Solid-state 13C CPMAS Research Articles

Aspects of solid state 13C CPMAS NMR spectroscopy in coals from the Balkan peninsula

The cross-polarized magic-angle-spinning NMR (CPMAS-NMR) technique was used in this work to assess the carbon distribution in coals of different rank (peat, lignite, xylite, sub-bituminous coal) from important deposits in Greece and Bulgaria. The technique is assumed to be only semiquantitative due to a number of interferences, such as spinning side bands (SSB) in the spectra, paramagnetic species in the samples, and low or remote protonation of aromatic carbons. The Bulgarian sub-bituminous coal shows the greatest amounts of aromatic structures. The lignite sample from the Drama basin Northern Greece, is relatively unaltered and largely unlettered, and shows the greatest amounts of aliphatic groups. The 13C-NMR spectra of Pliocene lignites from endemic areas in Serbia and Montenegro and Bosnia, taken from published papers, show significantly more intense resonance's for methoxyl phenolic, and polysaccharide moieties compared to the Drama lignite NMR spectrum. Xylite reveals high contents of carbohydrates.

Effect of N content and soil texture on the decomposition of organic matter in forest soils as revealed by solid-state CPMAS NMR spectroscopy

N has a controlling effect on litter biodegradation in the forest floor, while stabilization of organic matter in the mineral soil may be influenced by physical parameters related to soil texture. In this study, in order to understand the processes involved in soil organic matter (SOM) formation, the chemical composition of SOM was followed and evaluated with regards to N contents and soil texture. Samples were taken on sites covered with Norway spruce and displaying contrasting values of C/N ratios in the forest floor. The chemical structure of OM was characterized using solid-state CPMAS 13C and 15N nuclear magnetic resonance (NMR) spectroscopy, along with Proton Spin Relaxation Editing (PSRE) sequences. Four groups of sampling sites were defined based on the NMR spectra of Oh and A horizons. In each group displaying similar NMR characteristics, N content and soil texture could be highly different among sites. Some Oh horizons with similar NMR spectra had very different N contents. Highly humified OM in Oh horizons were observed mainly on sites with low N contents. Some A horizons with different soil texture displayed similar OM chemical structure. High contents of O-alkyl C in some A horizons could originate from higher fresh root material input.

Adsorption of styrene sulfonate vs. polystyrene sulfonate on layered double hydroxides

The adsorption properties of a water-soluble polymer, polystyrene sulfonate (PSS), on the surface of a layered double hydroxide (LDH), Zn 2Al(OH) 6Cl· nH 2O, an anionic clay of the hydrotalcite type, were investigated and compared to the adsorption of the monomer, styrene sulfonate (vinylbenzene sulfonate (VBS)). PSS adsorption can be described by the Freundlich model and is of the S-type, while the adsorption of VBS is of the Langmuir type. Solid-state 1H and 13C CP MAS NMR experiments confirm the strong interaction between the adsorbed monomer and the LDH inorganic framework. The shielding of the resonance peak of the aromatic carbon attached to the sulfonate group is transmitted through the carbonaceous skeleton to the vinylic carbon, which is more deshielded. This phenomenon is induced by the electrostatic binding between the molecule and the clay surface. This situation is observed to a lesser extent for the polymer. The adsorption of polymer changes the pore size distribution, creating a larger macropore volume compared to the pristine chloride material and to the adsorbed monomer phase. This is explained by the entanglement of the polymer, pushing apart the stacked units of the LDH.

Morphology of Alternating Poly(ester amide)s Based on 1,4-Butylene Established by 13C Solid-State NMR Relaxation Measurements

Alternating poly(ester amide)s consisting of 1,4-butylene and diol spacing entities (4NTm and 4NTm,p) were studied using solid-state NMR techniques. The direct monitoring of the NMR relaxation behavior of different ester and amide moieties suggested a significant impact of spacer length on the molecular dynamics. Crystallization domains of the diol spacers of annealed 4NTm as well as 4NTm,p poly(ester amide)s were identified by means of solid-state CP-MAS 13C T1ρ relaxation measurements. From solid-state 1H T1ρ relaxation measurements, the thickness of the lamellae could be estimated including the domain sizes. Quantitative analysis of 13C CP-MAS buildup curves yielded information on the crystallinity of the spacer groups. The macroscopic parameter Tm correlates on a molecular level with (macro)molecular dynamics, thickness of the lamellae, and crystallinity of diol spacers.

