Solid-state Cross-polarization Magic Angle Spinning Research Articles

Anomalous Swelling Behavior of Poly(N-vinylimidazole)-l-Poly(tetrahydrofuran) Amphiphilic Conetwork in Water Studied by Solid-State NMR and Positron Annihilation Lifetime Spectroscopy

Poly(N-vinylimidazole) homopolymer (PVIm) and poly(N-vinylimidazole)-l-poly(tetrahydrofuran) (PVIm-l-PTHF), a novel amphiphilic polymer conetwork (APCN), were synthesized to compare their solid state structure and investigate the swelling behavior of this unique conetwork in water. A short-range ordered structure stabilized by second-order interactions between the imidazole pendant groups was found in the PVIm homopolymer and in the PVIm phase of the dry conetwork as revealed by solid-state NMR 13C cross-polarization magic angle spinning (CP MAS) and two-dimensional 1H–13C frequency-switched Lee–Goldburg (FSLG) HETCOR measurements. With increasing swelling ratio, structural and conformational changes were recognized in the hydrophilic PVIm phase of the APCN. In the kinetic swelling study, unexpectedly, four different swelling ranges were identified by gravimetric measurements, solid-state NMR methods, and positron annihilation lifetime (PAL) spectroscopy before the APCN reached its equilibrium swelling st...

First determination of Cu adsorption on soil humin

Humic substances are heterogeneous mixtures of organic compounds occurring in huge amounts mainly in waters, soils, sediments and organic wastes. They are formed during the decay of living organisms. They play a very important role in many environmental processes including carbon sequestration, water cleaning and retention, soil erosion, fertility and pollutant retention. However, due to their complex nature, humic substances are still poorly characterized and much less known than living matter. Humin is the most insoluble and, in turn, the least understood fraction of humic substances. To our knowledge, no information is currently available on the adsorption and desorption behaviors of metal ions on soil humin. Here, we report the adsorption and desorption properties of Cu(II) on humin and humic acids isolated from a forest soil in northeast China using the batch equilibration method. Solid-state 13C cross-polarization magic angle spinning nuclear magnetic resonance (13C CPMAS NMR) spectroscopy was used to characterize and compare the chemical structures of humin and humic acid. The batch experiments’ results show that humin has a lower adsorption capacity and higher adsorption reversibility for Cu(II) than humic acid. The adsorption isotherms well fitted both the Langmuir and Freundlich equations. Humin, therefore, plays an important role in controlling the fate, transport and bioavailability of Cu(II) in the environment. The 13C CPMAS NMR spectra showed that compared with humic acid, humin was higher in alkyl C, carbohydrate C and phenolic C and was lower in methoxyl C, aryl C and carbonyl C. These findings mean that humin was less alkylated, more aliphatic and more hydrophobic.

Molecular-shape selective high-performance liquid chromatography: Stabilization effect of polymer main chain by alternating copolymerization

This work aims to clarify that stabilization or increased rigidity of polymer main chains as an organic stationary phase can lead the selectivity enhancement in high-performance liquid chromatography (HPLC). For this purpose, the alternating copolymer of octadecyl acrylate (ODA) with a cyclic monomer (N-octadecylmaleimide, OMI) as a rigid segment was synthesized and compared with the ODA homopolymer. Both of the polymer-grafted silicas (Sil-poly(ODA-alt-OMI) and Sil-poly(ODA), respectively) were prepared by radical polymerization on 3-mercaptopropyltrimethoxysilane-modified silica. The characterizations were carried out by elemental analyses, diffuse reflectance infrared Fourier transform (DRIFT), and solid-state 13C cross-polarization magic angle spinning nuclear magnetic resonance (CP-MAS-NMR) spectroscopies. Chromatographic behaviors were evaluated by the retention studies of shape-constrained isomers of polycyclic aromatic hydrocarbons (PAHs), isomers of tocopherol and carotenoids. Higher molecular-linearity selectivity toward PAHs was obtained on Sil-poy(ODA-alt-OMI) regardless of temperature changes but at temperature below 40°C, Sil-poly(ODA) showed better planarity selectivity than that of Sil-poy(ODA-alt-OMI). As a result, the higher separation ability toward tocopherols and carotenoids was obtained on Sil-poy(ODA-alt-OMI). These results indicate that the stabilization in the polymer main chain by alternating copolymerization and the stabilization in the side chains by a disordered-to-ordered phase transition were effective to enhance the molecular-shape selectivity.

