Cross-polarization Magic Angle Spinning Research Articles

Molecular evidence for the export of terrigenous organic matter to the north Gulf of Mexico by solid-state 13C NMR and Fourier transform ion cyclotron resonance mass spectrometry of humic acids

Sediment samples along a transect extending from the Mississippi River Birdsfoot Delta to the Mississippi Canyon on the Louisiana continental shelf were examined, by advanced analytical techniques, electrospray ionization coupled to a 12T Fourier transform ion cyclotron resonance mass spectrometer (ESI-FTICR-MS) and quantitative solid-state multiple cross polarization magic angle spinning (multi-CPMAS) 13C NMR, in an effort to understand the source and export of terrigenous organic matter to the Gulf of Mexico. Both NMR and mass spectral data indicate that condensed aromatics (CA) and carboxyl-containing aliphatic molecules (CCAM) are present at the mouth of the river, reflective of high contributions from terrigenous soil-like organic matter. Mass spectral peak magnitudes of CA diminish by 15%, with increasing distance offshore, and represent 30% of integrated NMR peak areas. In contrast, mass spectral and NMR CCAM peaks increase by 7 and 13%, respectively. These trends in humic acid extracts, provide novel molecular evidence of terrigenous organic matter deposition in offshore sediments.

Phenoloxidase activity and organic carbon dynamics in historic Anthrosols in Scotland, UK.

Phenolic compounds are chemical precursor building blocks of soil organic matter. Their occurrence can be inhibitory to certain enzymes present in soil, thereby influencing the rate of decomposition of soil organic matter. Microbe-derived phenoloxidases (laccases) are extracellular enzymes capable of degrading recalcitrant polyphenolic compounds. In this study, our aim was to investigate the relationships between phenoloxidase enzyme activity, organic carbon content and microbial abundance in the context of long-term anthropogenically amended soils. To achieve this, we used a series of complementary biochemical analytical methods including gas chromatography, enzyme assays and solid-state Carbon-13 Cross Polarisation Magic-Angle Spinning Nuclear Magnetic Resonance Spectroscopy (13C CPMAS NMR). Using several anthrosols found in St Andrews (Scotland, UK) that had been subjected to intense anthropogenic modification since the medieval period (11th century AD) to present-day, we were able to scope the impact of past waste disposal on soils. The long-term anthropogenic impact led to organic matter-rich soils. Overall, phenoloxidase activity increased by up to 2-fold with soil depth (up to 100 cm) and was inversely correlated with microbial biomass. Solid-state 13C NMR characterisation of carbon species revealed that the observed decline in soil organic matter with depth corresponded to decreases in the labile organic carbon fractions as evidenced by changes in the O/N-alkyl C region of the spectra. The increase in phenoloxidase activity with depth would appear to be a compensatory mechanism for the reduced quantities of organic carbon and lower overall nutrient environment in subsoils. By enzymatically targeting phenolic compounds, microbes can better utilise recalcitrant carbon when other labile soil carbon sources become limited, thereby maintaining metabolic processes.

Racing toward Fast and Effective 17O Isotopic Labeling and Nuclear Magnetic Resonance Spectroscopy of N-Formyl-MLF-OH and Associated Building Blocks.

Solid-state 1H, 13C, and 15N nuclear magnetic resonance (NMR) spectroscopy has been an essential analytical method in studying complex molecules and biomolecules for decades. While oxygen-17 (17O) NMR is an ideal and robust candidate to study hydrogen bonding within secondary and tertiary protein structures for example, it continues to elude many. We discuss an improved multiple-turnover labeling procedure to develop a fast and cost-effective method to 17O label fluoroenylmethyloxycarbonyl (Fmoc)-protected amino acid building blocks. This approach allows for inexpensive ($0.25 USD/mg) insertion of 17O labels, an important barrier to overcome for future biomolecular studies. The 17O NMR results of these building blocks and a site-specific strategy for labeled N-acetyl-MLF-OH and N-formyl-MLF-OH tripeptides are presented. We showcase growth in NMR development for maximizing sensitivity gains using emerging sensitivity enhancement techniques including population transfer, high-field dynamic nuclear polarization, and cross-polarization magic-angle spinning cryoprobes.

