Quantitative 13C Nuclear Magnetic Resonance Research Articles

Vinyl and methyl-ester groups in the insoluble polymer drug patiromer identified and quantified by solid-state NMR

Patiromer (Veltassa®) is a crosslinked, insoluble co-polymer drug used as a nonabsorbent potassium binder, approved for treatment of hyperkalemia. Quantitative solid-state 13C nuclear magnetic resonance (NMR) analysis with comprehensive peak assignment, component quantification, and calculation of mole and weight fractions of monomer units was performed on three doses of patiromer. The workflow is documented in detail. Spectrally edited solid-state 13C NMR spectra of patiromer show =CHn peaks of matching intensity at 116 and 141 ppm, characteristic of -CH=CH2 vinyl groups. Similar spectral features can be observed in earlier studies but were previously ignored. In this study, the vinyl signals are well-resolved in a 2-s direct polarization (DP) spectrum without and with dipolar dephasing, which confirms that these sp2-hybridized carbons are bonded to hydrogen and partially mobile, consistent with vinyl side groups from incompletely reacted divinyl crosslinkers. The vinyl groups account for 1.6% of all carbon, 3% of the monomer units, and nearly 1/3 of the crosslinkers. Furthermore, an unexpected OCH3 moiety accounting for ∼1.2% of all carbons was identified by spectral editing; its chemical shift of 54 ppm is more consistent with a methyl ester than with a methyl ether. It can originate from incomplete hydrolysis of ∼6% of methyl-2-fluoroacrylate, the main monomer of patiromer. Characteristic cross peaks in two-dimensional 1H–13C heteronuclear correlation NMR confirm the presence of the vinyl and OCH3 groups. Trace amounts of xanthan gum are also detected. The quantitative 13C NMR spectrum of patiromer has been matched in a simulation using a model with five monomer units.

Carbon capture in polymer-based electrolytes.

Nanoparticle organic hybrid materials (NOHMs) have been proposed as excellent electrolytes for combined CO2 capture and electrochemical conversion due to their conductive nature and chemical tunability. However, CO2 capture behavior and transport properties of these electrolytes after CO2 capture have not yet been studied. Here, we use a variety of nuclear magnetic resonance (NMR) techniques to explore the carbon speciation and transport properties of branched polyethylenimine (PEI) and PEI-grafted silica nanoparticles (denoted as NOHM-I-PEI) after CO2 capture. Quantitative 13C NMR spectra collected at variable temperatures reveal that absorbed CO2 exists as carbamates (RHNCOO- or RR'NCOO-) and carbonate/bicarbonate (CO32-/HCO3-). The transport properties of PEI and NOHM-I-PEI studied using 1H pulsed-field-gradient NMR, combined with molecular dynamics simulations, demonstrate that coulombic interactions between negatively and positively charged chains dominate in PEI, while the self-diffusion in NOHM-I-PEI is dominated by silica nanoparticles. These results provide strategies for selecting adsorbed forms of carbon for electrochemical reduction.

Research of novel polyamine-based biphasic absorbents for CO2 capture using alkanolamine to regulate the viscosity and mechanism analysis

Biphasic solvent has attracted widespread attention in CO2 chemical absorption technology due to its significant potential for reducing capture energy consumption. However, the high viscosity of CO2-rich phase after phase split could lead to issues such as high flow resistance, low heat transfer efficiency, and phase separation instability in application. To address these limitations, a strategy of using alkanolamine as a viscosity regulator for biphasic solvents was proposed. Diethanolamine(DEA), an alkanolamine regulator, was introduced to a system of polyamine/amide absorbent, and then a novel biphasic solvent of diethylenetriamine (DETA)/diethanolamine(DEA)/N, N-Dimethylacetamide(DMAC)/water(H2O) was developed. The viscosity of the CO2-rich phase solvent was reduced to 19.02 mPa⋅s, a significant decrease compared to the solution without DEA regulation. The novel solvent exhibited a high cyclic capacity of 2.08 mol/kg, which was 43.4 % higher than that of the solution without DEA, and a desorption rate twice as high as 30 wt% monoethanolamine(MEA). Quantitative 13C Nuclear Magnetic Resonance (NMR) and Molecular Dynamics (MD) simulations revealed the phase split and viscosity regulation mechanisms. It was proved that DETA species, especially carbamates, tend to self-aggregate with each other due to intermolecular hydrogen bonding with the CO2 loading increases, which leads to phase split and high viscosity of the saturated solution. Through DEA regulation, the protonation of carbamates and the generation of HCO3–/CO32– were promoted, which weakened the self-aggregation of carbamates species, decreasing the viscosity and the regeneration energy of saturated CO2-rich phase solution. The regeneration energy reached 2.19 GJ/ton CO2, which exhibited a 42.4 % reduction compared with that of 30 wt% MEA.

