Solid-state 13C Nuclear Magnetic Resonance Research Articles

Monitoring crystallite fusion of nanocellulose during colloid condensation

The crystallinity of cellulose decreases when bundled microfibrils are dispersed in water as cellulose nanofibers (CNFs) or physically separated into finer nanoscale fibrils or single microfibrils. The crystallinity of these CNFs is recovered when they become densely assembled through the dehydration of the dispersion. In this process, multiple CNFs are assumed to partially fuse, leading to the enlargement of crystallite widths. The mechanism of this CNF fusion is, however, not well understood. In this study, the recovery process of the crystallinity of CNFs was monitored by sampling wet CNF gels during condensation from a dilute dispersion to a dense aggregate, followed by wide-angle X-ray diffractometry (WAXD) and solid-state 13C nuclear magnetic resonance (NMR) spectroscopy analyses after supercritical drying. In the WAXD analysis, a two-step enlargement in the (2 0 0) crystal size was observed: the first step was a rapid increase in the range of solid content up to 1%, followed by a gradual increase in the range of 1–85%. The crystallinity index estimated by NMR hardly changed in the range of 0.5–30% but gradually increased in the range of 30–85%. A portion of the CNF samples, without drying, were also subjected to small-angle X-ray scattering and viscoelasticity analyses, indicating that the inter-CNF contact points in water significantly increased until reaching a solid content of 1%, and then at solid contents higher than 1%, the contact areas of each point gradually expanded. Finally, a mechanism of CNF fusion was proposed based on these results.

Structural and physical properties of proton-conducting polyacrylic acid/alginic acid/1,2,4-Triazole composite membranes

Composite membranes based on polyacrylic acid (PAA), alginic acid (AA), and triazole (Tz) ((1 − x)PAA–xAA–yTz) were developed. The effect of the membrane flexibility on the proton conductivity and thermal stability was examined. The local structure and molecular motion of the polymer matrix and Tz in the membranes were investigated by solid-state 13C and 2H nuclear magnetic resonance. The activity of the pseudoisotropic rotation of Tz increases with the increase in the flexibility of the composite membranes. This plays an important role in the proton conduction of (1 − x)PAA–xAA–yTz at high temperatures. The introduction of Tz into PAA improves its flexibility. However, the membrane with the highest flexibility became too soft to retain its shape at high temperatures, preventing the conductivity measurements. Adding an appropriate amount of AA to the PAA and Tz composite to reduce the membrane flexibility results in a significant enhancement in the proton conductivity and thermal stability.

Calcium carbonate regulates soil organic carbon accumulation by mediating microbial communities in northern China

Mineral organic complexes are essential for the storage of soil organic carbon (SOC) in agricultural soils. They are also affecting the CO2 emission reduction goals of known as the “doublecarbon target” (carbon peaking and carbon neutrality), as well as a landing point for achieving the 4 per 1,000 carbon enhancement initiative. As a typical soil mineral, calcium (Ca) plays a very critical role in regulating the accumulation of global organic carbon. Although calcium carbonate (CaCO3) has been shown to mediate the SOC accumulation process, especially in northern China, the relationship between Ca and SOC, and the underlying microbial mechanisms remain unclear. In this study, five soils (black soil, light chernozem soil, fluvo-aquic soil, sierozem soil, and loess soil) with different CaCO3 contents (4.29, 17.45, 98.66, 131.85, 143.82 g/kg, respectively) were selected to reveal the relationship among CaCO3, the SOC fraction and the chemical structure, and the bacterial community. The content of CaCO3 was determined by the gas volume method. Solid-state 13C nuclear magnetic resonance (NMR) spectroscopy was used to analyze the chemical structure of SOC, and 16S rRNA gene amplicon sequencing was used to analyze the bacterial community. The results showed that the contents of particulate organic carbon (POC) and mineral-associated organic carbon (MOC) in macro-aggregates were higher than that in micro-aggregates, and that POC was significantly higher than MOC in soil with high CaCO3. With an increase in the CaCO3 content, there was a decrease in the proportion of aromatic C and alkyl C, but an increase in the proportion of O-alkyl C in SOC, the relative abundance of Proteobacteria and Chloroflexi grew, and that of Acidobacteria decreased. Moreover, the overall diversity of the soil bacteria likewise showed a decreasing trend. High CaCO3 soils showed a positive correlation between Acidobacteria and macro-aggregates, and a negative correlation with clay and silt, when compared to low CaCO3 soils. Also, Chloroflexi and Gemmatimonadota showed the opposite relationship with SOC aggregates. CaCO3 influenced the relationship between SOC (fraction and chemical structure) and the bacterial community, resulting in changes in the SOC content within the aggregates. Our results indicate that CaCO3 plays an essential role in the accumulation of SOC and reveal the mechanisms of carbon sequestration in calcareous soils in northern China.