Fabrication of molecularly porous hyper-cross-linked thin film composite nanofiltration membrane using cyclic amine and linear cross-linker for highly selective organic solvent nanofiltration

A thin film composite molecularly porous hyper-cross-linked (TFC-MPCM) polyamide nanofiltration membrane was fabricated by interfacial polymerization using macrocyclic amine and linear cross-linker with acid chloride function at para-positions. The membrane was thoroughly characterized using Attenuated Total Reflectance-Fourier Transform Infra-red spectroscopy (ATR-FTIR), solid Cross Polarization-Magic Angle Spinning (CP-MAS) 13C NMR, Field Emission-Scanning Electron Microscopy (FE-SEM), Atomic Force Microscopy (AFM), Water Contact Angle (WCA), X-ray photoelectron spectroscopy (XPS) and Energy Dispersive X-ray spectroscopy (EDX) analysis showing the formation of continuous and dense polyamide active layer on the support. The membrane showed excellent performance in terms of permeate flux of the tested solvents including water, methanol, ethanol, isopropyl alcohol, acetone, n-hexane, and toluene. Membrane selectivity tests showed a rejection of >94% of Congo red (solute) from organic solvent (methanol) at 4 bar with a flux of 18.0 L m−2 h−1. The TFC-MPCM showed exceptional long-term stability in terms of rejection and flux.

A Description of the Local Structure and Dynamics of Ketoconazole Molecule by Solid‐State NMR Measurements and DFT Calculations: Proposition for NMR Crystallography

AbstractAn azole class antifungal agent, ketoconazole, is widely used in the treatment of mucosal fungal infections that arise due to AIDS immunosuppression, organ transplantation, and cancer chemotherapy. The structure and dynamics of various molecular moieties of ketoconazole are thoroughly studied by measuring chemical shift anisotropy tensor and site‐specific spin‐lattice relaxation time. The local correlation time at crystallographically different carbon nuclei sites is also calculated. The chemical shift anisotropy (CSA) parameters at the crystallographically distinct sites of ketoconazole are determined by the two‐dimensional phase‐adjusted spinning sideband (2D PASS) cross‐polarization magic angle spinning (CP‐MAS) solid‐state NMR experiment. The site‐specific spin‐lattice relaxation time is measured by the method outlined by Torchia (T1CP). The values of the principal components of CSA parameters extracted by the 2DPASS CP‐MAS ssNMR experiment are supported by density functional theory (DFT) calculations. The CSA parameters are high for those carbon nuclei, whose spin‐lattice relaxation rate is slow, and it is low for those carbon nuclei whose spin‐lattice relaxation rate is fast. It suggests that the spin‐lattice relaxation mechanism is mainly governed by chemical‐shift anisotropy interaction for these carbon nuclei. A huge variation of the spin‐lattice relaxation time and the local correlation time are observed for numerous carbon nuclei that reside on the side‐chain of the molecule. The spin‐lattice relaxation time varies from 500 s to 8 s, and the order of the local correlation time varies from s to s. These types of studies in which the chemical shift anisotropy (CSA) parameters and spin‐lattice relaxation time provide information about the electronic configuration and the spin dynamics at the various crystallographic locations of the drug molecule will enrich the field “NMR crystallography.” It will also help to develop the strategies for the administration of antifungal drugs by providing information about the structure and dynamics of various parts of the drug molecule.

Identification of a Novel Pyruvyltransferase Using 13C Solid-State Nuclear Magnetic Resonance To Analyze Rhizobial Exopolysaccharides.

