13C CPMAS NMR Spectroscopy Research Articles

Green and facile synthesis of cellulose nanofibres from Peltophorum pterocarpum pods cellulose using a eutectic solvent

ABSTRACT This study focuses on isolating, optimising and characterising cellulose from Peltophorum pterocarpum pods and synthesising cellulose nanofibres (CNF) using a eutectic solvent (ES). Three methods were evaluated: Soxhlet extraction, formic acid, and autoclave-assisted pre-treatment. The autoclave-assisted method yielded the highest cellulose content, approximately 43.6% w/w, at 121°C for 40 min. CP-MAS13C NMR and FTIR spectroscopy confirmed the cellulose’s carbon atoms and functional groups, and XRD analysis indicated a high crystallinity index (82.92%) and the transformation from cellulose I to cellulose II. SEM and TGA analyses assessed the morphological and thermal properties. CNFs were synthesised using a green solvent (ChCl/Lactic acid, 1:2) at 80°C, with TEM confirming their nanofibrous structure. The CNF zeta particle size was 262.1 nm, with a potential of −19.0 mV. The use of ES in the CNF synthesis is a novel and eco-friendly process that aligns with 5 of the 12 principles of green chemistry.

HRMAS 1H NMR and CPMAS 13C NMR spectroscopies coupled with chemometrics for the metabolomic investigation of commercial teas

In this study, the metabolome of different types of tea (i.e., black, green and earl grey) is explored by means of HRMAS 1H (i.e., semisolid state) NMR and CPMAS 13C (i.e., solid state) NMR spectroscopies. By elaborating the metabolomic data with unsupervised and supervised chemometric tools (PCA, PLS-DA), it was possible to set up classification models with the aim to discriminate the different types of tea as based on differences in their chemical composition. Both the applications of the NMR spectroscopies also allowed to obtain information about the metabolic biomarkers leading the differentiation among teas. These were mainly represented by phenolic compounds. Also, some non-phenolic compounds, such as amino acids, carbohydrates, and terpenoids, played important roles in shaping tea quality. The findings of this study provided useful insights into the application of solid and semisolid state NMR spectroscopies, in combination with chemometrics, in the context of food authentication and traceability.

Soil Organic Matter Composition in Urban Soils: A Study of Wrocław Agglomeration, SW Poland

In urban areas, because of anthropopressure, the transformation of the soil cover can lead to the complete destruction of the natural layout and properties of these soils. The object of this study was to determine the quantity and quality of soil organic matter (SOM) originating in the topsoil horizons of the central part of Wroclaw (SW of Poland). Fractional composition of SOM and humic substances (HS) analysis were performed. Elemental composition and CP MAS 13C NMR spectra for the humic acids (HA) were determined, and α (aromaticity) and ω (oxidation) ratios were calculated. Total organic carbon content ranged from 22.39 to 66.1 g kg–1, while that of total nitrogen ranged from 2.09 to 4.6 g kg1. In most analysed urban soils, the highest share in SOM was found for residual carbon (CR), while HA of low maturity was the predominant group over FA. CP MAS 13C NMR spectroscopy of HA molecules indicated the structure of the samples was dominated by compounds with low aromaticity cores and considerable contents of aliphatic components. In urban soils, efforts should be made to enhance organic matter transformation into more matured and stable forms via, e.g., compost application and chemical treatments, and lawn maintenance should be very strictly controlled and limited.

CP MAS 13C NMR Spectroscopy in Determination of Species-Specific Differences in Wood Composition

CP MAS 13C NMR Spectroscopy in Determination of Species-Specific Differences in Wood Composition

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.

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.

Sorption of pyridine-3-carboxylic acid and silver(I) from multicomponent aqueous solutions with Dowex-50 sulfonic cation exchange resin

The equilibrium distribution of pyridine-3-carboxylic acid, silver(I) ions, and protons between aqueous solutions and Dowex-50 sulfonic cation exchange resin was studied. The counter-ion composition of the cation exchange resin was determined by solving a system of equations for binary ion exchange selectivity coefficients and the mass balance equation. According to FT IR and CPMAS 13C NMR spectroscopy of solid samples, pyridine-3-carboxylic acid exists in the Dowex-50 phase as [H2L]+ cations. High distribution constants indicate that pyridine-3-carboxylic acid and silver can be concentrated in the polymer phase.

