Reactivity of dissolving pulp: characterisation using chemical properties, NMR spectroscopy and multivariate data analysis

The reactivity of dissolving pulp was experimentally determined in termsof residual cellulose in viscose. The correlations between 11 chemicalproperties of pulp and filter values and residual cellulose contents of viscosewere then investigated by multivariate data analysis. Both the viscose filtervalue and the residual cellulose were well modelled from the 11 propertiesby partial least squares regression. The results show that pulps with highacetone extractable fractions, high magnesium contents, low alkali resistanceand low viscosity, gave low viscose filter values and low residual cellulosecontents. Pulps with low residual cellulose contents also had low carboxylgroupcontents and low polydispersity. The results are interpreted as that in pulpwith high reactivity, the hemicellulose content is low and that the cellulosechains are shorter and more soluble in alkali. An explanation of the positiveeffect from the high extractive content is that the extractives facilitate thediffusion of carbon disulfide. A principal component analysis of CP/MAS¹³C-NMR spectral data of six pulp samples showed that differences inreactivity between the pulps could be explained by variations in the hydrogenbonds in the cellulose and/or changes in the glucosidic bonds. In a separatestudy electron beam processing enhanced the reactivity, i.e. lowered theresidual cellulose content, of the investigated pulps. The magnitude of theelectron dose, within the tested range (5.4–23.7 kGy), didnotseem to be important, but the reactivity within pulp sheets tended to be ratherinhomogeneous.     

Characterisation of indomethacin and nifedipine using variable-temperature solid-state NMR

We have characterised the stable polymorphic forms of two drug molecules, indomethacin (1) and nifedipine (2) by 13C CPMAS NMR and the resonances have been assigned. The signal for the C-Cl carbon of indomethacin has been studied as a function of applied magnetic field, and the observed bandshapes have been simulated. Variable-temperature 1H relaxation measurements of static samples have revealed a T1rho minimum for indomethacin at 17.8 degrees C. The associated activation energy is 38 kJ mol(-1). The relevant motion is probably an internal rotation and it is suggested that this involves the C-OCH3 group. Since the two drug compounds are potential candidates for formulation in the amorphous state, we have examined quench-cooled melts in detail by variable-temperature 13C and 1H NMR. There is a change in slope for T1H and T1rhoH at the glass transition temperature (Tg) for indomethacin, but this occurs a few degrees below Tg for nifedipine, which is perhaps relevant to the lower real-time stability of the amorphous form for the latter compound. Comparison of relaxation time data for the crystalline and amorphous forms of each compound reveals a greater difference for nifedipine than for indomethacin, which again probably relates to real-time stabilities. Recrystallisation of the two drugs has been followed by proton bandshape measurements at higher temperatures. It is shown that, under the conditions of the experiments, recrystallisation of nifedipine can be detected already at 70 degrees C, whereas this does not occur until 110 degrees C for indomethacin. The effect of crushing the amorphous samples has been studied by 13C NMR; nifedipine recrystallises but indomethacin does not. The results were supported by DSC, powder XRD, FTIR and solution-state NMR measurements.     

Analysis of human urine metabolites using SPE and NMR spectroscopy

Nuclear magnetic resonance (NMR) spectroscopic analysis of metabonome/metabolome has widespread applications in biomedical science researches. However, most of NMR resonances for urinary metabolites remain to be fully assigned. In the present study, human urine samples from two healthy volunteers were pre-treated with C18 solid-phase extraction and the resultant 5 sub-fractions were subjected to one- and two-dimensional NMR studies, including 1H J-Resolved, 1H-1H COSY, 1H-1H TOCSY, 1H-13C HSQC, and HMBC 2D NMR. More than 70 low molecular weight metabolites were identified, and complete assignments of 1H and 13C resonances including many complex coupled spin systems were obtained.     