The alphaproteobacterium Sinorhizobium meliloti secretes two acidic exopolysaccharides (EPSs), succinoglycan (EPSI) and galactoglucan (EPSII), which differentially enable it to adapt to a changing environment. Succinoglycan is essential for invasion of plant hosts and, thus, for the formation of nitrogen-fixing root nodules. Galactoglucan is critical for population-based behaviors such as swarming and biofilm formation and can facilitate invasion in the absence of succinoglycan on some host plants. The biosynthesis of galactoglucan is not as completely understood as that of succinoglycan. We devised a pipeline to identify putative pyruvyltransferase and acetyltransferase genes, construct genomic deletions in strains engineered to produce either succinoglycan or galactoglucan, and analyze EPS from mutant bacterial strains. EPS samples were examined by 13C cross-polarization magic-angle spinning (CPMAS) solid-state nuclear magnetic resonance (NMR). CPMAS NMR is uniquely suited to defining chemical composition in complex samples and enables the detection and quantification of distinct EPS functional groups. Galactoglucan was isolated from mutant strains with deletions in five candidate acyl/acetyltransferase genes (exoZ, exoH, SMb20810, SMb21188, and SMa1016) and a putative pyruvyltransferase (wgaE or SMb21322). Most samples were similar in composition to wild-type EPSII by CPMAS NMR analysis. However, galactoglucan produced from a strain lacking wgaE exhibited a significant reduction in pyruvylation. Pyruvylation was restored through the ectopic expression of plasmid-borne wgaE. Our work has thus identified WgaE as a galactoglucan pyruvyltransferase. This exemplifies how the systematic combination of genetic analyses and solid-state NMR detection is a rapid means to identify genes responsible for modification of rhizobial exopolysaccharides. IMPORTANCE Nitrogen-fixing bacteria are crucial for geochemical cycles and global nitrogen nutrition. Symbioses between legumes and rhizobial bacteria establish root nodules, where bacteria convert dinitrogen to ammonia for plant utilization. Secreted exopolysaccharides (EPSs) produced by Sinorhizobium meliloti (succinoglycan and galactoglucan) play important roles in soil and plant environments. The biosynthesis of galactoglucan is not as well characterized as that of succinoglycan. We employed solid-state nuclear magnetic resonance (NMR) to examine intact EPS from wild-type and mutant S. meliloti strains. NMR analysis of EPS isolated from a wgaE gene mutant revealed a novel pyruvyltransferase that modifies galactoglucan. Few EPS pyruvyltransferases have been characterized. Our work provides insight into the biosynthesis of an important S. meliloti EPS and expands the knowledge of enzymes that modify polysaccharides.

Stoichiomorphic halogen-bonded cocrystals: a case study of 1,4-diiodotetrafluorobenzene and 3-nitropyridine

The concept of variable stoichiometry cocrystallization is explored in halogen-bonded systems. Three novel cocrystals of 1,4-diiodotetrafluorobenzene and 3-nitropyridine with molar ratios of 1:1, 2:1, and 1:2, respectively, are prepared by slow evaporation methods. Single-crystal X-ray diffraction analysis reveals key differences between each of the nominally similar cocrystals. For instance, the 1:1 cocrystal crystallizes in the P21/n space group and features a single chemically and crystallographically unique halogen bond between iodine and the pyridyl nitrogen. The 2:1 cocrystal crystallizes in the [Formula: see text] space group and features a halogen bond between iodine and one of the nitro oxygens in addition to an iodine–nitrogen halogen bond. The 1:2 cocrystal crystallizes with a large unit cell (V = 9896 Å3) in the Cc space group and features 10 crystallographically distinct iodine-nitrogen halogen bonds. Powder X-ray diffraction experiments carried out on the 1:1 and 2:1 cocrystals confirm that gentle grinding does not alter the crystal forms. 1H → 13C and 19F → 13C cross-polarization magic angle spinning (CP/MAS) NMR experiments performed on powdered samples of the 1:1 and 2:1 cocrystals are used as spectral editing tools to select for either the halogen bond acceptor or donor, respectively. Carbon-13 chemical shifts in the cocrystals are shown to change only very subtly relative to pure solid 1,4-diiodotetrafluorobenzene, but the shift of the carbon directly bonded to iodine nevertheless increases, consistent with halogen bond formation (e.g., a shift of +1.6 ppm for the 2:1 cocrystal). This work contributes new examples to the field of variable stoichiometry cocrystal engineering with halogen bonds.