SOLID-STATE 13C NMR SPECTROSCOPY IN POLYSACCHARIDE ANALYSIS

Polysaccharides are high molecular weight compounds represented by long linear and/or branched chains of monosaccharide residues linked by a glycosidic bond. Currently, there is a huge and rapidly-growing interest in the chemistry of polysaccharides due to their widespread use in various spheres of human life. The study of polysaccharide structure is a complex and non-trivial task, and in this area solid-state 13C NMR spectroscopy are widely applied in recent years. The review analyzes the possibilities of solid-state 13C NMR spectroscopy for the study of polysaccharides and natural objects containing polysaccharides. The evolution of 13C solid-state NMR spectroscopy methods is shown with the main focus on the usage of the cross-polarization (CP) technique based on rotating the sample under the magic angle (MAS), since in this case the spectra are obtained without artifacts signals and with the best signal-to-noise ratio and high resolution. The review focuses on cellulose as the most widespread polysaccharide, in addition, the applicability of CP-MAS 13C NMR spectroscopy for the study of other polysaccharides, as well as plant materials, is considered. The represented examples clearly show that CP-MAS 13C NMR spectroscopy is the most powerful experimental method that allows to obtain information on both the composition and structure of polysaccharides, as well as the composition of various plant materials. Moreover, the combination of available equipment and various techniques of solid-state 13C NMR experiment will contribute to the progress of further research in the chemistry of polysaccharides and their derivatives.

Facile preparation of α,ω-diynes bearing a perfluoroalkylene linker –(CF2)n– (n = 4,6) and their application for Co- or Rh-catalyzed [2+2+2]cycloaddition reactions affording aromatic compounds with perfluoroalkylene units

α,ω-Diynes bearing a perfluoroalkylene linker HC≡C(CF2)nC≡H (n = 4,6) were obtained from commercially available α,ω-dienes H2C=CH(CF2)nCH=CH2 via bromination and dehydrobromination. In the presence of CoCl2-Zn-ZnI2 catalyst, the diyne HC≡C(CF2)4C≡H underwent [2+2+2] cycloaddition reactions with terminal alkynes to afford benzene derivatives fused with an octafluorocyclohexene moiety. In this reaction, trimerization of the diyne was observed as a major side reaction. Rh-catalyzed aromatization polymerization of the diyne HC≡C(CF2)6C≡H afforded an insoluble polymer consisting of a densely cross-linked, aromatic skeleton, which was characterized by solid-state CP-MAS 13C NMR and IR spectroscopy. This insoluble polymer exhibited high thermal stability, and engineering applications of the product polymer are being evaluated.

Green synthesis of quinolines via A3-coupling by using graphene oxide-supported Brønsted acidic ionic liquid

Graphene oxide-supported Bronsted acidic ionic liquid ([GrBenzImi]SO3H) has been prepared by covalent grafting of benzimidazole unit in the matrix of graphene oxide followed by reaction with 1,4-butane sultone and hydrochloric acid. [GrBenzImi]SO3H has been characterized by various techniques including Fourier transform infrared spectroscopy (FTIR), FT-Raman (FT-Raman spectroscopy), CP-MAS 13C NMR spectroscopy, thermogravimetric analysis, energy-dispersive X-ray analysis, Brunauer–Emmett–Teller surface area, X-ray diffraction, and transmission electron microscopy. [GrBenzImi]SO3H was successfully employed as heterogeneous catalyst in A3-coupling reaction of aryl aldehydes, anilines and phenylacetylene for the synthesis of 2,4-disubstituted quinolines using water/ethanol system (1:1) as green medium. [GrBenzImi]SO3H could be recycled six times without significant loss in the yield of product.