Correlation between the Molecular Structure and Viscosity Index of CTL Base Oils Based on Ridge Regression.

In China, coal-to-liquid (CTL) lube base oils with ultrahigh viscosity index (VI) are very popular. Since it consists of chain alkanes only and can be precisely characterized by molecular structures alone, quantitative 13C nuclear magnetic resonance (NMR) data are used to generate the average structural parameters (ASPs) of CTL base oil. In this work, the ASPs and bulk properties of CTL base oils were tested and compared with those of mineral base oils. Based on the test results, the correlation between the unique property of CTL base oil VI and ASPs was analyzed. To eliminate the effect of significant multicollinearity among the input variables, statistical methods such as ordinary least-squares (OLS), stepwise regression, and ridge regression methods were used to build the VI prediction model. The main findings are as follows: according to the 13C NMR spectrum, CTL base oils had a significantly higher content of isomeric chain alkanes (including several branching structures) than mineral base oil, while the content of cycloalkanes was zero; among several branched structures, the one with the largest difference in content is structure S67, which has the highest percentage in the iso-paraffin structures, all above 25.5% in CTL base oils and below 21.39% in mineral oils; according to the distillation curve of the simulated distillation (SimDist) analysis, CTL base oils with similar carbon number distribution showed lower boiling points, narrower distillation ranges, and higher distillation efficiencies than mineral base oil; correlation analysis showed that the average chain length (ACL), normal paraffins (NPs), and structure S67 caused the CTL base oil to exhibit a higher VI; and from 13C NMR data, the ridge regression model was used to obtain regression coefficients consistent with reality, and the expected VI could be well predicted with a correlation coefficient of 0.935.

Ambient-Pressured Acid-Catalysed Ethylene Glycol Organosolv Process: Liquefaction Structure-Activity Relationships from Model Cellulose-Lignin Mixtures to Lignocellulosic Wood Biomass.

Raising the awareness of carbon dioxide emissions, climate global warming and fossil fuel depletion has renewed the transition towards a circular economy approach, starting by addressing active bio-economic precepts that all portion amounts of wood are valorised as products. This is accomplished by minimizing residues formed (preferably no waste materials), maximizing reaction productivity yields, and optimising catalysed chemical by-products. Within framework structure determination, the present work aims at drawing a parallel between the characterisation of cellulose–lignin mixture (derived system model) liquefaction and real conversion process in the acidified ethylene glycol at moderate process conditions, i.e., 150 °C, ambient atmospheric pressure and potential bio-based solvent, for 4 h. Extended-processing liquid phase is characterized considering catalyst-transformed reactant species being produced, mainly recovered lignin-based polymer, by quantitative 31P, 13C and 1H nuclear magnetic resonance (NMR) spectroscopy, as well as the size exclusion- (SEC) or high performance liquid chromatography (HPLC) separation for higher or lower molecular weight compound compositions, respectively. Such mechanistic pathway analytics help to understand the steps in mild organosolv biopolymer fractionation, which is one of the key industrial barriers preventing a more widespread manufacturing of the biomass-derived (hydroxyl, carbonyl or carboxyl) aromatic monomers or oligomers for polycarbonates, polyesters, polyamides, polyurethanes and (epoxy) resins.