Effect of moisture uptake on the texture of dried laver Porphyra. (Nori) studied by mechanical characterization and NMR measurements

Mechanical property measurements, 1H T2 measurement by low-field (LF) NMR and 13C T1 measurement by high-resolution cross polarization/magic angle spinning (CP/MAS) solid-state NMR were carried out to evaluate the structural changes of Nori upon moisture uptake. The texture of dry Nori changed to be tough and then soft upon moisture uptake. The increase of 1H T2 and decrease of 13C T1 were observed with an increase of moisture content indicating the increase of the molecular mobility of Nori components. The results of the LF-NMR suggested that the increase of mobility of the inert protons in rigid components is more dominated than that of the labile protons in soft components when Nori becomes the soggy state, whereas the mobility of the soft part increases more by moisture uptake when Nori becomes the wet state. The changes of molecular mobility of each main component (proteins and porphyran) were well depicted by the 13C T1 measurement, which represented the hydration of porphyran and proteins in the pulps and binder part. The change of mechanical properties of Nori was successfully elucidated with the NMR relaxation measurements.

Synthesis, characterization and DNA binding of four imidazo[4,5-f]1,10-phenanthroline derivatives

The synthesis and crystal structures of four imidazo[4,5- f ]1,10-phenanthroline type compounds, namely 2,6-(dimethoxypyridyl)imidazo[4,5- f ]1,10-phenanthroline monohydrate (C 20 H 17 N 5 O 3 ) 1a , (indole)imidazo[4,5- f ]1,10-phenanthroline ethanol monosolvate monohydrate (C 23 H 21 N 5 O 2 ) 2a , (benzo[b]thiophene)imidazo[4,5- f ]1,10-phenanthroline (C 21 H 12 N 4 S) 3 , and (4,5-dimethylthiophene)imidazo[4,5- f ]1,10-phenanthroline (C 19 H 14 N 4 S) 4 , are reported. The compounds were characterized in dimethyl sulfoxide- d 6 (DMSO- d 6 ) solution by 1 H and 13 C NMR spectroscopy and in the solid-state by 13 C NMR spectroscopy using the cross-polarisation magic angle spinning (CP/MAS) technique. 1 H and 13 C liquid-state NMR spectra of 1 and 2 exhibit a sharpening of peaks upon heating, suggesting the presence of two tautomeric forms of 1 and 2 , this is confirmed by the presence of two distinct signals for the N-H protons in the 1 H spectra. This tautomeric effect was not observed in 3 and 4. 1a crystallised in the triclinic space group, P 1 ¯ with one molecule and one solvent water molecule in the asymmetric unit while 2a crystallised in the monoclinic space group, P 2 1 / c, with one molecule and two solvate molecules (CH 3 CH 2 OH and H 2 O) in the asymmetric unit. 3 and 4 both crystallised in the monoclinic space group, P 2 1 / n, each with one molecule in the asymmetric unit. 4 displays a positional disorder on the 4,5-thiophene moiety in a 60:40 ratio. When a drug candidate binds to DNA via intercalation, a hypochromic effect is observed in the spectra due to stabilised π-interactions between the base pairs of the DNA structure and the drug candidate. Contrastingly, if a drug candidate binds to DNA via electrostatic attraction, a hyperchromic effect is observed. The mode of binding as well as intrinsic binding constant (K b ) of 1a – 4 are reported herein. The spectra of 1a, 2a and 4 exhibit a hypochromic effect, thus interaction via π-interactions is suggested and the spectrum of 3 exhibits a hyperchromic shift, suggesting that the mode of binding of 3 occurs via electrostatic attraction. The K b values for 1a–4 range from 1.5 × 10 3 – 1.7 × 10 4 M −1 .