Synthesis of an oxygen-permeable block copolymer with catechol groups and its application in polymer-ceramic pressure-sensitive paint

An oxygen-permeable block copolymer, poly (2,2,2-trifluoroethyl-co-isobutyl methacrylate)-b-poly (N-acryloyldopamine) (FEM-b-PDOPA), in which the PDOPA segment acts as an adhesive section to attach TiO2 nanoparticles, was successfully synthesized via RAFT polymerization followed by a post-polymerization modification with dopamine. Conjugates of FEM-b-PDOPA with TiO2 nanoparticles were prepared by mixing them in chloroform and methanol. IR and solid-state CP-MAS 13C NMR spectroscopies clearly indicated the presence of FEM on the TiO2 nanoparticles. Thermogravimetric analysis of the resulting nanoparticles indicated that FEM-b-PDOPA, rather than FEM alone, was tightly bound to the TiO2 nanoparticles, and that the weight fraction was 2.5 wt%. Polymer-ceramic pressure-sensitive paint was prepared by mixing a luminescent dye, FEM, and TiO2 treated with either FEM-b-PDOPA or native TiO2. In comparison with the coating prepared using native TiO2, the pretreatment of TiO2 with FEM-b-PDOPA effectively reduced the photodegradation of the luminescent dye without deterioration in pressure and temperature sensitivity or dynamic response performance.

Graphene Oxide-Supported Ionic Liquid Phase Catalyzed Synthesis of 3,4-Dihydro-2H-naphtho[2,3-e][1,3]oxazine-5,10-diones

Graphene oxide-supported ionic liquid phase catalyst ([GrFemBenzImi]OH) has been prepared by covalent grafting of 1-N-ferrocenylmethyl benzimidazole in the matrix of functionalized graphene oxide followed by anion metathesis reaction. [GrFemBenzImi]OH has been characterized by fourier transform infrared (FT-IR) spectroscopy, fourier transform Raman (FT-Raman spectroscopy), CP-MAS 13C NMR spectroscopy, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD) and Brunauer–Emmett–Teller (BET) surface area. [GrFemBenzImi]OH served as a robust heterogeneous catalyst for the synthesis of bioactive 3,4-dihydro-2H-naphtho[2,3-e][1,3]oxazine-5,10-diones by reaction of formaldehyde, 2-hydroxy-1,4-naphthoquinone with structurally diverse aromatic anilines. Recyclability experiments were executed successfully for six consecutive runs.

Concepts and Misconceptions of Humic Substances as the Stable Part of Soil Organic Matter: A Review

In the last three decades, the concept of soil humic substances has been questioned in two main directions. Misinterpretations of CP MAS13C NMR spectroscopy led to the conclusion that soil organic matter is mainly aliphatic, questioning the theory of polymerization of humic substances from phenolic molecules. Conversely, some critics of humic substances assume that a great proportion of aromatic soil organic carbon originates from fire-affected carbon, often termed as black carbon (BC). However, the determination of BC in soil by two widely applied methods, the benzene polycarboxylic acid marker method and the UV method, is not reliable and seems to strongly overestimate the BC content of soils. The concept of humic substances continues to be relevant today. The polymerization of phenolic molecules that originate from the degradation of lignin or synthesis by microorganisms may lead to humic substances which can incorporate a variety of organic and inorganic molecules and elements. The incorporation, e.g., of triazines or surfactants into the humic matrix, leading to bound residues, illustrates that humic substances are important to explain central reactions in soil. Humic substances are also important to understand the availability of plant nutrients in soil, including P, Fe, and Cu, and they may have a direct effect on the growth of higher plants in soil. Therefore, there are good reasons to reformulate or to further develop the concepts and models of humic substances introduced and developed by M. Schnitzer, W. Flaig, W. Ziechmann, and F.J. Stevenson.

Thermal, Spectroscopic, and Crystallographic Analysis of Mannose-Derived Linear Polyols

The major diastereomer formed in the Barbier-type metal-mediated allylation of d-mannose has previously been shown to adopt a perfectly linear conformation, both in solid state and in solution, resulting in the formation of hydrogen-bonded networks and subsequent aggregation from aqueous solution upon stirring. Here, a comprehensive study of the solid state structure of both the allylated d-mannose and its racemic form has been conducted. The binary melting point diagram of the system was determined by differential scanning calorimetry analysis, and the obtained results, along with structure determination by single crystal X-ray diffraction, confirmed that allylated mannose forms a true racemate. Further examination by powder X-ray diffraction and CP MAS 13C NMR spectroscopy revealed polymorphism both in the pure enantiomer and in the racemate. In addition, the propargylated and hydrogenated analogues of allylated d-mannose were prepared and subjected to thermal and spectroscopic analyses. The crystal structure of the propargylated compound was successfully determined, showing a linear molecular conformation similar to that found for allylated d-mannose. Both new compounds likewise display aggregation behavior in water, further verifying that the low-energy linear conformation plays a significant role in this unusual behavior of these rodlike mannose derivatives.

