Solid-state 13C CPMAS Research Articles

Isolation and seasonal effects on characteristics of fulvic acid isolated from an Australian floodplain river and billabong

Fulvic acids from an Australian floodplain river and billabong were isolated using DEAE and DAX-8 resins, and characterised with the use of size exclusion chromatography and solid-state CP-MAS (13)C NMR spectroscopy. Differences between the two resin isolates were evident. Fulvic acids isolated using DEAE-cellulose had higher apparent M(n) and M(w) values, while the DAX-8 resin showed a slight preference for aliphatic components. Fulvic acids from the river and billabong had the same functional groups present, however, the river fulvic acids had higher apparent M(n) (number average molecular weight) and M(w) values (weight average molecular weight), and were more polydisperse than the billabong fulvic acid. There were no significant changes in the characteristics of the fulvic acid isolated from the river at four sampling times: summer, autumn, winter and spring. In contrast, fulvic acids isolated from a billabong displayed seasonal variation in molecular weights. This work emphasizes the importance in ecological studies of isolation procedure for the operationally defined fulvic acids.

Homogeneous and heterogeneous 4-( N, N-dialkylamino)pyridines as effective single component catalysts in the synthesis of propylene carbonate

4-( N, N-Dimethylamino)pyridine (DMAP) is shown to catalyze the reaction of propylene oxide with carbon dioxide in high yields without added co-catalyst. Moreover, propylene carbonate is the only product obtained when the reaction is conducted under rigorously dry conditions. This result contrasts previous findings indicating minimal or no conversion of the epoxide using DMAP alone. Additionally, a new immobilized DMAP analog has been synthesized that shows productivity comparable to the homogeneous catalyst. The supported catalyst is characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), N 2 physisorption, solid state 13C and 29Si CP-MAS NMR, and FT-Raman spectroscopy. This supported catalyst can be readily recovered without utilization of high temperature distillation.

Probing the interaction between di- and tri-functionalized carboxy-phosphonic acid and LDH layer structure

Abstract A series of carboxyphosphonate-derivatives of (Zn, Al) layered double hydroxide (LDH) was prepared and characterized by a combination of techniques including powder X-ray diffraction, FTIR spectroscopy and solid-state 13C CP-MAS and 31P MAS NMR spectroscopies. The number of carbon atoms, n = 1 or 2 in HO2C(CH2)nPO3H2, was found to have an influence on the accommodation of the interleaved molecule, the carboxylate function lying perpendicular or parallel to the inorganic sheets of the LDH host material. These observations are in agreement with NMR results which evidence an interaction of the interlayered molecules through either the carbonyl or the phosphonate group or both in the case of the larger molecule, N-(phosphonomethyl)iminodiacetic acid. The variation of the basal spacing of the hybrid materials as a function of the temperature indicates a rearrangement of the molecule within the host material gap.

Structural Characterization of Lignin from Leaf Sheaths of “Dwarf Cavendish” Banana Plant

Dioxane lignin (DL) isolated from leaf sheaths of banana plant (Musa acuminata Colla var. cavendish) and in situ lignin were submitted to a comprehensive structural characterization employing spectroscopic (UV, FTIR, solid state 13C CP-MAS NMR, liquid state 13C and 1H NMR) and chemical degradation techniques (permanganate and nitrobenzene oxidation). Results obtained showed that banana plant leaf sheath lignin is of HGS type with a molar proportion of p-hydroxyphenyl (H)/guaiacyl (G)/syringyl (S) units of 12:25:63. Most of the H units in DL are terminal phenolic coumarates linked to other lignin substructures by benzyl and Cgamma-ester bonds in contrast to ferulates that are mainly ether linked to bulk lignin. It is proposed that banana plant leaf sheath lignin is chemically bonded to suberin-like components of cell tissues by ester linkages via essentially hydroxycinnamic acid residues. beta-O-4 structures (0.31/C6), the most abundant in DL, comprise mainly S units, whereas a significant proportion of G units is bonded by beta-5, 5-5', and 4-O-5' linkages contributing to ca. 80% of condensed structures in DL.