The impact of maize straw incorporation on arsenic and cadmium availability, transformation and microbial communities in alkaline-contaminated soils

Increasing evidence of the uncertainty of crop straw returning in heavy metal-contaminated soil is a significant concern. The present study investigated the influence of 1 and 2% maize straws (MS) amendment on As and Cd bioavailability in two different alkaline soils (A-industrial and B-irrigation) after 56 days of ageing. Adding MS to the two soils decreased the pH by 1.28 (A soil) and 1.13 (B soil) and increased the concentration of dissolved organic carbon (DOC) by 54.40 mg/kg (A soil) and 100.00 mg/kg (B soil) during the study period. After 56 days of ageing, the overall NaHCO3–As and DTPA-Cd increased by 40% and 33% (A) and 39% and 41% (B) soils, respectively. The MS additions increased the alteration of As and Cd exchangeable and residual fractions, whereas advanced solid-state 13C nuclear magnetic resonance (NMR) revealed that alkyl C and alkyl O–C–O in A soil and alkyl C, Methoxy C/N-alkyl, and alkyl O–C–O in B soil significantly contributed to the As and Cd mobilisation. Collectively, 16 S rRNA analyses revealed Acidobacteria, Firmicutes, Chloroflexi, Actinobacteria and Bacillus promoted the As and Cd mobilisation following the MS addition, while principle component analysis (PCA) demonstrated that bacterial proliferation significantly influenced MS decomposition, resulting in As and Cd mobilisation in the two soils. Overall, the study highlights the implications of applying MS to As- and Cd-contaminated alkaline soil and offers the framework for conditions to be considered during As- and Cd-remediation efforts, especially when MS is the sole remediation component.

Molecular simulation of the adsorption and diffusion characteristics of CH4 in coal subjected to N-Methylpyrrolidone treatment

Chemical stimulation of the coal reservoir is a potential method for enhancing coalbed methane production. N-Methylpyrrolidone (NMP) solvent extraction is a promising chemical stimulation method. To evaluate the effects of NMP treatment on the adsorption and diffusion characteristics of CH4 in coal, the coal molecular model was established based on elemental analysis analysis, solid-state 13C nuclear magnetic resonance (13C NMR) and X-ray photoelectron spectroscopy (XPS). Then, the adsorption and diffusion characteristics of methane were simulated using Materials Studio software and the distribution of methane molecules around functional groups was studied. The simulation results show that: under the action of NMP solvent, the saturated adsorption capacity of methane molecules was reduced by 41.6%, and the diffusion capacity was increased by 1.72 times. Additionally, methane molecules were mainly enriched around hydroxyl groups and thiophenes, and adding NMP reduced the methane enrichment around functional groups. These show that NMP treatment can promote the diffusion of methane from coal matrix. Hydroxyl and thiophenes affect the diffusion of methane molecules. This study helps to understand the effect of NMP solvent on the adsorption and diffusion mechanism of coal methane from a molecular perspective.

Universal strategy for constructing antibioadhesive and robust coatings for wood

The demand for surface antibioadhesion of wood, the most widely used material for interiors, has increased due to health concerns. For achieving antibioadhesion, the surface energy of wood materials must be reduced and their micro/nanostructure roughness must be increased. Inspired by lotus leaves, poly(pentafluorophenyl isocyanide) (PFPI)-grafted wood (wood-g-PFPI) with micro/nanostructure roughness and low surface energy was developed by grafting PFPI into the wood structure at the molecular level via thiol–ene click chemistry. The chemical structure, morphology, and water contact angle of wood-g-PFPI were characterized via Fourier transform infrared spectroscopy, solid-state 13C nuclear magnetic resonance spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and contact angle measurements. Wood-g-PFPI10 exhibited excellent hydrophobicity (162°), antibacterial adhesion (Staphylococcus aureus and Escherichia coli), antifriction as well as self-cleaning properties, and biocompatibility owing to the increased surface roughness of the ring helical structure of the grafted PFPI. This method makes full use of the molecular characteristics of wood, so it can also be transferred to all the cellulosic substrates, such as fabric, paper and so on. Regardless of the size and space constraints of the substrate, this modification method has the potential for antibioadhesion and other applications of helical polymers.