MALDI-TOF, 13C NMR and FTIR analysis of the cross-linking reaction of condensed tannins by triethyl phosphate

Reaction of condensation and cross-linking of catechin monomer as a model of condensed (flavonoid) tannin extracts and of mimosa tannin itself, as well as of resorcinol with triethyl phosphate (TEP) have been investigated. FTIR, solid state CP-MAS 13C NMR, 31P NMR and MALDI-ToF spectroscopy studies revealed that reaction occurs mainly on the C3 of the flavonoid heterocycle ring and on the aromatic C4′ and C5′ carbons of the flavonoids B-ring, while TEP does not appear to react on the A-ring. A difference in the relative proportions of these two reaction sites for tannin and catechin has been noticed. The reactions appear to be dependent on the temperature. According to the thermogravimetric analysis, materials obtained from the reaction of tannin with TEP showed high thermal stability.

Semi-Continuous Heterophase Polymerization to Synthesize Nanocomposites of Poly(acrylic acid)-Functionalized Carbon Nanotubes

Two materials, pure poly(acrylic acid) (PAA) and nanocomposites with a matrix of PAA and carbon nanotubes (CNTs) as reinforcing agent were synthesized by semi-continuous heterophase polymerization (SHP). CNTs were prepared by a chemical vapor deposition technique and purified by steam. CNTs were characterized by a high resolution scanning electron microscopy (HRSEM) and Raman and Fourier transform infrared spectroscopies. Nanocomposites were prepared with: (i) purified CNTs (CNTsp) or (ii) purified and functionalized CNTs possessing an acyl chloride moiety (CNTsOCl). In both cases, the nanocomposites synthesis was carried out by in situ polymerization of acrylic acid (AA) by SHP. When CNTsOCl were used previously to the polymerization of AA, a series of specific amounts of CNTsOCl and AA were mixed to induce a chemical reaction between the carboxyl group of AA and the acyl chloride group of the CNTsOCl. The product, acrylic acid grafted to CNTsOCl (CNTsOCl-AA), was used to prepare the PAA-CNTsOCl nanocomposites. The PAA-CNTsOCl nanocomposites were characterized by HRSEM, Raman, FTIR and CPMAS 13C-NMR spectroscopies and also by thermogravimetric analysis (TGA). The results reveal that PAA-CNTsOCl nanocomposites were formed by PAA macromolecules grafted to CNTsOCl. The kinetic behavior observed for the synthesis of pure PAA or PAA-CNTsOCl nanocomposites by SHP was similar. Latexes of PAA-CNTsOCl nanocomposites were stable without formation of a precipitate of CNTsOCl for over 1.5 years, while latex prepared with CNTsp and PAA, was unstable and formation of a precipitate of CNTsp was observed immediately after its preparation. PAA-CNTsp nanocomposites were characterized only by TGA. Moreover, latex of the PAA-CNTsp nanocomposite that did not precipitate immediately after its preparation, turned into a gel; this gelation never occurred with the PAA-CNTsOCl nanocomposite latex.

Isolation and Characterization of Cellulose from Sweet Sorghum Bagasse

Sweet sorghum bagasse represents a potential low-cost biomass which can be valorized to produce different value-added lignocellulosic platform chemicals of economic importance. The focus of the present study is the pretreatment of sweet sorghum bagasse for efficient delignification, separation of pure cellulose and its structural characterization. Sweet sorghum bagasse was subjected to mechanical commutation followed by steam washing, organosolv extraction (methanol and toluene, 1:2) and alkaline hydrogen peroxide treatment for efficient delignification. Chemical analysis revealed that cellulose, hemicellulose and lignin content (per cent recovered) after different pretreatment was 720 g (98 %), 6 g (1.1 %) and 20 g (0.9 %), respectively. Structural characterization of untreated sweet sorghum bagasse and recovered cellulose was performed using FT-IR, CP-MAS 13C NMR spectroscopy, XRD, and thermogravimetric analyses. The cellulose preparation obtained after chemical pretreatments had typical cellulose structure with high crystallinity as compared to the untreated substrate. SEM micrographs revealed the surface topography wherein the waxy layer on the surface of this material disappeared and the texture became thinner and striated. The pretreatment methods employed were able to produce cellulose of high purity with >98 % lignin removal.

