Cross-polarization Magic-angle Spinning NMR Spectroscopy Research Articles

2-Mercaptopyrimidine-functionalized mesostructured silicas to develop electrochemical sensors for a rapid control of scopolamine in tea and herbal tea infusions

Mesostructured silicas were synthesized and chemically functionalized with a 2-mercaptopyrimidine (MPY)-derivative. Bare and functionalized silicas (MSU-2, HMS, SBA-15, MSU-2-MPY, HMS-MPY and SBA-15-MPY) were characterized by powder X-ray diffraction, nitrogen adsorption-desorption isotherms, transmission electron and scanning electron microscopy, 29Si and 13C cross-polarization magic-angle spinning NMR spectroscopy and elemental analysis, and used to prepare modified carbon paste electrodes (CPEs). The electrodes properties were studied using potassium ferrocyanide and scopolamine as probes employing cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Results proved that MPY groups on the silica surface were necessary to improve the sensitivity in the voltammetric determination of scopolamine. CPE modified with HMS-MPY exhibited higher peak current toward the oxidation of scopolamine, with a well-defined oxidation peak at + 1.1 V (vs. Ag/AgCl) in DPV. This fact can be attributed to the high electroactive area of this material, with 3 D wormhole-like channel structure that favored the scopolamine diffusion. Under optimum conditions, HMS-MPY-CPE exhibited a wider linearity range, from 0.9 to 200 μM, with a detection limit of 0.3 μM and good reproducibility by DPV. The developed sensor was successfully applied for a rapid determination of scopolamine in spiked tea and herbal tea infusion samples with good recoveries (between 83 ± 5 and 101 ± 1%).

Synthesis of anionic ionic liquids@TpBd-(SO3)2 for the selective adsorption of cationic dyes with superior capacity.

The discharge of industrial printing and dyeing wastewater is one of the main reasons for the increasing water shortage and deterioration. The treatment of dyestuff wastewater is an issue and needs to be urgently solved. In this work, anionic ionic liquid functional covalent organic materials (COMs) were firstly synthesized and used for the selective adsorption of cationic dyes. First, a series of sulfonic acid group (SO3H)-functionalized anionic TpPa-SO3, TpBd-(SO3)2, and TpCR-(SO3)2 were prepared, respectively, and then imidazole was grafted onto TpBd-(SO3)2 to obtain ImI@TpBd-(SO3)2. The full characterization using X-ray diffraction, FT-IR spectroscopy, 13C cross-polarization magic-angle spinning NMR spectroscopy, zeta-potentials, BET surface and pore analysis indicated that these COMs and ImI@TpBd-(SO3)2 exhibited different morphologies, porosities, and potentials. The effects of the type of dye, adsorption time, initial dye concentration, and pH on the adsorption of dyes on ImI@TpBd-(SO3)2 were systematically investigated, respectively. The results revealed that ImI@TpBd-(SO3)2 possessed good adsorption performance for nine different cationic dyes with adsorption capacities in the range from 2865.3 mg g−1 for methylene blue (MB) to 597.9 mg g−1 for basic orange 2 (BO), but little adsorption for anionic and neutral dyes, revealing charge selectivity. The adsorption ratio of ImI@TpBd-(SO3)2 for MB was as high as 74.0% at 10 min by using 1.0 mg material, owing to the post modification of TpBd-(SO3)2 with imidazole. The adsorption of MB on ImI@TpBd-(SO3)2 was pH dependent. The adsorption isotherm and kinetics fitted well with the Freundlich and pseudo second-order kinetic model, respectively. Finally, the very outstanding advantages of superior selective adsorption, desorption, convenient preparation, and low density of ImI@TpBd-(SO3)2 predicted its research and application potential in dye wastewater recovery.

A Model Study to Unravel the Complexity of Bio-Oil from Organic Wastes.

Binary and ternary mixtures of cellulose, bovine serum albumin (BSA) and tripalmitin, as biomass reference compounds for carbohydrates, proteins and triglycerides, respectively, were treated under hydrothermal liquefaction (HTL) conditions to describe the main reaction pathways involved in the process of bio-oil production from municipal organic wastes. Several analytical techniques (elemental analysis, GC-MS, atmospheric-pressure photo-ionisation high-resolution Fourier transform ion cyclotron resonance mass spectrometry, and 13 C cross-polarisation magic-angle spinning NMR spectroscopy) were used for the molecular-level characterisation of the resulting aqueous phase, solid residue and bio-oil, in particular. The main reaction pathways led to free fatty acids, fatty acid amides, 2,5-diketopiperazines and Maillard-type compounds as the main components of the bio-oil. The relationship of such compounds to the original components of the biomass was thus determined, which highlights the fate of the heteroatom-containing molecules in particular. Finally, the molecular composition of the bio-oils from our reference compounds was matched with that of the bio-oil from municipal organic waste biomass by comparing their high-resolution Fourier transform ion cyclotron resonance mass spectra, and we obtained a surprisingly high similarity. Hence, the ternary mixture acts as a reliable biomass model and is a powerful tool to clarify the degradation mechanisms that occur in the biomass under HTL treatment, with the ultimate goal to improve the HTL process itself by modulating the input of the organic starting matter and then the upgrading steps to bio-fuels.