Phosphorus/Sulfur-Enriched Reduced Graphene Oxide Papers Obtained from Recycled Graphite: Solid-State NMR Characterization and Electrochemical Performance for Energy Storage

The reduction of graphene oxide (GO) by means of thermal and/or chemical treatments leads to the production of reduced graphene oxide (rGO)—a material with improved electrical conductivity and considered a viable and low-cost alternative to pure graphene in several applications, including the production of supercapacitor electrodes. In the present work, GO was prepared by the oxidation of graphite recycled from spent Li-ion batteries using mixtures of sulfuric and phosphoric acids (with different H2SO4/H3PO4 ratios), leading to the production of materials with significant S and P contents. These materials were then thermally reduced, resulting in rGO papers that were investigated by solid-state 13C and 31P nuclear magnetic resonance, along with other methods. The electrochemical properties of the produced rGO papers were evaluated, including the recording of cyclic voltammetry and galvanostatic charge–discharge curves, besides electrochemical impedance spectroscopy analyses. The samples obtained by thermal reduction at 150 °C exhibited good rate capability at high current density and high capacitance retention after a large number of charge–discharge cycles. The results evidenced a strong relationship between the electrochemical properties of the produced materials and their chemical and structural features, especially for the samples containing both S and P elements. The methods described in this work represent, then, a facile and low-cost alternative for the production of rGO papers using graphite recycled from spent batteries, with promising applications as supercapacitor electrodes.

Stabilization of a flavoprotein for solid-state photo-CIDNP MAS NMR at room temperature by embedding in a glassy sugar matrix

Hyperpolarization via the solid-state photochemically induced dynamic nuclear polarization (photo-CIDNP) effect can be detected in frozen solutions of electron transfer proteins generating a radical-pair upon illumination. The effect has been observed in various natural photosynthetic reaction centers and in light-oxygen-voltage (LOV) sensing domains incorporating a flavin mononucleotide (FMN) as chromophore. In LOV domains, where a highly conserved cysteine is mutated to a flavin to interrupt its natural photochemistry, a radical-pair is generated by electron transfer from a nearby tryptophan to the photoexcited triplet state of FMN. During the photocycle, both the LOV domain and the chromophore are photochemically degraded, e.g., by the formation of singlet oxygen. This limits the time for collection of hyperpolarized nuclear magnetic resonance (NMR) data. We show that embedding of the protein into a trehalose sugar glass matrix stabilizes the protein for 13C solid-state photo-CIDNP NMR experiments which can be conducted at room temperature in a powder sample. Additionally, this preparation allows for incorporation of high amounts of protein further boosting the intensity of the detected signals from FMN and tryptophan at natural abundance. Signal assignment is aided by quantum chemical calculations of absolute shieldings. The underlying mechanism for the surprising absorption-only signal pattern is not yet understood. Comparison to calculated isotropic hyperfine couplings imply that the enhancement is not due to the classical radical-pair mechanism (RPM). Analysis of the anisotropic hyperfine couplings associated with solid-state photo-CIDNP mechanisms also show no simple correlation, suggesting a more complex underlying mechanism.

