Angle Spinning 13C NMR Spectroscopy Research Articles

Crystalline C-C and C═C Bond-Linked Chiral Covalent Organic Frameworks.

While crystalline covalent organic frameworks (COFs) linked by C-C bonds are highly desired in synthetic chemistry, it remains a formidable challenge to synthesize. Efforts to generate C-C single bonds in COFs via de novo synthesis usually afford amorphous structures rather than crystalline phases. We demonstrate here that C-C single bond-based COFs can be prepared by direct reduction of C═C bond-linked frameworks via crystal-to-crystal transformation. By Knoevenagel polycondensation of chiral tetrabenzaldehyde of dibinaphthyl-22-crown-6 with 1,4-phenylenediacetonitrile or 4,4'-biphenyldiacetonitrile, two olefin-linked chiral COFs with 2D layered tetragonal structure are prepared. Reduction of olefin linkages of the as-prepared CCOFs produces two C-C single bond linked frameworks, which retains high crystallinity and porosity as well as high chemical stability in both strong acids and bases. The quantitative reduction is confirmed by Fourier transform infrared and cross-polarization magic angle spinning 13C NMR spectroscopy. Compared to the pristine structures, the reduced CCOFs display blue-shifted emission with enhanced quantum yields and fluorescence lifetimes, while the parent CCOFs exhibit higher enantioselectivity than the reduced analogs when be used as fluorescent sensors to detect chiral amino alcohols via supramolecular interactions with the built-in crown ether moieties. This work provides an attractive strategy for making chemically stable functionalized COFs with new linkages that are otherwise hard to produce.

Hybrid nanocomposite based on poly-3-amine-7-methylamine-2-methylphenazine and single-walled carbon nanotubes

A polymer–carbon hybrid nanocomposite based on thermostable electroactive poly-3-amine-7-methylamine-2-methylphenazine (PAMMP) and single-walled carbon nanotubes (SWCNT) was synthesized for the first time via in situ oxidative polymerization. The SWCNT/PAMMP nanocomposite material was characterized by means of Fourier transform infrared spectroscopy, solid-state high-resolution magic angle spinning 13C NMR spectroscopy, X-ray diffraction, transmission and field emission scanning electron microscopy, differential scanning calorimetry and thermogravimetric analysis. The chemical structure of the synthesized SWCNT/PAMMP nanocomposite, as well as its thermal and electrical properties under different synthesis conditions, was studied.

Immobilization of zirconium-glycerolate nanowires on magnetic nanoparticles for extraction of urinary ribonucleosides.

The authors have immobilized nanowires made from zirconium glycerolate (ZrGly) on magnetite (Fe3O4) nanoparticles by applying a solvothermal growth process using metal-glycerolate as a precursor. The structure and the dissolution-recrystallization mechanism of the resulting Fe3O4@ZrGly composite were investigated by attenuated total reflection-FTIR, energy-dispersive X-ray analysis, thermogravimetric analysis and solid-state cross polarization/magic angle spinning 13C NMR spectroscopy. The interaction between the zirconium glycerolate in Fe3O4@ZrGly and cis-diols leads to efficient adsorption of riboncleosides which then can be quantified by HPLC with UV detection. The sorbent was successfully applied to the selective enrichment of adenosine, cytidine, uridine and guanosine from spiked human urine samples. The detection limit of the method is in the range from 1.7 to 19ng·mL-1 of nucleosides in spiked human urine, with relative standard deviationsof lower than 12.4% and recoveriesranging from 90.6 to 113%. Graphical abstract Fe3O4@ZrGly with high selectivity towards ribonucleosides was designed and applied for quantitation of urinary ribonucleosides.

Quantitative comparison of structure and dynamics of elastin following three isolation schemes by 13C solid state NMR and MALDI mass spectrometry

Methods for isolating elastin from fat, collagen, and muscle, commonly used in the design of artificial elastin based biomaterials, rely on exposing tissue to harsh pH levels and temperatures that usually denature many proteins. At present, a quantitative measurement of the modifications to elastin following isolation from other extracellular matrix constituents has not been reported. Using magic angle spinning 13C NMR spectroscopy and relaxation methodologies, we have measured the modification in structure and dynamics following three known purification protocols. Our experimental data reveal that the 13C spectra of the hydrated samples appear remarkably similar across the various purification methods. Subtle differences in the half maximum widths were observed in the backbone carbonyl suggesting possible structural heterogeneity across the different methods of purification. Additionally, small differences in the relative signal intensities were observed between purified samples. Lyophilizing the samples results in a reduction of backbone motion and reveals additional differences across the purification methods studied. These differences were most notable in the alanine motifs indicating possible changes in cross-linking or structural rigidity. The measured correlation times of glycine and proline moieties are observed to also vary considerably across the different purification methods, which may be related to peptide bond cleavage. Lastly, the relative concentration of desmosine cross-links in the samples quantified by MALDI mass spectrometry is reported.

