NMR Characterization Research Articles

New insights into the coalification of lignite from lignin: A comparison of their chemical structures

The structure of coal is considered to be a highly cross-linked network of macromolecules, which is formed by the polymerization of many structurally similar but not totally identical aromatic structural units. It is generally believed that coal is converted from biomass, which is composed of cellulose, hemicellulose, and lignin. Considering lignin as the only aromatic structure in biomass and lignite as a low-rank coal, we believe that there is an inextricable link between the structures of lignin and lignite. In this work, both Huolinhe lignite and enzymatic lignin can be oxidized to benzene carboxylic acids (BCAs), and the yield distribution of BCAs is very similar. By 13C NMR characterization, we have found that both lignin and lignite contain polycyclic aromatic clusters and their mole fractions of aromatic bridgehead carbon (Xb) are very close, which indicates that polycyclic aromatic clusters in lignite may be preserved from lignin. Combining the analysis of the supercritical ethanolysis products of Huolinhe lignite and enzymatic lignin, we found the structural units of enzymatic lignin contained more methoxy, phenolic hydroxyl groups, and C-O ether bonds, but fewer methylene chains than those of Huolinhe lignite.

Study on microwave synthesis mechanism of carbon dots based on NMR characterization

Carbon dots (CDs) have applications in various fields such as biomedicine and environmental monitoring because of its chemical stability and good biocompatibility etc. At present, one of the main points of CDs research is that the formation mechanism is not clear. The traditional hydrothermal method has a long cooling time and it is difficult to stop the reaction and obtain the product on time. Microwave reactors, however, can capture images and quickly heat and cool down. To monitor the reaction procedure and mechanism requires a special procedure. In this paper, nitrogen doped CDs (FA-CDs) with great water solubility, excellent stability and low cytotoxicity were prepared by microwave method with fumaric acid and arginine. The semi-in-situ NMR characterization of FA-CDs was carried out under different reaction times to track the reaction mechanism. The saturated chain in arginine and some double bonds in fumaric acid formed carbon nuclei, and the guanidine functional group, amino acid structures in arginine and carboxyl groups in fumaric acid were modified on the surface of FA-CDs. UV–vis absorbance spectra and fluorescence decay curves indicate that the luminescence properties of FA-CDs are mainly controlled by carbon nuclei and surface functional groups.

Isosteroidal Alkaloids from Fritillaria verticillata Willd. and Their NMR Spectroscopic Characteristics

Comprehensive SummaryChemical investigation of Fritillaria verticillata Willd. led to the isolation of eight novel isosteroidal alkaloids (1—4, 6, 9—11) and four known alkaloids (5, 7—8, 12), including three unprecedented cis‐fused D/E (13α, 17α) cevanine alkaloids (1—3), one rarely cis‐fused E/F (22α) cevanine alkaloid (6), and one uncommon 5β‐jervine‐type isosteroidal alkaloid featuring a cis‐fused A/B ring moiety (11). In order to establish the structures of 1, the calculated NMR with DP4+ evaluation was applied from the plausible structure candidates. The characteristic proton signals for distinguishing D/E conjunction of cevanine alkaloids were summarized. In addition, some proton and carbon signals α to nitrogen in 6 and 7 are unobservable due to the 14N nuclear quadrupolar relaxation, based on the NMR experiments in different solvents, calculated NMR method and X‐ray technology, their structures were determined. The NMR characteristics of cevanine alkaloids to distinguish orientation of long‐pair on nitrogen atom with β‐hydroxyl at C‐20 were also concluded. The anti‐inflammatory effects of compounds 1 and 4 were evaluated in LPS‐activated RAW 264.7 macrophages. Compound 4 decreased LPS‐induced releases of IL‐1β and IL‐17α in RAW264.7 cells in a dose‐dependent manner. Further mechanistic study revealed that 4 suppressed the phosphorylation of IκBα and p65 subunit to regulate the NF‐κB signaling pathway.

