Accurate quantification of aromaticity and nonprotonated aromatic carbon fraction in natural organic matter by 13C solid-state nuclear magnetic resonance

An improved approach for accurately determining the aromatic carbon fraction (fa) and nonprotonated aromatic carbon fraction (faN) in natural organic matter by solid-state 13C NMR is described. Quantitative peak areas are obtained from direct polarization 13C nuclear magnetic resonance (NMR) under high-speed magic angle spinning (MAS). The problem of overlap between aromatic and alkyl carbon resonances around 90-120 ppm in 13C NMR spectra is solved by a 13C chemical shift anisotropy (CSA) filter technique. After correction for residual spinning sidebands, an accurate value of the aromaticity fa is obtained. To obtain a quantitative faN fraction, dipolar dephasing was adapted for high-speed MAS 13C NMR; the separation of the signals of nonprotonated alkyl and aromatic carbons was achieved by CSA filtering plus dipolar dephasing. The method is demonstrated on a peat humic acid, yielding fa = 45 +/- 2% and faN = (0.64 +/- 0.07) x 45%.     

New structural information on a humic acid from two-dimensional 1H-13C correlation solid-state nuclear magnetic resonance

New information on the chemical structure of a peat humic acid has been obtained using a series of two-dimensional 1H-13C heteronuclear correlation solid-state NMR (HETCOR) experiments with different contact times and with spectral editing by dipolar dephasing and 13C transverse relaxation filtering. Carbon-bonded methyl groups (C-CH3) are found to be near both aliphatic and O-alkyl but not aromatic groups. The spectra prove that most OCH3 groups are connected directly with the aromatic rings, as is typical in lignin. As a result, about one-third of the aromatic C-O groups is not phenolic C-OH but C-OCH3. Both protonated and unprotonated anomeric O-C-O carbons are identified in the one- and two-dimensional spectra. COO groups are found predominantly in OCHn-COO environments, but some are also bonded to aromatic rings and aliphatic groups. All models of humic acids in the literature lack at least some of the features observed here. Compositional heterogeneity was studied by introducing 1H spin diffusion into the HETCOR experiment. Comparison with data for a synthetic polymer, polycarbonate, indicates that the separation between O-alkyl and aromatic groups in the humic acid is less than 1.5 nm. However, transverse 13C relaxation filtering under 1H decoupling reveals heterogeneity on a nanometer scale, with the slow-relaxing component being rich in lignin-like aromatic-C-O-CH3 moieties and poor in COO groups.     

Alginate monomer composition studied by solution- and solid-state NMR – A comparative chemometric study

The potential of using ¹H high-resolution (HR) magic angle spinning (MAS) nuclear magnetic resonance (NMR) of alginates suspended in D₂O or ¹³C cross-polarisation (CP) MAS NMR of alginate powders as an alternative method to the traditional ¹H solution-state NMR method for the analysis of the alginate monomer composition (mannuronate (M)/guluronate (G) ratio) has been investigated. The MAS NMR experiments can be performed directly on the intact alginate powders and thereby avoiding the relatively time-consuming and labour intensive sample preparation required for the traditional solution-state experiment. A total of 42 different sodium alginate samples were analysed and it was found that the M/G ratio derived from the HR-MAS NMR spectra were comparable to the M/G ratio calculated from the solution-state NMR spectra. However, both these methods overestimated the M/G ratio of samples with high calcium content. In contrast, the ¹³C CP-MAS NMR spectra were not affected by residual calcium in the samples and thus provided more consistent measurements independent on physico-chemical phenomena such as partial solubility, viscosity and interactions with ions. It is concluded that ¹³C CP-MAS NMR is a most suitable candidate for accurate analysis of the M/G ratio of intact alginate powders.     

