. Whereas, this equilibrium is hardly affected by the addition of 5 mole% SM-C18 a single population is visible in DMPC lipid bilayers suggesting that the lipid saturation is an important parameter. Furthermore, the DQ alpha-1, DQ beta-1 and p24 transmembrane helical domains were reconstituted into POPC or POPC/SM-C18 lipid bilayers where the fatty acyl chain of either the phosphatidylcholine or of the sphingolipid have been deuterated. Interestingly in the presence of both sphingolipid and polypeptide a strong decrease in the innermost membrane order of the POPC palmitoyl chain is observed, an effect that is strongest for DQ beta-1. In contrast, for the first time the polypeptide interactions were monitored by deuteration of the stearoyl chain of SM-C18. The resulting 2H solid-state NMR spectra show an increase in order for p24 and DQ alpha-1 which both carry the SM recognition motif. Thereby the data are suggestive that SM-C18 together with the transmembrane domains form structures imposing positive curvature strain on the surrounding POPC lipids. This effect is attenuated when SM-C18 is recognized by the protein.

Effects of deuteration on solid-state NMR spectra of single peptide crystals and oriented protein samples.

Extensive deuteration can be used to simplify NMR spectra by "diluting" and minimizing the effects of the abundant 1H nuclei. In solution-state NMR and magic angle spinning solid-state NMR of proteins, perdeuteration has been widely applied and its effects are well understood. Oriented sample solid-state NMR of proteins, however, is at a much earlier stage of development. In spite of the promise of the approach, the effects of sample deuteration are largely unknown. Here we map out the effects of perdeuteration on solid-state NMR spectra of aligned samples by closely examining differences in results obtained on fully protiated and perdeuterated samples, where all of the carbon sites have either 1H or 2H bonded to them, respectively. The 2H and 15N labeled samples are back-exchanged in 1H2O solution so that the amide 15N sites have a bonded 1H. Line-widths in the 15N chemical shift, 1H chemical shift, and 1H-15N dipolar coupling frequency dimensions were compared for peptide single crystals as well as membrane proteins aligned along with the phospholipids in bilayers with their normals perpendicular to the direction of the magnetic field. Remarkably, line-width differences were not found between fully protiated and perdeuterated samples. However, in the absence of effective 1H-1H homonuclear decoupling, the line-widths in the 1H-15N heteronuclear dipolar coupling frequency dimension were greatly narrowed in the perdeuterated samples. In proton-driven spin diffusion (PDSD) experiments, no effects of perdeuteration were observed. In contrast, in mismatched Hartmann-Hahn experiments, perdeuteration enhances cross-peak intensities by allowing more efficient spin-exchange with less polarization transfer back to the carbon-bound 1H. Here we show that in oriented sample solid-state NMR, the effects of perdeuteration can be exploited in experiments where 1H-1H homonuclear decoupling cannot be applied. These data also provide evidence for the possible contribution of direct 15N-15N dilute-spin mixing mechanism in proton-driven spin diffusion experiments.

On the Difficulties and Pitfalls with the Analysis of Solid-State 13C NMR Spectra in Graphitic Materials

The difficulties and pitfalls with the interpretation of solid-state 13C nuclear magnetic resonance (NMR) spectra in graphitic materials are discussed in detail here, with special emphasis on the case of 13C-enriched samples, which have been used in several recent NMR studies. The issues with the spectral simulation and the interpretation of the spectral parameters obtained by some arbitrary models reported in the recent literature are examined and alternative methods to obtain informative experimental data and to analyze them in a more appropriate way are presented.