Chemical synthesis, NMR characterization, and anticancer activity of androstene derivatives with a C17-side chain

Cancer remains one of the leading causes of death, worldwide. In addition, the lack of efficacy and selectivity of chemotherapeutic agents for cancer cells is a challenge that needs to be addressed through the development of new drugs. Since aminosteroids are of interest in fighting cancer, our group previously reported antiproliferative activity on several cancer cell lines of two representatives, RM-133 and RM-581. To extend the structure–activity relationship study of aminosteroids, of which RM-133 (androstane) and RM-581 (estrane) are the main candidates, we performed the chemical synthesis and biological evaluation on lung (SHP-77), breast (T-47D) and prostate (DU-145, PC-3 and LAPC-4) cancer cells of four analogues of RM-581. We moved the functionalized side chain from position 2 of the androstane and estrane derivatives to incorporate it into a new chain located at position 17.Chemical synthesis took place in 2 steps from steroidal side-chain carboxylic acids, allowing to obtain 4 steroid derivatives with acceptable yields, which were fully characterized by nuclear magnetic resonance spectroscopy (1H and 13C NMR). After the evaluation of compounds 12–15, lower antiproliferative activities varying from 12 to 54%, 0–33% and 0–63% were observed for SHP-77, DU-145 and PC-3 cell lines, respectively, while higher activities varying from 33 to 62% and 45–84% were observed for T-47D and LAPC-4 cell lines, respectively, when tested at 10 µM. Overall, it was observed that these aminosteroids have a lower cytotoxic activity than that of RM-581 and, that moving the side chain from steroid position C2 to C17 is clearly detrimental for antiproliferative activity. However, this work has enabled us to expand our knowledge of the structural requirements to maintain the anticancer activity of aminosteroid derivatives.

Self‐dispersible waterborne comb‐like polyester with alkali resistance and pigment‐dispersion capability

AbstractWaterborne polyester is a common eco‐friendly material in which ester bonds are easy to hydrolyze. Therefore, we synthesized a series of waterborne comb‐like polyesters (WCPEs) with hydrophilic side chains through aza‐Michael addition under green and mild conditions. The physicochemical structure of the polyesters was verified by 1H NMR, FTIR, and GPC characterizations. The pH value of dispersions dropped by less than 0.7 after storage for 2 months. The dispersions remained stable after 6 months at room temperature. In addition, the WCPEs exhibited good wetting and dispersing ability for pigment particles as Tego 740 W, which is a mature pigment dispersant product for waterborne coatings. Moreover, the cross‐linked WCPEs exhibited excellent chemical resistance, there was only 1.2% weight loss, and almost no mechanism properties decline for cross‐linked transparent films even after treatment under an alkaline environment for 20 days. Thus, the synthesized WCPE has potential application as an alkali resistance eco‐friendly material, and possesses excellent performance as pigment‐dispersion resin.

Preparation of Functionalized Amides Using Dicarbamoylzincs.

We report a new convenient preparation of dicarbamoylzincs of type (R1R2NCO)2Zn by the treatment of ZnCl2 and formamides R1R2NCHO with LiTMP in THF (15 °C, 15 min) or by the reaction of formamides R1R2NCHO with TMP2Zn (25 °C, 16 h). This second method tolerates sensitive groups such as an ester, ketone or nitro function. Reaction of these dicarbamoylzincs with allylic, benzylic, aryl, alkenyl bromides, acid chlorides, aldehydes or enones provided various polyfunctional amides in 47–97 % yields. 13C NMR characterization of these new carbamoylzinc derivatives is reported.

Study on the structure and physicochemical properties of fenugreek galactomannan modified via octenyl succinic anhydride

To improve the mechanical strength of borax-crosslinked fenugreek galactomannan hydrogels and broaden the application field of galactomannan-based hydrogels, fenugreek galactomannan (FG) was esterified via octenyl succinic anhydride (OSA), and the parameters affecting the esterification reaction were systematically studied. The optimum process for OSA-modified FG (OFG) was as follows: FG concentration 1.5 wt%, n (OSA): n (FG) = 2, n (4-dimethylamino-pyridine, DMAP): n (FG) = 4, and reaction time 12 h. Under this condition, the degree of substitution (DS) was 0.31, and the product yield was 115.05 %. Characterization of FT-IR, H1 NMR, and HPLC confirmed that the OSA group was successfully introduced into the FG skeleton. The mechanical strength of borax crosslinked OFG hydrogel (OFGH) is 18 times higher than that of FG hydrogel. OFGH shows excellent self-healing, injectable properties and electrical conductivity. This will further expand the application of borax crosslinked galactomannan-based hydrogels in the fields of sensors, drug delivery, and wound dressing.