Unmasking melon by a complementary approach employing electron diffraction, solid-state NMR spectroscopy, and theoretical calculations-structural characterization of a carbon nitride polymer

Poly(aminoimino)heptazine, otherwise known as Liebig's melon, whose composition and structure has been subject to multitudinous speculations, was synthesized from melamine at 630 degrees C under the pressure of ammonia. Electron diffraction, solid-state NMR spectroscopy, and theoretical calculations revealed that the nanocrystalline material exhibits domains well-ordered in two dimensions, thereby allowing the structure solution in projection by electron diffraction. Melon ([C(6)N(7)(NH(2))(NH)](n), plane group p2 gg, a=16.7, b=12.4 A, gamma=90 degrees, Z=4), is composed of layers made up from infinite 1D chains of NH-bridged melem (C(6)N(7)(NH(2))(3)) monomers. The strands adopt a zigzag-type geometry and are tightly linked by hydrogen bonds to give a 2D planar array. The inter-layer distance was determined to be 3.2 A from X-ray powder diffraction. The presence of heptazine building blocks, as well as NH and NH(2) groups was confirmed by (13)C and (15)N solid-state NMR spectroscopy using (15)N-labeled melon. The degree of condensation of the heptazine core was further substantiated by a (15)N direct excitation measurement. Magnetization exchange observed between all (15)N nuclei using a fp-RFDR experiment, together with the CP-MAS data and elemental analysis, suggests that the sample is mainly homogeneous in terms of its basic composition and molecular building blocks. Semiempirical, force field, and DFT/plane wave calculations under periodic boundary conditions corroborate the structure model obtained by electron diffraction. The overall planarity of the layers is confirmed and a good agreement is obtained between the experimental and calculated NMR chemical shift parameters. The polymeric character and thermal stability of melon might render this polymer a pre-stage of g-C(3)N(4) and portend its use as a promising inert material for a variety of applications in materials and surface science.     

Comparison between different data pre-treatment methods in the analysis of forage samples using near-infrared diffuse reflectance spectroscopy and partial least-squares multivariate calibration method

Moisture and protein content of alfalfa samples from Catalonia (Spain) have been analyzed by near-infrared (NIR) diffuse reflectance spectroscopy and multivariate calibration methods. In order to remove systematic variation in experimental data, such as base-line and multiplicative scatter effects, the evaluation of different data pre-processing methods is performed. Different figures of merit are used for quality assessment and comparison of these pre-treatment methods.     

Traceability study of hay with a mass spectrometer based on ion-molecule reactions of krypton,xenon and mercury using multivariate data analysis

The application of mountain hay for wellness purposes has led to a substantial valorisation. To assure the quality associated with the high standards of production, which are often related to a characteristic distribution of plants and a variety of essential oils, a mass spectrometer, based on ion-molecule-reactions (IMR) of mercury, krypton and xenon, was employed to analyse characteristic VOCs of hay such as coumarin or typical monoterpenes and then used to develop an approach for the traceability of single hay samples based on concepts of multivariate statistics. The application of the primary gases to aqueous solutions of the pure compounds shows their suitability to deal with this problem, reveals important factors for the creation of a measurement set-up of such gas mixtures and indicates different mechanisms for the fragmentation, as shown for coumarin. The limit of determination (3*s_R/SEN) for aqueous solutions of p-cymene is 0.13?mg?L^?1 using PLS1 and the presented combined mercury and xenon set-up, which confirms that this strategy is appropriate for an integration of compounds, which are present in low concentrations only, into a qualitative model. The results of the principal component analyses (PCA) of 136 hay samples were verified for the suitability to characterize single types of hay using three measurements of nine mountain hay samples, three normal hay samples and three aftermath samples for evaluation and applying SIMCA for classification at a significance level of 5%. The traceability of mountain hay samples is good (93% correctly classified) and can be used to protect these valuable samples.     

Detection of refined olive oil adulteration with refined hazelnut oil by employing NMR spectroscopy and multivariate statistical analysis

NMR spectroscopy was employed for the detection of adulteration of refined olive oil with refined hazelnut oil. Fatty acids and iodine number were determined by ¹H NMR, whereas ³¹P NMR was used for the quantification of minor compounds including phenolic compounds, diacylglycerols, sterols, and free fatty acids (free acidity). Classification of the refined oils based on their fatty acids content and the concentration of their minor compounds was achieved by using the forward stepwise canonical discriminant analysis (CDA) and the classification binary trees (CBTs). Both methods provided good discrimination between the refined hazelnut and olive oils. Different admixtures of refined olive oils with refined hazelnut oils were prepared and analyzed by ¹H NMR and ³¹P NMR spectroscopy. Subsequent application of CDA to the NMR data allowed the detection of the presence of refined hazelnut oils in refined olive oils at percentages higher than 5%. Application of the non-linear classification method of the binary trees offered better possibilities of measuring adulteration of the refined olive oils at a lower limit of detection than that obtained by the CDA method.     