Insight into the mechanisms for pyrolyzing organic macromolecular structure of subbituminous coal by comparing the extraction and flash pyrolysis

Investigating the organic structure of coal is an essential basic research for producing clean fuels and value-added fine chemicals by the clean and efficient utilization of coal. As a consequence, the structural characteristics of organic macromolecular in subbituminous coal (SBC) were analyzed at different levels using multiple destructive and non-destructive technical strategies. Correspondingly, the pyrolysis mechanisms of SBC organic macromolecular structure were investigated to understand through the molecular level correlation group component from extraction portion (EP) and flash pyrolysis (FP). In detail, solid-state 13C nuclear magnetic resonance analysis indicates that carbon skeleton of SBC mainly consists of aliphatic carbons (48.5%) and aromatic carbons (50.3%). The number of substituents on each aromatic ring in SBC is up to 2 on average and aliphatic linkages connect 3–4 aromatic rings. X-ray photoelectron spectrometer analysis exhibits that the >C–O- groups, pyrrolic, and sulfonic sulfurs of organic components are the most abundance O-, N-, and S-containing species, which is consistent with Fourier transform infrared and solid-state 13C nuclear magnetic resonance. The destructive analysis with thermogravimetric implies that organic macromolecular structure in SBC consists different types of covalent bonds (>Cal-X) with different strength. Furthermore, the contents of chain alkanes (CAs, 17.4%), arenes (62.7%), and oxygen-containing organic species (OCOSs, 18.0%) in EP from SBC (EPSBC), while the CAs (53.1%), alkenes (7.4%), arenes (27.3%), and OCOSs (7.5%) in FP of SBC (FPSBC). Comprehensive comparative analysis of detectable small molecule species from EPSBC and FPSBC further indicate that the cleavage > Cal-X bridge bonds of organic macromolecular structure in SBC attack by active hydrogen (H‧) through the pyrolysis reaction to obtain more alkenes, CAs, alkanols, and phenols.

Alkoxide-Decorated Copper Nanoparticles on Amidine-Modified Polymers as Hydrogenation Catalysts for Enabling H2 Heterolysis

Direct formation of Cu nanoparticles was accomplished on an amidine- and guanidine-functionalized polymer (polystyrene-bound 1,8-diazabicyclo[5.4.0]undec-7-ene (PS-DBU) and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (PS-TBD), respectively) by thermal treatment of Cu(acac)2 (acac = acetylacetonato) in methanol under pressurized H2. The immobilized structure was characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES), elemental analysis, and microscopic analysis. X-ray photoelectron spectroscopy (XPS) data indicated that the nanoparticles consisted of Cu(0) and oxygenated Cu(I). The Cu(0)/Cu(I) ratio was determined by X-ray absorption spectroscopy. In particular, X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) studies indicated the inclusion of alkoxides bound to Cu nanoparticles. Further 13C-labeled experiments allowed us to identify the Cu methoxide species by solid-state 13C nuclear magnetic resonance (NMR). A series of alkoxide-incorporated Cu nanoparticles were proven to facilitate H2 heterolysis and were applied in the catalytic hydrogenation of CO2 to formate salts in the presence of a nitrogen base. The catalytic activity increased with decreased mean particle size and increased Cu(I) content, indicating that the Cu(I) alkoxide species played an indispensable role in hydrogenation. The combination of Cu/PS-DBU and 2-tert-butyl-1,1,3,3-tetramethylguanidine (BTMG) achieved a maximum turnover number of 2450 at 100 °C without leaching or aggregation of the nanosized catalysts.

Solid-state 13C NMR spectroscopic study of supercritical CO2 catalyzation treated polyethylene terephthalate textiles for platinum metallization

In this study, polyethylene terephthalate (PET) textiles were metallized with Pt via supercritical carbon dioxide (sc-CO2) catalyzation, using palladium(II) hexafluoroacetylacetonate (Pd(hfac)2) as the Pd catalyst source. The effects of the treatments on the structural changes and molecular mobility of PET were elucidated by solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. The carbonyl and nonprotonated aromatic carbons and the methylene and protonated aromatic carbons were analyzed from the NMR spectra using a three-component model (crystalline, rigid amorphous, and mobile amorphous components), which inferred that the PET polymer textile comprised one crystalline and two amorphous regions. Additionally, when Pd catalyzation was performed on the textile under sc-CO2 conditions, the crystalline peak of the carbonyl carbon exhibited a chemical shift into a higher magnetic field, and the spin–lattice relaxation time increased. These results implied that Pd could exist in the vicinity of the CO carbon. The X-ray diffraction studies also showed crystallinity of PET increased by sc-CO2 catalyzation, while sc-CO2 annealing without Pd(hfac)2 did not increase it. Therefore, Pt films were successfully coated on the PET via catalytic plating using sc-CO2. The catalyzation reduced the molecular mobility of the PET polymer, indicating the incorporation of the catalytic metal into the polymer chain. The carbonyl carbon peak simultaneously shifted to a higher field, implying that the catalytic Pd could approach the carbonyl groups. The detailed analysis of the structure and molecular mobility provides valuable information that can contribute to the development of novel conductive materials.

