Solid-state 13C CPMAS Research Articles

Compositional relationships between organic matter in a grassland soil and its drainage waters

SummaryWe present a novel study of the compositional relationships between soil organic components extractable in aqueous extractants and those in sub‐soil drainage and surface runoff waters from the soil. The surface soil (0–20 cm) of a stagnogley in long‐term grassland was sequentially and exhaustively extracted in aqueous media at pH values of 7, 10.6 and 12.6. Extracts from the soils and their runoff and drainage waters were processed by the procedures of the International Humic Substances Society (IHSS), and fractionated into humic, fulvic, and XAD‐4 acids. Elemental, δ13C, δ15N, sugar, amino acids, and solid state CPMAS 13C NMR analyses were used to identify similarities and differences between the fractions from the different extracts. There were few differences between the compositions of drainage water samples taken 1 year apart, and these had compositional features similar to those from the more highly oxidized fractions isolated from the soil at pH 7. There were significant differences between the humic components from the drainage waters and isolated from the soil at pH 7 and those of the humic fractions isolated at the higher pH values whose compositions are more clearly related to origins in plants. The compositions of the surface runoff waters indicate origins in transformed plant and animal manures on the soil surface, whereas those of the deep drainage waters originate in more extensively transformed materials, including products of microbial metabolism. The resin technique used in the fractionation allowed the isolation of novel humic acid fractions from the soil extracts, in particular at pH 7 and 12.6. These fractions clearly originated in microbial sources, were rich in saccharides and amino acids (peptides), and low in lignin‐derived components.

Carbon-13 CP-MAS NMR studies of some lichens of the Genus Cladonia section Cladina

The solid state 13C CP-MAS NMR (carbon-13 Cross Polarisation Magic Angle Spinning Nuclear Magnetic Resonance) technique has the potential of monitoring the chemical composition in the solid state of an intact plant sample [1,2].

Phosphoric acid-doped poly(1-vinyl-1,2,4-triazole) as water-free proton conducting polymer electrolytes

The development of anhydrous proton conducting membrane is important for the operation of polymer electrolyte membrane fuel cell (PEMFC) at intermediate temperature (100–200 °C). In the present work, poly(1-vinyl-1,2,4-triazole), PVTri was produced by free radical polymerization of 1-vinyl-1,2,4-triazole with a high yield. The molecular weight of the homopolymer was measured via gel permeation chromatography (GPC) and M w was found to be 104,216 g/mol. The structure of the homopolymer was proved by solid state 13C CP-MAS NMR spectroscopy. The polymer was doped with phosphoric acid at various molar ratios x = 1 and x = 2. The proton transfer from H 3PO 4 to the triazole rings was proved with Fourier-transform infrared spectroscopy (FT-IR). Thermogravimetry (TG) analysis showed that the samples are thermally stable up to approximately 250 °C. Differential scanning calorimetry (DSC) results illustrated the homogeneity of the materials as well as the plasticizing effect of the dopant. The electrochemical stability of the materials was studied by cyclic voltammetry (CV). The proton conductivity of these materials increased with dopant concentration and the temperature. In the anhydrous state, the proton conductivity of PVTri 1 H 3PO 4 is 5 × 10 − 3 S/cm at 150 °C and the conductivity of PVTri 2 H 3PO 4 was 4 × 10 − 3 S/cm at 140 °C.

Structural studies of pyrido[1,2- c]pyrimidine derivatives by 13C CPMAS NMR, X-ray diffraction and GIAO/DFT calculations

New 1-aryl- or 1-heteroaryl-piperazinylbutyl derivatives with pyrido[1,2- c]pyrimidine imide moiety, with the expected higher selectivity to 5-HT 1A receptors, have been synthesized. Five hydrochlorides and one base were studied by solid-state 13C CPMAS NMR spectroscopy. 13C chemical shifts indicated that the piperazine ring nitrogen N-1 was protonated. The crystal structure of the base (with 4′F, 3″-CF 3 substituents) was determined by X-ray crystallography. The pyridopyrimidine fragment is essentially planar, and aromatic substituent at C4 is twisted by 59.0°. The crystals are stabilized mainly by the C O…H C interactions. The analysis was completed by theoretical calculations of the shielding constants at the GIAO/DFT (B3LYP/6-311+G ∗∗) level.