Structure and Dynamics of Wheat Starch in Breads Fortified with Polyphenols and Pectin: an ESEM and Solid-State CP/MAS 13C NMR Spectroscopic Study

Two sets of breads formulated with a 20% difference in water quantity in the absence (control bread), or presence (fortified bread) of high methoxyl pectin (HM) and an apple, kiwifruit, or blackcurrant polyphenol (PP) extract (APE, KPE or BPE) were examined by Environmental Scanning Electron Microscopy (ESEM) and Cross Polarization/Magic Angle Spinning 13C NMR Spectroscopy. ESEM revealed that all the bread doughs had similar microstructures, comprising starch granules and yeast cells embedded in a continuous gluten matrix. However, the microstructure of the finished breads differed. NMR studies revealed differences in amylopectin-related crystalline domains and the amylose-related amorphous domains among the breads. All the breads showed V-type or amorphous starch structures by NMR, and the control bread may also contain some A-type starch. Breads formulated with 20% extra water showed a greater degree of starch gelatinization, a smoother crumb microstructure, and a lower amorphous starch content. It is feasible to incorporate PPs and pectin in breads at reasonably high concentrations.

ChemInform Abstract: Azo Pigments and Their Intermediates. A Reinvestigation of the Tetrazotization of 1,4-Diaminoanthraquinone.

The azotization of 1,4-diaminoanthraquinone (1) by n-amyl nitrite in glacial acetic was reinvestigated. The structure of a red-brown precipitate, which was previously identified as anthraquinone-1,4-tetrazonium dichloride (3) by Schaarschmidt, was found to be incorrect. In this work, we have identified the red-brown solid as 4-aminoanthraquinone-1-diazonium chloride (2), a diazotized product of 1. The yield of 2 was 80%. The tetrazonium dichloride 3 was actually formed in minute quantity and is soluble in acetic acid. The tetrazonium product of 1 can be isolated as tetrafluoroborate salt 4 in 3.4% yield by adding fluoboric acid into the acetic acid solution. The structure 4 was confirmed by IR and cross-polarization magic angle spinning13C NMR spectroscopy. Further investigations showed that 1 can be quantitatively tetrazotized by nitrosylsulfuric acid in 78% sulfuric acid. The tetrazonium product was isolated as 4 in 74% yield. Key words: 1,4-diaminoanthraquinone, diazotization, tetrazotization, azo pigm...

Solid-state NMR characterization of switchgrass cellulose after dilute acid pretreatment

Background: Switchgrass (Panicum virgatum L.) is being considered as a potential feedstock for bioethanol production and extensive research is ongoing to establish the optimum pretreatment conditions for switchgrass. Cellulose comprises the most abundant biopolymer in the biosphere and its crystalline/ultrastructure is considered to be related to biomass recalcitrance. This study investigates the effects of dilute acid pretreatment on ultrastructural features of switchgrass cellulose. Results: In this study, switchgrass was pretreated in a pilot-scale reactor at 190°C (0.05 g sulfuric acid per gram of dry switchgrass) with 25% total solid loading and a reactor residence of 1 min. Cellulose was isolated from the pretreated and untreated switchgrass. The impact of pretreatment on the ultrastructure of cellulose was determined by solid-state cross polarization/magic angle spinning 13C NMR spectroscopy. Switchgrass demonstrated a preferable degradation of amorphous cellulose regions during dilute acid pretreatment. The pretreated switchgrass cellulose showed an 18% increase in crystallinity index when compared with the untreated switchgrass. Line-fitting analysis of the C-4 region of 13C NMR spectra revealed that the relative proportion of crystalline and paracrystalline celluloses in switchgrass was observed to increase after dilute acid pretreatment, accompanied with a concurrent decrease of the relative abundance of fibril surface cellulose. Conclusion: After dilute acid pretreatment, most of the hemicellulose in switchgrass was removed. The amorphous cellulose regions in switchgrass were degraded preferably during dilute acid pretreatment and the cellulose crystallinity index of pretreated switchgrass increased. Pretreated switchgrass had an increase in relative proportion of crystalline and paracrystalline cellulose in comparison to the starting material.