GC-MS and GC-FID analyses of the volatile constituents of Brachychiton rupestris and Brachychiton discolor,their biological activities and their differentiation using multivariate data analysis

Abstract

The volatile constituents of the leaves and flowers of Brachychiton rupestris and Brachychiton discolor (Malvaceae) were characterized by GC-FID and GC-MS. A total of 92 compounds were identified. The major component of B. rupestris leaves was α-farnesene (34.57%) while in the flowers it was n-heptacosane (29.5%). (8Z, 11Z, 14Z)-heptadecatrienal (21.2%) in the leaves and palmitic acid (83.49%) in the flowers represent the abundant ingredients of B. discolor. Unsupervised pattern recognition techniques of multivariate data analysis exemplified by hierarchical cluster analysis (HCA) and principle component analysis (PCA) relying upon chromatographic results effectively discriminate the two related species. Also, both investigated species were assessed for their cytotoxic and antimicrobial efficacy. Results revealed that B. discolor flowers showed the highest cytotoxicity against human lung carcinoma (A-549) cell lines with IC₅₀ equals 7.98?μg/mL, whereas B. discolor leaves exhibited the highest antimicrobial potency against all tested microorganisms namely Streptococcus pneumonia, Bacillus subtilis, Escherichia coli as well as Aspergillus fumigatus and Geotrichum candidum (MICs between 0.98 and 15.63?µg/mL) except for Salmonella typhi.     

Polymorphism of N,N'-diacetylbiuret studied by solid-state 13C and 15N NMR spectroscopy, DFT calculations, and X-ray diffraction

The molecular configuration and crystal structure of solid polycrystalline N,N′′‐diacetylbiuret (DAB), a potential nitrogen‐rich fertilizer, have been analyzed by a combination of solid‐ and liquid‐state NMR spectroscopy, X‐ray diffraction, and DFT calculations. Initially a pure NMR study (“NMR crystallography”) was performed as available single crystals of DAB were not suitable for X‐ray diffraction. Solid‐state ¹³C NMR spectra revealed the unexpected existence of two polymorphic modifications (α‐ and β‐DAB) obtained from different chemical procedures. Several NMR techniques were applied for a thorough characterization of the molecular system, revealing chemical shift anisotropy (CSA) tensors of selected nuclei in the solid state, chemical shifts in the liquid state, and molecular dynamics in the solid state. Dynamic NMR spectroscopy of DAB in solution revealed exchange between two different configurations, which raised the question, is there a correlation between the two different configurations found in solution and the two polymorphic modifications found in the solid state? By using this knowledge, a new crystallization protocol was devised which led to the growth of single crystals suitable for X‐ray diffraction. The X‐ray data showed that the same symmetric configuration is present in both polymorphic modifications, but the packing patterns in the crystals are different. In both cases hydrogen bonds lead to the formation of planes of DAB molecules. Additional symmetry elements, a two‐fold screw in the case of α‐DAB and a c‐glide plane in the case of β‐DAB, lead to a more symmetric (α‐DAB) or asymmetric (β‐DAB) intermolecular hydrogen‐bonding pattern for each molecule.     

One-dimensional polymers based on [{CpMo(CO)2}2(mu,eta2-P2)]: solid-state conformation analysis by NMR spectroscopy and DFT calculations

Reaction of the complex [{CpMo(CO)2}2(mu,eta2-P2)] (1) with CuI halides leads to the quantitative formation of the novel one-dimensional linear polymers [CuX{Cp2Mo2(CO)4(mu,eta2:eta1:eta1-P2)}](infinity) (X=Cl (4), Br (5), I (6)). The same products 4 and 5 were obtained when 1 was treated with CuCl2 and CuBr2, respectively. The solid-state structures are compared and their remarkable influence on the respective (31)P magic angle spinning (MAS) NMR spectra is interpreted with the help of density functional theory (DFT) calculations on the model compounds [{(CuX)2{Cp2Cr2(CO)4(mu,eta(2):eta1:eta1-P2)}2}3] (X=Cl (4 a), Br (5 a)) in which the molybdenum atoms are replaced by their lighter homologue chromium.     