Structure–solid-state CPMAS 13C NMR correlation in palladacycle solvates (pseudo-polymorphs) with a transformation from Z′ = 1 to Z′ = 2

The dinuclear µ-acetato-µ-benzophenone iminato palladium complex [{(C∧N)Pd}2(µ-OAc)(µ-NCPh2)] (1) [C∧N = N,N-dimethylbenzylamine-κN,κC)] is prepared by reaction of [{(C∧N)Pd(µ-OAc)}2] with benzophenone imine and [NBu4]OH in ethanol. The dinuclear palladacycle 1 can crystallize with different solvents molecules as 1·1.5C6H5CH3, 1·0.25C6H5CH3 (Z′ = 2), 1·1.5C6H6 and 1·C6H14 (n-hexane) upon hexane diffusion into a toluene, benzene or CH2Cl2 solution, respectively. The structure of 1·0.25C6H5CH3 with two palladacycle molecules and two partly occupied toluene molecules in the asymmetric unit (Z′ = 2) is a consequence of partial toluene solvent loss from 1·1.5C6H5CH3 (Z′ = 1) as was followed by solid-state CPMAS 13C NMR. The transformation from Z′ = 1 to Z′ = 2 (crystal “on the way”?) toluene solvate can proceed in a solid-state single-crystal-to-crystal transition as evidenced from multiple single-crystal X-ray diffraction studies, also when the crystals are still in their mother liquor. During this transformation the remaining toluene crystal solvent becomes “locked in” (immobile from static 2H (D) NMR, only lost above 80° from TGA) and the crystals of 1·0.25C6H5CH3 (Z′ = 2) remain crystalline in air in the absence of mother liquor or toluene, different from the other solvates. A rotational disorder of one of the benzene molecules in 1·1.5C6H6 (Z′ = 1) around its pseudo-six-fold axis is supported by the line-shape analysis of the static 2H (D) spectrum.

Spectral and chemical evidence for the direct formation of carboxylic groups in aerobically oxidised water-soluble fullerenes

The synthesis of oxidised water-soluble fullerenes, prepared by chemically-induced aerobic oxidation, yields functionalised carbon cluster structures, which are oxidised by the covalent insertion of different oxygen units. Their strictly pH-dependent behaviour in aqueous solutions appears to be properly ascribed to the existence of directly attached carboxylic moieties. The presence of these groups, which are usually neglected and underestimated, has been thoroughly investigated. Several concurrent spectral (UV–VIS, XPS, solid-state 13C CPMAS NMR, FT-IR, Raman, EDAX, TGA-MS, ESI-MS) and chemical (acid–base behaviour, salt precipitation by metal-complexation, carboxylic functionalisation) methods have provided a definitive set of consistent evidence, indicating for the first time the direct linkage of carboxylic groups on water-soluble fullerenes prepared in this manner.

Conjugation of kojic acid with chitosan

Direct and non-direct conjugation of kojic acid with chitosan was carried out according to the following approaches: (a) covalent binding of chlorokojic acid to chitosan via free amino groups, and (b) complexation of kojic acid with iron(III) bound to chitosan. Obtained products were analysed by organic elemental analysis and spectroscopic methods. The maximal degree of substitution was ∼0.2 mol/mol for the chitosan–kojic acid conjugates. The triple chitosan–FeO(OH)–kojate complex contained these components in the molar ratio of 1:0.48:0.07. UV–vis absorption, FT-IR and Raman spectra of the obtained products showed characteristic bands of bound kojic acid and thus confirmed that both ways of kojic acid binding were efficient. Solution 1H NMR and solid state 13C CP-MAS NMR spectra of the chitosan–kojic acid conjugates supported the predicted way of 4-oxypyranone binding to chitosan. UV–vis absorption spectra of the chitosan films subsequently modified with ferric chloride and kojic acid indicated that the ligand molecules are bound to peripheral iron(III) cations of FeO(OH) subcolloidal particles arranged on the surfaces of a film.