Evaluation of the dual retention properties of stationary phases based on silica hydride: Perfluorinated bonded material.

The synthesis of a new perfluorinated stationary phase based on silica hydride using a hydrosilation reaction was investigated. The material was characterized by elemental analysis, diffuse reflectance infrared Fourier transform spectroscopy and (13) C cross-polarization magic-angle spinning NMR spectroscopy. The retention properties of this new material were tested in the reversed-phase and normal-phase mode. Variable buffer strength experiments at two pH conditions for selected polar compounds were used to compare the new phase to hydrophilic interaction liquid chromatography retention. These results and previous data reported in the literature were used to postulate differences in the retention mechanism between hydrophilic interaction liquid chromatography and silica hydride-based stationary phases.

Preparation and characterisation of Ce:YAG -polycarbonate composites for white LED

Ce:YAG-polycarbonate composites were prepared with several amounts of Ce:YAG in the range 0.1–5 wt.% by using melt compounding. The structure and morphology of the composites were investigated by means of X-ray diffractometry and transmission electron microscopy. The optical properties of the composites were studied by using photoluminescence spectroscopy. The intermolecular interaction between the polymer and the filler surface was investigated using 13C cross-polarization magic-angle spinning NMR spectroscopy (13C {1H} CP-MAS NMR). The results showed that the dispersion of the particles in the polymer, and the optical properties, depend on the Ce:YAG amount. The composites were combined with a blue LED in order to test their performance in a white LED device. Results indicate that more suitable light is obtained using the Ce:YAG-PC composite loaded at 2 wt.%.

Concentration-dependant selective removal of Cr(III), Pb(II) and Zn(II) from aqueous mixtures using 5-methyl-2-thiophenecarboxaldehyde Schiff base-immobilised SBA-15

5-Methyl-2-thiophenecarboxaldehyde (MTC)-derived Schiff base was immobilised over SBA-15 (TS-SBA-15) via a two-step modification procedure. Initially, (3-aminopropyl)triethoxysilane (APTES) was heterogenised over SBA-15 (NH2-SBA-15), and the Schiff base formation was followed by a reaction with MTC in hot methanol. X-ray diffraction and transmission electron microscopy showed that the SBA-15, NH2-SBA-15 and TS-SBA-15 materials had mesoscopically ordered, hexagonal symmetry and well-defined morphologies. 29Si magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy revealed a change in the silicon environment during modification. The N2 sorption experiments showed that the material has a large surface area (623 m2 g−1), acceptable pore diameter (6.5 nm) and reasonable pore volume (1.23 cm3 g−1) to accommodate the guest molecules inside the pore channels. Organic functionalisation was determined successfully by Fourier transform infrared and 13C cross-polarisation magic-angle spinning NMR spectroscopy. The optimal condition for the removal of Cr(III), Pb(II) and Zn(II) from water was explored by varying the parameters, such as pH, stirring time, initial concentration and amount of adsorbent. The results suggested that TS-SBA-15 can achieve the adsorption maximum within 6 h at pH 6.5. The adsorbent exhibited moderate-to-good adsorption ability towards the three metal ions under these experimental conditions. The selective adsorption performance of TS-SBA-15 from binary mixture was examined by keeping equal concentrations of metal ions in the mixture. TS-SBA-15 was more selective towards Cr(III) ions from both the binary and ternary mixtures at pH 6.5. The effect of the metal ion concentration over mole adsorption selectivity in the ternary mixture was examined by doubling the concentration of at least one metal ion in the mixture. The result was compared with the ternary mixture containing equal concentrations of metal ions. The reusability test showed that TS-SBA-15 can be recycled for at least six consecutive cycles without losing its adsorption ability.