Two copolymer-grafted silica stationary phases prepared by surface thiol-ene click reaction in deep eutectic solvents for hydrophilic interaction chromatography

Two new copolymer-grafted silica stationary phases were prepared and employed in hydrophilic interaction chromatography (HILIC). 2-(Dimethylamino)ethyl methacrylate (DMAEMA) are copolymerized with itaconic acid (IA) and acrylic acid (AA) respectively, via thiol-ene click reaction on silica surface with deep eutectic solvents (DES) as new solvents. The obtained poly(DMAEMA-co-itaconic acid)-grafted silica (Sil-PDM-PIA) and poly(DMAEMA-co-acrylic acid)-grafted silica (Sil-PDM-PAA) were characterized by Fourier transform infrared spectroscopy, elemental analysis and solid-state 13C NMR spectra. Their hydrophilic interaction performances were evaluated by separating nucleosides, nucleobases, saccharides, and amino acids. Compared with previous reported poly(itaconic acid)-grafted silica (Sil-PIA) and poly(acrylic acid)-grafted silica (Sil-PAA) stationary phases, these two new copolymer-grafted silica performed higher selectivity and better separation for polar analytes in HILIC.

In-situ Nitrous Acid Generation over Silica Imidazole Catalyst for Dyes Production

The objective of this research is to prepare a new type of heterogeneous catalyst and to study its usage for in-situ nitrous acid generation to form a diazonium salt. The high pure silica (> 95%) was produced by burning the clean rice husk at 800 °C. After that, the silica was transferred to sodium silicate using 1.0 M of NaOH, followed by immobilizing with 3-(chloropropyl)triethoxysilane in a simple one-pot synthesis. Finally, the material was refluxed with (0.015 mol) of p-xylyl di-imidazolium chloride. The silicon solid-state nuclear magnetic resonance shows the Q4, Q3, T3, and T2 chemical shifts at expected position. Carbon solid-state nuclear magnetic resonance spectrum shows different peaks at different chemical shifts related to the carbon structures of the organic moieties. The catalyst is stable up to 277 ºC according to the thermal analysis. TEM images show smooth and porous regularly shaped particles with an estimation size of ca. 5 nm. Coupling reaction of aromatic compounds was carried out with a diazonium salt of aniline to yield a monoazo dye. All dyes were showed matching the elemental analysis with the theoretical calculation. Besides this, the spectrum of FT-IR and UV-Visible were recorded. The catalyst was stable, easy separation from the reaction mixture, and reusable by a simple experimental procedure. The catalyst could be used successfully for the nitrous acid generation.

Integrated soluble polymer and mesoporous silica as a double–type support to immobilize tertiary amine–Ru/diamine–bifunctionality for aza–addition/reduction cascade reaction

Exploiting advantages of a double–type support to create an active site–isolated heterobifunctional catalyst is beneficial to an efficiently sequential organic transformation. Herein, an integrated soluble polymer and mesoporous silica as a double–type support to immobilize the tertiary amine–Ru/diamine–bifunctionality for the construction of an active site–isolated catalyst is developed, where the tertiary amine–functionality is tethered in the outer soluble polymer and chiral ruthenium/diamine–functionality is anchored within the inner mesoporous silica. Electron microscopy images, together with analyses of solid–state NMR spectra, disclose that catalyst possesses the uniformly distributive morphology with well–defined single–site ruthenium/diamine active centers. As envisaged, the heterobifunctional catalyst performs a highly efficient aza–Michael addition/asymmetric transfer hydrogenation enantioselective cascade reaction, where the outer tertiary amine–functionality enables a high reactivity to afford β–secondary amino ketones via an aza–Michael addition reaction of enones and amines, and the inner chiral ruthenium/diamine–functionality guarantees a high enantioselectivity to chiral γ–secondary amino alcohols via an asymmetric transfer hydrogenation of β–secondary amino ketones. Furthermore, this catalyst can also be recovered easily and recycled for six runs, showing a practical preparation of aryl–substituted γ–secondary amino alcohols.