Ru nanoparticles stabilized by organosilane fragments: Influence of the initial Si/Ru ratio and thermal stability

The decomposition of the organometallic ruthenium precursor [Ru(COD)(COT)] (COD: 1,5-cyclooctadiene; COT: 1,3,5-cyclooctatriene) in mild conditions (20 °C, 3 bar H2) in n-pentane leads, in the presence of octylsilane (H3SiC8H17) to the formation of stable Ru nanoparticles with narrow size distribution. The solids obtained after washing and drying were fully characterized by elemental analysis, TEM with EDX, infra red measurements as well as solid state 13C CP-MAS NMR investigations. The influence of the initial octylsilane/Ru(COD)(COT) ratio ranging from 0.2 to 2.0 was studied. It was observed that the size of the nanoparticles decreases with the initial Si/Ru ratio. The thermal stability of these nanoparticles (Si/Ru = 1) was also studied and as expected the size of the particles drastically increases after treatment under H2 at 500 °C, while surprisingly under neutral atmosphere, there is only a slight increase.

Sulfonic acid functionalized mesoporous silicas and organosilicas: Synthesis, characterization and catalytic applications

Ethane bridged mesoporous organosilicas and MCM-41 having sulfonic acid groups in the pore channels were prepared by co-condensation method as well as grafting method, using 3-mercaptopropyltriethoxysilane (3-MPTS) as the sulfur precursor. TEM and N 2 sorption isotherm analysis revealed that the mesoporous structural ordering is retained after the functionalization and modifications of organic groups while FT-IR, Raman, XPS and solid-state 13C CP MAS NMR shows the presence of sulfonic acid groups and the stability of the mesoporous framework. The catalytic activity of the developed materials was evaluated in the liquid phase Claisen–Schmidt condensation reaction of acetophenone with benzaldehyde, to probe the effect of mesoporous support surfaces as well as the role of preparation methods. Results showed that sulfonic acid functionalized ethane–silica samples were more active, selective and stable than the conventional sulfonic acid containing mesoporous catalysts.

Synthesis, characterization, and cadmium(II) uptake of iminodiacetic acid-modified mesoporous SBA-15

An organic–inorganic hybrid mesoporous material, iminodiacetic acid (IDA)-modified mesoporous SBA-15, was prepared by a two-step post-grafting method. By means of solid-state 13C CP-MAS NMR, thermogravimetic analysis (TGA), Fourier transform infrared (FT-IR), as well as X-ray photoelectron spectroscopy (XPS), the structural and physicochemical properties of the materials were characterized. The cadmium(II) uptake experiments show that the iminodiacetic acid-modified mesoporous SBA-15 (IDA-SBA-15) exhibits excellent ability to remove cadmium(II) from aqueous solutions. The cadmium(II) adsorption isotherm of iminodiacetic acid-modified mesoporous SBA-15 (IDA-SBA-15) is in good accordance with the Langmuir equation.

Cerium(III/IV) and Cerium(IV)–Titanium(IV) Citric Complexes Prepared in Ethylene Glycol Medium

Cerium(III/IV) and Ce(IV)–Ti(IV) citric complexes were synthesized in ethylene glycol medium under conditions similar to those of the polymerized complex method (PCM). Solution phase 1H, 13C NMR, solid state 13C CP MAS NMR and IR spectroscopy, and X-ray powder diffractometry were used to characterize the composition and structure of the synthesized products. Thermal decomposition of the isolated complexes was studied and a scheme of the processes taking place is proposed. Complexes of Ce(III) can be prepared at low temperature (40°C), only. In the presence of Ti(IV) ions, the oxidation takes place even at this temperature. A mixed-metal nature of the Ce(IV)–Ti(IV) complexes is established. The comparison between their composition and the one of analogous lanthanide(III)–Ti(IV) citrates contributes to the elucidation of the complexation process mechanism in the case of the PCM application. The increased charge of the complexation agent in the Ce4+–Ti4+ complex (in comparison with Ln3+–Ti4+ citrates) is “compensated” by the increase of the relative number of the ligands with deprotonated OH group.

