Quantitative 13C NMR Spectroscopy Research Articles

Synthesis of Random, Gradient, and Block-like Terpolycarbonates via One-Pot Terpolymerization of Epoxide, CO2, and Six-Membered Cyclic Carbonates

Multi-polymerization is regarded as a valuable strategy to tailor material performances by incorporating well-chosen monomers and tuning monomer sequence distributions in the polymer backbones. Despite that considerable advances have been made in the past decades, the modification of CO2-based polycarbonate materials is still in its infancy. In this contribution, a series of polycarbonate terpolymers with diverse chain structures were fabricated through a dissymmetric Cr complex-catalyzed one-pot terpolymerization of cyclohexene oxide (CHO), CO2 with six-membered cyclic carbonates (6CCs). The reaction conditions (temperature, feeding ratio, and CO2 pressure) as well as the 6CC substituents played a critical role in tailoring the sequence distributions of CHO/CO2/6CC terpolymers from random to gradient or block-like sequences. It was noteworthy that the average lengths of both sequences could be modulated by adjusting the feeding monomer ratios or reaction temperature, as detected by quantitative 13C NMR spectroscopy of purified terpolymers. Besides, DSC revealed that the glass-transition temperature of the obtained terpolymers had a wide range of 69.5–115.5 °C based on the polymer architecture.

Impact of Hydrogen Bonds on CO2 Binding in Eutectic Solvents: An Experimental and Computational Study toward Sorbent Design for CO2 Capture

Choline-based amino acid ionic liquids with anions glycinate, β-alaninate, phenylalaninate, and prolinate were synthesized and mixed with ethylene glycol to form lower-viscosity benign eutectic solvents for CO2 capture. The highest capacity measured was 0.7 moles of CO2 per mole of ionic liquid (2 moles CO2 per kg solvent) for a 1 to 2 mole ratio mixture of choline prolinate to ethylene glycol at 1 bar of CO2 and 25 °C. Under 5000 ppm of CO2, half of this capacity was realized. Through a combined study of quantitative 13C NMR spectroscopy, molecular dynamics simulations and density functional theory calculations, we show that hydrogen bonding in the eutectic solvent prevents proton-transfer between prolinate anions upon CO2 absorption, which occurs in the absence of ethylene glycol and deactivates binding sites. Blocking this proton transfer leads to a higher binding capacity compared to neat choline prolinate. This work demonstrates the impact of hydrogen bonding on the CO2 binding mechanism and energetics, as well as physical and thermal properties in eutectic solvents, thus addressing an unmet need and informing future studies on the development of benign sorbents for capturing CO2 from dilute streams.

Investigation of Partial Oxidation of Methane in a Cold Plasma Reactor with Detailed Product Analysis

Cold plasma is a partially ionized state of matter that unites high reactivity and mild conditions. Therefore, cold plasma reactors are intriguing for reaction engineering. In this work, a laboratory scale dielectric barrier discharge (DBD) cold plasma reactor was designed, set up, and used for studying the influence of the specific energy input (SEI) on the product spectrum of the partial oxidation of methane. In total, 23 experiments were carried out near ambient conditions with a molar reactant ratio of methane to oxygen of 2:1 at SEI between 0.3 and 6.0 J cm−3. The feed also contained argon at a mole fraction of 0.75 mol mol−1. The product stream was split into a fraction that was condensed in a cold trap and the remaining gaseous fraction. The latter was analyzed at-line in a gas chromatograph equipped with a dual column and two carrier gases. The condensed fraction was analyzed by qualitative and quantitative 1H and 13C NMR spectroscopy, Karl Fischer titration, and sodium sulfite titration. In the product stream, 16 components were identified and quantified: acetic acid, acetone, carbon dioxide, carbon monoxide, ethanol, ethane, ethene, ethylene glycol, formaldehyde, formic acid, hydrogen, methanol, methyl acetate, methyl hydroperoxide, methyl formate, and water. A univariant influence of the SEI on the conversions of methane and oxygen and the selectivities to the products was observed. The experimental results provided here are an asset for developing reaction kinetic models of the partial oxidation of methane in DBD plasma reactors.