Position-specific isotope effects during alkaline hydrolysis of 2,4-dinitroanisole resolved by compound-specific isotope analysis, 13C NMR, and density-functional theory

Compound-specific isotope analysis (CSIA), position-specific isotope analysis (PSIA), and computational modeling (e.g., quantum mechanical models; reactive-transport models) are increasingly being used to monitor and predict biotic and abiotic transformations of organic contaminants in the field. However, identifying the isotope effect(s) associated with a specific transformation remains challenging in many cases. Here, we describe and interpret the position-specific isotope effects of C and N associated with a SN2Ar reaction mechanism by a combination of CSIA and PSIA using quantitative 13C nuclear magnetic resonance spectrometry, and density-functional theory, using 2,4-dinitroanisole (DNAN) as a model compound. The position-specific 13C enrichment factor of O–C1 bond at the methoxy group attachment site (εC1) was found to be approximately -41‰, a diagnostic value for transformation of DNAN to its reaction products 2,4-dinitrophenol and methanol. Theoretical kinetic isotope effects calculated for DNAN isotopologues agreed well with the position-specific isotope effects measured by CSIA and PSIA. This combination of measurements and theoretical predictions demonstrates a useful tool for evaluating degradation efficiencies and/or mechanisms of organic contaminants and may promote new and improved applications of isotope analysis in laboratory and field investigations.

Evaluating the bio-application of biomacromolecule of lignin-carbohydrate complexes (LCC) from wheat straw in bone metabolism via ROS scavenging

Lignin-carbohydrate complexes (LCC) arebiomacromolecules that can be obtained from different biomass. Even some works have shown the LCC can efficiently scavenge the intracellular and endogenous reactive oxygen species (ROS), while little work has been carried out to investigate the potential application of LCC for ROS-related treatment in biological filed, especially for the treatment of periprosthetic osteolysis in vivo. In this work, Lignin-rich (LCC-A) and carbohydrate-rich (LCC-B) fractions in wheat straw are isolated and used as the ROS scavenger to promote osteoblast differentiation and inhibit osteoclast differentiation. The chemical composition and structures are characterized by high performance anion exchange chromatography (HPAEC) and nuclear magnetic resonance (NMR) technologies (quantitative 13C NMR and 2D-HSQC NMR), respectively. The results showed LCC-A possesses higher in vitro ROS-scavenging ability than LCC-B (89.8% vs 57.8%) and to inhibit osteoclast differentiation, whereas LCC-B more significantly activates cellular antioxidant activities via the KEAP1-NRF2-ARE pathway (218.5% vs 438.0% in the level of HO-1), thus promoting osteoblast differentiation in an inflammatory environment. Moreover, the therapeutic administration of LCC-A and LCC-B for Ti-particle-induced osteolytic murine calvariae showed both of them positively regulate and restore the bone metabolism, while preventing calvaria impairment. Hence, LCC from wheat straw exhibits efficient bone protective effects, suggesting it may be used as the promising ROS scavenger for clinical treatment of periprosthetic osteolysis.

Fourier Transform Infrared and Solid State 13C Nuclear Magnetic Resonance Spectroscopic Characterization of Defatted Cottonseed Meal-Based Biochars

Conversion to biochar may be a value-added approach to recycle defatted cottonseed meal, a major byproduct from the cotton industry. In this work, complete slow pyrolysis at seven peak temperatures ranging from 300 to 600°C in batch reactors was implemented to process cottonseed meal into biochar products. Elemental analysis, attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy and quantitative solid state 13C nuclear magnetic resonance (NMR) spectroscopy were applied to characterize raw meal and its derived biochar products. The biochar yield and organic C and total N recoveries decreased as the peak pyrolysis temperatures was elevated. However, most of the mineral elements including P in cottonseed meal were retained during pyrolysis and became enriched in biochar as a result of the decreased mass yield. The spectral data showed that pyrolysis removed the functional groups of biopolymers in cottonseed meal, producing highly aromatic structures in biochars. With increasing pyrolysis temperature, alkyl structures decreased progressively in the biochar products and became negligible at higher temperatures (550 and 600°C). Quantitative analysis of FT IR data revealed that the values of a simple 3-band (1800,1700, and 650 cm-1)-based R reading of the biochars were linearly related to the pyrolysis temperature, and showed strong correlations with decreasing aromaticity and increasing alkyl, aliphatic C-O/N and carbonyl signal intensities in the 13C NMR spectra. Therefore, the cheaper and faster FT-IR measurement could be used as a routine conversion indicator of pyrolysis of lignocellulosic biomass instead of the more expensive and time-consuming NMR spectroscopy.