Binding of 2,4,6-trinitrotoluene, aniline, and nitrobenzene to dissolved and particulate soil organic matter

The distribution of TNT* (the sum of TNT and its degradation products), aniline, and nitrobenzene between particulate organic matter (POM), dissolved soil organic matter (DOM), and free compound was studied in controlled kinetic (with and without irradiation) and equilibrium experiments with mixtures of POM and DOM reflecting natural situations in organic rich soils. The binding of TNT* to POM was fast, independent of irradiation, and adsorption isotherms had a great linear contribution (as determined by a mixed model), indicative of a hydrophobic partitioning mechanism. The binding of TNT* to DOM was slower, strongly enhanced under nonirradiated conditions, and adsorption isotherms were highly nonlinear, indicative of a specific interaction between TNT derivatives and functional groups of DOM. Nitrobenzene was associated to both POM and DOM via hydrophobic partitioning, whereas aniline binding was dominated by specific binding to POM and DOM functional groups. On the basis of nitrobenzene and TNT* adsorption parameters determined by a mixed Langmuir + linear model, POM had 2-3 times greater density of hydrophobic moieties as compared to DOM. This difference was reflected by a greater (O + N)/C atomic ratio for DOM. The sum of C-C and C-H moieties, as determined by X-ray photoelectron spectroscopy (XPS), and the sum of aryl-C and alkyl-C, as determined by solid-state cross-polarization magic-angle spinning (CP-MAS) 13C NMR, could only qualitatively account for differences in adsorption parameters. Aliphatic C was found to be more important for the hydrophobic partitioning than aromatic C. On the basis of nonlinear adsorption parameters,the density of functional groups reactive with aniline and TNT derivatives was 1.3-1.4 times greater in DOM than in POM, which was in fair agreement with 13C NMR and XPS data for the sum of carboxyl and carbonyl groups as potential sites for electrostatic and covalent bonding. We conclude that in contaminated soils characterized by continuous leaching of DOM, formation of TNT derivatives (via biotic and abiotic reductive degradation) and their preference for specific functional groups in DOM may contribute to a significant transportation of potentially toxic TNT compounds into surface waters and groundwaters.     

CP/MAS 13C NMR技术分析酸提取对烟草果胶产率和结构的影响

为研究烟草果胶的精细结构和掌握果胶提取的关键因素,采用交叉极化/魔角旋转固态核磁光谱技术(CP/MAS13C NMR)考察了酸提取条件(pH、温度和提取时间)对烟草果胶产率、纯度(质量分数)及结构的影响。结果表明:①在pH 1.5和85℃条件下提取1.5 h时,烟草果胶得率最高,为10.87%,但在pH 2.0和95℃条件下提取1.5 h时,聚半乳糖醛酸(PGA)的纯度最高,为78.4%。②提取条件对烟草果胶的结构也有一定的影响,pH=1.5~2.5时,果胶的甲酯度(DM)和乙酰度(DA)均随pH升高而增大,随温度升高而降低,随提取时间延长而显著下降。      

Conformation and location of amorphous and semi-crystalline regions in C-type starch granules revealed by SEM,NMR and XRD

The conformations and locations of amorphous and semi-crystalline regions in C-type starch granules from Chinese yam were evaluated by a combination of morphology and spectroscopy studies during acid hydrolysis. Scanning electron micrographs showed that amorphous or less crystalline areas were essentially located in the centre part of C-type starch granules, whereas the semi-crystalline and amorphous growth rings were found mainly in the outer part of the granules. ¹³C cross-polarization magic angle spinning NMR (¹³C CP/MAS NMR) showed that amorphous regions were hydrolyzed faster than the crystalline ones. In addition, B-type polymorphs were shown to be hydrolyzed more rapidly than A-types. Powder X-ray diffraction (XRD) also revealed that the B-polymorph was hydrolyzed more rapidly than the A-type. XRD showed that the amorphous or less crystalline areas were mainly located in the core of starch granules, while the amorphous growth rings are distributed toward the outside of the granules and alternatively arranged with semi-crystalline growth rings. The amorphous or less crystalline areas predominantly consisted of the B-polymorph whereas the outer semi-crystalline and amorphous growth rings were mostly composed of the A-polymorph.     