Ce:Y3Al5O12–Poly(methyl methacrylate) Composite for White-Light-Emitting Diodes

A Ce:YAG-poly(methyl methacrylate) (PMMA) composite was prepared by using the melt compounding method. The structure and morphology were investigated by X-ray diffractometry, transmission electron microscopy, and small-angle X-ray scattering. The optical properties (emission, excitation, and fluorescence decay rate) of the composite were studied by using photoluminescence spectroscopy. The polymer–filler interactions were studied using 13C cross-polarization magic-angle spinning NMR spectroscopy (13C{1H} CP-MAS NMR). The results indicated that Ce:YAG particles are well-dispersed in the PMMA matrix without loss of their luminescence properties or significant spectral shift, thus suggesting that this composite can be valuable for advanced applications in white LED manufacture. A demonstration of its efficiency in white LED devices is also reported.

Synthesis and Skeletal Transformations of Trinuclear Palladium and Nickel Phosphido Complexes

Trinuclear phosphido complexes of palladium and nickel were synthesized and characterized. [M{(2-Me2NC6H4)PPh}(OAc)]3 [M = Pd (2), Ni (6)] were obtained from the respective acetate, [Pd(OAc)2]3 or [Ni(OAc)2(H2O)4], in reactions with the secondary aminophosphane (2-Me2NC6H4)PHPh (1). The chloride derivative [Pd{(2-Me2NC6H4)PPh}Cl]3 (4a) was generated from the reaction of the chelating ligand 1 with Na2PdCl4. The reaction of the acetate 2 with p-toluenesulfonic acid (pTsOH) led to the formation of the tosylate analogue [Pd{(2-Me2NC6H4)PPh}(OTs)]3 (3). From the reaction of the tosylate trimer 3 with CsCl, CsBr or NaI, the substitution products [Pd{(2-Me2NC6H4)PPh}X]3 [X = Cl (4a), Br (4b), I (4c)] were isolated. From the reaction of the acetate 2 with HBF4 or HClO4 in acetonitrile, the solvent adduct [Pd(NP)(NCCH3)]33+ was isolated as the BF4– (5a) or ClO4– salt (5b). The phosphido-bridged complexes were characterized by single-crystal structural analyses (2, 4, 5a and 6), solution NMR experiments, and in the case of 2 and 4a by solid-state 31P cross-polarization magic-angle spinning NMR spectroscopy. The crystal structures show the six-membered (MP)3 cores in twist-boat or boat conformations that appear to be maintained in solution, according to NMR evidence. A search for (MP)3 structures in the Cambridge Structural Database reveals that these two conformations are the most common ones (46 % twist-boat, 21 % boat, 17 % chair).

Preparation of high‐selective HPLC packing materials based on alternating copolymer‐grafted silica

Three alternating copolymer-grafted silica stationary phases for use in high-selective RP-HPLC were prepared from two vinyl monomers selected from styrene, N-methylmaleimide, N-octadecylmaleimide, and octadecyl acrylate; they were characterized by elemental analyses, thermogravimetric analysis, diffuse reflectance infrared Fourier transform spectroscopy, and (13)C cross-polarization magic-angle spinning NMR spectroscopy. Aspects of molecular-shape selectivity were evaluated for three different columns using Standard Reference Material 869b, Column Selectivity Test Mixture for Liquid Chromatography. The best selectivity for isomer separations was obtained for the stationary phase prepared with a copolymer of octadecyl acrylate and N-octadecylmaleimide, which was able to separate 16 polycyclic aromatic hydrocarbons (Standard Reference Material 1647e) in an isocratic elution. In this paper, the effectiveness of this phase is also demonstrated by separation of tocopherol isomers.

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.

13C CPMAS NMR Spectroscopy as a Versatile and Quantitative Tool for Determination of Mercury Adsorption Capacity in Thiol-Functionalized Mesoporous Silica SBA-1

13C cross-polarization magic angle spinning (CPMAS) NMR spectroscopy is demonstrated to be a valuable characterization tool for quantitative measurements of Hg2+ adsorption capacity in thiol-functionalized mesoporous silica SBA-1 (Santa Barbara Amorphous-1). This is the first report on the investigation of the spectral change in the 13C CP signals for mercaptopropyl-functionalized mesoporous materials doped with different Hg2+ concentrations. The chemical shift of the carbon atom adjacent to the thiol group is sensitive to the binding of the mercury ion, and its peak intensity can be used as a quantitative sensor for the amount of the mercury ion adsorbed. The 13C CPMAS NMR results are in good agreement with inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analysis.

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.