Effects of steric/basic properties of Lewis bases on the degree of aggregation of zinc(II) pivalate complexes

A triangular [Zn 3( μ 3-OH)(OC(O) t Bu)( μ 2 - κ 1 O: κ 1 O′–O 2C t Bu) 4(3,5-lutidine) 3] ( 1), a paddlewheel based dinuclear [Zn( μ 2- κ 1 O: κ 1 O′–O 2C t Bu) 2L] 2 [L = 2,4-lutidine ( 2), 3,4-lutidine ( 3), and 2,3-lutidine ( 4)] and an hourglass based linear trinuclear [Zn 3( μ 2 - κ 1 O: κ 1 O′-O 2C t Bu) 6(pyridine) 2] ( 5) complexes were synthesized to understand the role of subtle steric/basic properties of Lewis bases on the degree of aggregation of the products. The mononuclear Zn(OC(O) t Bu) 2·2H 2O was also prepared in order to probe the origin of the μ 3-OH moiety in complex 1. Complexes 1– 5 and Zn(OC(O) t Bu) 2·2H 2O were characterized by microanalytical, IR, TGA/DTA, solution ( 1H and 13C) NMR, solid-state cross-polarization magic angle spinning (CP-MAS) 13C NMR, mass spectral data and single crystal X-ray diffraction data. Complex 1 represents the first example of a discrete trinuclear zinc(II) carboxylate complex that contains a [Zn 3( μ 3-OH)] 5+ core with zinc atoms in three distinct geometries namely a distorted tetrahedral, trigonal bipyramidal, and octahedral. A plausible mechanism for the formation of complexes 1– 5 was explained with the aid of point zero charge (pzc) model.

Recyclable mesoporous silica-supported chiral ruthenium-(NHC)NN-pincer catalysts for asymmetric reactions

New stable chiral [RuHClCO((NHC)NN)] and [RuCl2(p-cymene)((NHC)NN)] pincer complexes with a pendant silyloxy group ((NHC)NN: (S)-1-((6-((3-aryl-2,3-dihydro-1H-imidazol-1-yl)methyl)pyridin-2-yl)methyl); R-N-(3-(triethoxysilyl)propyl)pyrrolidine-2-carboxamide, aryl = mesityl, 2,6-diisopropylphenyl; R = Me, Ph) were synthesized and grafted onto a mesoporous silica MCM-41 through the siloxane linkage, and the resulting supported ruthenium catalysts were highly active and recyclable catalysts for the asymmetric hydrogenation of alkenes and cyclopropanation of styrenes. The solid catalysts were characterized with a variety of methods including solid state cross-polarization magic-angle spinning (CP MAS) 13C NMR, FT-IR, and elemental analysis. Excellent activity and enantioselectivity was observed for these supported Ru-catalysts owing to readily accessible and uniform catalytic sites within the large channels of MCM-41 and short diffusion lengths for the organic compounds. The high accessibility introduced by the structure of the support allows the preparation of highly efficient immobilized catalysts which can duplicate the activity of the homogeneous analogues. No deactivation of the catalysts was observed after repeated recycling.

Siloxane−TiO2 Hybrid Nanocomposites. The Structure of the Hydrophobic Layer

Anatase−brookite titanium dioxide nanoparticles are derivatized with two commercial trifunctional siloxanes by a mild impregnation method. The filmed titania nanoparticles are characterized by X-ray diffraction, N2 adsorption at subcritical temperatures (BET and BJH methods), and contact angle determinations. Starting from siloxane contents of 9%, the particles show highly hydrophobic properties (contact angle around 140−150°), complete buoyancy over water, and excellent self-cleaning properties. Solid-state 29Si cross-polarization magic angle spinning nuclear magnetic resonance (29Si CP/MAS NMR) is used to investigate the mode of attachment of the siloxane molecules to the TiO2 surface. The combination of these results with X-ray photoelectron spectroscopy and attenuated total reflectance Fourier transform infrared spectroscopy provides unique information on the structure of the chemisorbed siloxane layer. The siloxane groups covalently attached to the TiO2 surface may serve as powerful linkers for different functionalities.