Granular structure and allomorph position in C-type Chinese yam starch granule revealed by SEM,C CP/MAS NMR and XRD

The crystalline microstructure and polymorphism of C-type starch from Chinese yam were evaluated by scanning electron microscope (SEM), ¹³C cross-polarization magic-angle spinning NMR (¹³C CP/MAS NMR) and powder X-ray diffraction (XRD) technique and acid hydrolysis method. Morphological changes during acid hydrolysis showed that the amorphous or the less crystalline areas were essentially located at the center part of C-type starch granules whereas the semi-crystalline and amorphous growth rings were found mainly in the outer part of the granules. ¹³C CP/MAS NMR and XRD results revealed that B-type allomorph was hydrolyzed more rapidly than A-type one. The amorphous or less crystalline areas were predominantly composed of B-allomorph whereas the outer semi-crystalline and amorphous growth rings were mostly composed of A-type allomorph. The A- and B-type allomorph coexisted in the individual C-type starch granule. B-type allomorph basically existed at the center part of the granules which was surrounded by the A-type allomorph in the peripheral part of granules.     

Cross-polarization/magic-angle spinning 13C nuclear magnetic resonance study of cellulose I-ethylenediamine complex

Complete assignments of the cross-polarization/magic-angle spinning (CP/MAS) 13C nuclear magnetic resonance (NMR) spectrum of the cellulose I-ethylenediamine (EDA) complex, which is the intermediate of the reaction from cellulose I to cellulose III(I), were performed. In this paper, we used the 13C-enriched cellulose that was biosynthesized by Acetobacter xylinum ATCC10245 strain from culture medium containing D-(2-13C), D-(3-13C), or D-(5-13C)glucose as a carbon source. After conversion into cellulose I-EDA complex by sufficient EDA treatment, the CP/MAS 13C NMR spectra of the 13C-enriched cellulose I-EDA complexes were measured. As a result, 13C resonance lines of each carbon of the cellulose moiety in the complex appeared as a singlet, suggesting that all glucose residues of the complex are magnetically equivalent. The difference in chemical shifts for each carbon between cellulose I-EDA and cellulose I(alpha), I(beta), and III(I), respectively, suggests that the conformation of the cellulose chains for cellulose I-EDA differs from that for cellulose I(alpha), I(beta), and III(I). In addition, fitting analysis of the 13C spectrum of Valonia cellulose I-EDA complex revealed that the complex contains one EDA molecule per two glucose residues in the cellulose chain.     

The structure of C-type Rhizoma Dioscorea starch granule revealed by acid hydrolysis method

Scanning electron microscope (SEM), X-ray powder diffraction (XRD) and cross polarisation/magic-angle spinning (CP/MAS) ¹³C nuclear magic resonance (NMR) have been used for the structural characterisation of C-type starch granule during acid hydrolysis. SEM shows that the amorphous areas mainly locate the core part of C-type starch granules, while the crystalline areas mainly exist in the peripheral region of starch granules. XRD analysis reveals that the B-type polymorph present in the C-type starch granule are preferentially degraded or degraded faster than the A-type polymorph. NMR spectra confirm that the amorphous regions in the starch granules are firstly hydrolysed and could be hydrolysed completely as long as the hydrolysis time is sufficient. After 40 days of hydrolysis, the acid-modified starch shows typical A-type characteristics upon analysis of the XRD pattern or the ¹³C CP/MAS NMR spectra.     

Analysis of atomic scale chemical environments of boron in coal by 11B solid state NMR

Atomic scale chemical environments of boron in coal has been studied by solid state NMR spectroscopy including magic angle spinning (MAS), satellite transition magic angle spinning (STMAS), and cross-polarization magic angle spinning (CPMAS). The (11)B NMR spectra can be briefly classified according to the degree of coalification. On the (11)B NMR spectra of lignite, bituminous, and sub-bituminous coals (carbon content of 70-90mass%), three sites assigned to four-coordinate boron ([4])B with small quadrupolar coupling constants (≤0.9 MHz) are observed. Two of the ([4])B sites in downfield are considered organoboron complexes with aromatic ligands, while the other in the most upper field is considered inorganic tetragonal boron (BO(4)). By contrast, on the (11)B NMR spectra of blind coal (carbon content >90mass%), the ([4])B which substitutes tetrahedral silicon of Illite is observed as a representative species. It has been considered that the organoboron is decomposed and released from the parent phase with the advance of coal maturation, and then the released boron reacts with the inorganic phase to substitute an element of inorganic minerals. Otherwise boron contained originally in inorganic minerals might remain preserved even under the high temperature condition that is generated during coalification.     