Charcoal Fine Residues Effects on Soil Organic Matter Humic Substances, Composition, and Biodegradability

Biochar has been shown as a potential mean to enhance carbon sequestration in the soil. In Brazil, approximately 15% of the produced charcoal is discarded as charcoal fines, which are chemically similar to biochar. Therefore, we aimed to test charcoal fines as a strategy to increase soil carbon sequestration. Charcoal fines of hardwood Mimosa scabrella were incorporated into a Cambisol down to 10 cm (T1 = 0 and T4 = 40 Mg ha−1) in Southern Brazil. Soil samples were collected (0–30 cm) 20 months after charcoal amendment. Soil organic matter (SOM) acid extract, humic acid, fulvic acid, and humin fractions were separated. Solid-state 13C nuclear magnetic resonance (NMR) spectra from charcoal and SOM in T1 and T4 were obtained before and after 165 days of incubation under controlled conditions. Charcoal increased soil carbon as fulvic (10–20 cm) and humic acids (10–30 cm) and, especially, as humin (0–5 cm), which probably occurred due to the hydrophobic character of the charcoal. The 13C NMR spectra and mean residence times (MRT) measured from incubation essays indicated that the charred material decomposed relatively fast and MRT of T1 and T4 samples were similar. It follows that the charcoal fines underwent similar decomposition as SOM, despite the high charcoal dose applied to the soil and the high aryl C contribution (78%) to the total 13C intensity of the charcoal NMR spectra.

47,49Ti solid-state NMR and DFT study of Ziegler-Natta catalyst: Adsorption of TiCl4 molecule onto the surface of MgCl2

In Ti-based Ziegler-Natta catalysts (ZNCs), disagreements exist concerning which lateral surface of the MgCl2 support adsorbs Ti species so as to be an active site for the catalysis of polymerization. In the present paper, we investigated the local structure of TiCl4 adsorbed onto the surface of MgCl2 by 47,49Ti solid-state nuclear magnetic resonance (NMR) spectra at 21.8 T along with density functional theory (DFT) calculations. The magic-angle-spinning NMR spectrum of the TiCl4/MgCl2 adduct sample prepared by 20 h of milling, which exhibited broadened and shifted peaks compared to that of the sample without milling, was simulated by a Czjzek model considering the distribution of quadrupole interaction parameters. The electric field gradient and chemical shielding tensors of 49Ti were obtained via DFT calculations for model molecules of TiCl4, 2TiCl4, and Ti2Cl8 adsorbed onto the (110), (104), and (104)-step defect surfaces of MgCl2. By comparing the obtained NMR parameters, the 47,49Ti NMR spectrum of the milled sample was assigned to TiCl4 adsorbed onto the (104) surface of MgCl2, which may not be a principal component of adsorption.

An insoluble naphthalenediimide derivative as a highly stable cathode material for lithium-ion batteries

A new naphthalenediimide derivative, 2, 7-di (1, 2, 4-triazolyl) benzophenanthroline-tetraone (3-DTBPT) is synthesized by the condensation reaction of 1, 4, 5, 8-naphthalenetetracarboxylic anhydride (NTCDA) and 3-amino-1, 2, 4-triazole (3-AT). The 3-DTBPT material is characterized by Fourier transform infrared spectrum, X-ray diffraction, thermogravimetric analysis, solid state NMR spectra, field emission scanning electron microscopy, elemental analysis and Brunauer-Emmett-Teller surface. 3-DTBPT is insoluble in organic electrolyte. When used as a cathode material of lithium-ion batteries, 3-DTBPT exhibits an excellent cyclic stability, keeping a specific capacity of 110 mA h g−1 and a nearly 94.8% capacity retention after 50 cycles at 50 mA g−1. Our work provides an effective route for overcoming the dissolution problem of organic electrode materials and obtains a potential material for the long-cycle-life and flexible organic rechargeable batteries.

Tuning Carbon Dioxide Adsorption Affinity of Zinc(II) MOFs by Mixing Bis(pyrazolate) Ligands with N-Containing Tags.