Solid-State 13C NMR Study of Poly(vinyl alcohol) Gels

Poly(vinyl alcohol) (PVA) with 55% and 61% syndiotacticity, and their related dry and hydrated gels obtained by two different freeze–thawing cycles have been investigated using the solid-state 13C CP-MAS NMR technique. From a comparative analysis of the spectra, evidence was obtained that the gelation process largely disrupts the intramolecular hydrogen-bonded network of the PVA. The addition of water to the dry gels favours their swelling, destroying intra-chain hydrogen bonds between hydroxyl groups as a function of the degree of tacticity and the gelation procedure, and promotes the formation of new networks of interchain hydrogen bonds. Information on the dynamics of the polymeric domains in the kilohertz range has been obtained from the analysis of the spin relaxation times T1ρ(1H) and T1ρ(13C), indicating that homogeneous arrangements of the amorphous or swollen polymeric chains exist, independent of the preparation method or the tacticity of the PVA chains.

A Py–GC–MS and NMR spectroscopy study of organic nitrogen in Mangrove Lake sediments

Solid-state CP–MAS 13C and 15N nuclear magnetic resonance (NMR) spectroscopy and flash pyrolysis–gas chromatography–mass spectrometry (Py-GC–MS) techniques have been used to characterize the organic-rich sedimentary deposit from Mangrove Lake, Bermuda. The chemical nature of organic nitrogen in sediment samples from different depths was studied as it relates to the early diagenesis of proteinaceous material in the reducing marine environment. Although the majority of proteins were lost during early diagenesis, part of the proteinaceous material became resistant to proteolysis and chemical hydrolysis. The proteinaceous material is proposed to have survived early diagenesis via encapsulation by refractory, aliphatic organic matter.

Role of hydroxy-aluminosilicate ions (proto-imogolite sol) in the formation of humic substances

Little is known of the role of solution species of soil aluminosilicates in the formation of humic substances. Catalysis by hydroxy-aluminosilicate (HAS) ions, one of the major forms of soluble aluminum and silicon and the precursor of noncrystalline aluminosilicates in acidic natural environments, in catechol humification was investigated in this study by using UV-visible, FTIR, and solid state 13C CP–MAS NMR spectroscopies, X-ray diffractometry, atomic force microscopy, and elemental analysis. Hydroxy-aluminosilicate ions substantially promoted the oxidative polymerization and ring cleavage of catechol, resulting in the formation of black precipitates of humic macromolecules. This abiotic catalysis by HAS ions merits close attention in understanding the formation and related geochemistry of humic substances especially in acidic environments in temperate and subtropical regions.

Influence of the melamine content in melamine-urea-formaldehyde resins on formaldehyde emission and cured resin structure

The effect of melamine content in melamine-urea-formaldehyde (MUF) resins on the formaldehyde emission and resin structure was investigated using six MUF resins synthesized with different F/(M + U) and M/U molar ratios. The formaldehyde emission from the plywood decreased as the F/(M + U) molar ratio decreased and the M/ U molar ratio increased. In addition, the bond performance was enhanced as the M/U molar ratio increased in the MUF resins with a fixed F/(M + U) molar ratio. Quantitative solution13C-NMR spectra of MUF resins revealed that the MUF resins with a high melamine content consisted of more highly branched crosslinkage structure and free melamine compared to the resins with low melamine contents. Furthermore, solid-state13C CP-MAS NMR spectra of cured MUF resins proved that more methylol groups, dimethylene ether, and branched methylene structures were present in the MUF resins with a higher F/(M + U) molar ratio, leading to increased bond strength and formaldehyde emission. There is no significant difference in the linkage structure of the cured resins with the same F/(M + U) and different M/U molar ratios except the ratios of carbonyl carbon of urea and triazine carbon of melamine. Therefore, the lower formaldehyde emission from cured MUF resins with a higher M/U molar ratio might be ascribed to the stronger linkages between triazine carbons of melamine than those of urea carbons. Consequently, the melamine contributed to strong crosslinking linkages in the cured resin structures, leading to lower formaldehyde emission and better bond performance.