Sulfonation of the interlayer surface of kaolinite

The interlayer surface of kaolinite was functionalized with sulfonic acid groups through the grafting of propane sultone. The presence of the modifier was confirmed by the increase of the d001-value from 7.1 Å (starting kaolinite) to 12.3 Å. The formation of stable Al-O-C bond following the ring-opening reaction of the cyclic sultone was confirmed both by the 13C NMR and FTIR characterizations. After a full washing of the modified material with water, the clay mineral appears as functionalized flat particles with thicknesses not exceeding 0.02 μm. This was the consequence of the delamination, due to the ionization of the grafted sulfonic acid groups in water, followed by a substantial decrease of the interlayer cohesive force. The nanohybrid material with structural formula determined from the thermo gravimetric analysis, Al2Si2O5(OH)3.77(O(CH2)3SO3H)0.23, was tested as adsorbent for methylene blue, a cationic dye. The amount adsorbed was at least two times higher compared to pristine kaolinite (76.8 μmol g−1 instead of 32.9 μmol g−1). This performance was less important than expected because the dye was adsorbed as trimer (according to the UV–Vis analysis of the aqueous suspension of the modified clay in dye solution), a too bulky configuration to fit in the interlayer space of the modified kaolinite.

Characterization of 1H NMR and 13C NMR Spectrometry and Antibacterial Activities of 4-tert-Butylbenzoyl Amoxicillin

The synthesis of 4-tert-butylbenzoyl amoxicillin has been done by reacting amoxicillin with 4-tert-butylbenzoyl chloride. The product was characterized using proton and carbon-13 spectrometry. Antibacterial activity of 4-tert-butylbenzoyl amoxicillin against Escherichia coli, Bacillus subtilis, and Staphylococcus aureus was tested using paper disk diffusion method. Results showed that 4-tertbutylbenzoyl amoxicillin had a specific spectrum activity. Antibacterial test of 4-tert-butylbenzoyl amoxicillin showed clear zones around the disc paper for Escherichia coli, Bacillus subtilis, and Staphylococcus aureus. The study results indicated 4-tert-butylbenzoyl amoxicillin has antimicrobial properties but is categorized as a less-effective antibiotic agent based on the response to bacterial growth inhibition.

Small-crystal and hierarchical SAPO-11 molecular sieve synthesized via three-stage crystallization method and hydroisomerization performance of corresponding NiWS supported catalyst

In order to prepare non-noble metal supported hydroisomerization catalyst with high catalytic performance, this work first proposed a novel three-stage crystallization method to synthesize small-crystal and hierarchical SAPO-11 molecular sieve, and prepared the corresponding NiWS supported catalyst for the hydroisomerization of n-hexadecane. The physicochemical properties of the small-crystal and hierarchical SAPO-11 molecular sieve and the NiWS supported catalyst were analyzed via a series of characterization methods. It was found that the crystal size of SAPO-11-S was reduced to 21.8 nm and the particle size was reduced to 70–140 nm. SAPO-11-S was superior to SAPO-11-C in pore properties and acidity. The reason for the increase of the number of medium-strong B acid sites in SAPO-11-S was investigated by 29Si MAS NMR characterization, and the formation mechanism of SAPO-11-S was proposed by tracking and analyzing the crystallization process of SAPO-11-S. The decrease of crystal size of SAPO-11 molecular sieve effectively improved the sulfidation degree of active metals and the dispersion degree of the active phase of the catalyst, and promoted more active phases to form “type II active phase”. Compared with NiW/SAPO-11-C, NiW/SAPO-11-S showed higher catalytic activity and isomerization selectivity, and the maximum i-hexadecane yield of NiW/SAPO-11-S was 44.77% higher than that of NiW/SAPO-11-C.