The four zinc(II) mixed-ligand metal-organic frameworks (MIXMOFs) Zn(BPZ)x(BPZNO2)1-x, Zn(BPZ)x(BPZNH2)1-x, Zn(BPZNO2)x(BPZNH2)1-x, and Zn(BPZ)x(BPZNO2)y(BPZNH2)1-x-y (H2BPZ = 4,4'-bipyrazole; H2BPZNO2 = 3-nitro-4,4'-bipyrazole; H2BPZNH2 = 3-amino-4,4'-bipyrazole) were prepared through solvothermal routes and fully investigated in the solid state. Isoreticular to the end members Zn(BPZ) and Zn(BPZX) (X = NO2, NH2), they are the first examples ever reported of (pyr)azolate MIXMOFs. Their crystal structure is characterized by a three-dimensional open framework with one-dimensional square or rhombic channels decorated by the functional groups. Accurate information about ligand stoichiometric ratio was determined (for the first time on MIXMOFs) through integration of selected ligands skeleton resonances from 13C cross polarized magic angle spinning solid-state NMR spectra collected on the as-synthesized materials. Like other poly(pyrazolate) MOFs, the four MIXMOFs are thermally stable, with decomposition temperatures between 708 and 726 K. As disclosed by N2 adsorption at 77 K, they are micro-mesoporous materials with Brunauer-Emmett-Teller specific surface areas in the range 400-600 m2/g. A comparative study (involving also the single-ligand analogues) of CO2 adsorption capacity, CO2 isosteric heat of adsorption (Qst), and CO2/N2 selectivity in equimolar mixtures at p = 1 bar and T = 298 K cast light on interesting trends, depending on ligand tag nature or ligand stoichiometric ratio. In particular, the amino-decorated compounds show higher Qst values and CO2/N2 selectivity vs the nitro-functionalized analogues; in addition, tag "dilution" [upon passing from Zn(BPZX) to Zn(BPZ)x(BPZX)1-x] increases CO2 adsorption selectivity over N2. The simultaneous presence of amino and nitro groups is not beneficial for CO2 uptake. Among the compounds studied, the best compromise among uptake capacity, Qst, and CO2/N2 selectivity is represented by Zn(BPZ)x(BPZNH2)1-x.

Mechanisms on the impacts of humic acids on persulfate/Fe2+-based groundwater remediation

Persulfate (PS) has been increasingly applied for in situ chemical oxidation of organic contaminants in groundwater, while the impacts of humic acids (HAs) on the efficiency of persulfate/Fe2+-based remediation are not well understood. This study examined the effects of HAs originating from different places, including three commercial HAs and two soil HAs, on 2,4-dinitrotoluene (DNT) degraded by PS/Fe2+. DNT degradation by PS/Fe2+ was dependent on the types and concentrations of HAs and pH in solution. The positive correlation between the first order kinetic rate constant of DNT degradation by PS/Fe2+/HAs and the conditional stability constant (KM) indicates that the complexation of HAs with Fe3+ was beneficial to the degradation of DNT. The first order kinetic rate constant of DNT degradation by PS/Fe2+/HAs correlated well with their absorbance intensity of HAs at 465 or 665 nm. High positive correlation coefficients indicated that π-electrons of HAs strongly influenced DNT degradation, which was consistent with the results provided by solid-state 13C NMR spectra. Two-dimensional correlation spectroscopy (2DCOS) analysis confirmed that the fulvic-like fraction of HAs is prior to the humic-like fraction complexed with Fe3+.

Structures and Dynamics of Secondary and Tertiary Alkylphosphine Oxides Adsorbed on Silica.

The three secondary phosphine oxides [CH2 =CH(CH2 )4 ]2 HPO (1), [CH2 =CH(CH2 )5 ]2 HPO (2), and [CH2 =CH(CH2 )6 ]2 HPO (3), and two diphosphine dioxides, {[CH2 =CH(CH2 )6 ]2 PO(CH2 )7 }2 (4) and {[CH2 =CH(CH2 )6 ]2 PO(CH2 )4 }2 (5), incorporating long methylene chains, are described. The single crystal X-ray structures of 1, 2, and 5 have been determined. The phosphine oxides 3, 4, and 5 have been adsorbed on silica in submonolayer quantities to give 3 a-5 a. The 1 H, 13 C, and 31 P solid-state NMR spectra of polycrystalline 3-5 have been analyzed and compared with those of 3 a-5 a. The changes of the solid-state NMR characteristics upon adsorption and the surface mobilities of the phosphine oxides are discussed.