Carbon-13 solid-state NMR of soil organic matter - using the technique effectively

Solid-state 13C CPMAS NMR offers many options for characterizing carbon in soil organic matter (SOM). Its effectiveness, however, is often limited by a poor understanding of the techniques, and lack of hands-on access and training opportunities for students. Of nearly 250 modern NMR systems in Canada, approximately one is genuinely available for SOM studies, and there is poor communication between NMR operators and SOM users. While quantitative reliability can be addressed to some extent by multiple contact-time experiments or single-pulse (Bloch decay) spectra, it is also important to consider the effects of spectrometer background, spinning sidebands (especially with higher magnetic fields) and processing operations such as line-broadening, phasing and baseline correction. In many studies, more consideration needs to be given to instrument specifications, the type of information needed, and whether sample fractionation or pretreatment should be used. Structural information can be greatly enhanced by dipolar-dephasing and sideband suppression sequences. Sequences based on relaxation differences can reveal pools of carbon with different structures. Data analysis can be enhanced by principal component analysis, spectrum deconvolution and difference spectra. Studies of xenobiotics and C metabolism can be greatly aided by 13C-labeling. However, a key limitation to SOM applications remains the gap in culture and expectations of the users. Key words: Soil organic matter, 13C CPMAS NMR, Bloch decay, dipolar dephasing, spinning sidebands

Structural Characterization and Iron(III) Binding Ability of Dimeric and Polymeric Lignin Models

To understand the complexation in solution and the sorption of iron(III) on soluble and solid fractions of lignin, a dimeric model (guaiacyl-β-guaiacylglycerol ether, called β-O-4) and a polymeric model (dehydrogenation polymer resulting from polymerization of coniferyl alcohol) of lignin have been synthesized and characterized with chromatographic, solution, and solid state 13C CP-MAS NMR and XPS spectroscopies. The β-O-4 dimer is a monoacid (HL). Potentiometric studies in aqueous solution at 25°C and 1 mol L−1 ionic strength (KNO3) indicated formation of two stable complexes, FeL2+ and probably FeL(OH)+, which shows that the soluble fraction of lignin binds metals, indicating that they are transported by water through the soils. The binding of iron(III) on the DHP polymer was then investigated. The sorption experiments have shown a great affinity of iron for the solid with a maximum of adsorption since pH 5. A pulsed-ESR study has revealed surface oxidation by the iron(III) cation, which leads to iron(II) and semiquinonic radicals on the polymer surface, with a radical concentration of about 5×1017 spin/g.

Degree of oxidation of LDL determines differential gene expression in monocytes

Cuticular fractions of the important northern berries sea buckthorn (Hippophaë rhamnoides) and black currant (Ribes nigrum), and the suberized membrane of red peel potato (Solanum tuberosum var. Asterix), were investigated for the first time with solid state spectroscopic methods. In addition, the ester-bonded aliphatic monomers were analyzed as TMS derivatives by GC–MS after depolymerization with NaOMe catalyzed methanolysis. The fractions inspected by solid state 13C CP-MAS NMR and FT-IR spectroscopy included isolated cuticular and suberin-enriched membranes, i.e. raw cutin and suberin, the non-depolymerizable fractions and further cellulase- and pectinase-resistant fractions. Spectroscopic results supported the findings of the monomeric composition of ester-bound cutin, confirmed the presence of polysaccharides and an aromatic, possibly lignin-like, fraction and also suggested the presence of a non-degradable cutan-type polymer in the berry cuticular fraction. Black currant peel cutin and receptacle cutin were found to differ from each other in composition, notably in terms of the abundance of monomeric, aromatic and polysaccharide fractions. Some effect of latitudinal growth on the composition of cuticular fractions was observed for black currants grown in northern and southern Finland. The spectra of potato suberin were similar to the spectra of black currant receptacles, but the berry had even higher proportions of aromatic components.

Spectroscopic characterization of cyclic GMP in dimethylsulfoxide and water solutions

We report the spectroscopic characterization of cGMP, which has an important biological role as a second messenger. NMR and Raman spectroscopies were used to characterize the cGMPH and cGMPNa structure in solution (water and dimethylsulfoxide). The spectroscopic results show that for cGMPH in dimethylsulfoxide the N7 position is free and the proton is localized on the phosphate group. By addition of 1 and 2 HCl equivalents to cGMPNa in the same solvent the first equivalent protonates the phosphate group while the second is localized on the N7 position of the guanine ring. On the contrary, for cGMPH in water the proton is mainly localized on the N7 guanine ring with an equilibrium depending on pH. Therefore, the solvent has a major effect in determining the protonation site in cGMPH. Solid state CP-MAS 13C NMR spectrum of cGMPH suggests N7 protonation, phosphate group ionization and a sugar conformation different from that of the salt.