Substituent distribution of propyl cellulose studied by nuclear magnetic resonance

A series of propyl cellulose (PC) samples with different degrees of substitution (DS) ranging from 0.34 to 2.02 were prepared by a slurry method using propyl bromide as the etherification reagent. Two-dimensional nuclear magnetic resonance (NMR) studies were performed to identify the 1H and 13C chemical shifts of eight anhydroglucose units (AGUs) in PC chains including un-, 2-mono-, 3-mono-, 6-mono-, 2,3-di-, 2,6-di-, 3,6-di-, and 2,3,6-tri-substituted ones. In addition, the mole fractions (χ) of these AGUs in the studied PC samples and their changes with DS were determined from the quantitative 13C NMR spectra. The obtained χ−DS profiles were different from those of methyl and ethyl celluloses prepared by a similar slurry method, indicating that the molecular sizes of the substituent reagents utilized for cellulose ethers strongly affected their substituent distributions.

Catalytic Fast Pyrolysis of Poly (Ethylene Terephthalate) (PET) with Zeolite and Nickel Chloride.

The pyrolysis of poly (ethylene terephthalate) (PET) in the presence of ZSM-5 zeolite and NiCl2 as a catalyst was studied at different temperatures under N2 atmosphere. Quantitative 13C nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FT-IR) were applied to characterize the waxy and solid residue. The carboxyl and aliphatic hydroxyl groups in the waxy residue have been greatly depleted after the use of zeolite during pyrolysis on the basis of the results of 13C NMR and FT-IR analysis. The proportion of aromatic hydroxyl groups increased by 21.82% when the mass ratio of zeolite to PET was set to 2.0/1.0. The results indicate that ZSM-5 is able to facilitate the decomposition of carboxyl, aliphatic groups, and ether bonds in the primary products produced from the pyrolysis of PET. In addition, the deoxygenation effects on the waxy products have been significantly enhanced with the addition of zeolite based on the results of NMR.

Quantification of Mixtures of C2 and C3 Hydroxy Acids and Products of Glycerol Oxidation by High‐Performance Liquid Chromatography and Quantitative 13C NMR

AbstractThe aim of this study was to develop an improved general method for detecting and quantifying mixtures of hydroxy acids and other products of glycerol oxidation in aqueous media, to prevent the confusions that can occur due to similarities and interactions between these compounds depending on media conditions. Standard potential products of glycerol oxidation—glycerol, glyceraldehyde, dihydroxyacetone, glyceric acid, lactic acid, glycolic acid, glyoxylic acid, oxalic acid, tartronic acid, and mesoxalic acid—were analyzed by high‐performance liquid chromatography (HPLC) and quantitative 13C nuclear magnetic resonance (NMR), in mixtures of known composition. The results obtained were concordant with the known compositions tested. HPLC was more accurate than quantitative 13C NMR for simple mixtures, but 13C NMR was required for complex mixtures containing dihydroxyacetone and glycerol, oxalic acid and mesoxalic acid, or glyoxylic acid and tartronic acid, pairs of compounds not well separated or detected by HPLC. As proof‐of‐concept, an unknown mixture generated by glycerol oxidation was analyzed by HPLC and quantitative 13C NMR. The results obtained were concordant and allowed accurate determination of the composition of the sample, which contained mesoxalic acid as the major product, with oxalic acid, tartronic acid, and glyceric acid as by‐products.