Antimicrobial polyurethane catheters synthesized by grafting-radiation method doped with silver nanoparticles

Tecoflex® polyurethane catheters were surficial modified with acrylic acid (AAc) to obtain a hydrophilic material able to host antimicrobial agents. The grafted catheters were prepared by the oxidative pre-irradiation technique using 60Co as the gamma-ray source. Graft kinetics was studied by varying the applied dose and the reaction time to obtain catheters with different grafting yields. Modified catheters were characterized by infrared spectroscopy (FTIR-ATR), thermogravimetric analysis (TGA), Cross-polarization Magic-angle spinning nuclear magnetic resonance in solid-state (CP/MAS 13C NMR), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS). The modified catheters displayed notable hydrophilicity absorbing water; besides, they exhibited a critical pH of 6.5 because of grafting presence. The graft endowed the catheters with the ability to load silver nanoparticles acquiring biocidal properties with the ability to prevent bacterial proliferation on its surface. Silver-impregnated catheters showed notable antimicrobial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacteria, presenting inhibiting halos of 8.1 and 10.2 mm on the catheter surroundings, respectively. The biocide property was confirmed when silver-impregnated catheters were challenged in a killing test against both bacteria, eradicating up to 80% of the bacterial population depending on the amount of loaded silver NPs.

Study of the structure and dynamics at various parts of the antibacterial drug molecule cefpodoxime proxetil

The structure and dynamics of cefpodoxime proxetil are elucidated by measuring chemical shift anisotropy (CSA) tensor, spin-lattice relaxation time, and local correlation time at twenty-one crystallographically different 13C nuclei sites. The principal components of CSA tensor of cefpodoxime proxetil are extracted by the two-dimensional phase adjusted sinning sideband (2DPASS) cross-polarization magic angle spinning (CP-MAS) solid-state NMR experiment, and the spin-lattice relaxation time is measured by the method outlined by Torchia(T1CP). The local correlation time is calculated by bearing in mind that the spin-lattice relaxation mechanism of 13C nuclei is mainly governed by the CSA interaction and the heteronuclear dipole-dipole interaction. The aminothiazole ring, β-lactam ring, and dihydrothiazine ring provide stability to the drug molecule and increase the affinity of the drug to penicillin-binding proteins (PBPs) receptors. The principal components of CSA parameters, spin-lattice relaxation time, and local correlation time vary substantially for carbon nuclei residing on these three rings. These signify that not only the electronic environment, but the molecular conformation, and the local dynamics are also altered within the ring. The substitution of the acyl side chain, oxime group, and the aminothiazole ring at the C7 position of the β-lactam ring enhances the antibacterial activity and the binding affinity of the drug. A huge variation of the spin-lattice relaxation time and local correlation time is observed in those regions. The change in the electron charge distribution and nuclear spin dynamics at different parts of the drug molecule is clear by CSA and spin-lattice relaxation measurements, which will enrich the field “NMR crystallography”.

The Boltzmann-Monte-Carlo-Percolation (BMCP) model on pyrolysis of coal: The quantitative correction on CP/MAS 13C solid-state NMR spectra and insight on structural evolution during coalification

Because of the Nuclear Overhauser Effect (NOE), the quantitative bonds’ population can hardly be obtained directly from Cross-polarization Magic Angle Spinning (CP/MAS) 13C solid-state Nuclear Magnetic Resonance (NMR) spectra. Thus, correction must be carried out to obtain the bonds’ population with high precision. In this work, the correction factor was derived from Solomon equation, and the previously developed Boltzmann-Monte-Carlo-Percolation (BMCP) model was employed reversely to the calculate correction factor from the tar yields of coal pyrolysis. The results showed that correction on the bonds’ population from tar yields improved the prediction results both on the bonds’ population and product distribution; the correction factor showed an abrupt trend corresponding to coalification jumps. Furthermore, an empirical equation for calculating the correction factor was obtained. The success of the correction indicates that the pyrolysis behaviors of coals under moderate conditions are governed by the bonds’ population, and BMCP model is a proper way to describe the structure–activity relationship quantitatively.