Structural characterization of monomeric and oligomeric arylamides by solution and solid‐state NMR spectroscopy

An extensive study of both liquid‐ and solid‐state NMR spectroscopy was undertaken in order to elucidate the structural features of a phenyleneterephthalamide oligomer (OPTA) and of some related diarylamides. 1D‐ and 2D‐COSY measurements allowed us to assign completely the proton signals of the title compounds in solution, while 1D‐, 2D‐HETCOR and 2D‐COLOC measurements were used to assign ¹³C resonances. Solid‐state ¹³C NMR experiments, by conventional cross‐polarization (CP) at different contact times and with the dipolar dephased CP technique, were used to characterize these molecules in the solid state. Such techniques allowed us to differentiate among different carbon atoms; in the resulting spectra it was then possible to observe the selective appearance of signals from protonated and quaternary carbon atoms. It was also ascertained that the limited structural mobility of the insoluble OPTA, existing as a single monophasic species, can be explained in terms of hydrogen‐type bonds present in the solid state. Copyright © 2002 John Wiley & Sons, Ltd.     

Orthogonal signal correction, wavelet analysis, and multivariate calibration of complicated process fluorescence data

In this paper, multivariate calibration of complicated process fluorescence data is presented. Two data sets related to the production of white sugar are investigated. The first data set comprises 106 observations and 571 spectral variables, and the second data set 268 observations and 3997 spectral variables. In both applications, a single response, ash content, is modelled and predicted as a function of the spectral variables. Both data sets contain certain features making multivariate calibration efforts non-trivial. The objective is to show how principal component analysis (PCA) and partial least squares (PLS) regression can be used to overview the data sets and to establish predictively sound regression models. It is shown how a recently developed technique for signal filtering, orthogonal signal correction (OSC), can be applied in multivariate calibration to enhance predictive power. In addition, signal compression is tested on the larger data set using wavelet analysis. It is demonstrated that a compression down to 4% of the original matrix size — in the variable direction — is possible without loss of predictive power. It is concluded that the combination of OSC for pre-processing and wavelet analysis for compression of spectral data is promising for future use.     

Structure determinations of nitrogen compounds with the aid of NQR, NMR, and ESCA spectroscopy

Since it is often necessary or desirable to determine the structures of compounds containing nitrogen directly via the nitrogen atoms, the nuclear quadrupole resonance (NQR) and the nuclear magnetic resonance (NMR) as well as the photoelectron and the Auger-electron spectroscopy (ESCA) of nitrogen are becoming increasingly important. A comparative review of these three methods on the basis of measurement effect, information obtainable, applications, and limitations forms the subject of this article.     

Conformational analysis of new 14-membered ring diketal dilactam macrocycles: molecular mechanics, liquid and solid state NMR studies

A conformational study of new diversely substituted 14-membered diketal dilactam macrocycles was conducted by NMR spectroscopy in liquid and solid states, molecular mechanics calculations and, for one compound, a previous X-ray analysis. The results obtained by the different techniques show that the conformations depend closely on whether the molecules are chiral or achiral and on the stereochemistry of the ketal OMe groups. In achiral compounds, the most stable conformation of each compound has, in both the liquid and solid states, the two NH-CO links positioned perpendicular to the macrocycle plane, lending to the trans-7,7′-OMe macrocycles 6b and 7b a rectangular [3434]-type structure. In contrast, in chiral compounds, the most stable conformations are not the same in the liquid and solid phases. In the liquid state the conformations are set by the presence of one or two N₄-H?O_1′, N_4′-H?O₁ intramolecular hydrogen bonds that position the amide group parallel to the macrocycle plane, whereas in the solid state the amide moieties again adopt a perpendicular position which can be stabilized, when the 3-R substituent is not too bulky, by intermolecular N-H?OC bonds between parallel sheets, and exceptionally, in the cis-7,7′-OMe-3,3′-Ph compound 1c, by a π-π stacking effect between the phenyl groups.     

Dynamic mechanical analysis (DMA), 13c solid state nmr and micro-thermomechanical studies of historical parchment

DMA and solid state ¹³C NMR techniques were used to measure historical parchment samples within the framework of the project (MAP) Micro Analysis of Parchment (EC contract No. SMT4-96-2101) in collaboration with the School of Conservation in Copenhagen. DMA was used in both thermal scan and creep modes. Thermal scans provided information on the transitions associated with the collagen polymer. Microthermal analysis was also used to obtain information on the topography and thermal conductivity of sample areas of 100 μm. Localised heating enabled measurements of softening transitions in the sample. This behaviour is influenced by the chemical composition of parchment. 13C NMR provided information on the carbon atoms associated with the polypeptide chains of the collagen in parchment. The behaviour of samples immersed in water and measured in DMA creep mode was used to measure the shrinkage behaviour of the parchment samples. The different but complementary techniques provided a means for characterising the physicochemical state of parchment samples. This revised version was published online in July 2006 with corrections to the Cover Date.