Copolymers Prepared by Exchange Reactions Enhance the Properties of Miscible Polymer Blends

Although many polymers are not miscible or chemically incompatible, some form miscible blends, which feature tunable properties relative to those of their constituent polymers. Here, we introduce an approach to enhance the mechanical properties of miscible blends of a thermoplastic polyurethane and a sustainable polyester, polycaprolactone (PCL), by introducing a copolymer of the two corresponding monomers. Rather than polymerizing the copolymers from new monomers, they were generated by a solvent-free, ester/urethane bond-exchange process conducted during the coextrusion of polyurethane and PCL. Urethane/ester exchange was confirmed by quantitative 13C NMR spectroscopy, along with well-defined size-exclusion chromatography of the copolymers. Extrusion time and temperature affected the extent of exchange, with shorter residence times and lower temperatures giving limited bond exchange and blockier copolymers. In contrast, longer extrusion times and higher temperatures provided more extensive exchange and approximately random copolymers. Mixtures of the polyurethane and polyester homopolymers with 10 wt % copolymer demonstrated improved tensile stress and strain relative to coextruded mixtures of thermoplastic polyurethane and polyethylene because of the enhanced crystallization of the miscible homopolymer blend facilitated by the added copolymer compatibilizer. This approach represents a simple and general strategy for obtaining copolymers from homopolymers rather than using specialized polymerization techniques, allowing for products from mixed polymer waste to be used as compatibilizers or otherwise enhance the properties of the original homopolymer mixtures.

Cationization of Eucalyptus Kraft LignoBoost Lignin: Preparation, Properties, and Potential Applications.

Current changes toward a more biobased economy have recently created tremendous renewed interest in using lignin as a valuable source for chemicals and materials. Here, we present a facile cationization approach aiming to impart kraft lignin water-solubility, with similar good features as lignosulfonates. Eucalyptus globulus kraft lignin obtained from a paper mill black liquor by applying the LignoBoost process was used as the substrate. Its reaction with 3-chloro-2-hydroxypropyl-trimethylammonium chloride (CHPTAC) in an aqueous alkaline medium was studied to assess the impact of different reaction conditions (temperature, time, educt concentration, molar CHPTAC-to-lignin ratio) on the degree of cationization. It has been shown that at pH 13, 10 wt % lignin content, 70 °C, and 3 h reaction time, a CHPTAC-to-lignin minimum molar ratio of 1.3 is required to obtain fully water-soluble products. Elemental analysis (4.2% N), size-exclusion chromatography (Mw 2180 Da), and quantitative 13C NMR spectroscopy of the product obtained at this limit reactant concentration suggest introduction of 1.2 quaternary ammonium groups per C9 unit and substitution of 75% of the initially available phenolic OH groups. The possible contribution of benzylic hydroxyls to the introduction of quaternary ammonium moieties through a quinone methide mechanism has been proposed. Since both molecular characteristics and degree of substitution, and hence solubility or count of surface charge, of colloidal particles can be adjusted within a wide range, cationic kraft lignins are promising materials for a wide range of applications, as exemplarily demonstrated for flocculation of anionic dyes.