Controllable organosilane monolayer density of surface bonding using silatranes for thiol functionalization of silica particles for liquid chromatography and validation of microanalytical method for elemental composition determination

The present work systematically investigates a new strategy for the functionalization of silica gel using alkyl silatrane chemistry instead of alkylsilanes for synthesis of chromatographic stationary phases. In this work, silica was chemically modified for further functionalization by a thiol-ene click reaction. Thus, 3-mercaptopropylsilatrane (MPS) was used which is capable to form self-assembled monolayers (SAM) on top of silanol surfaces in a controlled manner as previously shown for silicon wafers. The utility of this chemistry for stationary phase synthesis in liquid chromatography was not evaluated yet. Hence, silica surface modifications using MPS were studied in comparison to established 3-mercaptopropyltrimethoxysilane (MPTMS) chemistry. First, the employed elemental analysis method was validated and it showed excellent intra-day and inter-day precisions (typically less than 5% RSD). It could be shown that the reaction kinetics of MPS was roughly 35-times faster than with MPTMS. After 30 min reaction time with MPS, the thiol content reached 74% of the maximal coverage. Due to controlled chemistry with MPS, which does not lead to oligomeric siloxane network at the silica surface, the ligand coverage was lower. However, multiple silanization cycles with MPS led to a dense surface coverage (around 4 µmol m−2). 29Si cross polarization/magic angle spinning (CP/MAS) solid-state NMR revealed distinct T1/T2/T3 ratios for MPS and MPTMS materials with up to 80% T3 (indicative for trifunctional siloxane linkage) for MPS and around 20% T3 for MPTMS. This indicates a more homogeneous, thinner monolayer film of MPS on the silica surface, as compared to an irregular thick oligomeric siloxane network with MPTMS. Bonding of quinine carbamate as chiral selector afforded an efficient chiral stationary phase (CSP) for chromatographic enantiomer separation. Separation factors were comparable to MPTMS-bonded CSP, however, chromatographic efficiency was much better for the MPS-bonded CSP. H/u curves indicated a reduced mass transfer resistance by roughly factor 3 for MPS- compared to MPTMS-bonded CSP. This confirms better chromatographic performance of surfaces with homogeneous monolayer compared to network structures on the silica surface which suffer from poor stationary phase mass transfer.

Structure and dynamics of sodium alginate as elucidated by chemical shift anisotropy and site-specific spin-lattice relaxation time measurements.

The biocompatible, biodegradable, linear copolymer sodium alginate is fabricated from [Formula: see text] linked [Formula: see text]-D-mannuronic acid (M block) and [Formula: see text]-L-guluronic acid (G-block). It has wide applications in drug delivery, cell encapsulation, and commercial application in the textile, cosmetics, paper, food, biomedical, and pharmaceutical industries. The structure and dynamics of sodium alginate were here investigated by measuring chemical shift anisotropy (CSA) parameters, spin-lattice relaxation time, and molecular correlation time. The principal components of the CSA tensor were determined by two-dimensional phase-adjusted spinning sideband (2DPASS) cross-polarization magic angle spinning (CP-MAS) SSNMR. The alternating M and G blocks of both equatorial and axial links are associated with greater overall flexibility. The molecular correlation time of the carboxyl carbon of both G and M blocks is faster than for the anomeric carbon and pyranose carbon. This is further experimental evidence of the coexistence of two different dynamics within the polysaccharide chains of sodium alginate, which was previously established by 1H-13C dipolar profile analysis. The relaxation time of the para-crystalline region of sodium alginate is comparable with that of chitosan, but it is much shorter than that of cellulose and chitin. The order of the molecular correlation time of sodium alginate and chitosan is also the same. Hence, it can be concluded that sodium alginate exhibits greater flexibility than cellulose and chitin. These types of investigation into the local electronic configuration and nuclear spin dynamics at various carbon nuclei sites of the biopolymer at atomic-scale resolution will help in the design of biomimetic materials.

Dinuclear Copper Complex Immobilized on a Janus-Type Material as an Interfacial Heterogeneous Catalyst for Green Synthesis.