Accessing Quantitative Degrees of Functionalization on Solid Substrates via Solid-State NMR Spectroscopy

The development of a solid-state nuclear magnetic resonance (NMR) method allowing the quantification of active sites (i.e., residual vinyl groups) accessible for chemical functionalization on the surface of poly(divinyl benzene) microspheres is presented. Residual vinyl groups of poly(divinyl benzene) microspheres (PDVB55 and PDVB80) were quantified via solid-state 13C cross-polarization magic-angle spinning (CP-MAS) NMR spectroscopy. In addition, 13C CP-MAS NMR spectroscopy allows the comparison of core and grafted microspheres functionalization on the same (arbitrary) scale in a short measuring time. This scale was calibrated by an extended absolute quantification of the vinyl groups using 13C single pulse excitation (SPE) MAS NMR spectroscopy. The degree of cross-linking of the microspheres was calculated to be 30 and 50% for PDVB55 and PDVB80 microspheres, respectively. The number of active groups per nominal surface area is 110 and 179 groups per nm2 for PDVB55 and PDVB80 microspheres, respectively. The loading capacities of the microspheres (e.g., 0.61 and 0.65 mmol·g−1) are not too far removed from those found in Merrifield resins of comparable sizes.

Effects of soil organic matter composition on unfrozen water content and heterotrophic CO 2 production of frozen soils

Several recent studies have highlighted the importance of soil organic matter (SOM) mineralization at high latitudes during winter for ecosystem carbon (C) balances, and the ability of the soil to retain unfrozen water at sub-zero temperatures has been shown to be a major determinant of C mineralization rates. Further, SOM is believed to strongly influence the liquid water contents in frozen surface layers of boreal forest soils and tundra, but the mechanisms and specific factors involved are currently unknown. Here we evaluate the effects of the chemical composition of SOM on the amount of unfrozen water, the pore size equivalents in which unfrozen water can exist, and the microbial heterotrophic activity at sub-zero temperatures in boreal forest soils. To do this, we have characterized the chemical composition of SOM in forest soil samples (surface O-horizons) using solid state CP-MAS (cross polarization magic angle spinning) NMR spectroscopy. The acquired information was then used to elucidate the extent to which different fractions of SOM can explain the observed variations in unfrozen water content, pore size equivalents, and biogenic CO 2 production rates in the examined soil samples under frozen conditions (−4 °C). The data evaluation was done by the use of principal component analysis (PCA) and projections to latent structures by means of partial least square (PLS). We conclude that aromatic, O-aromatic, methoxy/ N-alkyl and alkyl C are the major SOM components affecting frozen boreal forest soil’s ability to retain unfrozen water and sustain heterotrophic activity (95% confidence level). Our results reveal that solid carbohydrates have a significant negative impact (95% confidence level) on CO 2 production in frozen boreal spruce forest soils, in contrast to the positive effects of carbohydrate polymers during unfrozen conditions. We conclude that the hierarchy of environmental factors controlling SOM mineralization changes as soils freeze. The effect of SOM composition on pore size distribution and unfrozen water content has a superior influence on SOM mineralization and hence on heterotrophic CO 2 production of frozen soils.