Investigation of structural and optical properties of Pr3+ doped and Pr3+/Dy3+ co-doped multicomponent bismuth phosphate glasses for visible light applications

Pr3+ doped 59.5P2O5+15Bi2O3+10BaF2+10xF+05TeO2+0.5Pr6O11 glasses and Pr3+/Dy3+ co-doped 59P2O5+15Bi2O3+ 10BaF2+ 10xF + 05TeO2+0.5Dy2O3+0.5Pr6O11 glasses (where xF = LiF, NaF, MgF2, KF, CaF2 and SrF2) were synthesized using melt quenching route. Structural properties were researched for different modifier fluorides. With the dopant constant concentration the absorption and luminescence intensity variance influenced by this multicomponent incorporation has been observed. The energy transfer between resonance levels of Pr3+ and Dy3+ through fluorescence studies also examined for Mg and Sr glasses. Long-range nature of prepared glasses, morphological studies with elemental probe, various functional groups pertaining to glass matrices and the non-bridging oxygen bonds with PO4 tetrahedron or depolymarization of oxygen bonds in the presence of the modifier cations with phosphates were thoroughly understood with PXRD, FTIR and 31P NMR characterizations. Judd-Ofelt (J-O) theory has been adopted to estimate important optical parameters. From the fluorescence studies laser characteristic parameters such as optical band gains (σe × τR) and gain bandwidths (σe × Δλeff) were calculated and compared in the present fabricated glasses influenced by various modifiers.

Cryptococcus neoformans capsule regrowth experiments reveal dynamics of enlargement and architecture

The polysaccharide capsule of fungal pathogen Cryptococcus neoformans is a critical virulence factor that has historically evaded characterization. Polysaccharides remain attached to the cell as capsular polysaccharide (CPS) or are shed into the surroundings in the form of exopolysaccharide (EPS). While a great deal of study has been done examining the properties of EPS, far less is known about CPS. In this work, we detail the development of sonication, French Press, and glucanex digestion to both remove the capsule and produce ‘capsule ghosts.’ The ability of sonication to strip cells of capsular material while maintaining survival allowed us to explore of capsule regrowth dynamics, immune modulation, as well as NMR characterization of removed material. Development of these new methodologies will allow for exciting future work exploring cell wall capsule dynamics and improving the characterization of CPS.

Structural elucidation and targeted valorization of poplar lignin from the synergistic hydrothermal-deep eutectic solvent pretreatment

Elucidating the structural variations of lignin during the pretreatment is very important for lignin valorization. Herein, poplar wood was pretreated with an integrated process, which was composed of AlCl3-catalyzed hydrothermal pretreatment (HTP, 130–150 °C, 1.0 h) and mild deep-eutectic solvents (DES, 100 °C, 10 min) delignification for recycling lignin fractions. Confocal Raman Microscopy (CRM) was developed to visually monitor the delignification process during the HTP-DES pretreatment. NMR characterizations (2D-HSQC and 31P NMR) and elemental analysis demonstrated that the lignin fractions had undergone the following structural changes, such as dehydration, depolymerization, condensation. Molecular weights (GPC), microstructure (SEM and TEM), and antioxidant activity (DPPH analysis) of the lignins revealed that the DES delignification resulted in homogeneous lignin fragments (1.32 < PDI < 1.58) and facilitated the rapid assemblage of lignin nanoparticles (LNPs) with controllable nanoscale sizes (30–210 nm) and excellent antioxidant activity. These findings will enhance the understanding of structural transformations of the lignin during the integrated process and maximize the lignin valorization in a current biorefinery process.

Estimating Water Content in Water–Oil Mixtures and Porous MEDIA They Saturate: Joint Interpretation of NMR Relaxometry and Dielectric Spectroscopy

This article deals with the topical problem of estimating water content in water–oil mixtures within porous media they saturate, according to low-field NMR relaxometry and dielectric spectroscopy. The aim of the research is experimental validation of the capability of complex data interpretation to acquire information on the filtration-volumetric properties of drill cuttings, relaxation characteristics of oil-containing fluids, the water/oil ratio in water–oil mixtures, and their saturation of drill cuttings to control the composition of liquids produced from boreholes. The studies are carried out on samples of cuttings and oils taken from fields in the Northern regions of the West Siberian oil-and-gas province, where NMR studies have not been performed before. Based on the experimental data obtained, the possibility of water content assessment in water-in-oil mixtures and porous media they saturate were proved through NMR relaxometry. With the use of the proposed methodology, the amount of water in oil–water mixtures was established, and their main NMR characteristics were determined. The relative error in evaluating the proportion of water in mixtures based on high-viscosity oils is less than 10%, and about 20% for those based on light oils. When determining the oil–water ratio in the pore space of the drill cuttings, the error is about 15%. It was proven that joint use of these two techniques makes it possible to increase the reliability of the oil–water ratio assessment of all the samples studied. Furthermore, it was revealed that the NMR spectrum shifts to the right, and the spectrum of the complex permittivity shifts downwards during the transition from high-viscosity oils to light ones.