Laccase-catalyzed oxidative modification of lignosulfonates from acidic sulfite pulping of eucalyptus wood

Abstract Lignosulfonates (LS) from acidic magnesium-based sulfite cooking of Eucalyptus globulus wood were modified via laccase-catalyzed oxidative treatment with the aim to improve their performance as plasticizing additives in concrete formulations. The target parameters were the increment of molecular weight (Mw) and the amount of oxidized groups. The laccase-assisted oxidation under optimized conditions (40°C, pH 4.5, enzyme loads of 83–500 U g−1 for 90 min) allowed Mw increment up to 11-fold and almost doubled the amount of carbonyl and carboxyl groups without using any mediators. Modified LS maintained their solubility in water and possessed a zeta- potential close to that of initial LS. The characterization of modified LS has been carried out by ultraviolet-visible (UV-Vis), Fourier transform infrared-attenuated total reflectance (FTIR-ATR) and quantitative 13C nuclear magnetic resonance (NMR) spectroscopy, and the sulfonic and phenolic groups were assessed by conductometric titration. It was concluded that LS polymerization occurred mostly via the formation of new aryl ether bonds (two thirds of the modification) and biphenyl bonds (the remaining third). However, part of the newly formed bonds of unknown origin are temperature labile and cleaved during the concentration of LS at pH 4 and 80°C under vacuum, which led to the reduction of the Mw of the modified lignin to almost one third.

Labile and recalcitrant components of organic matter of a Mollisol changed with land use and plant litter management: An advanced 13C NMR study

Soil organic matter (SOM) changes with land use and soil management, yet the controlling factors over the chemical composition of SOM are not fully understood. We applied quantitative 13C nuclear magnetic resonance and spectral editing techniques to measure chemical structures of SOM from different land use types. The land use types included a native grassland (nGL), a crop land with straw burning in the field (bCL), a restored grassland (rGL) and a cropland with straw removed out of the field (rCL) for 28years. The abundances of OCH groups from carbohydrates were higher in the SOMs of the nGL and rGL than in those of the rCL and bCL, while the abundances of OCH3 and aromatic CO groups from lignin were higher in the SOMs of the three-ever cultivated lands (rGL, rCL and bCL) than in that of the nGL. Although aromatic CC groups were most dominant in the Mollisols, they did not consistently decrease after the burnings of straw were ceased in the fields of the rCL and rGL compared to the bCL with continuous burning. In addition, the COO groups were bound with the aromatic CC groups in all the land use types, and the sizes of the aromatic clusters were affected by the land use types. The labile and recalcitrant components were correlated with SOC contents the mineral-associated and particular SOM in a contrasting way. Our results suggested that the chemical composition of SOM in the Mollisol depended on land use types, and that labile and recalcitrant components might be protected through mineral associations and aggregation, respectively. The most abundant aromatics in the Mollisols might not just be pyrogenic and could be oxidized to different extents, depending on field drainage conditions.

Chemical nature of soil organic carbon under different long-term fertilization regimes is coupled with changes in the bacterial community composition in a Calcaric Fluvisol

Fertilization is an important factor influencing the chemical structure of soil organic carbon (SOC) and soil microbial communities; however, whether any connection exists between the two under different fertilization regimes remains unclear. Soils from a 27-year field experiment were used to explore potential associations between SOC functional groups and specific bacterial taxa, using quantitative multiple cross-polarization magic-angle spinning 13C nuclear magnetic resonance and 16S rRNA gene sequencing. Treatments included balanced fertilization with organic materials (OM) and with nitrogen (N), phosphorus (P), and potassium (K) mineral fertilizers (NPK); unbalanced fertilization without one of the major elements (NP, PK, or NK); and an unamended control. These treatments were divided into four distinct groups, namely OM, NPK, NP plus PK, and NK plus control, according to their bacterial community composition and SOC chemical structure. Soil total P, available P, and SOC contents were the major determinants of bacterial community composition after long-term fertilization. Compared to NPK, the OM treatment generated a higher aromatic C–O and OCH3 and lower alkyl C and OCH abundance, which were associated with the enhanced abundance of members of the Acidobacteria subgroups 6 and 5, Cytophagaceae, Chitinophagaceae, and Bacillus sp.; NP plus PK treatments resulted in a higher OCH and lower aromatic C–C abundance, which showed a close association with the enrichment of unclassified Chloracidobacteria, Syntrophobacteraceae, and Anaerolineae and depletion of Bacillales; and NK plus control treatments resulted in a higher abundance of aromatic C–C, which was associated with the enhanced abundance of Bacillales. Our results indicate that different fertilization regimes changed the SOC chemical structure and bacterial community composition in different patterns. The results also suggest that fertilization-induced variations in SOC chemical structure were strongly associated with shifts in specific microbial taxa which, in turn, may be affected by changes in soil properties.