Synthesis of pristine graphene-like behaving rGO thin film: Insights into what really matters

Despite the huge expansion of GO/rGO market, there is a clear lack of experimental studies on getting high quality, large scale GO and rGO nanosheets/thin films, which is a critical requirement for electronic applications. In this work, a detailed experimental study on the effect of lateral sheet size on properties of GO/rGO, supported by density functional theory (DFT) calculations, is presented for the first time, to help prepare pristine graphene-like rGO. Furthermore, we investigated the effect of thermal reduction at low temperature (200 °C), under ambient pressure, on the corresponding electronic properties of rGO. Current-voltage (I–V) analysis, optical and electron microscopy, atomic force microscopy, Raman, XPS, and quantitative 13C NMR spectroscopy were used to study and optimize rGO. The optimized rGO-field-effect transistor (rGO-FET) device exhibited the highest charge carrier mobilities, i.e. 2,962 (holes) and 2,183 (electrons) cm2/V.s. Furthermore, the transconductance characteristic curve of rGO-FET showed the ambipolar behavior of high-quality graphene, with Dirac point around zero. In addition, the optical band gap of rGO nanosheets (∼0.4 eV), prepared in this work, is among the smallest reported band gaps for rGO. These findings highlight the significance of our study for synthesizing large-scale graphene-like rGO thin film, for ultra-fast, low-power transistor applications.

Narrow distillation cuts for an improved characterisation of crude oil: an insight on heteroatoms in heavy fraction molecules

A light Arabian crude oil was separated by distillation into 27 fractions, including 25 very narrow distillation cuts, the light ends, and a vacuum residue (VR), which were extensively characterised using standard methods. Overall, the properties matched well with those predicted by H/CAMS software, indicating a successful distillation. Then, quantitative 13C NMR spectroscopy, SIMDIS, and molecular weight (MW) distribution by mass spectrometry were used to derive an improved correlation between the MW and boiling point for the entire crude oil, in particular for the VR fraction. This allowed determining the mass fractions of sulphur and nitrogen containing compounds across the crude oil boiling range, reaching up to approximately 100% in the VR fraction. The corresponding low abundance of pure hydrocarbon molecules in the VR fraction is important for modelling purposes and processing technologies. [Received: May 3, 2019; Accepted: July 24, 2019]

Nuclear Magnetic Resonance Characterization of Renewable Products from a Two‐Step Ex‐Situ Hydropyrolysis Vapor Upgrading Process

AbstractA novel two‐step ex‐situ hydropyrolysis vapor upgrading (HPVU) process can generate tailored oxygenated hydrocarbon products from lignocellulosic biomass by adjusting vapor upgrading temperature. Such products, containing varied oxygen contents (ranging from 2 to 17 wt%), are different from traditional petroleum hydrocarbons and conventional biomass‐derived pyrolysis oil. Elucidation of the comprehensive structural motif of these unconventional products is critical for development and deployment of the HPVU process. To this end, two‐dimensional heteronuclear 1H‐13C NMR techniques were employed to first provide single‐ and multiple‐bond correlations between protons and carbons characteristic of different organic functional groups. The distribution of carbon functional groups was further determined by quantitative 13C NMR spectroscopy with full relaxation and well‐defined chemical shift regions obtained from diverse NMR methods. Phenols and ketones were identified as the main oxygenate species in these renewable products. At higher vapor upgrading temperatures, a decrease in oxygenate species and an increase in alkylation on aromatic rings were observed. Of particular importance, compared to pyrolysis oil, the amounts of thermally unstable oxygenate species, such as aldehyde, carboxylic acid, and carbohydrate, were found to be minimal, suggesting good thermal stability of these renewable hydrocarbon products.

Quantitative Insights into the Fast Pyrolysis of Extracted Cellulose, Hemicelluloses, and Lignin.

The transformation of lignocellulosic biomass into bio‐based commodity chemicals is technically possible. Among thermochemical processes, fast pyrolysis, a relatively mature technology that has now reached a commercial level, produces a high yield of an organic‐rich liquid stream. Despite recent efforts to elucidate the degradation paths of biomass during pyrolysis, the selectivity and recovery rates of bio‐compounds remain low. In an attempt to clarify the general degradation scheme of biomass fast pyrolysis and provide a quantitative insight, the use of fast pyrolysis microreactors is combined with spectroscopic techniques (i.e., mass spectrometry and NMR spectroscopy) and mixtures of unlabeled and 13C‐enriched materials. The first stage of the work aimed to select the type of reactor to use to ensure control of the pyrolysis regime. A comparison of the chemical fragmentation patterns of “primary” fast pyrolysis volatiles detected by using GC‐MS between two small‐scale microreactors showed the inevitable occurrence of secondary reactions. In the second stage, liquid fractions that are also made of primary fast pyrolysis condensates were analyzed by using quantitative liquid‐state 13C NMR spectroscopy to provide a quantitative distribution of functional groups. The compilation of these results into a map that displays the distribution of functional groups according to the individual and main constituents of biomass (i.e., hemicelluloses, cellulose and lignin) confirmed the origin of individual chemicals within the fast pyrolysis liquids.