Detection of nucleotide binding to Na,K-ATPase in an aqueous membrane suspension by 13C cross-polarization magic-angle spinning NMR spectroscopy

Binding of uniformly 13C labelled ATP to Na,K-ATPase was studied by 13C cross-polarization magic-angle spinning (CP-MAS) NMR. In the presence of 30 mM Na + , and with sample- and time-averaging, NMR spectra obtained at 4 °C exhibited several resonances for the bound nucleotide. Chemical shifts suggested that site-specific changes in the micro-environment or conformation of the nucleotide occurred in the high affinity binding site. These experiments permit further studies of nucleotide dynamics, structure and binding under physiologically relevant conditions.

Solid-state NMR characterization of the putative membrane anchor of TWD1 from Arabidopsis thaliana

Structure and membrane interaction of a 31 amino acid residue fragment of the membrane bound FKBP-like protein twisted dwarf 1 (TWD1) from Arabidopsis thaliana was investigated by solid-state NMR spectroscopy. The studied peptide TWD1(335-365) contained the putative membrane anchor of the protein (residues 339-357) that was previously predicted by sequence hydrophobicity analysis. The TWD1 peptide was synthesized by standard solid phase peptide synthesis and contained three uniformly (13)C- and (15)N-labelled residues (Phe 340, Val 350, Ala 364). The peptide was incorporated into either multilamellar vesicles or oriented planar membranes composed of an equimolar ternary phospholipid mixture (POPC, POPE, POPG), where the POPC was sn-1 chain-deuterated. (31)P NMR spectra of the membrane in the absence and in the presence of the peptide showed axially symmetric powder patterns indicative of a lamellar bilayer phase. Further, the addition of peptide caused a decrease in the lipid hydrocarbon chain order as indicated by reduced quadrupolar splittings in the (2)H NMR spectra of the POPC in the membrane. The conformation of TWD1(335-365) was investigated by (13)C cross-polarization magic-angle spinning NMR spectroscopy. At a temperature of -30 degrees C all peptide signals were resolved and could be fully assigned in two-dimensional proton-driven (13)C spin diffusion and (13)C single quantum/double quantum correlation experiments. The isotropic chemical shift values for Phe 340 and Val 350 exhibited the signature of a regular alpha-helix. Chemical shifts typical for a random coil conformation were observed for Ala 364 located close to the C-terminus of the peptide. Static (15)N NMR spectra of TWD1(335-365) in mechanically aligned lipid bilayers demonstrated that the helical segment of TWD1(335-365) adopts an orientation perpendicular to the membrane normal. At 30 degrees C, the peptide undergoes intermediate time scale motions.

Determination of the location of naphthalene in the zeolite ZSM-5 host framework by solid-state 1H/29Si CP MAS NMR spectroscopy

The location of naphthalene in the zeolite ZSM-5 has been determined from solid-state 1H/29Si cross-polarization (CP) magic-angle-spinning (MAS) NMR data alone. With the peaks in the 29Si spectrum assigned to the inequivalent Si sites in the zeolite from a two-dimensional INADEQUATE spectrum, the rates of cross polarization between the 1H nuclei of the guest sorbate molecules and the 29Si nuclei of the zeolite framework were used to determine the location of the naphthalene molecules by exploiting the proportional relationship between cross-polarization rate constants and 1H/29Si dipolar coupling second moments. The NMR structure determination was carried out on three different selectively deuterium-labeled naphthalene molecules (naphthalene-d0, α-naphthalene-d4, and β-naphthalene-d4). The average of the molecule locations in agreement with all three sets of NMR data was found to be in excellent agreement with an existing single crystal XRD structure of the naphthalene–ZSM-5 complex.Key words: solid-state NMR, cross polarization, zeolites, host–guest complexes, structure determination.

29Si cross-polarization magic-angle spinning NMR spectroscopy––an efficient tool for quantification of thaumasite in cement-based materials

Abstract 29Si{1H} cross-polarization (CP) magic-angle spinning (MAS) NMR spectroscopy is a powerful and reliable tool for the quantification of thaumasite in cement-based materials. The most efficient method for quantifying thaumasite from 29Si{1H} CP/MAS NMR spectra is described and it is shown that the method allows detection of thaumasite contents below approximately 10 wt.% with a relative precision of 15% and contents above 10 wt.% with a relative precision of 10%. The applicability of 29Si{1H} CP/MAS NMR for quantification of thaumasite is demonstrated for different Portland cement pastes and shows that thaumasite contents as low as 0.2–0.5 wt.% can be detected in cementitious systems with low concentrations of paramagnetic impurities. For a Portland cement containing various amounts of limestone dust and stored at 5 °C in a MgSO4 solution, large quantities of thaumasite have been detected. Furthermore, the quantity of thaumasite is found to be less sensitive to the amount of added limestone dust. For samples of a Portland cement with a fixed content of limestone dust but different quantities of added gypsum, the increased contents of gypsum are observed to result in larger quantities of thaumasite after prolonged hydration.