Soil Organic Matter Processes in Old‐Growth Redwood Forest Canopies

Organic soils up to 1 m thick cover tree surfaces within the canopies of old‐growth redwood [Sequoia sempervirens (D. Don) Endl.] forests 50 m or more above the ground. Very little is known about litter quality and litter decomposition processes within these canopies. A combination of solid‐state cross‐polarization magic‐angle spinning 13C nuclear magnetic resonance (NMR) spectroscopy, natural 13C and 15N isotopic analyses, and proximate analyses were used to gain insight into soil organic matter accumulation and decay processes within two arboreal soils. Arboreal soil, redwood, and fern (Polypodium scouleri Hook. & Grev.) litter as well as epiphyte roots were analyzed. Proximate analyses showed that the arboreal soil parent materials contained a high concentration of the acid residue fraction (i.e., Klason lignin), from 379 g kg−1 for fern rhizomes up to 652 g kg−1 for redwood bark litter. This high concentration of acid residue fraction in the soil parent materials probably promotes organic matter accumulation within the tree crown. Results from 13C NMR spectroscopy analyses indicated a preferential decomposition of carbohydrates and an accumulation of alkyl structures from the redwood and fern litter to the <2‐mm soil materials and from the Oi to the Oa horizons in both soils. On the other hand, there was no consistent variation in terms of C/N ratios and stable isotope composition along the depth gradient, suggesting that organic matter in these soils has undergone limited microbial processing but instead reflects the selective preservation of recalcitrant litter moieties.

Dissolution of Microcrystalline Cellulose in Phosphoric Acid—Molecular Changes and Kinetics

In this study, we aimed to dissolve microcrystalline cellulose (MCC) with phosphoric acid to obtain high-quality fermentable saccharides. MCC was directly dissolved in phosphoric acid (the concentration was 83%) for 10 hours at temperatures of 30, 50, and 70 °C. The structural changes of MCC were determined in detail with X-ray powder diffraction, solid-state cross-polarization magic angle spinning 13C-NMR, and X-ray photoelectron spectroscopy. The kinetics of MCC decrystallization during treatment with phosphoric acid was also compared at 30, 50, and 70 °C. With the assumption of first order kinetics, the Arrhenius parameters of K, A0 and Ea were calculated. The rate constants of decrystallization reaction (K) were 0.06, 0.17, and 0.12 h-1 respectively. The pre-exponential factor (A0) was 1.2 × 106 h-1, and the activation energy (Ea) was 42.4 k J/mol.

CdS Magic-Sized Nanocrystals Exhibiting Bright Band Gap Photoemission via Thermodynamically Driven Formation

CdS magic-sized nanocrystals (MSNs) exhibiting both band gap absorption and emission at 378 nm with a narrow bandwidth of approximately 9 nm and quantum yield (QY) of approximately 10% (total QY approximately 28%, in hexane) were synthesized via a one-pot noninjection approach. This CdS MSN ensemble is termed as Family 378. It has been acknowledged that magic-sized quantum dots (MSQDs) are single-sized, and only homogeneous broadening contributes to their bandwidth. The synthetic approach developed is ready and highly reproducible. The formation of the CdS MSQDs was carried out at elevated temperatures (such as 90-140 degrees C) for a few hours in a reaction flask containing bis(trimethylsilyl)sulfide ((TMS)(2)S) and Cd(OAc)(OA) in situ made from cadmium acetate dihydrate (Cd(OAc)(2).2H(2)O) and oleic acid (OA) in 1-octadecene (ODE). Low OA/Cd and high Cd/S feed molar ratios favor this formation, whose mechanism is proposed to be thermodynamically driven. (13)C solid-state cross-polarization magic-angle spinning (CP/MAS) nuclear magnetic resonance (NMR) demonstrates that the capping ligands are firmly attached to the nanocrystal surface via carboxylate groups. With the cross-polarization from (1)H of the alkyl chains to surface (113)Cd, (113)Cd NMR is able to distinguish the surface Cd (471 ppm) bonding to both -COO(-) and S and the bulk Cd (792 ppm) bonding to S only. DOSY-NMR was used to determine the size of Family 378 ( approximately 1.9 nm). The present study provides strategies for the rational design of various MSNs.

Effect of Aluminum Speciation and Structure Characterization on Preferential Removal of Disinfection Byproduct Precursors by Aluminum Hydroxide Coagulation