Formation Constants and Conformational Analysis of Carbamates in Aqueous Solutions of 2-Methylpiperidine and CO2 from 283 to 313 K by NMR Spectroscopy.

Quantitative 13C nuclear magnetic resonance (NMR) spectroscopy was used to investigate the speciation in (2-methylpiperidine + H2O + CO2) systems at 283.2-313.2 K. The carbamate of 2-methylpiperidine(2-methylpiperidine- N-carboxylate) was shown for the first time to be a stable species in aqueous solutions. The spectroscopic results were used to obtain temperature-dependant formation constants for the carbamate using a simplified model for the activity coefficients from which the standard molar enthalpy of reaction was estimated. The results were incorporated into a self-consistent chemical equilibrium model, which includes vapor-liquid equilibria and all aqueous species, including the formation of carbamate. The predominant conformation of the sterically hindered carbamate, which was determined using two-dimensional exchange spectroscopy NMR, has the methyl group in the axial orientation and is in agreement with the density functional theory quantum chemical calculations.

Characterization of the Low Molar Ratio Urea⁻Formaldehyde Resin with 13C NMR and ESI⁻MS: Negative Effects of the Post-Added Urea on the Urea⁻Formaldehyde Polymers.

The structural changes during three-step synthesis of low-molar ratio urea–formaldehyde (UF) resin were tracked by quantitative 13C nuclear magnetic resonance (13C NMR) analysis and electrospray ionization-mass spectrometry (ESI–MS). Condensations that produced polymers were found to be linked by ether bonds in addition to hydroxymethylation reactions at the first alkaline stage with a formaldehyde to urea ratio of 2:1. Considerable formation of branched methylene linkages, with the highest content among all the condensed structures, was the key feature of the acidic stage. Notable changes were observed for the chemical structures and molecular masses of the resin components after the formaldehyde to urea molar ratio was lowered to 1.2 by adding post-urea at the final alkaline stage. Specifically, most of the branched hydroxymethyl groups on the polymers were cleaved, resulting in a significant decrease in the branching degree of the polymers. The performance degradation of the UF resin was attributed to this debranching effect and the production of components with low molecular masses. Based on the observations, the curing pattern of low molar ratio UF resin was postulated and branched polymeric formaldehyde catcher bearing urea-reactivity was proposed.

Abundant Nonprotonated Aromatic and Oxygen-Bonded Carbons Make Humic Substances Distinct from Biopolymers

The nature of humic substances (HSs) extracted from soil organic matter and their distinction from degrading plant material has recently been called into question. Quantitative solid-state 13C nuclear magnetic resonance (NMR) analyses, in good agreement with elemental analysis, show that HSs are distinct from common biopolymers, refuting claims to the contrary made based on 1H-detected NMR spectra of the same standard peat humic acid as studied here. Aromatic carbons not bonded to hydrogen or oxygen, which are rare (≤10%) in common biomolecules, constitute a large fraction (28%–33%) of prairie soil and peat humic acids. Oxygen-bonded nonprotonated carbons such as aryl ketones, nonprotonated alkyl C–O, and abundant COOH groups are also characteristic of humic and fulvic acids but not observed in plant biopolymers. These distinctive structural differences between HSs and biopolymers challenge the recent proposal that HSs are unremarkable intermediates in a continuum of degrading biomolecules.