Fractionation of natural organic matter in drinking water and characterization by 13C cross-polarization magic-angle spinning NMR spectroscopy and size exclusion chromatography.

Natural organic matter from drinking water sources was fractionated, and the fractions were characterized by NMR and SEC with the aim of relating NOM structure to treatability. Organic matter was isolated from two Australian surface waters (Horsham, Moorabool) by reverse osmosis and from a groundwater (Wanneroo) by anion exchange. The isolates were fractionated according to polarity and charge by resin adsorption. 13C NMR spectra of the freeze-dried fractions showed the most hydrophobic fraction to be high in aliphatic and aromatic carbon while slightly hydrophobic organics have more carbonyl and alkoxyl carbon. The Horsham and Wanneroo hydrophilic fractions show strong alkoxyl signals attributed to carbohydrate. Moorabool hydrophilics contain aromatic (phenolic) carbon; the apparent absence of carbohydrate appears to be an artifact. Size-exclusion chromatograms were recorded on the original and fractionated organics with both UV and dissolved organic carbon detection. The Horsham and Moorabool organics have similar molecular size distributions while Wanneroo is dominated by strongly absorbing species having large hydrodynamic radii. The hydrophobic and charged hydrophilic fractions also have high apparent MW, while the neutral fraction is higher in low-MW compounds of relatively low specific absorbance, suggestive of carbohydrates.

Controlled synthesis of stable poly(vinyl formamide- co -vinyl amine)/silica hybrid particles by interfacial post-cross-linking reactions

The chemical synthesis and the physicochemical properties of stable poly(vinyl formamide-co-vinyl amine)/silica hybrid particles are presented. Copolymers of poly(vinyl formamide) (PVFA) and poly(vinyl amine) (PVAm) and their protonated forms were adsorbed onto silica from aqueous solutions. The influences of the pH strength and the ion concentration of the aqueous solution as well as the copolymer composition (degree of hydrolyzation of PVFA), and the molecular mass on the adsorption process were investigated by electrokinetic measurements, potentiometric titration, and quantitative elemental analyses. Silica surface-charge neutralization is achieved at a pH strength above 10 for highly hydrolyzed (95%) PVFA polymers. Decreasing the amino content in the PVAm chain shifts successively both the point of zero charge and the isoelectric point to lower pH values. PVFA-co-PVAm layers onto silica are adsorbed weakly. To fix these layers irreversibly, cross-linking reactions with (4,4′-diisocyanate)diphenyl methane were carried out on the surface of solid PVFA-co-PVAm/silica hybrid particles suspended in acetone. The cross-linking reaction, which is connected with the conversion of amino groups, is also a tool to control the surface charge of the PVFA-co-PVAm/silica hybrids. X-ray photoelectron spectroscopy and solid-state 13C cross-polarization magic-angle spinning NMR spectroscopy were used to obtain information on the number of and the structure of the functionalized polyelectrolyte layers on silica. The success of cross-linking was also shown by the results of these spectroscopic methods.

13C CPMAS NMR spectroscopy as a probe for porphyrin–porphyrin and host–guest interactions in the solid state

Solid-state 13C cross-polarisation magic-angle spinning (CPMAS) NMR spectra of a range of metalloporphyrin monomers, dimers, trimers and various host–guest adducts have been obtained. Interpretation of these spectra provides information on crystal packing (molecular stacking) and host–guest interactions in the solid state. X-Ray structures are reported for a para- and meta-substituted zinc porphyrin monomer. Comparison of the CPMAS data with the X-ray data of these selected monomers provides convincing evidence for the crystal packing assignment based on both solid state techniques.

Zeise's salt studied by high resolution solid state 13C CPMAS and 1H SPEDA NMR spectroscopy

Polycrystalline Zeise's salt ( K(CH 2 CH 2 PtCl 3⊎x H 2 O ) was investigated by high resolution solid state 13C CPMAS (cross polarization magic-angle spinning) and 1H SPEDA (single pulse excitation with delayed acquisation) NMR spectroscopies using different rotor spinning speeds. Though the 13C and 1H nuclei are respectively two and three bond lengths separated from the 35 37 Cl nuclei, both the 13C and 1H spectral lineshapes are influenced by the second and higher order dipolar couplings between 13C and 1H and the quadrupole spins 35 37 Cl . An extra splitting or broadening resulting from the coupling between 13C and 195Pt is also found. The high resolution 1H spectrum is also influenced by 1H 195Pt coupling. A computer program was developed to simulate theoretically the observed 13C and 1H NMR spectral lineshapes.