Speciation of copper by using a new fullerene derivative as a mixed-mode sorbent

A new fullerene derivative was synthesized by photochemical reaction of C60 fullerene and rubeanic acid in a toluene–ethanol medium. The synthetic procedure was optimized by UV–visible spectroscopy, using the spectrum for C60 fullerene as reference; C60–rubeanic acid derivative, a novel adduct of C60 fullerene, exhibits an increased absorption band between 425 and 500 nm corresponding to the maximum absorption of rubeanic acid. The dark brown solid obtained was characterized by elemental analysis, and XRD and solid state 13C CP–MAS NMR spectroscopies. The band observed at 61.8 ppm is typical of sp3 atoms in the modified fullerene that forms by addition of amines to double bonds in fullerene, which bond covalently to the rubeanic acid group to form a monoadduct. The C60–rubeanic acid derivative can thus be used as a mixed-mode sorbent material for the speciation of cationic and neutral species. The adsorptive potential of the new derivative as a model for the preconcentration of copper traces on the pendant group of rubeanic acid, and neutral copper complexes (e.g. the pesticide copper oxinate) on the fullerene core has for the first time been assessed in this work. Both species are initially retained by the derivative and subsequently discriminated by sequential elution with various reagents. The proposed automatic method can accurately resolve mixtures of both types of copper species in ratios from 1 : 17 to 17 : 1 with relative errors less than 7%.

Catechin Transformation As Influenced by Aluminum

Polyphenols (catechins) are vital biomolecules in tea plants (Camellia sinensis), which are well-known as typical Al accumulators. However, the interaction between Al and catechin remains obscured. The objective of the present study was to investigate the effect of Al on the transformation of (+)-catechin. Solutions with OH/Al molar ratios of 2.5 (pH 5.5) and 3.0 (pH 7.0) prepared at Al/catechin molar ratios (R) of 0, 0.2, 0.4, 0.6, 0.8, and 1.0 were aged for 7 and 30 days, respectively. The precipitates were collected and examined by wet chemistry, X-ray diffraction, transmission electron microscopy, electron spin resonance (ESR), cross-polarization magic angle (CPMAS) 13C nuclear magnetic resonance (13C NMR) analyses, and Fourier transformation infrared absorption spectrometry (FT-IR). The weight of the precipitates increased with increasing Al/catechin molar ratios and with prolonged aging. The molar ratios of Al/catechin in the precipitates increased with increasing initial Al/catechin molar ratios and were close to the initial solution Al/catechin molar ratios. The chemical analysis and spectroscopic studies indicated that Al was bonded with catechin, forming a 1:1 type complex. The reaction of crystalline catechin with Al resulted in the formation of X-ray noncrystalline precipitates. The solid-state CPMAS 13C NMR spectra of the precipitates show the change in chemical shifts of catechin as a result of catechin complexation with Al. The FT-IR spectra of the Al-catechin precipitates also show the loss of absorption bands of several functional groups compared with catechin. The FT-IR data substantiate this reasoning. The ESR spectra of the precipitates show a single symmetrical line devoid of any fine splitting, indicating the presence of free radicals of semiquinones, which are commonly present in humified materials.

Investigation of the Core−Shell Interface in Gold@Silica Nanoparticles: A Silica Imprinting Approach

The nature of the self-assembled core-shell interface in gold@silica nanoparticles synthesized via a 3-aminopropyltrimethoxysilane (APTMS) route is investigated using materials synthesis as a sensitive tool for elucidating interfacial composition and organization. Our approach involves condensation of the gold@silica nanoparticles within a silica framework for synthesis of a composite gold-silica material containing approximately 30 wt % gold. This material contains one of the highest gold loadings reported, but maintains gold core isolation as ascertained via a single surface plasmon resonance absorption band frequency corresponding to that of gold nanoparticles in dilute aqueous solution. The immobilized gold cores are subsequently etched using cyanide anion for the synthesis of templated porosity, which corresponds to the space that was occupied by the gold. Characterization of immobilized amines is performed using probe molecule binding experiments, which demonstrate a lack of accessible amines after gold removal. Solid-state 13C CPMAS NMR spectroscopy on these materials demonstrates that the amount of amine immobilization must be less than 10% of the expected yield, assuming that all of the APTMS becomes bound to the gold nanoparticle template. These results require a core-shell interface in the gold@silica nanoparticles that is predominantly occupied by inorganic silicate species, such as Si-O-Si and Si-OH, rather than primary amines. Such a result is likely a consequence of the weak interaction between primary amines and gold in aqueous solution. Our method for investigating the core-shell interface of gold@silica nanoparticles is generalizable for other interfacial structures and enables the synthesis of bulk imprinted silica using colloidal templates.