Decomposition of adsorbed VX on activated carbons studied by 31P MAS NMR

The fate of the persistent OP nerve agent O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate (VX) on granular activated carbons that are used for gas filtration was studied by means of 31P magic angle spinning (MAS) NMR spectroscopy. VX as vapor or liquid was adsorbed on carbon granules, and MAS NMR spectra were recorded periodically. The results show that at least 90% of the adsorbed VX decomposes within 20 days or less to the nontoxic ethyl methylphosphonic acid (EMPA) and bis(S-2-diisopropylaminoethane) {(DES)2}. Decomposition occurred irrespective of the phase from which VX was loaded, the presence of metal impregnation on the carbon surface, and the water content of the carbon. Theoretical and practical aspects of the degradation are discussed.     

Variation in phenanthrene sorption coefficients with soil organic matter fractionation: the result of structure or conformation?

Sorption of phenanthrene to varying soil types was investigated to better understand sorption processes. Humic acid and humin fractions were isolated from each soil sample, and sorption coefficients were measured by batch equilibration. Samples were characterized by carbon analysis and 13C cross polarization magic angle spinning (CP/ MAS) nuclear magnetic resonance (NMR) spectroscopy. Measured organic carbon-normalized sorption coefficients (Koc) of the fractions were greater in all cases when compared to the soils. The humin fractions exhibited greater Koc values than did source samples, suggesting that fractionation may reorganize organic matter in humin resulting in an increased availability of and/or more favorable sorption domains. Mass balance calculations revealed that the sum of sorption to the fractions is greater than sorption to the whole sample. The greatest difference between sorption values was found to occur with the mineral soils, suggesting that clay minerals influence the physical conformation of soil organic matter (SOM) and availability of sorption domains. The mass balance, sorption data, and a lack of consistent trends between observed Kco values and solid-state 13C NMR data suggest that the physical conformation of SOM and chemical characteristics both play important roles in sorption processes.     

Solid-state and multidimensional solution-state NMR of solid phase extracted and ultrafiltered riverine dissolved organic matter

In this study we used multidimensional solution-state NMR to elucidate the differences in the chemical composition of solid phase extracted and ultrafiltered DOM isolates. DOM was isolated from water sampled from an oligotrophic river, the River Tagliamento (Italy). The recovery of total DOM was up to 42% with both isolation techniques. In addition to 1- and 2-D solution-state NMR, we also applied 1-D solid-state 13C NMR spectroscopy for DOM characterization. 13C NMR spectroscopy only produced broad overlapping resonances, thus allowing a bulk characterization of DOM composition. However, it demonstrated that the bulk chemical composition of the two DOM fractions exhibited minor spatial-temporal changes. The 2-D experiments (TOCSY, HMQC) showed that the solid phase extracted hydrophobic DOM contained predominantly aliphatic esters, ethers, and hydroxyl groups, whereas the ultrafiltered DOM was comprised partially of peptides/protein, with further evidence for a small amount of aliphatic/fatty acid material. Sugars were present in both DOM fractions. The results show the two isolation techniques selected for different suites of compounds within the bulk DOM pool.     

彩色棉中色素对纤维微结构的影响

应用X-射线衍射、固体核磁共振(CP／MAS^13C NMR)等现代测试手段对彩色棉进行研究。结果表明：色素的存在影响了纤维结晶的形成，去除色素有利于提高结晶度、增大结晶尺寸；彩色棉纤维中色素主要分布在胞腔内，部分在次生胞壁的纤维素中；超临界CO2萃取和碱精练加工后，彩色棉纤维中色素的分布发生了显的变化。     

