NMR spectroscopy in combination with statistical methods was used to study vacuum residues and vacuum gas oils from 32 crude oils of different origin. Two chemometric metodes were applied. Firstly, ...principal component analysis on complete spectra was used to perform classification of samples and clear distinction between vacuum residues and vacuum light and heavy gas oils were obtained. To quantitatively predict the composition of asphaltenes, principal component regression models using areas of resonance signals spaned by 11 frequency bins of the ¹H NMR spectra were build. The first 5 principal components accounted for more than 94 % of variations in the input data set and coefficient of determination for correlation between measured and predicted values was R.sup.2 = 0.7421. Although this value is not significant, it shows the underlying linear dependence in the data. Pseudo two-dimensional DOSY NMR experiments were used to assess the composition and structural properties of asphaltenes in a selected crude oil and its vacuum residue on the basis of their different hydrodynamic behavior and translational diffusion coefficients. DOSY spectra showed the presence of several asphaltene aggregates differing in size and interactions they formed. The obtained results have shown that NMR techniques in combination with chemometrics are very useful to analyze vacuum residues and vacuum gas oils. Furthermore, we expect that our ongoing investigation of asphaltenes from crude oils of different origin will elucidate in more details composition, structure and properties of these complex molecular systems. Keywords: NMR, PCA, PCR, crude oils, vacuum residues and gas oils, asphaltenes
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IZUM, KILJ, NUK, ODKLJ, PILJ, PNG, SAZU, UL, UM, UPUK
Identification and characterization of asphaltenes, the most polar and predominantly aromatic components of crude oil, still post a challenge for researchers in the oil industry, owing to their ...complex molecular architecture. Recently, much effort has been devoted to understanding their structure and physicochemical properties. In this paper, a combination of diffusion-ordered NMR spectroscopy (DOSY) and statistical multiway methods was used to investigate petroleum samples and asphaltenes of different origin. Such multiway TUCKER3 decomposition has been used for the first time to analyze the two-dimensional matrix of complex nuclear magnetic resonance (NMR) data for petroleum samples. DOSY NMR spectra of 50 samples (45 for establishing the statistical model and 5 for its validation) were recorded and evaluated by an in-house-developed code incorporating multiway analysis to set up a tool for predicting their identity and origin. A statistical model was developed that can identify and separate asphaltene samples from those of crude oils, vacuum and atmospheric residues, and resins, which is not possible directly from the NMR spectra. Furthermore, the model clearly demonstrated that all asphaltene samples clustered into the same group, irrespective of the geographical origin, implicating their structural and size similarities. The validity of the model was further tested by analyzing an additional set of asphaltenes. It has been demonstrated that the proposed approach is very useful for analyzing complex oil mixtures and has the potential for developing a robust quantitative model.
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IJS, KILJ, NUK, PNG, UL, UM
•Fagopyrins were isolated and characterised from buckwheat material.•UV–Vis absorption, NMR spectroscopy and mass spectrometry methods were utilised.•Two novel structures are fagopyrin A and ...fagopyrin E.•Sensitive and high-resolution HPLC analytical method was developed.
Buckwheat products are commonly used in health foods and food supplements. However, public awareness regarding the presence of photodynamic naphthodianthrones fagopyrins that can cause photosensitization is low. At least two additional compounds with structures similar to that of fagopyrin are known to exist; however, the structures of these compounds have never been determined. In this work, we improved the extraction procedure and the chromatographic analysis of fagopyrins by developing a simple, sensitive and high-resolution high performance liquid chromatography (HPLC) analytical method using fluorescence detection. We observed at least six fagopyrin derivatives, which were isolated and characterized via UV–Vis absorption, NMR spectroscopy and mass spectrometry. We determined the structures of two new derivatives (fagopyrin A and fagopyrin E) and proved the existence of protofagopyrins that can transform into fagopyrins upon light exposure. Our methods complement the existing knowledge regarding fagopyrins and will allow for their further analysis, isolation and investigation of their biological activity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Seven title compounds 12a–g and the (S)-prolinate analogue 13 were prepared in five steps from 2-nitrobenzoic acid (7). Reduction of the nitro group followed by derivatization of the so formed ...anilines 14 gave the N-alkyl-(15a–c), N-acyl-(16a,b and 19), and N-vinyl derivative 20. NMR spectra of (S)-alanine and (S)-proline derived compounds 12, 13, 14–16, 19, and 20 exhibited two sets of signals corresponding to pairs of conformational diastereomers. The free energy barriers of rotation, ΔG ‡ 298 = 82–86 kJ mol–1, were determined by 1H NMR for 12a, 12d, 12f, and 12g and evaluated by DFT calculations.