The nature of soil organic matter affects sorption of pesticides. 1. Relationships with carbon chemistry as determined by 13C CPMAS NMR spectroscopy.

The structural composition of soil organic matter (SOM) was determined in twenty-seven soils with different vegetation from several ecological zones of Australia and Pakistan using solid-state CPMAS 13C NMR. The SOM was characterized using carbon types derived from the NMR spectra. Relationships were determined between Koc (sorption per unit organic C) of carbaryl(1-naphthylmethylcarbamate) and phosalone (S-6-chloro-2,3-dihydro-2-oxobenzoxazol-3-ylmethyl O,O-diethyl phosphorodithioate) and the nature of organic matter in the soils. Substantial variations were revealed in the structural composition of organic matter in the soils studied. The variations in Koc values of the pesticides observed for the soils could be explained only when variations in the aromatic components of SOM were taken into consideration. The highly significant positive correlations of aromaticity of SOM and Koc values of carbaryl and phosalone revealed that the aromatic component of SOM is a good predictor of a soil's ability to bind such nonionic pesticides.

13C and 15N NMR shieldings of 1,2,4‐diazaphospholes in the solid state and in solution

The solid state 13C and 15N CPMAS NMR spectra of 3,5‐di‐tert‐butyl‐1,2,4‐diazaphosphole 4 and 3,5‐diphenyl‐1,2,4‐diazaphosphole 5 have been recorded. The X‐ray structure of the first compound was already known (it is a cyclic dimer with localized N–H protons) while the structure of the second cannot be determined due to the difficulty to grow suitable single crystals. NMR results pointed out that 4 is a “classical” compound while 5 is probably a tetramer showing Intermolecular Solid‐State Proton Transfer (ISSPT). GIAO/ab initio calculations have been carried out to estimate the absolute 1H, 13C and 15N shieldings. The agreement with the experimental chemical shifts is good enough to assign the signals of carbons C‐3 and C‐5.

Composition and distribution of organic matter in physical fractions of a rehabilitated mine soil rich in lignite-derived carbon

After open-cast mining operations in the eastern states of Germany, extremely acid overburden material with a high lignite content (up to 50 g OC/kg soil) is relocated and deposited at a spoil bank. For rehabilitation, these substrates are amended with alkaline ash from lignite-fired power stations and reforested with coniferous or broad-leaved trees. The aim of this study was to identify the allocation of lignite and recently formed humified compounds in soil compartments as separated by physical fractionation procedures. Samples were taken from the soil surface (0–5 cm, Ai horizon) and from the subsoil (1 m depth, Cv horizon) under red oak ( Quercus rubra, age 36 years). Organic matter in bulk soils as well as in particle-size and density fractions was analysed for elemental composition, magnetic susceptibility, chemical structure by solid-state 13C CPMAS NMR spectroscopy and lignite content by 14C activity measurements. The contribution of lignin to the particle size fractions was estimated using CuO oxidation. In the bulk soil as well as in the physical fractions, carbon species related to lignite and carbon species related to plant litter occur in mixture. The 2000–630 μm fraction was found to be dominated by plant litter compounds whereas the 630–6.3 μm fractions consist mainly of aromatic and aliphatic carbon, most probably indicative of lignite and carbonaceous particles which were added to the Ai horizon during amelioration and airborne contamination with lignite combustion products. In the <2.0 μm fraction, CuO oxidation indicated that aromatic C compounds are derived from lignite rather than from recent plant lignin compounds. Physical fractionation with subsequent characterisation of the organic matter present in the fractions revealed that recently formed soil organic matter (SOM) consists mainly of partly altered plant residues rather than humic substances.

Synthesis and Characterization of Syndiotactic Styrene−Ethylene Block Copolymers

Six samples of styrene−butadiene block copolymers (sPS−B 1−6) containing a range of styrene molar fractions (xS = 0.9−0.16) were prepared using MAO-activated CpTiCl3 and converted to the corresponding styrene-1-butene-ethylene terpolymers (sPS−PE, 1h−6h) through the selective hydrogenation of the unsaturated butadiene segments with p-toluenesulfonhydrazide. The monomer compositions and chemical microstructures of the sPS−PE copolymers were determined by 1H NMR (xS = 0.93−0.1) and 13C NMR, respectively. The chemical shift assignments of the monomer tetrads (SSSS, SSEE, EESE, EEbE, EEEE, SEES, EEES; S = styrene, E = ethylene, b = 1-butene) were also determined by 13C NMR as well as the average monomer block lengths (nS = 72−4; nE = 2−51). The block structure of the sPS−PE copolymers was further confirmed by DSC (differential scanning calorimetry), WAXD (wide-angle X-ray diffraction), and solid-state CP-MAS 13C NMR (cross polarization magic angle spinning) analysis. The sPS−PE samples with high styrene conte...