13C CP/MAS NMR光谱法分析烟草果胶的含量和结构

采用CP/MAS 13C NMR光谱法分析烟草果胶的含量和结构。对烟草果胶进行了优化提取后, 再对其13C NMR光谱图C-6吸收峰区域进行了详细研究, 用于计算果胶中半乳糖醛酸(GalA)、甲酯度(DM) 和乙酰度(DA) 的含量, 并就建立的定量方法与经典的色谱法和重量法进行了比较。结果表明, CP/MAS 13C NMR光谱法测定烟草样品中果胶的含量是可靠的, 化学位移和峰面积可用来计算烟草果胶分子的组成、甲酯度和乙酰度, 同步实现烟草中果胶的含量和结构分析。      

Chemical characterization and sorption capacity measurements of degraded newsprint from a landfill

Newsprint samples collected from 12-16 ft (top layer (TNP)), 20-24 ft (middle layer (MNP)), and 32-36 ft (bottom layer (BNP)) below the surface of the Norman Landfill (NLF) were characterized by infrared (IR) spectroscopy, cross-polarization, magic-angle spinning 13C nuclear magnetic resonance (CP-MAS 13C NMR) spectroscopy, and tetramethylammonium hydroxide (TMAH) thermochemolysis gas chromatography/mass spectrometry (GC/MS). The extent of NLF newsprint degradation was evaluated by comparing the chemical composition of NLF newsprint to that of fresh newsprint (FNP) and newsprint degraded in the laboratory under methanogenic conditions (DNP). The O-alkyl/alkyl, cellulose/lignin, and lignin/resin acid ratios showed that BNP was the most degraded, and that all three NLF newsprint samples were more degraded than DNP. 13C NMR and TMAH thermochemolysis data demonstrated selective enrichment of lignin over cellulose, and TMAH thermochemolysis further exhibited selective enrichment of resin acids over lignin. In addition, the crystallinity of cellulose in NLF newsprint samples was significantly lower relative to that of FNP and DNP as shown by 13C NMR spectra. The yield of lignin monomers from TMAH thermochemolysis suggested that hydroxyl groups were removed from the propyl side chain of lignin during the anaerobic decomposition of newsprint in the NLF. Moreover, the vanillyl acid/aldehyde ratio, which successfully describes aerobic lignin degradation, was not a good indicator of the anaerobic degradation of lignin on the basis of the TMAH data. The toluene sorption capacity increased as the degree of newsprint degradation increased or as the O-alkyl/alkyl ratio of newsprint decreased. The results of this study further verified that the sorbent O-alkyl/ alkyl ratio is useful for predicting sorption capacities of natural organic materials for hydrophobic organic contaminants.     

The use of simultaneous 1H & 31P magic angle spinning nuclear magnetic resonance measurements to characterize energy metabolism during the conversion of muscle to meat

In order to investigate the potential of magic angle spinning nuclear magnetic resonance (MAS NMR) in the elucidation of post‐mortem metabolism in muscle biopsies, simultaneous ¹H and ³¹P MAS NMR measurements were made continuously on post‐mortem (20 min to 24 h) muscle longissimus samples from rabbits. The animals had either been or not been given adrenaline (0.5 mg kg^?1 4 h pre‐slaughter) to deplete stores of muscle glycogen. The intracellular pH was calculated from ¹H spectra, and the post‐mortem rate of formation of lactate was followed and quantified. Comparison of measurements made on muscle samples from rabbits treated with adrenaline with measurements made on muscle samples from untreated rabbits revealed significant effects of adrenaline treatment on both pH (pH24 h = 6.42 vs. pH24 h = 5.60) and formation of lactate (16 mmol g^?1 vs. 65 mmol g^?1). The ³¹P NMR spectra were used to follow the rate of degradation of ATP and phosphocreatine. The present study clearly shows that MAS NMR has potential for the study of post‐mortem energy metabolism.     