Humic acid was coagulated by aluminum chloride and pokyaluminum (PACl) at different pH conditions. Aluminum speciation was investigated in details through combining electrospray ionization mass spectrometer (ESI-MS) with solid-state 27Al magic-angle spinning nuclear magnetic resonance (MAS NMR). Freeze-dried flocs from coagulation precipitates were analyzed by Fourier transform infrared (FTIR) and solid-state 13C cross-polarization magic angle spinning (CPMAS) NMR. This study also evaluated removal of disinfection byproduct (DBP) precursors by PACI and AlCl3 coagulation during coagulation process. Particular emphasis was paid to the role of aluminum speciation and structure characterization in the preferential removal of precursors by coagulation. The results indicated that prehydrolyzed or in situ formed Al13 species during coagulation process exhibited preferential removal for corresponding DBP precursors with relative structures. On one hand, for DBP precursors with aromatic and carboxylic structures, in situ Al13 species were preferentially bound to these DBP precursors. Thus, more DBP precursors with aromatic and carboxylic structures were removed by AlCl3 than those by PACl at pH 5.0. On the other hand, for DBP precursors with aliphatic structures, aluminum coagulation was not responsible for reducing these precursors. However, oligomeric aluminum species and preformed Al13 species were weak preferentially bound to DBP precursors with aliphatic structures.

Sampling Methods for Quantification of Solid-state Phases in Powder Samples with Solid-state NMR Spectroscopy

To minimize the variance in the quantification of solid-state phases in powder samples, gently placing polycrystalline samples one next to another directly in a sample holder is better than trying to mix them homogeneously prior to transferring to a sample holder. However, the solid-state cross polarization-magic angle spinning (CP-MAS) nuclear magnetic resonance (NMR) spectroscopy results demonstrated that it is essential in this sampling method to place all the samples in the location of consistent signal sensitivity. The same sampling method may be employed in other spectroscopic quantification techniques of solid-state phases if the method to limit the sample to the location with uniform signal sensitivity in the sample holder is adapted to each technique.

Use of ionic liquid for the enzyme‐catalyzed polymerization of phenols

AbstractIonic liquid and buffer mixture media are first reported in the peroxidase‐catalyzed polymerization of phenol. Yield of 100% with molecular weights of 7000 KDa, as assessed by size‐exclusion chromatography (SEC), were attained using 1‐butyl‐3‐methylimidazolium tetrafluoroborate–buffer mixtures with added hydrogen peroxide. The simplicity of the process and the low vapor pressure of the solvent media allow an eco‐friendly alternative to the general synthesis of polyphenolic‐type biopolymers. Evidence for the consequent polyphenol (PPO) was obtained from solid‐state 13C cross‐polarization magic angle spinning (CP‐MAS) NMR spectroscopy and FT‐IR. Copyright © 2009 John Wiley & Sons, Ltd.

Cadmium(II) Cysteine Complexes in the Solid State: A Multispectroscopic Study

Cadmium(II) cysteinate compounds have recently been recognized to provide an environmentally friendly route for the production of CdS nanoparticles, used in semiconductors. In this article, we have studied the coordination for two cadmium(II) cysteinates, Cd(HCys)(2) x H(2)O (1) and {Cd(HCys)(2) x H(2)O}(2) x H(3)O(+)ClO(4)(-) (2), by means of vibrational (Raman and IR absorption), solid-state NMR ((113)Cd and (13)C), and Cd K- and L(3)-edge X-ray absorption spectroscopy. Indistinguishable Cd K-edge extended X-ray absorption fine structure (EXAFS) and Cd L(3)-edge X-ray absorption near edge structure (XANES) spectra were obtained for the two compounds, showing similar local structure around the cadmium(II) ions. The vibrational spectra show that the cysteine amine group is protonated (NH(3)(+)) and not involved in bonding. The (113)Cd solid-state cross-polarization magic angle spinning NMR spectra showed a broad signal in the approximately 500-700 ppm range, with the peak maximum at about 650 ppm, indicating three to four coordinated thiolate groups. Careful analyses of low-frequency Raman and far-IR spectra revealed bridging and terminal Cd-S vibrational bands. The average Cd-S distance of 2.52 +/- 0.02 A that constantly emerged from least-squares curve-fitting of the EXAFS spectra is consistent with CdS(4) and CdS(3)O coordination. Both structural models yielded reasonable values for the refined parameters, with a slightly better fit for the CdS(3)O configuration, for which the Cd-O distance of 2.27 +/- 0.04 A was obtained. The Cd L(3)-edge XANES spectra of 1 and 2 resembled that of the CdS(3)O model compound and showed that the coordination around Cd(II) ions in 1 and 2 cannot be exclusively CdS(4). The small separation of 176 cm(-1) between the infrared symmetric and antisymmetric COO(-) stretching modes indicates monodentate or strongly asymmetrical bidentate coordination of a cysteine carboxylate group in the CdS(3)O units. The combined results are consistent with a "cyclic/cage" type of structure for both the amorphous solids 1 and 2, composed of CdS(4) and CdS(3)O units with single thiolate (Cd-S-Cd) bridges, although a minor amount of cadmium(II) sites with CdS(3)O(2-3) and CdS(4)O coordination geometries cannot be ruled out.