The structure–activity relationship of fire retardant phosphorus compounds in wood

Sawdust of Scots Pine sapwood was chemically modified with various alkyl- and phenylchlorophosphorus compounds. The formation of covalent bonds was confirmed with solid state CP-MAS 13C NMR. According to thermogravimetric analysis (TGA), all phosphorus compounds decreased the temperature for the maximum rate of pyrolysis (from 350 °C to max. 240 °C) and increased the char formation (from 25% to max. 54%). Variation of the alkyl groups (C2–C8) had no significant effect. Phenylphosphates decrease the temperature of pyrolysis more efficiently than the alkyl analogues, due to higher thermal stability. The order in which the phenylphosphorus compounds affect the pyrolysis of the modified sawdust is consistent with their acidity order: organophosphate > organophosphonate ≫ organophosphinate. All phosphorus compounds used in this study reduce the equilibrium moisture content (EMC). Whereas the results obtained with the dialkyl phosphates are relatively poor, significant reductions in EMC can be achieved with the phenylphosphorus compounds.

Characterization of polyelectrolyte complexes between chondroitin sulfate and chitosan in the solid state

Chondroitin sulfate (ChS) was used to form polyelectrolyte complexes with chitosan (ChI), and its potential as a colon-targeted drug carrier was investigated. In order to determine the optimal conditions for the formation of a stable polyelectrolyte complex, the formation of ChS/ChI complexes was examined at two different pH values with various weight ratios, or at a fixed molar ratio of ChS/ChI of 1/2 under various pH conditions. The molar compositions of the various ChS/ChI complexes were quantitated with the use of solid-state 13C CP MAS NMR. The equivalent molar ratios of the complexes ranged from 0.47 to 0.54, in agreement with the data determined by elemental analysis. The fact that these values were close to 0.5 suggests that most of the --OSO3- and the --COO- groups on ChS formed strong electrostatic interactions with the --NH3+ groups on ChI, obeying a simple stoichiometric reaction between two oppositely charged moieties. Similar compositions of the complexes were obtained under most conditions tested; however, different strengths of the interactions between the two polysaccharides were noted from measurements of the water-associated transition and thermal degradation temperatures and the degree of ChS dissolution. FTIR and 13C NMR clearly showed H-bond formation at low pH, indicating that in addition to the varying degrees of electrostatic interaction, H bonding may be involved in complex formation. The highest degradation temperature, as determined by thermal gravimetric analysis, and the lowest ChS sol fraction, as measured by gel permeation chromatography, were observed with the complex prepared at pH 5, with a 1:1 mole ratio of the two opposite charges in feed. This complex also exhibited the highest water-associated transition temperature, as determined by differential scanning calorimetry. Furthermore, the swelling behavior of these complexes was pH dependent; this is a property that can potentially be exploited to control drug release from these complexes under specific pH conditions.

The Use of 13C Labeling to Enhance the Sensitivity of 13C Solid-State CPMAS NMR to Study Polymorphism in Low Dose Solid Formulations

13C labeling was used to enhance the sensitivity of 13C solid-state NMR to study the effect of tabletting on the polymorphism of a steroidal drug. The steroidal drug Org OD 14 was 13C labeled and formulated into tablets containing only 0.5–2.5% active ingredient. The tablets were subsequently studied by solid-state 13C CPMAS NMR. The crystalline form present in tablets could readily be analyzed in tablets. No change in crystalline form was observed as a result of formulation or in subsequent stability studies. Solid-state NMR in combination with 13C labeling can, in suitable cases, be used as a strategy to study the effect of formulation on the polymorphism of low dose drugs. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:458–463, 2005

Isomeric [RuCl2(dmso)2(indazole)2] complexes: ruthenium(ii)-mediated coupling reaction of acetonitrile with 1H-indazole