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super(1)H NMR chemical shift, line width, indirect nuclear splitting value, peak area integration value, and spin-lattice and spin-spin relaxation times at 298 K are compared for low-concentration ...isotropic solutions of n-octylammonium n-octadecanoate prepared via different techniques and conditions using dried, distilled, and degassed deuterochloroform and the nontreated solvent containing tetramethylsilane. The nature of the variation of observed spectral parameters and relaxation/rotational behavior with chemical composition (presence of oxygen and other paramagnetic species, stabilizer, impurities, and degradation products) of the solvent, history of the solution, and sample containment are analyzed. Relaxation times are interpreted in terms of monomer structure and reorientation and internal rotation modes as a function of atomic position along the n-alkyl chains. Collectively, the relaxation behavior of the surfactant complies with the two-step model of fast picosecond internal rotations of different size segments containing methylene groups separated in timescale from slower large segment and overall molecular tumbling modes of the monomer. Fast motional phenomena do not appear to be appreciably influenced by the chemistry of the solvent in contrast to spectral parameters such as chemical shift and line width of the labile ammonium protons. A model is also presented to explain anomalous variation of the peak area integration value with chemical shift of the ammonium resonance peak.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
^sup 1^H NMR chemical shift, line width, indirect nuclear splitting value, peak area integration value, and spin-lattice and spin-spin relaxation times at 298 K are compared for low-concentration ...isotropic solutions of n-octylammonium n-octadecanoate prepared via different techniques and conditions using dried, distilled, and degassed deuterochloroform and the nontreated solvent containing tetramethylsilane. The nature of the variation of observed spectral parameters and relaxation/rotational behavior with chemical composition (presence of oxygen and other paramagnetic species, stabilizer, impurities, and degradation products) of the solvent, history of the solution, and sample containment are analyzed. Relaxation times are interpreted in terms of monomer structure and reorientation and internal rotation modes as a function of atomic position along the n-alkyl chains. Collectively, the relaxation behavior of the surfactant complies with the two-step model of fast picosecond internal rotations of different size segments containing methylene groups separated in timescale from slower large segment and overall molecular tumbling modes of the monomer. Fast motional phenomena do not appear to be appreciably influenced by the chemistry of the solvent in contrast to spectral parameters such as chemical shift and line width of the labile ammonium protons. A model is also presented to explain anomalous variation of the peak area integration value with chemical shift of the ammonium resonance peak.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
1
H NMR chemical shift, line width, indirect nuclear splitting value, peak area integration value, and spin–lattice and spin–spin relaxation times at 298 K are compared for low-concentration ...isotropic solutions of
n
-octylammonium
n
-octadecanoate prepared via different techniques and conditions using dried, distilled, and degassed deuterochloroform and the nontreated solvent containing tetramethylsilane. The nature of the variation of observed spectral parameters and relaxation/rotational behavior with chemical composition (presence of oxygen and other paramagnetic species, stabilizer, impurities, and degradation products) of the solvent, history of the solution, and sample containment are analyzed. Relaxation times are interpreted in terms of monomer structure and reorientation and internal rotation modes as a function of atomic position along the
n
-alkyl chains. Collectively, the relaxation behavior of the surfactant complies with the two-step model of fast picosecond internal rotations of different size segments containing methylene groups separated in timescale from slower large segment and overall molecular tumbling modes of the monomer. Fast motional phenomena do not appear to be appreciably influenced by the chemistry of the solvent in contrast to spectral parameters such as chemical shift and line width of the labile ammonium protons. A model is also presented to explain anomalous variation of the peak area integration value with chemical shift of the ammonium resonance peak.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Novel polymeric systems with antibacterial properties based on medical-grade polyvinyl chloride and antibiotics (Ampicillin, Minocycline, and Rifampicin) in the concentrations up to 1 wt% were ...prepared by thermoplastic compounding. Thermal stability of the antibiotics was corroborated by IR spectroscopy, X-ray diffraction, differential scanning calorimetry, and
1
H nuclear magnetic resonance spectroscopy. The effect of chemical structure on mechanical properties of the prepared systems was determined by tensile testing measurements and correlated with optical microscopy observations. In vitro antibacterial properties of samples were determined by agar diffusion and adhesion test against Gram-negative and Gram-positive bacteria. Antibiotic release experiments in distilled water and physiological saline solution and follow-up detecting by Ultraviolet–Visible spectroscopy were carried out. A mathematical model was applied to evaluate the release kinetics of the antibiotics from prepared polymeric systems. The results show significant influence of antibiotic’s chemical structure on all studied characteristics of the systems due to the various interactions with polyvinyl chloride matrix.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
A seven-step synthesis of 1-substituted 5-(2-acylaminoethyl)-1
H-pyrazole-4-carboxamides
20 as the pyrazole analogues of histamine was developed. The synthesis starts with a three-step preparation of ...N(1)-substituted methyl 5-(2-
tert-butoxycarbonylaminoethyl)-1
H-pyrazole-4-carboxylates
7 from commercially available Boc-β-alanine (
1). Subsequent four-step transformation of the key-intermediates
7 into the final products
20 was performed following two complementary reaction sequences comprising acidolytic removal of the Boc group, hydrolysis of the COOMe group, amidations of the COOH group, and acylations of the NH
2 group. The structures of pyrazole derivatives were determined by spectroscopic methods and by X-ray diffraction.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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