Studies of Organic Matter in Composting, Vermicomposting, and Anaerobic Digestion by 13C Solid-State NMR Spectroscopy

Composting, vermicomposting, and anaerobic digestion are three commonly applied processes for the transformation of organic waste into valuable products for soil amendment. The application of compost, vermicompost, and digestate to soil requires specific properties, such as maturity and stability, strongly related to the composition of organic matter. 13C solid-state Nuclear Magnetic Resonance (SSNMR) has often been applied to follow the transformation of organic matter during waste treatment processes, as well as to assess the quality of the produced amendments and the effectiveness of the treatments. Thanks to the possibility of associating the 13C chemical shift to different functional groups of biomacromolecules present in the waste feedstocks and in the final products, thorough characterizations of organic matter have been performed exploiting 13C cross-polarization magic angle spinning experiments, and semiquantitative descriptions of the evolution of the different groups during composting, vermicomposting and anaerobic digestion have been reported. Here, these studies are reviewed with the aim of highlighting the potential of the application of 13C SSNMR to these complex materials, as well as the critical issues and perspectives.

Chronic Warming and Nitrogen-Addition Alter Soil Organic Matter Molecular Composition Distinctly in Tandem Compared to Individual Stressors

Forest soils are major reservoirs of carbon (C), but these stores are threatened by increasing global temperatures and atmospheric nitrogen (N) deposition. These environmental stressors can alter soil microbial communities and soil organic matter (SOM) biogeochemistry through a variety of mechanisms. To investigate the impact of chronic warming, N-addition, and simultaneous warming and N-addition (warming + N) on forest soils, soil samples from the Harvard Forest Soil Warming and Nitrogen Addition (SWaN) experiment were analyzed after 14 years. Elemental analysis, targeted compound analysis by gas chromatography–mass spectrometry, and 13C nuclear magnetic resonance (NMR) spectroscopy were used to analyze changes in SOM in both the organic and mineral (0–10 cm) soil layers. Overall, changes in the molecular composition and microbial biomass were observed, but the extent of differences was unique to warming, N-addition, and warming + N treatments. Specifically, N-addition slowed SOM decomposition as measured via solid-state 13C NMR, while warming and warming + N accelerated SOM decomposition. Continued SOM decomposition after 14 years with warming + N signified a pronounced change to observations made after 4 and 10 years of experimental treatment. This is also demonstrative of how a two-factor approach leads to a unique molecular-level response that cannot be predicted from experiments with individual stressors alone. This study emphasizes the need to observe environmental stressors in tandem using a combination of molecular-level approaches to obtain a comprehensive understanding of how persistent anthropogenic activity will fundamentally alter forest soil systems.

Preparation and characterization of glucose-based covalent organic polymer coated silica as stationary phase for high-performance liquid chromatography

Carbohydrate is a renewable, sustainable, hydrophilic, and biodegradable natural product, which is widely used in the field of adsorption. In this study, a glucose-based covalent organic polymer (COP) coated silica was fabricated by facile solvent knitting reaction between tetrabenzylglucose and silica-phenyl with anhydrous aluminum trichloride as catalyst, forming a core-shell stationary phase (donated as SiO2@COPBn-glu) for high performance liquid chromatography. The prepared SiO2@COPBn-glu was characterized by scanning electron microscopy, transmission electron microscopy, Fourier-transform infrared spectrometry, solid-state 13C nuclear magnetic resonance spectrometry, X-ray photoelectron spectroscopy, and N2 adsorption-desorption experiments. Owing to the coexistence of benzene units and alkyl, hydroxyl and ether groups in the skeleton of COPBn-glu shell, the developed chromatographic packing exhibited reversed-phase/hydrophilic interaction mixed-mode with multiple retention mechanisms, such as hydrophobic, π-π, hydrogen bonding, and electron donor-acceptor interactions. The results revealed that the SiO2@COPBn-glu column demonstrated excellent selectivity and retention behavior for both hydrophilic and hydrophobic compounds with good repeatability and stability. Meanwhile, the chromatographic performance of the prepared SiO2@COPBn-glu column was compared with a C18 column to assess the role of the coating COPBn-glu shell. Therefore, the development of the SiO2@COPBn-glu stationary phase expands the potential application of COPs in separation field.