Cross polarisation/magic angle spinning 13C-NMR spectroscopic studies of cellulose structural changes in hardwood dissolving pulp process

Abstract Cross polarisation/magic angle spinning 13C NMR spectroscopy has been used to study structural changes in cellulose induced by the dissolving pulp process. The cellulose structure in several dissolving pulps was investigated for commercial and laboratory cooked Eucalyptus 92α and 96α. The average lateral dimension, or average thickness, of the cellulose fibril aggregates is related to the amount of surface area exposed and could be one controlling factor for the chemical reactivity of commercial dissolving pulps during modification reactions. The thickness of the cellulose fibril aggregates governs the amount of surface area present in the fibre wall, and cellulose surface material constitutes the part of the cellulose that is directly accessible to reagents. In all sample series investigated, the raw pulp was found to be less aggregated than the corresponding bleached final pulp. Furthermore, an irreversible increase in fibril aggregate width was observed on free drying for both laboratory cooked and commercial pulps. Upon rewetting with water, the freely dried 96α pulp was found to be more aggregated than the freely dried 92α pulp, although sugar analysis showed very similar carbohydrate compositions. As indicated by the molecular mass distribution, the commercial 92α pulp contained larger amounts of degraded cellulose; this may be a plausible explanation for the different behaviour of the 92α and 96α pulps during free drying.

Solid-State NMR Analysis of Fluorinated Single-Walled Carbon Nanotubes: Assessing the Extent of Fluorination

Fluorinated single-walled carbon nanotubes (F-SWNTs) have been characterized by magic angle spinning 13C NMR spectroscopy and the results correlated with Raman, IR, and X-ray photoelectron spectroscopy measurements. The 13C NMR shift for the sp3 fluorine-substituted (CF) carbon atoms of the SWNT sidewall is observed at δ = 83.5 ppm. This apparently unusual shift compared to those of most other tertiary alkyl fluorides is confirmed to be due to the CF moieties from ab initio calculations on an 80-carbon fragment of the 5,5 (armchair) SWNT and is in good agreement with the predominance of 1,2-addition rather than 1,4-addition of fluorine. The lack of observable scalar 13C−19F coupling for the CF carbon signal over a wide range of spinning speeds and at two different field strengths apparently results from interaction between 19F−19F and 13C−19F dipolar couplings and from magnetization exchange between the 13C doublet components caused by fluorine spin diffusion. The assignment of the 83.5 ppm peak is furthe...

The First Metal-Based Paullone Derivative with High Antiproliferative Activity in Vitro

9-Bromo-7,12-dihydroindolo[3,2-d][1]benzazepin-6(5H)-one, kenpaullone, which displays similarities in the activity profile to flavopiridol, was modified by chemical transformations at the lactam unit to provide a peripheral binding site able to accommodate metal ions. The first metal-based paullone has been prepared and characterized by single-crystal X-ray diffraction methods, solid-state cross-polarization magic angle spinning 13C NMR spectroscopy, electrospray ionization mass spectra, and electronic spectra. The gallium complex [GaL2]Cl.2.5H2O, the metal-free ligand (HL), and the starting compound used for the preparation of HL were assessed in vitro for their cytotoxicity in a panel of human tumor cell lines. The gallium complex was found to be 1.5-18-fold more cytotoxic than HL, with an average IC50 value of 2.0 microM.

Silica gel functionalized with resacetophenone: synthesis of a new chelating matrix and its application as metal ion collector for their flame atomic absorption spectrometric determination

Silica gel modified with 3-aminopropyltriethoxysilane was anchored with resacetophenone to prepare a new chelating surface (or matrix). It was characterized with cross polarization magic angle spinning 13C NMR spectroscopy and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and used for the separation and preconcentration of Cu(II), Pb(II), Ni(II), Fe(III), Cd(II), Zn(II) and Co(II) prior to their determination by flame atomic absorption spectrometry (FAAS). The optimum pH ranges for quantitative sorption are 6.0–7.5, 5.5–7.5, 5.0–7.0, 6.5–7.5, 6.0–7.5, 6.0–7.0 and 6.0–7.5 for Cu, Pb, Fe, Zn, Co, Ni and Cd, respectively. All the metals can be desorbed with 3 mol dm −3 HCl or HNO 3. The sorption capacity for these metal ions is in range of 57.8–365.0 μmol g −1 of chelating matrix. Tolerance limits for electrolytes NaNO 3, NaCl, NaBr, Na 2SO 4 and Na 3PO 4 and cations Ca(II) and Mg(II) in the sorption of these metal ions are reported. Preconcentration factors of 200, 300, 150, 250, 250, 200 and 200 for Cd, Co, Zn, Cu, Pb, Fe and Ni, respectively, are obtained and t 1/2 values are <1 min except for Cd. 95% extraction by a batch method takes ≤25 min. The simultaneous enrichment and determination of all the metals are possible if the total load of the metal ions is less than the sorption capacity. In river water samples all these metal ions were enriched with the present matrix and determined with a flame atomic absorption spectrometer (R.S.D. ≤ 7.7%). Copper contents of pharmaceutical samples (vitamin capsule) were preconcentrated with the present chelating matrix and estimated with flame AAS, with R.S.D. ∼ 2.2%. The results are in the good agreement with the certified value, 0.4 mg/g of capsule.