Structural evidence for soil organic matter turnover following glucose addition and microbial controls over soil carbon change at different horizons of a Mollisol

Soil organic matter (SOM) in subsoils stores more than half of terrestrial organic carbon (C), and may sequestrate more C with increasing organic input due to its low C content (or high mineral reactivity) and high chemical stability. Organic inputs can stimulate microbial decomposition of native SOM (known as the priming effect), while being microbially decomposed and transformed into SOM. Yet, microbial controls over these processes and their influence on soil carbon change in soil profile remain elusive because of technical challenge to separate them. We overcame this challenge by employing a novel approach of combining 13C and 12C isotopes with quantitative solid-state 13C nuclear magnetic resonance (NMR). We used soil samples taken from three soil horizons in a Mollisol profile that dominated with fused-ring aromatics for a 43-day incubation. The signal intensities of the most dominant fused-ring aromatics and nonpolar alkyl groups were reduced due to the priming effect following the addition of 12C enriched glucose. Those signal intensities of O-alkyl and nonpolar alkyl groups increased in SOM spectra following the addition of 13C-labeld glucose, demonstrating accumulation of glucose and microbial residues. With the increasing glucose concentration, priming effect estimated using isotopic method and the magnitudes of signal loss estimated using 13C NMR both increased as exemplified for the Ap horizon soil. However, soil organic C content increased only when the added glucose concentration was beyond a previously non-quantified priming saturation threshold (between 36.0 and 100.0 g glucose-C kg−1 SOM-C). The increase of soil organic C was larger in the subsoils than in the topsoil due to lower microbial biomass, higher microbial growth efficiency (MGE) and mineral reactivity, which were related to the reduced priming effect and enhanced accumulation of microbial and glucose residues in the subsoils. The higher MGE in the subsoils agreed with stronger shifts of microbial community composition, characterized by phosphorous lipid fatty acid profiling, with changing glucose concentration during the incubation. Our findings highlighted the importance of priming saturation threshold, microbial mediation and mineral reactivity, but not SOM recalcitrance, in controlling the dynamics of SOM. Our study provided a novel approach to quantify these parameters and understand the controlling factors in relation to different plant types and soil types.

Molecular-Level Structural Insight into Clarified Oil by Nuclear Magnetic Resonance (NMR) Spectroscopy: Estimation of Hydrocarbon Types and Average Structural Parameters

A direct and easy-to-grasp methodology based on the combination of quantitative 1H and 13C nuclear magnetic resonance (NMR) has been developed for the estimation of total aromatics, saturates, and several important structural parameters, such as aromaticity, average number of aromatic rings per molecule, average number of aromatic carbon atoms per molecule, average molecular weight, degree of aromatic substitution, degree of aromatic condensation, nature of condensation, and substitution to aromatic ring, etc. for clarified oil (CLO) from Indian oil refineries. These parameters, along with HPLC analysis data for di- to penta-ring aromatics, provide a molecular-level understanding of this potentially valuable feedstock, which can thus be correlated with process parameters for needle coke production from CLO. The method exploits the concept of group molecular weight (GMWt) and uses three empirical equations governing the nature of aromatic condensation. The various types of CLO that originated from Indian o...

Reaction of glycine with glyoxylate: Competing transaminations, aldol reactions, and decarboxylations

The reactions of glycine, a simple amino acid, with glyoxylate, a simple α-oxocarboxylate, were investigated in water as a function of time, pH, and temperature and followed using a combination of quantitative 13C nuclear magnetic resonance and high-resolution mass spectrometry. Three sets of experiments are reported: (1) reaction of 13C-labeled glycine with unlabeled glyoxylate, (2) reaction of unlabeled glycine with 13C-labeled glyoxylate, and (3) the reaction of 13C-labeled glycine with 13C-labeled glyoxylate. Competing transaminations, aldol reactions, and decarboxylations were observed; the mechanistic description for each of these processes is presented. 3-Hydroxy-2-aminosuccinate, a product of reaction between glycine and glyoxylate, was shown to promote both the decarboxylation of glyoxylate and transamination of glyoxylate to glycine. These observations may have implications for the mechanism of attenuation of ethylene glycol toxicity.