We herein describe a rational design of a heterogeneous catalyst composed of a dinuclear cuprate anion being immobilized electrostatically on one surface of Janus-type nanosheets while the other surface is decorated with highly hydrophobic octyl groups. The catalyst was found to be well dispersible in the organic phase of a biphasic aqueous/organic mixture. It was characterized by means of elemental analysis, atomic absorption spectroscopy, mass spectrometry, N2 absorption-desorption analysis, thermogravimetric analysis, scanning electron microscopy (SEM), and solid-state 13C and 29Si cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy. The Janus nature of the catalyst was investigated by employing a selective surface labeling method and by means of SEM. The catalyst shows higher activity compared to a non-Janus analogue in a biphasic synthesis. It was successfully used for the azide-alkyne cycloaddition and the Chan-Lam C-N coupling reaction. In addition, new and simple ways have been established for the production of a coumarin-triazole derivative and for the synthesis of the biologically active compound Monastrol via a solvent-free Biginelli reaction. The role of the dinuclear copper centers is discussed mechanistically.

"Hidden" CO2 in Amine-Modified Porous Silicas Enables Full Quantitative NMR Identification of Physi- and Chemisorbed CO2 Species.

Although spectroscopic investigation of surface chemisorbed CO2 species has been the focus of most studies, identifying different domains of weakly interacting (physisorbed) CO2 molecules in confined spaces is less trivial as they are often indistinguishable resorting to (isotropic) NMR chemical shift or vibrational band analyses. Herein, we undertake for the first time a thorough solid-state NMR analysis of CO2 species physisorbed prior to and after amine-functionalization of silica surfaces; combining 13C NMR chemical shift anisotropy (CSA) and longitudinal relaxation times (T1). These methods were used to quantitatively distinguish otherwise overlapping physisorbed CO2 signals, which contributed to an empirical model of CO2 speciation for the physi- and chemisorbed fractions. The quantitatively measured T1 values confirm the presence of CO2 molecular dynamics on the microsecond, millisecond, and second time scales, strongly supporting the existence of up to three physisorbed CO2 species with proportions of about 15%, 15%, and 70%, respectively. Our approach takes advantage from using adsorbed 13C-labeled CO2 as probe molecules and quantitative cross-polarization magic-angle spinning to study both physi- and chemisorbed CO2 species, showing that 45% of chemisorbed CO2 versus 55% of physisorbed CO2 is formed from the overall confined CO2 in amine-modified hybrid silicas. A total of six distinct CO2 environments were identified from which three physisorbed CO2 were discriminated, coined here as “gas, liquid, and solid-like” CO2 species. The complex nature of physisorbed CO2 in the presence and absence of chemisorbed CO2 species is revealed, shedding light on what fractions of weakly interacting CO2 are affected upon pore functionalization. This work extends the current knowledge on CO2 sorption mechanisms providing new clues toward CO2 sorbent optimization.

Direct Preparation of *MRE Zeolites with Ultralarge Mesoporosity: Strategy and Working Mechanism.

Introduction of mesopore is critical for applications where mass-transport limitations within microporous networks, especially for zeolite with one-dimensional microporous network, hinder their performance. Generally, the creation of mesopore in zeolite through a direct synthesis route is strongly dependent on complex and expensive organic molecules, which limits their commercial application. Here, we successfully developed a facile synthesis route for preparing ZSM-48 zeolite (*MRE topology) with ultralarge mesoporosity in which typical 1,6-hexylenediamine worked as an organic structure-directing agent, innovatively assisted by a simple crystal growth modifier (tetraethylammonium bromide, TEABr). The working mechanism of TEABr during crystallization was revealed and proposed on the basis of TEM, thermal gravimetric mass spectrum, and 13C cross-polarization magic angle spinning NMR characterization results. In the process, TEA+ ions preferentially interacted with the solid during the induction period, which effectively suppressed the aggregation of ZSM-48 primary nanorods. As a result, ultralarge mesoporosity of 0.97 cm3·g-1 was constructed through the stacking of the nanorods. Interestingly, TEA+ ions only took part in the crystallization process and did not occlude in the pores of the final zeolites indicating its potential in recyclability. Moreover, similar synthesis strategy could be applied for the preparation of hierarchical ferrierite zeolites, implying the universality of this strategy. Compared with a conventional sample, ZSM-48 zeolite with ultralarge mesoporosity showed superior catalytic stability in the m-xylene isomerization reaction due to its significantly enhanced diffusion and mass transfer capability, which will greatly promote the practical application of ZSM-48 zeolite.