Identification of black carbon derived structures in a volcanic ash soil humic acid by Fourier transform ion cyclotron resonance mass spectrometry

Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), coupled with cross-polarization magic angle spinning 13C nuclear magnetic resonance (NMR) spectroscopy and Kendrick mass defect analysis, was used to study the molecular composition of an aromatic carbon-rich humic acid extracted from a dark black soil from Iwata, Japan. Black carbon, produced by the incomplete combustion of fossil fuels and organic matter, has been suggested as a major component of humic acids having intense peaks in the aromatic and carboxyl regions of the 13C NMR spectrum. Taking advantage of the high resolving power of FT-ICR MS to make precise formula assignments, three different types of highly carboxylated polycyclic aromatic compounds were identified in the sample: linearly fused aromatic structures, aromatic structures linked by carbon-carbon single bonds, and highly condensed aromatic structures. These carboxylated aromatic structures have a low mass defect in their mass spectra due to their abundance of oxygen and deficiency of hydrogen. This mass defect is observed in the vast majority of peaks present in the entire mass spectrum, differentiating them from structures that are hydrogen-rich (e.g., fatty acids, proteins, carbohydrates). Thus, we conclude that the bulk of the sample analyzed is comprised of these heavily carboxylated, hydrogen-deficient, condensed aromatic structures, features believed to be characteristic of black carbon-like material.     

Fluorescence excitation-emission matrix regional integration to quantify spectra for dissolved organic matter

Excitation-emission matrix (EEM) fluorescence spectroscopy has been widely used to characterize dissolved organic matter (DOM) in water and soil. However, interpreting the > 10,000 wavelength-dependent fluorescence intensity data points represented in EEMs has posed a significant challenge. Fluorescence regional integration, a quantitative technique that integrates the volume beneath an EEM, was developed to analyze EEMs. EEMs were delineated into five excitation-emission regions based on fluorescence of model compounds, DOM fractions, and marine waters or freshwaters. Volumetric integration under the EEM within each region, normalized to the projected excitation-emission area within that region and dissolved organic carbon concentration, resulted in a normalized region-specific EEM volume (phi(i,n)). Solid-state carbon nuclear magnetic resonance (13C NMR), Fourier transform infrared (FTIR) analysis, ultraviolet-visible absorption spectra, and EEMs were obtained for standard Suwannee River fulvic acid and 15 hydrophobic or hydrophilic acid, neutral, and base DOM fractions plus nonfractionated DOM from wastewater effluents and rivers in the southwestern United States. DOM fractions fluoresced in one or more EEM regions. The highest cumulative EEM volume (phi(T,n) = sigma phi(i,n)) was observed for hydrophobic neutral DOM fractions, followed by lower phi(T,n) values for hydrophobic acid, base, and hydrophilic acid DOM fractions, respectively. An extracted wastewater biomass DOM sample contained aromatic protein- and humic-like material and was characteristic of bacterial-soluble microbial products. Aromatic carbon and the presence of specific aromatic compounds (as indicated by solid-state 13C NMR and FTIR data) resulted in EEMs that aided in differentiating wastewater effluent DOM from drinking water DOM.     

Characterization of water-soluble organic carbon in urban atmospheric aerosols using solid-state 13C NMR spectroscopy

Solid-state 13C nuclear magnetic resonance (NMR) spectroscopy has been used to investigate the distribution of carbon functional groups in urban Atlanta aerosol fine (PM2.5) particles. Carbonaceous aerosol particles comprise a significant fraction of the ambient particle mass and are environmentally significant as they may influence radiative and cloud-nucleating properties and can also produce adverse health effects upon inhalation. The water-soluble organic carbon (WSOC) fraction was extracted from multiple 24 h integrated high-volume quartz filter samples and further separated into recovered hydrophobic and hydrophilic fractions using an approach similar to that used to extract humic and fulvic acids from aqueous samples. Solid-state 13C NMR results indicate that WSOC in urban atmospheric aerosol particles is mostly aliphatic in nature (approximately 95% by C mass) with major contributions from alkyl and oxygenated alkyls (approximately 80%), carboxylic acid (approximately 10%), and aromatic functional groups (approximately 4%). The aromatic C is associated with the recovered hydrophobic fraction of WSOC. These spectra have been compared to the 13C NMR results obtained from Suwannee River humic acid and a fractionated biomass burning sample. WSOC, and more importantly, its recovered hydrophobic fraction, is found to be only qualitatively similar to aqueous humic material. The biomass burning sample is significantly different from urban Atlanta WSOC and is composed of substantial amounts of sugar derivatives and phenolic compounds, as expected. The NMR results demonstrate the potential of this technique to investigate aerosol WSOC composition and to study its variations with changes in parameters such aerosol sources.