Cyanide- and carboxylate-functionalized cubic mesoporous silicas SBA-1: Synthesis, characterization and reactivity of organic functional groups

Highly ordered cubic ( Pm 3 ¯ n ) mesoporous silicas SBA-1 functionalized with a high density of cyanide and carboxylate groups were synthesized by one-pot co-condensation of tetramethoxysilane (TMOS) and 2-cyanoethyltriethoxysilane (CNTES) using cetyltriethylammonium bromide (CTEABr) as the structure-directing agent under strongly acidic conditions. A high degree of structural ordering is still retained up to 25 mol% CNTES loading (based on silicon) in the synthesis mixture. The simultaneous existence of chemically attached cyanide and carboxylate ester moieties was evidenced by solid-state 13C CPMAS (cross polarization magic angle spinning) NMR. The relative concentrations between cyanide and carboxylate ester functional groups in the resulting mesoporous silicas are strongly dependent on the synthesis parameters such as acid type, acid concentration and reaction time. By controlling these synthesis parameters, the contents of the cyanide functional groups incorporated can be tuned, and their transformation into carboxylate ester groups can be followed. With increasing HCl concentration and reaction time, the cyanide functional groups incorporated convert progressively into carboxylate ester groups after solvent extraction with an HCl/ethanol mixture. While using H 2SO 4 as an acid medium, on the other hand, the cyanide functional groups can be totally transformed into carboxylate ester groups. The generation of carboxylic acid functionalities can be achieved either by solvent extraction with only ethanol (without HCl) or post-dealkylation treatment of carboxylate ester groups in concentrated HCl. The acid type and concentration and the silicon source also have a profound influence on the particle morphology of mesoporous silicas.

Single-Sized CdSe Nanocrystals with Bandgap Photoemission via a Noninjection One-Pot Approach

The manuscript addresses the synthesis and characterization of one colloidal CdSe single-sized nanocrystal ensemble exhibiting bandgap absorption and emission peaking at 463 and 465 nm, respectively, with full width at half-maximum of ca. 8 nm. This ensemble is called Family 463; also, these single-sized quantum dots (QDs) are termed as magic-sized quantum dots (MSQDs). A magic-sized quantum dot (MSQD) ensemble is similar to a regular quantum dot (RQD) ensemble but consisting of single-sized nanocrystals; meanwhile, MSQDs do not grow in size any more with longer reaction periods or higher temperature, after their well development during synthesis. The CdSe MSQDs were synthesized via a noninjection one-pot approach with long reaction periods at elevated temperature, with cadmium acetate dihydrate (Cd(OAc)2·2H2O) and elemental selenium as Cd and Se sources, respectively, one long-chain fatty acid as ligands, and 1-octadecene (ODE) as a reaction medium. Different carboxylic acids with the carbon-chain length ranging from C2 to C24, the number of which refers to the total number of carbons, were investigated. Deficient acid feed amount with respect to Cd is crucial for the formation of the CdSe MSQDs, leading to the resulting Cd precursor Cd(OAc)x(OOC−(CH2)n−CH3)2-x (with tunable activity). It was also found that the fatty acids of C12−C18, with low acid-to-Cd and high Cd-to-Se feed molar ratios and the growth temperature of 200−240 °C, are optimum for MSQD Family 463, regarding the yield, purity, and their bandgap photoluminescent (PL) efficiency. Interestingly, in the initial stage of the formation at the growth temperature of 140−160 °C, there may be an “isomer competing” process. 13C solid-state cross-polarization magic-angle spinning (CP/MAS) nuclear magnetic resonance (NMR) indicates that the capping carboxylate groups are firmly attached to the nanocrystals, which allows cross-polarization from 1H of the alkyl chains to 113Cd. Thus 113Cd NMR is able to distinguish surface (422 ppm) bonding to both −COO and Se and bulk (680 ppm) Cd species bonding to Se only. The CdSe MSQD Family 463 possesses long shelf-storage stability. The synthetic approach introduced here is ready and reproducible, featuring large-scale production. The present study on the growth kinetics of CdSe MSQD Family 463 brings insights for rational design strategies toward various MSQD ensembles with different sizes, via the choice of acids and their feed amount affecting the activity of the resulting Cd precursor.