Reaction of the antitumor complex trans-[Ru(III)Cl4(Hind)2]- (Hind = indazole) with an excess of dimethyl sulfoxide (dmso) in acetone afforded the complex trans,trans,trans-[Ru(II)Cl2(dmso)2(Hind)2] (1). Two other isomeric compounds trans,cis,cis-[Ru(II)Cl2(dmso)2(Hind)2] (2) and cis,cis,cis-[Ru(II)Cl2(dmso)2(Hind)2] (3) have been obtained on refluxing cis-[Ru(II)Cl(2)(dmso)(4)] with 2 equiv. of indazole in ethanol and methanol, respectively. Isomers 1 and 2 react with acetonitrile yielding the complexes trans-[Ru(II)Cl2(dmso)(Hind){HN=C(Me)ind}].CH3CN (4.CH3CN) and trans,cis-[Ru(II)Cl2(dmso)2{HN=C(Me)ind}].H2O (5.H2O), respectively, containing a cyclic amidine ligand resulting from insertion of the acetonitrile C triple bond N group in the N1-H bond of the N2-coordinated indazole ligand in the nomenclature used for 1H-indazole. These are the first examples of the metal-assisted iminoacylation of indazole. The products isolated have been characterized by elemental analysis, IR spectroscopy, UV-vis spectroscopy, electrospray mass-spectrometry, thermogravimetry, differential scanning calorimetry, 1H NMR spectroscopy, and solid-state 13C CP MAS NMR spectroscopy. The isomeric structures of 1-3 and the presence of a chelating amidine ligand in 4 and 5 have been confirmed by X-ray crystallography. The electrochemical behavior of 1-5 and the formation of 5 have been studied by cyclic voltammetry.

Structural analysis of water-soluble and -insoluble β-glucans of whole-grain oats and barley

Water-soluble and water-insoluble (1→3),(1→4)-β- d-glucans were isolated from whole-grain oats and barley and digested with lichenase. The oligosaccharides thus produced were analysed using anion-exchange chromatography with pulse-amperometric detection (HPAEC-PAD). The FT-IR, 1H NMR and solid-state 13C CP-MAS NMR spectra of the β-glucans were also measured. Analyses of the ratio of oligosaccharides with degrees of polymerisation 3 and 4 (DP3:DP4) showed small structural differences between oats and barley and between the water-soluble and water-insoluble β-glucans. The molar masses analysed using the SEC-HPLC method were 500,000 g/mol for the soluble β-glucans of both oats and barley and <200,000 g/mol for the insoluble β-glucans. No differences were found in the FT-IR and NMR spectra.

Novel polysilazanes as precursors for silicon nitride/silicon carbide composites without “free” carbon

Polysilazanes with chemical composition Si 4N 4CH x ( x = 12–14) were obtained on two different reaction pathways. In the first route three equivalents of dichlorosilane, H 2SiCl 2, were mixed with one equivalent of methyldichlorosilane, H 3CSiHCl 2, and reacted with ammonia to yield [(SiH 2–NH) 3(H 3CSiH–NH)] n ( 1) after appropriate work-up. In the second route, dichlorosilane was reacted with methylamine and ammonia in a 3:1 ratio to deliver [(SiH 2–NH) 3(SiH 2–NCH 3)] n ( 2). The raw products were further cross-linked by base-catalyzed dehydrocoupling reactions involving Si H and N H units to yield products 1a and 2a, respectively. The molecular structure of 1 and 2 was investigated by means of high resolution 1H, 13C{ 1H}, and 29Si{ 1H} NMR spectroscopy in C 6D 6 solution as well as by IR spectroscopy. Because of the insolubility of the cross-linked products 1a and 2a solid state 1H, 13C, and 29Si CP-MAS NMR in combination with IR spectroscopy were applied for their spectroscopic characterization. Chemical compositions were determined using elemental analysis. Thermolysis in an argon atmosphere up to 1400 °C of the cross-linked products delivered Si 3N 4/SiC ceramics in ∼94% yield. The absence of “free” carbon was revealed by mass spectra-coupled thermogravimetric analysis (TGA). These investigations indicated a one-step decomposition in the 250–700 °C range with predominant evaporation of hydrogen. In contrast, elimination of methane and ammonia ( 1) or methane and methylamine ( 2) was below 0.5 mass%. Additionally, neutron wide angle scattering proved the absence of a “free” carbon phase. High-temperature properties were investigated using high temperature TGA as well as XRD, EDX and TEM of annealed ceramic samples. The onset of crystallization in both materials was around 1500 and 1300 °C (1 atm N 2), respectively, and α- as well as β-Si 3N 4 formed besides α/β-SiC. Above 1900 °C ceramics derived from both 1a and 2a decomposed to α/β-SiC/β-Si 3N 4/α-Si composites.