NMR characterization of fluid mobility in low-permeability conglomerates: An experimental investigation of spontaneous imbibition and flooding

Understanding fluid mobility during spontaneous imbibition (SI) and flooding is important for the enhancement of oil recovery. Many researches on SI, water flooding (WF), and N2 flooding (NF) have been published, but an in-depth understanding of the oil mobility at the pore scale is still inadequate in low-permeability reservoirs. To solve this problem, SI, WF, and NF experiments were performed on the low-permeability conglomerates of the Baikouquan Formation and the Urho Formation in the Mahu Sag. Moreover, online NMR was introduced to monitor the oil volume in pores with different sizes in real-time. Considering the wettability, mineral compositions, and pore structure, we established a schematic diagram to reveal the fluid mobility mechanism. The results show that the micropores in the low-permeability conglomerates are more hydrophilic, whereas the other pores are more lipophilic. During SI, the movable oil is mainly distributed in the micropores in the form of clay-bound oil (CBO), which is discharged from the rock through the meso/macropores. High hydrophilicity contributes to a high imbibition rate and oil recovery from SI, while the pore structure only affects the imbibition rate. During WF, the movable oil is contributed by CBO in the micropores and free oil (FO) in the pores controlled by throats >0.3 μm. During NF, the movable oil is mainly distributed in the pores controlled by > 0.1 μm throats, existing as FO and part capillary-bound oil (CAO). The results demonstrate that NF is effective to enhance the oil recovery of tight reservoirs, while WF is only effective for tight reservoirs with better pore structure (high Vr > 0.3 μm).

A synergistic hydrothermal-deep eutectic solvents (DES) pretreatment for acquiring xylooligosaccharides and lignin nanoparticles from Eucommia ulmoides wood

To achieve an effective deconstruction for preparation of xylooligosaccharides (XOS) and lignin nanoparticles (LNPs) from Eucommia ulmoides, a synergistic pretreatment was successfully developed. Herein, the hemicelluloses were preferentially dissociated in acetic acid-catalyzed hydrothermal pretreatment (HTP) for preparation of XOS, and the hydrothermally-pretreated substrate was then subjected to deep eutectic solvents (DES) delignification for fabrication of LNPs. Results showed that the optimal yield (33.88% based on xylan) of XOS is obtained under the given HTP condition (170 °C, 0.5 h). NMR characterization showed that the linkages of lignin were mainly composed of β-O-4, β-β, β-5, etc. Besides, GPC analysis showed that the molecular weight of DES lignin fractions was lower (1130–1200 g/mol) than those of corresponding parent lignin fractions (8500–9620 g/mol). Further TEM characterization indicated that the optimal LNPs fraction has a narrow size distribution and the corresponding size is ranged from 60 to 110 nm. In short, the synergistic pretreatment could be used as a green and cost-effective approach for the development of bio-based chemicals and biomaterials from Eucommia ulmoides biomass.

Microscopic Structure and Binding Mechanism of the Corrosion-Protective Film of Oleylpropanediamine on Copper in Hot Water

The structure of the film formed by oleylpropanediamine (OLDA) on the copper (Cu) metal surface in water at 150 °C was investigated by combining quantitative NMR and surface characterization methods. We succeeded in quantifying the amount of film formation by precisely determining all mass balances in the systems examined. 2D IR microscopic mapping showed that the film thickness is uneven in the horizontal direction with a length scale of ∼100 μm and hundreds of OLDA layers. This film thickness was also confirmed by AFM. The analysis of the C–H stretching vibrational frequency disclosed that the alkyl chains are highly ordered in the layers close to the Cu surface and are conformationally disordered in the layers distant from the Cu surface in the thicker portion of the film. Combining XPS measurements using argon gas cluster ion beam etching with the ICP-AES analysis, we revealed that the key to multiple layering is the formation of a coordination complex of the unprotonated amino groups of OLDA with Cu that presumably results in polymer chain-like network structures. Contact angle measurements at different OLDA concentrations and treatment times showed that the water repellency of the film originated from the thick layering of OLDA molecules with disordered hydrophobic chains.