Deterioration of Microstructures and Properties in Ancient Architectural Wood from Yingxian Wooden Pagoda (1056 AD) during Natural Aging

The Yingxian Wooden Pagoda (1056 AD), located in Shanxi province, China, is a unique architectural pure-wooden artifact standing for a millennium. Despite its longevity, the structures and properties of the ancient architectural woods used in its construction have been significantly degraded due to long-term natural aging, which has profoundly impacted the preservation of this valuable cultural heritage. To better understand this degradation, we studied the deterioration of a baluster (Larix principis-rupprechtii Mayr.) from Yingxian Wooden Pagoda. The study employed various analytical techniques, including optical microscopy, atomic force microscopy, Fourier-transform infrared spectroscopy, solid-state 13C nuclear magnetic resonance spectroscopy, X-ray diffraction, and nanoindentation technology, to evaluate the microstructures and properties of the ancient architectural woods. Results indicated that the destruction of wood cell walls was primarily transverse transwall destruction and interfacial debonding and that the degradation of chemical components was primarily in the hemicellulose (xylan) and amorphous region of cellulose. The reduced elastic modulus and hardness of tracheid cell walls in the ancient architectural woods were higher than in recent larch woods. This study would help deepen understanding of wood deterioration during long-term natural aging for the subsequent preservation and protection of wooden cultural heritages and longer use of ancient timber constructions.

13C, 25Mg, and 43Ca Solid-State NMR for the Purpose of Dolomitic Marbles Provenance Elucidation.

The study of the provenance of dolomitic marble artefacts has become relevant since it was discovered that quarries of this marble other than that of Cape-Vathy located on the island of Thasos have been exploited since Antiquity. To improve our knowledge about the provenance of materials and the extent of their dispersion, multiple archaeometric studies were performed in the past including isotope analyses, petrography, cathodoluminescence, and elemental analyses. In the present work, solid-state nuclear magnetic resonance (NMR) spectroscopy has been added to this panel of techniques. NMR allows the characterization of the material at a molecular level by looking at different nuclei: carbon, magnesium, and calcium. Statistical analysis of the data collected on both quarry samples and archaeologic items was also implemented and clearly demonstrates the efficiency of a holistic approach for provenance elucidation. Finally, the first 25Mg NMR tests have shown the potential of this technique to discriminate between dolomitic marbles of different provenance. The results are discussed in terms of their historical meaning and illustrate the exploitation of sources of dolomitic marbles other than the Greek Thasos source.

Synthesis, spectroscopic characterization, antibacterial activity and antiproliferative profile of a new silver(I) complex of 5-fluorocytosine

In this paper, we report the synthesis, structural characterization, and explore the potential antibacterial and antiproliferative activities of a new silver(I) complex of the nucleotide analogue 5-fluorocytosine, Ag-5FC. Elemental and thermogravimetric (TGA) analyses led to the minimal formula AgC4H4FN3O·H2O. Infrared (FT-IR) and solid-state 13C nuclear magnetic resonance (NMR) spectroscopic analyses indicate that the ligand coordinates to the metal ion by its nitrogen and oxygen atoms. High resolution mass spectrometric (HRMS) data confirmed the proposed composition of the complex as well as the presence of recombination species in solution. Molecular modeling reinforces the proposed N,O-coordination of 5FC to silver as indicated by IR data with a possible structure of the complex in a dimeric form, of coordination formula [Ag(C4H4FN3O)(OH2)]2. The complex showed a modest antimicrobial activity (MIC = 4.3 mmol⋅L−1) against Gram-negative (Pseudomonas aeruginosa and Escherichia coli) and Gram-positive (Staphylococcus aureus and Bacillus cereus) strains. Despite the low solubility, the Ag-5FC complex totally inhibited the proliferation of colon (HT-29), multidrug resistant ovarian (NCI/ADR-RES), prostate (PC-3), and renal (786–0) tumor cell lines in a concentration range of 6.2 to 9.3 µmol L−1. Further studies are necessary to confirm efficiency and safety for continuing the pre-clinical evaluation of the Ag-5FC complex.