Investigation of Biomasses and Chars Obtained from Pyrolysis of Different Biomasses with Solid-State 13C and 23Na Nuclear Magnetic Resonance Spectroscopy

A number of biomass samples (reed, pine pellets, Douglas fir wood chips, wheat straw, peach stones, and olive residue), pretreated biomass samples (leached wheat straw, leached peach stones, and leached olive residue), as well as their chars obtained by pyrolysis using different heating rates (5, 10, and 20 degrees C/min) at the end temperature of 800 degrees C were characterized with C-13 and Na-13 nuclear magnetic resonance (NMR) spectroscopy. In the case of the biomass samples, C-13 solid-state cross-polarization magic-angle spinning (CPMAS) NMR was used, resulting in spectra indicating the various groups of carbons present in the biomass samples. No evidence was found that the leaching process could affect the carbon composition of the biomass samples. In the char samples, only aromatic groups of carbon were left, shown by C-13 solid-state single-pulse MAS NMR. According to the results, the origin of biomass, the leaching procedure, and the different heating rates do not affect the char carbon composition. Therefore, it could be assumed that the carbon structure does not affect the reactivity of the char. Na-23 single-pulse solid-state MAS NMR was applied to investigate the sodium environment in the biomass and char samples. Despite experimental difficulties, we were able to observe definite differences in line width and shifts of the studied compounds. This proves that leaching affects the fuel properties, i.e., sodium chemistry in a biomass sample, and therefore, it could be assumed that the char reactivity is affected. Higher magnetic fields and more sophisticated techniques of resolution enhancement multiple-quantum magic-angle spinning (MQ-MAS) or double rotation (DOR) may provide more detailed local information regarding the sodium environment in biomasses and their char samples.

A Novel Green Template for the Synthesis of Mesoporous Silica

Mesoporous pure silicas and functionalized silica with a narrow pore size distribution centered at 3.8 nm were prepared by a novel template, amphiphilic dendritic polyglycerol. The resulting silica materials were characterized by electron microscopy; nitrogen adsorption; (1)H, (13)C, and (29)Si solid-state cross-polarization magic-angle spinning NMR spectroscopy. It was shown that the template could be completely removed from the pure and functionalized silica in an environmentally friendly way by means of a simple water extraction procedure. Furthermore, it was shown that these materials could be easily functionalized, for example, by employing aminopropyl groups. Thus, a new environmentally friendly pathway to this fascinating class of silica material has been opened.

Carbon-13 CP MAS NMR Study on Structures of Octadecyl Chains Influenced by Co-Presence of 3-Aminopropyl Chains on SBA-15

Functionalized SAB-15 samples by octadecyltrimethoxysilane (OTC) were studied by 13C magic angle spinning (MAS) cross polarization (CP) nuclear magnetic resonance (NMR) spectroscopy. In the SBA-15 sample fully functionalized by 3-aminopropyltrimethoxysilane (APS) and OTC in 1:1 molar ratio, octadecyl chains were observed to have, on average, more trans conformation than those in the SBA-15 samples fully modified by OTC only. Our results confirm that long chain molecules tend to organize themselves better in the co-presence of short chain molecules on the surface of mesoporous materials by packing of the different length chains in an interdigitized fashion even when the short chains are long enough to have three carbons and a functional group at the ends. In addition, our results indicate that solid-state 13C CP MAS NMR spectroscopy is a simple and non-destructive method to probe the molecular structures of the domains composed of long alkyl chains.