DETERMINATION OF WOOD COMPOSITION USING SOLID-STATE 13C NMR SPECTROSCOPY

In recent years, solid-state 13C NMR spectroscopy using the technique of cross-polarization (CP) and sample rotation at a magic angle (MAS) has been widely used in the analysis of plant materials, including wood. Knowledge of the composition, structure and behavior of wood components under various conditions is of great importance, since the properties of wood materials depend on this. In this work, differences in the composition of wood belonging to various tree species growing in central Russia (spruce, aspen, birch, oak, linden, pine, poplar and larch) were revealed using CP MAS 13C NMR spectroscopy. The assignment of various peaks in CP MAS 13C NMR spectra to the main components of wood was carried out. It was shown that cellulose is present in its amorphous and crystalline forms, the presence of lignin was unambiguously confirmed by the signals of aromatic carbon atoms, and hemicelluloses were detected by the signals from the carbon atoms of methyl groups of acetylxylose and L-rhamnose. According to the integral intensities, the total ratio of cellulose and hemicelluloses to lignin was determined: the largest amount of lignin was found in coniferous wood (spruce, larch and pine), and the smallest amount of lignin was detected in deciduous species (aspen, oak, linden, birch and poplar).

One pot synthesis of new cross-linked chitosan-Schiff' base: Characterization, and anti-proliferative activities

Four novel chitosan hydrogels were successfully synthesized through the cross-linking reaction of chitosan with different concentrations of ethyl 5-(3,5-dihydroxy-1,4-dioxan-2-yl)-2-methylfuran-3-carboxylate. Their structures were confirmed by Fourier transform infrared spectroscopy (FT-IR), 13C Cross polarization magic angle spinning nuclear magnetic resonance spectroscopy (CP/MAS 13C NMR), ultraviolet-visible spectroscopy, thermogravimetric analysis (TGA, DTA), and X-ray diffraction (XRD). Cytotoxicity on hepatocellular carcinoma (HepG-2) cell line and a normal African green monkey kidney (Vero) cell line were studied using the MTT assay. The resultant hydrogels showed a good inhibitory effect comparing to the un-modified parent; the hydrogels with the lowest degree cross-linking (0.125 and 0.25 mol cross-linker per one chitosan residue) showed potent anticancer activity in the HepG2 cells with IC50 of 57.9 and 80.9 μg/ml, respectively. These results show that the newly synthesized cross-linked chitosan derivatives demonstrated more selectivity to the HepG2 than the Vero cells, indicating its potential for Investigation in the cure of hepatocellular carcinoma.

CP MAS 13C NMR SPECTROSCOPY IN DETERMINATION OF SPECIFIC DIFFERENCES IN COMPOSITION OF WOOD

In recent years solid-state 13C NMR spectroscopy using the technique of cross-polarization (CP) and sample rotation at a magic angle (MAS) has been used in the analysis of plant materials, including wood. Knowledge of the composition, structure and behavior of wood components in different conditions is of great importance, since the properties of wood materials depend on this. In this work differences in the composition of various tree species wood in central Russia (birch, aspen, spruce, and larch) were revealed using CP MAS 13C NMR spectroscopy. Assignment of various peaks in CP MAS 13C NMR spectra with the main components of wood was carried out. It was shown that cellulose is presented in amorphous and crystalline forms, the presence of lignin is unambiguously confirmed by signals of aromatic carbon atoms, and hemicellulose is detected by signals from carbon atoms of methyl groups of acetylxylose and L-rhamnose. According to the integral intensities, the total proportion of cellulose and hemicellulose in relation to lignin was determined: the largest amount of lignin was found in coniferous wood (spruce, larch), and the smallest amount of lignin was detected in deciduous species (aspen and birch).