Heterogeneous para-phenylamino sulfonic acid ligand functionalized on MCM-41 derived from rice husk ash: Selective mono-alkylated products of tert-butylation of phenol

A new organo-inorganic hybrid material was prepared by immobilizing 3-(4-aminophenylamino)propane-1-sulfonic acid onto functionalized mesoporous MCM-41 via simple post-synthesis method. The hybrid organo MCM-41 preserved its hexagonal honey-comb configuration after both surface chemical modification and immobilization of sulfonic acid ligand. XRD analysis exhibited three well-resolved diffraction peaks corresponding to the highly ordered mesostructure. The five intense carbon peaks of solid-state CP-MAS 13CNMR spectroscopy confirmed the grafting of sulfonic acid ligand onto the well-structured MCM-41. Surface properties of the material revealed a pore size of 1.98nm and surface area of 468m2g−1. The catalytic performance of this hybrid material was tested in the alkylation of phenol with tert-butanol (TBA) and showed a high catalytic activity leading to 99.5% conversion of tert-butyl alcohol and high selectivity to monoalkylated products.

Chemical Modification of Kraft Lignin: Effect on Chemical and Thermal Properties

Esterified kraft lignins (KL) were prepared by reaction with maleic anhydride (MA), succinic anhydride (SA), and phthalic anhydride (PA) in acetone solutions. The esterified lignins were characterized using ATR-FTIR, solid state CP-MAS 13C NMR spectroscopy, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). PA modification resulted in the highest weight gain percent (WGP) when compared to MA and SA modifications. Spectroscopic analysis revealed decreases in hydroxyl content and increases in carbonyl (C=O) and ester groups of the modified KL as a result of esterification. The hydrophobic properties of the modified lignin increased. The MA- and SA-modified KL showed an increased thermal stability compared to unmodified KL. PA-modified lignin presented distinct thermal decomposition stages, which showed rapid degradation at lower temperature. The results of this study indicate that it is possible to change the basic properties of kraft lignin by anhydride modification to facilitate the production of high performance composites.

Surface-Bound Ruthenium Diimine Organometallic Complexes: Excited-State Properties.

Ruthenium complexes of the general formula [Ru(CO)(H)(L2)(L′2)][PF6] (L2 = trans-2PPh3, L′ = η2-4,4′-dicarboxybipyridine (1); L2 =trans-2Ph2PCH2CH2COOH, L′2 = bipyridine (2); L2 = Ph2PCHCHPPh2, L′ = η2-5-amino-1,10-phenanthroline (3); L2 = trans-2PPh3, L′2 = η2-4-carboxaldehyde-4′-methylbipyridine (4)) have been shown to have longer emission lifetimes and higher quantum yields in solution compared with more symmetrical molecules such as [Ru(bpy)3][Cl]2. Compound 4 is obtained as a mixture with the corresponding acetal, 4′. These less symmetrical complexes have been covalently immobilized on the surface of silica polyamine composites, and their photophysical properties have been studied. The surface-bound complexes have been characterized by solid-state CPMAS 13C, 31P, and 29Si NMR, UV–vis, and FT-IR spectroscopies. Excited-state lifetime studies revealed that, in general, the lifetimes of the immobilized complexes are 1.4 to 8 times longer than in solution and are dependent on particle size (300–500 μm versus 10–20 nm average diameter silica gels), polymer structure (linear poly(allylamine) versus branched poly(ethylenimine)), and the type of surface tether. One exception to this trend is the previously reported complex [Ru(bpy)2(5-amino-1,10-phenanthroline)][PF6]2 (5), where only a slight increase in lifetime is observed. Only minor changes in emission wavelength are observed for all the complexes. This opens up the possibility for enhanced heterogeneous electron transfer in photocatalytic reactions.