Cadmium tri- tert-butoxysilanethiolates: Structural and spectroscopic models of metal sites in proteins

Syntheses and crystal structures of two molecular, heteroleptic cadmium complexes with CdS 2NO 2 and CdS 2N 2 kernels are described. Bis(tri- tert-butoxysilanethiolate)(1-methylimidazole)cadmium(II) and bis(tri- tert-butoxysilanethiolate)bis(1-methylimidazole)cadmium(II) coexist at equilibrium in chloroform solutions with varying concentrations of bis[bis(tri- tert-butoxysilanethiolate)cadmium(II)] and 1-methylimidazole. The equilibrium is characterized by solution 113Cd NMR spectra. Solid state CP MAS 13C, 29Si, 113Cd NMR data for the complexes are also reported, analyzed and compared with the results obtained for cadmium-substituted proteins. The similarities and differences between the structures of cadmium complexes and their zinc analogues are discussed.

Synthesis and mechanical properties of quaternary salts of chitosan-based films for food application

A novel method is described to synthesize quaternary salts of chitosan with dimethylsulfate and subsequently cast films. In an attempt to improve both mechanical and hydrophobic characteristics, the chitosan was previously modified by N-alkylation, introducing 4, 8 and 12 carbons moieties into the polymeric chain. Analysis by FTIR and solid-state CP-MAS 13C NMR spectroscopy confirmed the success of both alkylation and quaternization processes. The average degree of quaternization of these N-methylated derivatives was calculated to be 35%. DMA measurements indicated that chitosan and its derivative films are typically brittle materials, exhibiting similar non-linear viscoelastic behaviors. The films of unmodified chitosan have a very small strain (∼2.8%), though they were the most resistant films (Young's modulus = 2283 MPa; tensile strength >44.0 MPa). In general, the alkyl-chitosan derivatives appear to be more plastic than chitosan films but less resistant, e.g., for butyl chitosan: maximum strain = 13.1%; tensile strength = 13.4 MPa and Young's modulus = 171 MPa. Conversely the quaternization reaction increased the hardness of the parent sample, viz. for quaternary salt of dodecyl chitosan: maximum strain = 2.6%; tensile strength = 38.3 MPa and Young's modulus = 1792 MPa.

Synthesis and Polymerization of a Four-Arm Star with Pendent Cyclopentadienyliron Moieties

The synthesis of the title complex was achieved via the reaction of a η6-p-dichlorobenzene-η5-cyclopentadienyliron cation with an organic four-arm core to produce the tetrairon complex. This tetrairon-containing core was subsequently polymerized via nucleophilic aromatic substitution with various dinucelophiles such as 4,4′-thiobenzenethiol, bisphenol-A, 4,4′-(1-phenylethylidene)bisphenol, 4,4′-biphenol, bis(4-hydroxyphenyl)methane, producing five different cross-linked cationic organoiron polymers. Another cross-linked polymer was produced via direct polymerization of the four-arm organic core with the η6-p-dichlorobenzene-η5-cyclopentadienyliron cation. Due to the poor solubility of these cross-linked polymers, solid-state 13C CPMAS NMR was performed in order to verify that polymerization was successful. Thermogravimetric analysis (TGA) revealed that following the decoordination of the cyclopentadienyliron moieties, the polymers were thermally stable. Differential scanning calorimetry (DSC) showed that the polymers exhibited glass transition temperatures (T g’s) ranging from 104 to 146°C.