Quantitation in the regioselectivity of acylation of glycosyl diglycerides: total synthesis of a Streptococcus pneumoniae α-glucosyl diglyceride.

The fidelity of acylation regioselectivity in the synthesis of mixed glycosyl diacylglycerols can be accurately measured by quantitative 13C NMR spectroscopy using a 1-13C-labelled fatty acid and a paramagnetic relaxation enhancement agent. Exquisite regioselectivity is achieved using a stepwise acylation/substitution of a glycosyl β-bromohydrin, which is applied to the total synthesis of Streptococcus pneumoniae Glc-DAG-s2.

Recovery and Utilization of Palm Oil Mill Effluent Source as Value-Added Food Products.

The environmental impacts of palm oil mill effluent (POME) have been a concern due to the water pollution and greenhouse gases emissions. Thus, this study was conducted to recover the value-added products from POME source before being discharged. The samples, before (X) and after (Y) the pre-recovery system in the clarification tank were sampled and analysed and proximate analysis indicated that both samples are energy rich source of food due to high contents of fats and carbohydrates. GCMS analysis showed that the oil extracts contain predominantly palmitic, oleic, linoleic and stearic acids. Regiospecific analysis of oil extracts by quantitative 13C-NMR spectroscopy demonstrated that both oil extracts contain similar degree of saturation of fatty acids at sn-2 and sn-1,3 positions. The samples are rich in various phytonutrients, pro-vitamin A, vitamin E, squalene and phytosterols, thus contributing to exceptionally high total flavonoid contents and moderate antioxidant activities. Overall, samples X and Y are good alternative food sources, besides reducing the environmental impact of POME.

Investigation of physicochemical properties of arabinogalactan of different larch species

Samples of arabinogalactan (AG) were isolated by aqueous extraction from wood of different larch species (Larix sibirica Ledeb., Larix gmelinii (Rupr.) Rupr., Larix cajanderi Mayr., and Larix olgensis var. Koreana) and studied by HPLC, IR spectroscopy, and quantitative 13C NMR spectroscopy. The wood of the studied larch species was shown to contain significant amount of arabinogalactan (10–17% of the a.d.w. mass) and could be a source of its industrial production. The studied AG samples had similar structural and molecular-mass characteristics. This fact could facilitate the product standardization during its industrial production both from the wood of a single larch species and from mixed raw materials.

Efficient 1-Hexene Trimerization with Triazacyclohexane Chromium Catalysts and Detailed Product Analysis by 13C NMR

Triazacyclohexane chromium precatalysts are described which catalyze the selective trimerization of 1-pentene, 1-hexene, and 1-octene with unprecedented activity, reaching nearly 5000 turnovers in 1 h. The isomer distribution of the trimers has been analyzed in detail by application of quantitative 13C NMR spectroscopy to 13C labeled samples. All endocyclic elimination products predicted by the metallacyclic mechanism have been characterized, and many have been confirmed by their independent syntheses. Significant variations in the isomer distribution are observed on variation of the ligand bulk. Quantification gave considerable insights into the relative abundance of metallacyclic intermediates, with 1,3-substituted chromacyclopentanes being by far the most abundant resting state. Ring expansion selectivity favors 1,2-insertion into the less hindered Cr–C bond, but some 2,1-insertion products have also been identified.