Understanding the molecular structure of Datong coal by combining experimental and computational study

Understanding the structure of coal is crucial to explain its chemical reactivity. In order to study the microstructure characteristics of coal in-depth, ultimate analysis, solid-state 13C nuclear magnetic resonance (13C-NMR), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) are used to analyze the Datong coal. The results show that the aromaticity of Datong coal is 62.60%, and the ratio of aromatic bridge carbon to aromatic peripheral carbon is 0.238, indicating that more naphthalene and anthracene are in the aromatic structure of coal. Hydroxyl (C–O), carbonyl (C=O) and carboxyl (COO–) are the main oxygen-containing groups in coal, and the nitrogen element mainly exists in the form of pyrrole and pyridine. The main substitution modes on the benzene ring are di- and tri-substituted. Based on the above analysis, the 2D and 3D macromolecular models are constructed and optimized by using computer-aided modeling. The model is verified by 13C-NMR and FTIR spectra with density functional theory calculations. The coal molecular formula is defined as C149H112O24N2. The reaction sites in coal structure are oxygen-containing functional groups and aliphatic structures (–CH, –CH2). Therefore, the molecular structure of Datong coal has been systematically described and understood at the molecular level based on experimental data and quantum chemical calculations.

Synthesis of Enantioselective Solid Tandem Catalysts with Tethered Molecular Functionalities

A synthetic protocol was developed to prepare a bifunctional heterogeneous catalyst with phosphonic acid and cinchonidine moieties tethered to a mesoporous silica support (SBA-15). The nature of the bond of the molecular groups to the surface was characterized by 29Si solid-state nuclear magnetic resonance (NMR), and the retention of the integrity of the tethered groups throughout the individual synthetic steps was characterized by 13C and 31P solid-state NMR. The ratio of acidic to basic sites could be controlled by tuning the intermediate acid-site removal procedure, which relies on the use of UV/ozonolysis and was quantified by a combination of the analysis of pore-size distribution data (extracted from N2 adsorption–desorption isotherms), acid–base titrations, and carbon and nitrogen elemental analysis. The performance of the resulting catalysts was tested for two processes, a deacetylation-Henry reaction sequence and a chiral cyano-ethoxycarbonylation reaction. In comparison with equivalent physical mixtures of two monofunctional SBA-15-catalysts with tethered phosphonic acid or tethered cinchonidine, respectively, the bifunctional catalysts displayed less activity but higher selectivity in the first system, with the surface silanol groups also playing an important role. In the second reaction, all activities were comparable, and enhanced enantioselectivity was observed with the new bifunctional catalyst. For the first reaction, a 1:1 ratio of coverages of the acidic and basic functionalities offered optimum performance, but in the second, more cinchonidine than phosphonic acid was needed. The catalysts also proved to be quite robust and to retain their activity after several recycling cycles.

Molecular insights into the methane adsorption capacity of coal under microwave irradiation based on solid-state 13C-NMR and XPS

Coalbed stimulation is a process of increasing coalbed methane (CBM) production by opening, enlarging, and extending the length, width, and connectivity of pores and fractures/cleats. Microwave irradiation is a promising thermal stimulation technique for coal reservoirs. To investigate the effects of microwave heating on the methane adsorption capacity of Pingdingshan bituminous coal, molecular models were constructed based on proximate analysis, ultimate analysis, solid-state 13C nuclear magnetic resonance (13C-NMR), and X-ray photoelectron spectroscopy (XPS). The results show that the condensation degree of the aromatic ring in Pingdingshan coal is 0.18, and the molecular formula is C143H153N3O5. Microwave irradiation causes the cracking of aromatic hydrocarbons, and the molecular formula of coal evolves into C132H133N3O4. After microwave irradiation, the saturated adsorption number of CH4 molecule decreases from 12 to 7, indicating that microwave heating can promote methane to diffuse from the coal matrix. Carboxyl and pyrrole are not favorable for methane adsorption. Microwave irradiation has the weakest effect on carbonyl. This study contributes to understanding the effect of microwave heating on CH4 adsorption mechanism of coal from the molecular perspective.