Amphiphilic PPESK- g-PEG graft copolymers for hydrophilic modification of PPESK microporous membranes

Amphiphilic graft copolymers comprising poly(phthalazinone ether sulfone ketone) (PPESK) backbones and poly(ethylene glycol) (PEG) side chains were synthesized and blended into PPESK casting solutions to prepare hydrophilic and anti-fouling microporous membranes. The graft copolymer was prepared by a modified Williamson etherification method. Sodium alkoxide of methoxyl PEG (PEG–ONa) was used to react with chloromethylated PPESK (CMPPESK). FT-IR spectroscopy, 1H NMR and solid-state 13C CP-MAS NMR analysis confirmed the covalent linking of PEG with PPESK backbones. The incorporation ratio of PEG calculated from 1H NMR was in agreement with that from TGA tests. The graft products were added into PPESK casting solutions to prepare composite porous membranes using phase inversion method. X-ray photoelectron spectroscopy (XPS) and water contact angle examinations indicated that the grafting copolymers were preferentially excluded to the membrane-coagulant interface during membrane forming, contributing the membranes with improved hydrophilicity and surface wettability. Compared with the neat membrane, the blend membranes exhibited a larger surface pore size and less susceptible to protein fouling.

Synthesis of amphiphilic poly(phthalazinone ether sulfone ketone)-graft-poly(ethylene glycol) graft copolymers via Williamson etherification

Amphiphilic graft copolymers consisting of poly(phthalazinone ether sulfone ketone) (PPESK) backbones and poly(ethylene glycol) (PEG) side chains were synthesized via reaction of chloromethylated PPESK (CMPPESK) with a sodium alkoxide of methoxyl PEG (PEG- ONa). The reactive precursor, CMPPESK, was prepared by the chloromethylation of PPESK with chloromethylether (CME) using concentrated H2SO4 as reaction medium. FTIR spectroscopy, 1H-NMR and Solid-state 13C CP-MAS NMR analysis confirmed the covalent linking of PEG with PPESK backbones. The PEG content in the graft copolymers from 1H-NMR analysis varied from 21.0 to 37.2 wt %, which was approximately in agreement with that calculated from TGA tests. The graft products have good solubility in many aprotic polar solvents and can be slightly swelled by water and ethanol, but water insoluble. Contact angle measurements revealed that the hydrophilicity of PPESK was significantly improved by the introduction of PEG graft chains, indicating the graft copolymer is a potential hydrophilic additive for PPESK membranes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007.

Rotational Dynamics in a Crystalline Molecular Gyroscope by Variable-Temperature 13C NMR, 2H NMR, X-Ray Diffraction, and Force Field Calculations

A combination of solid-state 13C CPMAS NMR, 2H NMR, X-ray-determined anisotropic displacement parameters (ADPs), and molecular mechanics calculations were used to analyze the rotational dynamics of 1,4-bis[3,3,3-tris(m-methoxyphenyl)propynyl]benzene (3A), a structure that emulates a gyroscope with a p-phenylene group acting as a rotator and two m-methoxy-substituted trityl groups acting as a stator. The line shape analysis of VT 13C CPMAS and broad-band 2H NMR data were in remarkable agreement with each other, with rotational barriers of 11.3 and 11.5 kcal/mol, respectively. The barriers obtained by analysis of ADPs obtained by single-crystal X-ray diffraction at 100 and 200 K, assuming a sinusoidal potential, were 10.3 and 10.1 kcal, respectively. A similar analysis of an X-ray structure solved from data acquired at 300 K suggested a barrier of only 8.0 kcal/mol. Finally, a rotational potential calculated with a finite cluster model using molecular mechanics revealed a symmetric but nonsinusoidal potential that accounts relatively well for the X-ray-derived values and the NMR experimental results. It is speculated that the discrepancy between the barriers derived from low and high-temperature X-ray data may be due to an increase in anharmonicity, or to disorder, at the higher temperature values.