Influence of a low content of PEO segment on the thermal, surface and morphological properties of triblock and diblock PCL copolymers

Two series, one of triblock (PCL/PEO/PCL) and the other of diblock (PCL/PEO) copolymers were prepared by ring-opening polymerization of e-caprolactone catalized with tin(II) octoate and by using dihydroxy or monohydroxy poly(ethylene oxide) as the macroinitiator. The PEO block length was fixed (Mn 1,000 g/mol) and the PCL block lengths (Mn 10,000-40,000 g/mol) were tailored by changing weight ratio of e-CL/PEO. The copolymers’ structure was confirmed by 1H and quantitative 13C NMR spectroscopy while their molecular weights were determined by GPC analysis. The thermal properties and the degree of crystallinity of the copolymers were investigated and compared by using DSC and WAXS. Both types of copolymers were semicrystalline with the orthorhombic PCL crystal lattice. The surface morphology of the copolymer films was investigated by using optical microscopy and AFM analysis, which confirmed the spherulitic lamellar structure with spherulites of different diameters. Data indicated that a low content of PEO segment had an influence on thermal degradation behavior, crystallinity and morphology of copolymers. Roughness of copolymer films was affected by the content of PEO and correlated with the spherulites’ diameter. The small changes in water and moisture absorption properties of copolymers compared to homopolymer PCL were observed.

Dependence of Copolymer Sequencing Based on Lactone Ring Size and ε-Substitution.

The copolymerization of an ε-substituted ε-lactone, menthide (MI), and a range of nonsubstituted lactones (6-, 7-, 8-, and 9-membered rings) was investigated in order to determine the factors that affect the sequencing of the MI copolymers. Analysis by quantitative 13C NMR spectroscopy showed the copolymerization of MI with a nonsubstituted lactone of ring size 7 or less produced a randomly sequenced copolymer, as a consequence of the smaller lactone polymerizing first and undergoing rapid transesterification as MI was incorporated. Conversely, copolymerization with larger ring lactones (ring size 8 and above) produced block-like copolymers as a consequence of MI polymerizing initially, which does not undergo rapid transesterification side reactions during the incorporation of the second monomer. Terpolymerizations of a small ring lactone, macrolactone, and menthide demonstrated methods of producing lactone terpolymers with different final sequences, depending on when the small ring lactone was injected into the reaction mixture.

Species distribution of CO2 absorption/desorption in aqueous and non-aqueous N-ethylmonoethanolamine solutions

The CO2 absorption and desorption in N-ethylmonoethanolamine (EMEA) solutions were carried out using an absorption−desorption apparatus and the species distribution was explored using the quantitative 13C NMR spectroscopy. EMEA+ethanol solution had a much lower CO2 loading (0.547mol CO2/mol EMEA) than EMEA+H2O solution (0.799mol CO2/mol EMEA) due to the lower concentration of alky carbonate generated in EMEA+ethanol solution than the corresponding bicarbonate/carbonate as generated in EMEA+H2O solution and the no further reaction of carbamate with CO2 in EMEA+ethanol solution. The EMEA regeneration efficiency of the EMEA+ethanol solution at 363, 373 and 383K (55.44, 86.86 and 100.00%) was much higher than EMEA+H2O solution at corresponding temperatures (27.56, 30.25 and 38.80%), which was mainly influenced by the decomposition of carbamate, while the existence of bicarbonate prevented carbamate decomposing.