Preparation and properties of biodegradable poly (lactic acid)/ethylene butyl acrylate glycidyl methacrylate blends via novel vane extruder

ABSTRACTIn this work, poly (lactic acid) (PLA) and elastomer ethylene-butyl acrylate-glycidyl methacrylate terpolymer (EBA-GMA) containing epoxy groups were melt-blended using a novel vane extruder. The solid-state 13C nuclear magnetic resonance spectra (13C-NMR) and the Fourier-transform infrared (FTIR) spectroscopy proved that epoxy groups of EBA-GMA reacted with the carboxylic acid or hydroxyl groups of PLA during melt blending, resulting in a grafted structure which improved the interfacial adhesion of PLA/EBA-GMA blends. The phase morphology, mechanical and thermal properties were investigated to identify the effect of EBA-GMA weight fraction on the properties of PLA/EBA-GMA blends. Thermogravimetric analysis revealed that the incorporation of EBA-GMA improved the thermal stability of PLA. The impact strength of the annealed PLA80/20EBA-GMA binary blend increased up to ten times compared without annealing process.

Solid state NMR and computational studies on cyclopentadienyl lithium.

Lithiumcyclopentadienide, previously identified to be an endless polymer in the ligand-free solid state, was investigated by 13C- and 6Li-CP/MAS NMR spectra, and by B3LYP-GIAO theoretical calculations. By spectra simulation, the axially symmetric 13C-shift tensor components were identified to be δ11 = δ22 = 151.5ppm, δ33 = 15.5ppm. The 6Li-tensor components are δ11 = δ22 = +1.0ppm, δ33 = -43.0ppm. This extremely high field component is due to cumulative ring current effects. B3LYP-GIAO/TZVP calculations on the tensor principal components agree remarkably well with the measurements. A new and very simple method of preparing air-sensitive compounds for solid-state NMR analyses is described. Graphical abstract Shielding tensor main components from slow-speed solid state NMR spectra.

DFT-Assisted Solid-State NMR Characterization of Defects in Li2MnO3.

The complete description of defective structures and their impact on materials behavior is a great challenge due to difficulties associated with their reliable characterization in the nanoscale. In this paper, density functional theory (DFT) calculations are used to elucidate the solid-state nuclear magnetic resonance (NMR) spectra of Li2MnO3 which, combined with X-ray diffraction (XRD), provide a full description of disorder in this compound. While XRD allows accurate quantification of planar defects, the use of solid-state NMR reveals limited vacancy concentrations that were undetected by XRD as NMR is highly sensitive to the atomic local environments. The combination of these methods is here proved highly effective in overcoming the challenges of describing in great detail limited concentrations of disorder in transition metal oxides, providing information about structural variables that are essential to their application.

Evaluation of molecular properties of humic acids from vermicompost by 13 C-CPMAS-NMR spectroscopy and thermochemolysis–GC–MS

The molecular characteristics of different vermicomposts, produced with variable rates of cattle manure and cotton residues, and of related humic acids were determined by 13C-CPMAS NMR and Off-line pyrolysis THM-GC–MS. The analyses highlighted a composition of mature vermicomposts based on differential amounts of lignocellulosic fraction and alkyl compounds inherited from original biomasses, thus revealing a decrease of overall hydrophobic character at increasing amounts of cotton input. The evaluation of molecular parameters derived from both solid state NMR spectra and from the specific biomarkers released by thermochemolysis suggested that the humification process was mainly characterized by the selective preservation of specific lignin derivatives. The potential bioactive properties of humic acids were hence evaluated in a bioassays test on maize seedlings. The humic extracts showed a differential response in root growth-promoting effect, depending on the specific molecular features. The higher bioactivity found in humic components isolated from vermicompost with no or low addition of cotton residues, supported the role of the overall hydrophobic character and of the large content of bioavailable lignin units and nitrogen moieties. These results confirm that the combination of solid state NMR and thermochemolysis are valuable and efficient tools to assess the molecular quality of natural organic matter. The detailed molecular characterization of compost materials may hence represent a useful requirement to select the most suitable application of bulk biomasses and derived fractions for soil organic matter managements.