Preparation of a mercaptopropyl bonded silica intermediate in supercritical carbon dioxide: Synthesis, characterisation and chromatography of a quinine based chiral stationary phase

This research examines the preparation of a mercaptopropyl bonded silica intermediate in supercritical carbon dioxide (sc-CO 2) and the subsequent conversion in sc-CO 2 to a quinine derived chiral stationary phase (CSP). The effects of reaction temperature, pressure and time on the surface coverage of the silica intermediate were investigated when porous silica particles (Exsil-Avanti, 3 μm) were reacted with 3-trimethoxymercaptopropylsilane in sc-CO 2. We present results which demonstrate that a stable mercaptopropyl bonded silica intermediate can be successfully prepared under supercritical conditions of 40 °C, 483 bar, in a substantially reduced reaction time of 1 h with superior surface coverages compared to organic solvent based methods. The further utility of this supercritical fluid technology was demonstrated by the free radical addition of a quinine derived chiral selector onto a mercaptopropyl bonded silica intermediate in sc-CO 2. This supercritical fluid generated chiral stationary phase (CSP) was utilised for the direct LC enantioseparation of a series of 3,5-dinitrobenzoyl (DNB) amino acids. Bonded silica samples were characterised using elemental analysis, diffuse reflectance infrared fourier transform (DRIFT) spectroscopy, solid state 13C and 29Si CP-MAS NMR spectroscopy, and thermogravimetric analysis (TGA). This supercritical fluid functionalisation approach offers an efficient and cleaner alternative to existing organic solvent based approaches for the preparation of bonded silica phases.

Immobilization of Ru(II) complex on functionalized SBA-15 and its catalytic performance in aqueous homoallylic alcohol isomerization

SBA-15-like mesoporous silicas functionalized with high contents of organic amine groups were synthesized by co-condensation of tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTES) in the presence of triblock copolymer P123 under acidic conditions. This method provided mesoporous silica with APTES: TEOS molar ratio ranging from 1:15 to 1:6. Further immobilization of dichlorotris(triphenylphosphine)-ruthenium(II) complex onto the functionalized support led to the formation of highly efficient and recoverable heterogeneous catalyst (Ru-AP). Characterizations using XRD, TEM and N 2 adsorption–desorption isotherms demonstrated that the NH 2-modified SBA-15 still retained highly ordered mesopore arrays even after immobilization of ruthenium complexes. Solid state 29Si MAS NMR and 13C CP MAS NMR and Raman investigations confirmed the presence of organic amine groups and RuCl 2(PPh 3) 3 complex on silica frameworks. The Ru-AP heterogeneous catalyst exhibited almost the same activity and selectivity as the corresponding RuCl 2(PPh 3) 3 homogeneous catalyst in the water mediated isomerization of 1-phenyl-3-buten-1-ol. The superiority of the Ru-AP was that it could be easily separated from the reaction system and used repetitively without obviously losing activity and selectivity at least for four times.

Isolation and seasonal effects on characteristics of fulvic acid isolated from an Australian floodplain river and billabong

Fulvic acids from an Australian floodplain river and billabong were isolated using DEAE and DAX-8 resins, and characterised with the use of size exclusion chromatography and solid-state CP-MAS (13)C NMR spectroscopy. Differences between the two resin isolates were evident. Fulvic acids isolated using DEAE-cellulose had higher apparent M(n) and M(w) values, while the DAX-8 resin showed a slight preference for aliphatic components. Fulvic acids from the river and billabong had the same functional groups present, however, the river fulvic acids had higher apparent M(n) (number average molecular weight) and M(w) values (weight average molecular weight), and were more polydisperse than the billabong fulvic acid. There were no significant changes in the characteristics of the fulvic acid isolated from the river at four sampling times: summer, autumn, winter and spring. In contrast, fulvic acids isolated from a billabong displayed seasonal variation in molecular weights. This work emphasizes the importance in ecological studies of isolation procedure for the operationally defined fulvic acids.