Solid-state characterization of chitosans derived from lobster chitin

Two samples of chitosan (CH1 and CH2) of different molecular weights and degrees of deacetylation were prepared from lobster chitin under two different processes. Solid-state properties of CH1 and CH2 were characterized and compared with four commercial chitosans prepared from crab and fresh shrimp shells. Infrared spectroscopy (IR), solid-state CP-MAS 13C NMR, powder X-ray diffraction and differential scanning calorimetric techniques were used to characterize the molecular structure and solid-state properties of the materials. Changes in the crystallinity and polymorphic forms of CH1 and CH2 were attributable to the different process conditions used. The differences in crystallinity were confirmed by powder X-ray diffraction data. The methods of preparation of CH1 and CH2 did not significantly influence the bulk, tap and true densities of the bulk material, but they affected the flow properties of CH1 and CH2. In conclusion, the physicochemical properties of the present chitosans prepared from lobster chitin (CH1 and CH2) are comparable with those of commercial chitosan materials of crab or shrimp shell origin.

Solid state 13C CP MAS NMR study of molecular motions and interactions of urea adsorbed on cotton cellulose

The surface interaction between cotton cellulose and urea was studied by measuring solid state 13C CP MAS NMR spectra and relaxation times. The investigation of cotton cellulose surface interactions is inherently difficult as the surface regions constitute only a small proportion of cotton fibers and an important part of these investigations has been to identify and develop useful experimental methods. The results have provided detailed insight into the interactions and motions of urea at the cotton cellulose surface. It is found that the interactions have no discernible effects on the crystallinity and polymorphic form of cellulose. This suggests that urea does not penetrate the cellulose microfibrils and distort the internal hydrogen bonding structure but interact with the cotton cellulose surface. The relaxation techniques used in this paper make it possible to identify several cellulose components including the crystalline and amorphous regions that are not directly resolved in the spectra. Another advantage of the relaxation methods is that it becomes possible to study details of molecular motion in both the crystalline and amorphous regions that may be related to the mechanical properties of the cellulose microfibrils. It has been possible to describe the surface interaction between urea and cotton cellulose in terms of the motion of the urea molecules. The interaction at the cotton cellulose surface makes the urea molecules more mobile as revealed by the lineshapes and relaxation characteristics. The study of the motion makes it possible to obtain a description of the orientation of the urea molecules at the cotton cellulose surface. This orientation is determined by numerous intermolecular interactions and provides a constraint on the intermolecular potential. The results suggest that the urea molecules interact preferentially at hydrophilic defects on the surface such as depressions and grooves by hydrogen bonding with surface hydroxyl groups. The shape of these surface defects is directly reflected in the orientation of the urea molecules at the binding sites. The experiments have been shown to be selective, monitoring only urea molecules interacting with the cotton cellulose surface. This makes urea an excellent probe molecule to study cotton cellulose surfaces.

Hydrosolubilization of Large Aromatic Molecules: Facile Synthesis and Characterization of Water-Soluble Derivatives of Decacyclene

Application of a mild-condition reductive/oxidative protocol to the large poorly-conjugated aromatic structure of decacyclene affords a water soluble oxygenated amphiphilic material which has been characterized and compared with the hydrocarbon precursor by means of solution 1H NMR and solid-state 13C CPMAS NMR, vibrational, electron, and mass spectroscopies. The nature of the different oxygenated moieties covalently attached to decacyclene framework is elucidated and the role of molecular O2 in the oxidizing reaction path of reduced decacyclene is discussed.