Soil microbial biomass and organic matter composition in soils under cultivation

To determine whether there is a relationship between the composition of soil organic matter and the activity of the soil microbial biomass, the composition of the organic matter in 12 typical arable soils in Northwest Germany was investigated by wet chemical analysis and CPMAS cross polarization magic angle spinning 13C-NMR spectroscopy. The data were correlated with the microbial biomass as estimated by substrate-induced respiration. A strong correlation between the microbial biomass and alkylic C compounds was observed (r=-0.960***). Recalcitrant substances were enriched in this fraction, which were classified as humic acids according to the wet chemical procedure. The microbial decomposition of these humic acids is probably retarded, due to their chemical structure and/or physical bonding, when the soil microbial biomass activity is limited.

Characterization of some cell-wall components of untreated and SO 2-treated wheat straw

Chemical and physical properties of cell walls (CW) and CW components have been studied in untreated wheat straw (WS) and SO 2-treated wheat straw (SO 2-WS). The concentration of water-soluble total free monomeric phenolics was 47.1 mg per 100 g and 129 mg per 100 g straw dry matter in WS and SO 2-WS, respectively. The major solubilizing effect of the SO 2 treatment was exerted on ferulic acid, the concentration of which increased tenfold. Matrix complexes extracted by 1 N NaOH from CW of wheat straw subjected to ball-milling plus Trichoderma reesei cellulase pretreatment underwent high-per-formance size exclusion chromatography to assess the molecular weight distribution. Most (84%) of the matrix complexes extracted from WS were in the range of 1600–23000 Da, whereas those originating from SO 2-WS showed a more dispersed pattern, with mol ecular weights of up to and beyond 125 000 Da. The weight average molecular weight (M wt) was 10 500 Da and 35 000 Da for the matrix complexes of WS and SO 2-WS, respectively. Total monosaccharide content of matrix complexes was 36.4 g per 100 g and 42.5 g per 100 g in WS and SO 2-WS, respectively, with xylose as the major (70–80%) component. Solid-state cross-polarization-magic angle spinning 13C NMR spectroscopy of neutral detergent fiber preparations of wheat straw showed a decline in the intensity of signals at 89 ppm and 65 ppm in response to SO 2 treatment and in vitro digestion, respectively. The distribution of carbons in CW chemical groups and components as determined by the NMR analysis was found to be close to values obtained by wet chemistry.

ChemInform Abstract: Azo Pigments and Their Intermediates. Electronic Structure of “Bisazo” Pigments by Cross‐Polarization Magic Angle Spinning 13C NMR Spectroscopy.

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Azo pigments and their intermediates. A reinvestigation of the tetrazotization of 1,4-diaminoanthraquinone

The azotization of 1,4-diaminoanthraquinone (1) by n-amyl nitrite in glacial acetic was reinvestigated. The structure of a red-brown precipitate, which was previously identified as anthraquinone-1,4-tetrazonium dichloride (3) by Schaarschmidt, was found to be incorrect. In this work, we have identified the red-brown solid as 4-aminoanthraquinone-1-diazonium chloride (2), a diazotized product of 1. The yield of 2 was 80%. The tetrazonium dichloride 3 was actually formed in minute quantity and is soluble in acetic acid. The tetrazonium product of 1 can be isolated as tetrafluoroborate salt 4 in 3.4% yield by adding fluoboric acid into the acetic acid solution. The structure 4 was confirmed by IR and cross-polarization magic angle spinning13C NMR spectroscopy. Further investigations showed that 1 can be quantitatively tetrazotized by nitrosylsulfuric acid in 78% sulfuric acid. The tetrazonium product was isolated as 4 in 74% yield. Key words: 1,4-diaminoanthraquinone, diazotization, tetrazotization, azo pigments.