NMR Characterization of Lignans.

Lignans are particularly interesting secondary metabolites belonging to the phenyl-propanoid biosynthetic pathway. From the structural point of view, these molecules could belong to the aryltetralin, arylnaphtalene, or dibenzylbutyrolactone molecular skeleton. Lignans are present in different tissues of plants but are mainly accumulated in seeds. Extracts from plant tissues could be characterized by using the NMR-based approach, which provides a profile of aromatic molecules and detailed structural information for their elucidation. In order to improve the production of these secondary metabolites, elicitors could effectively stimulate lignan production. Several plant species are considered in this review with a particular focus on Linum species, well recognized as the main producer of lignans.

Polyether sulfone and Li6.4La3Zr1.4Ta0.6O12 based polymer-in-ceramic electrolyte with enhanced conductivity at low temperature for solid state lithium batteries

Developing solid state lithium batteries (SSLBs) is an essential step to overcome current safety and energy density issues of traditional Li-ion batteries. As the core component of SSLBs, a solid electrolyte with high ionic conductivity, great physical and chemical properties is still under exploration. Herein, a novel “polymer in ceramic” composite polymer-ceramic electrolytes (CPEs) is reported, which is composed of a polyether sulfone (PESF) polymer and cubic Li6.4La3Zr1.4Ta0.6O12 (LLZTO) ceramic with high contents (up to 80 wt. %). The as-prepared PESF-LLZTO CPEs possess good heat resistance and high mechanical strength to maintain structural integrity. The optimized 0.2PESF-0.8LLZTO CPEs exhibits an excellent ionic conductivity of 4.13×10−4 S cm−1 with a tLi+value as high as 0.64 at 20 °C after wetted by trace wetting agent (6.0 ul cm−2). More impressively, the ionic conductivity is still reached 1.49×10−4 S cm−1 at -10 °C and 9.42×10−4 S cm−1 at 80oC. Meanwhile, the 0.2PESF-0.8LLZTO CPEs shows a broad electrochemical window (≤4.8 V vs. Li+/Li) and an excellent compatibility with Li metal. Density functional theory calculations and 6Li solid-state NMR characterizations suggest that strong interactions among LLZTO, PESF and wetting agents contribute to the enhanced conductivity. As a proof for practical application, the Li||0.2PESF-0.8LLZTO CPEs||LiFePO4 full cells deliver a specific discharge capacity of 133.2 mAh g−1 at 2.0 C, and successfully run over 80 cycles at 0.5 C without capacity attenuation at 20 °C. The full cell also demonstrates a possibility for the application at low temperature down to -10oC and high temperature up to 60oC. This work brings a new perspective for high-performance SSLBs.

Isolation, NMR characterization and bioactivity of a (4-O-methyl-α-D-glucurono)-β-D-xylan from Campomanesia xanthocarpa Berg fruits

Hemicellulose-type polysaccharides were isolated from Campomanesia xanthocarpa fruits by alkaline extraction and submitted to fractionation processes giving rise to eluted (GE-300) and retained (GR-300) fractions. GE-300 presented a mixture of galactoglucomannans (GGM) and glucuronoxylans (MGX), while the GR-300 fraction is composed only of MGX. In this way, the chemical structure of MGX, investigated by 1D 1H, 13C and 2D 1H–13C HSQC, 1H–1H COSY and 1H–13C HMBC NMR spectroscopy, revealed that the chemical structure of polysaccharide is a (4-O-methyl-α-D-glucurono)-D-xylan. Deep and precise NMR chemical shift determination of clean and specific 1H NMR glycosyl units were developed by 1D TOCSY and 1D NOESY analysis. This approach demonstrated unequivocally that 4-O-methyl-α-D-glucopyranosyl uronic acid group is linked to O-2 of a (1 → 4)-β-D-xylan in the main chain. Furthermore, MGX scavenged DPPH radical (0.5 to 1.0 mg mL−1) and was not cytotoxic to human dermal fibroblasts at concentrations up to 1.0 mg mL−1, as demonstrated by neutral red and crystal violet assays, evidencing in vitro biocompatibility. The structure elucidation of GR-300 together with its bioactivity assessment contributed to better understand the chemical characteristics of C. xanthocarpa hemicelluloses and may provide structural basis for future structure-property studies.