Synthesis and characterization of alkylene-bridged silsesquicarbodiimide hybrid xerogels

Hybrid polymers consisting of flexible organic chains within an inorganic silsesquicarbodiimide network of the type [(NCN) 1.5Si-(CH 2) x -Si(NCN) 1.5] n (where x=2, 6, and 8) were prepared by mild sol–gel polycondensation reactions of bis(trichlorosilyl)alkanes and bis(trimethylsilyl)carbodiimide. The presence of the NCN groups in xerogel structures was identified by FTIR spectra. The composition and molecular structures were characterized by elemental analysis, solid-state 13C CP MAS- and 29Si CP MAS-NMR spectroscopies, and XRD. Scanning as well as transmission electron microscopies were used to examine the morphology of the xerogels. In addition, the pore structure of the materials was examined by the gas adsorption (BET) method and it is found that the surface area decreased with increasing length of the alkylene spacing group.

Molecular characterization of dissolved organic matter in freshwater wetlands of the Florida Everglades

In this study, the molecular composition of dissolved organic matter (DOM), collected from wetlands of the Southern Everglades, was examined using a variety of analytical techniques in order to characterize its sources and transformation in the environment. The methods applied for the characterization of DOM included fluorescence spectroscopy, solid state 13C CPMAS NMR spectroscopy, and pyrolysis-GC/MS. The relative abundance of protein-like components and carbohydrates increased from the canal site to more remote freshwater marsh sites suggesting that significant amounts of non-humic DOM are autochthonously produced within the freshwater marshes, and are not exclusively introduced through canal inputs. Such in situ DOM production is important when considering how DOM from canals is processed and transported to downstream estuaries of Florida Bay.

Synthesis and conformational study of silk model polypeptides [Ala-Gly] 12 by solid-state NMR

A series of well-defined model polypeptides of Bombyx mori silk fibroin, [Ala-Gly] n ( n=12 and 5–9), [Ala d4Gly] 12 and [Gly d2Ala] 12, (where Ala, Gly, Ala d4 and Gly d2 denote l-alanine, glycine, 2,3,3,3-deuterated l-alanine and 2,2-deuterated glycine residues, respectively), were successfully synthesized by an automatic solid phase peptide synthesizer. Followed by treatment with 9 M lithium bromide (LiBr) solution to convert their conformation from the silk II to the silk I form. We determined the intrinsic 1H, 13C and 15N NMR chemical shifts of Ala and Gly residues, characteristic to the silk I and silk II forms in Bombyx mori, by high-resolution and solid-state 13C CP-MAS, 1H CRAMPS, 1H– 13C HETCOR and 15N CP-MAS NMR measurements. Next, we demonstrated that it is necessary at least 12 amino acid residues ( n=6) in the [Ala-Gly] n-I series for the formation of stable silk I form by 13C CP-MAS NMR. Finally, we found that the intrinsic 1H and 13C chemical shifts of the specific deuterium labeled polypeptides, [Ala d4-Gly] 12 and [Gly d2-Ala] 12, cause a meaningful chemical shift displacement, suggesting that the deuterium interacts with proton and/or carbon atoms in the solid state. Thus, the selective deuterium labeling has a potential to useful for the structural analysis by 1H NMR in the solid state.

Nonaqueous, Molecular Precursor Route to Hybrid Inorganic/Organic Zirconia−Silica Materials Containing Covalently Linked Organic Bridges

New hybrid inorganic/organic materials possessing zirconium in the inorganic framework have been synthesized. Co-thermolyses in sealed reactors (toluene, AlCl3 catalyst, 155 °C) of Zr[OSi(OtBu)3]4 in the presence of (EtO)3Si(CH2)nSi(OEt)3 (n = 1, 2) or (EtO)3Si(C6H4)nSi(OEt)3 (n = 1, 2; C6H4 = 1,4-phenylene) monomers rapidly yielded monolithic, transparent gels. The resulting xerogels were amorphous and exhibited high surface areas and high surface coverages of OH functionalities. Solid-state 29Si and 13C CP MAS NMR spectroscopies were used to establish the presence of intact, organic bridging groups and to verify the presence of unreacted ethoxy groups. Energy-dispersive X-ray spectroscopy was used to elucidate the elemental composition and distribution throughout the material, and atomic force microscopy was used to probe surface adhesive properties.