A study on biosynthesis of “citral” in lemongrass (C. flexuosus) cv. Suvarna

Incorporation of [1-13C]-glucose and fosmidomycin was achieved in young and rapidly expanding (aged 15 days) leaves of lemongrass (C. flexuosus) cv. suvarna to elucidate biosynthetic origin of citral (3,7-dimethyl-2,6-octadienal). Analyses of the resultant 13C-labeling patterns of citral by quantitative 13C-NMR spectroscopy revealed significant %13C enrichment at carbons C-3, C-5, C-7 and C-9 in citral. This labeling pattern of the citral is in accordance with their biosynthesis via 2C-methyl-d-erythritol-4-phosphate (MEP) pathway. However, incorporation of [1-13C]-glucose achieved in the presence of fosmidomycin resulted in a 13C-labeling pattern of citral which did not match with labeling pattern characteristic of the MEP pathway. In addition, we studied the activity pattern of the DXR enzyme following fosmidomycin (25, 50, 75 and 100 μM concentrations) treatment of the young (aged 15 days) leaves for 48 h. The results revealed that fosmidomycin (100 μM) caused drastic inhibition (>50 %) of the DXR enzyme activity. The levels of the citral measured in the fosmidomycin treated leaves were also found to be reduced with decrease the activity of DXR enzyme. In conclusion, the results of the present work revealed the presence of the MEP pathway and its role in the biosynthesis of citral in lemongrass. In addition, the critical role of the DXR enzyme in the citral biosynthesis is highlighted. This is the first report on elucidation of the MEP pathway in lemongrass and may help in deeper understanding of the monoterpene biosynthesis and regulation in the genus Cymbopogon of high industrial significance.

Synthesis and Postpolymerization Modification of One-Pot ω-Pentadecalactone Block-like Copolymers.

We report the one-pot copolymerization of ω-pentadecalactone (PDL) to produce tri- and diblock-like copolymers with the ability to undergo postpolymerization modification. The ε-substituted ε-lactone (εSL), menthide (MI), was copolymerized with PDL to introduce side chain functionality into poly(ω-pentadecalactone) (PPDL) copolymers. The copolymerization was followed by quantitative 13C NMR spectroscopy, which revealed that the polymerization of MI occurred before the incorporation of PDL into the polymer chain to form a block-like copolymer. Transesterification side reactions were not found to occur interblock, although intrablock transesterification side reactions occurred only within the PPDL section. The same effect was demonstrated across a range of relative molar equivalents of monomers, and the generality of the approach was further demonstrated with the copolymerization of PDL with other εSL monomers. Finally, the copolymerization of PDL with an alkene-functionalized εSL was shown to produce one-pot PDL block-like copolymers that could undergo postpolymerization modification by thiol-ene addition to produce block copolymers with a range of characteristics in a simple procedure.

Synthesis, composition, and properties of metal complexes with organic ligands derived from glucose

Natural biologically active compounds are formed from aqueous solutions of various carbohydrates in the presence of transition metal ions as catalysts. Their composition and properties as polycoordination compounds are insufficiently understood. Metal complexes with organic ligands were synthesized from salts of various metals (Fe3+, Co2+, Cu2+, and Mn2+) and glucose. The composition and properties of the metal complexes with organic ligands were studied by quantitative 13C NMR spectroscopy and adsorption polarography.

Synthesis of ω-Pentadecalactone Copolymers with Independently Tunable Thermal and Degradation Behavior

ω-Pentadecalactone (PDL) was copolymerized with lactones of varying sizes (6-, 7-, 9-, and 13-membered rings) in order to characterize the properties of PDL copolymers throughout the lactone range for copolymerizations catalyzed by magnesium 2,6-di-tert-butyl-4-methylphenoxide (Mg(BHT)2(THF)2). Kinetics of the copolymerization reactions were studied using quantitative 13C NMR spectroscopy, which revealed that the polymerization of the smaller, strained lactone monomer occurred rapidly before the incorporation of PDL into the polymer. Furthermore, all polymers were randomly sequenced as a consequence of transesterification side reactions that occurred throughout polymerization. The copolymers were all shown to cocrystallize to produce polymers with melting and crystallization temperatures that displayed a linear relationship with respect to monomer ratio. Differences in degradation behavior of the smaller lactones enabled the synthesis of PDL copolymer materials that displayed independently controllable thermal and degradation properties.