AlPO 4-41 aluminophosphate molecular sieve: a new reproducible synthesis route involving diisopropylformamide as template precursor

Until now, pure AlPO 4-41 aluminophosphate was difficult to synthesize, the product being often admixed with other microporous solids, such as AlPO 4-11 and/or AlPO 4-31. In this study, we propose a new reproducible synthesis route of AlPO 4-41. Nevertheless, some traces of an aluminophosphate hydrate, which decompose at 200°C co-crystallize. The AFO-type aluminophosphate is obtained from a quasi-non-aqueous system involving diisopropylformamide (DiPF) as solvent in addition to restricted amounts of water. During the synthesis, DiPF is decomposed into carbon monoxide and diisopropylamine. The latter is occluded into the AlPO 4-41 framework and acts as a template as the crystallization proceeds. The slow and in situ release of the amine in the reaction batch is a key factor for the formation of the AFO-type material. The as-synthesized AlPO 4-41 is characterized by chemical bulk analysis, XRD and solid state 13C CP MAS NMR spectroscopy.

Hybrid organic–inorganic gels containing perfluoro-alkyl moieties

Perfluoroalkyltrialkoxysilanes were prepared by hydrosilylation of the allylic or vinylic derivatives with trialkoxysilane or with trichlorosilane (followed by a quantitative methanolysis). The hydrolysis and polycondensation of these precursors were performed in the presence of tetrabutylammoniumfluoride (TBAF) as the catalyst, leading to a series of new polysilsesquioxanes, which were characterized by solid state 13C and 29Si CPMAS NMR. The porosity and surface area of these materials were determined by N 2 absorption experiments. Thermogravimetric analyses (TGA) were also performed. The surface properties of films prepared from these silsesquioxanes were studied by contact angle measurements. The hybrids having fluoroalkyl groups at the surface of the material showed a better thermostability and a higher hydrophobic and oleophobic character than their hydrocarbon analogues.

13C CPMAS studies of plant cell wall materials and model systems using proton relaxation-induced spectral editing techniques

The solid state 13C CPMAS NMR spectra of plant cell walls are often complex owing to superposition of resonances from different polysaccharides and the heterogeneity of the cell wall assembly. In this paper, we describe the application of a set of proton relaxation-induced spectral editing (PRISE) experiments which combine 1H relaxation properties (T1, T1ρ, T2) with 13C high resolution spectroscopy (CPMAS) to relate the dynamics of the plant cell walls and model systems to their domain structural details. With PRISE it has been found that in plant cell wall materials, cellulose is always associated with the long components of spin–lattice relaxation in both the laboratory and rotating frames whereas non-cellulose polysaccharides (pectin and hemicellulose) are associated with the short ones. For the proton T2 relaxation, cellulose is only associated with the short component (below 20 μs), pectin contributes to both the short component and the long one.

Preliminary communication 13C CPMAS NMR of 5,10,15,20-tetrakis(4-n-dodecylphenyl)-porphyrin: dynamics of aliphatic chains in discotic lamellar mesophases

Solid state 13C CPMAS NMR spectra of 5,10,15,20-tetrakis(4-n-dodecylphenyl)porphyrin (C12 TPP) have been studied to elucidate the microscopic structures and dynamics in the mesophases. The temperature dependence of 13C CPMAS NMR in the aliphatic regions is discussed mainly in relation to the phase transitions. The spectra for the aliphatic chains showed remarkable changes with the phase transition from crystal to lower mesophase (ML) and from lower to higher mesophase (ML). It was found that the aliphatic chains partially melt in the ML phase, while they melt totally in the ML phase. The spectra in the aromatic region did not vary greatly with the transitions from crystal to ML and from ML to ML, which probably means that the molecular D4h symmetries are distorted in these mesophases, as in the crystal, on the time scale observed by NMR (~kHz).