Change of chemical bonding of nitrogen of polymeric N-heterocyclic compounds during pyrolysis

Pyrolysis experiments were carried out with polymeric model compounds containing defined forms of bound nitrogen. The chosen compounds, polyvinylcarbazole, polyvinylpyridine and polyvinylpyrrolidone, were pyrolysed in a fixed bed annular reactor at 873 and 1173 K. The functionalities of the nitrogen in the precursors as well as that in the derived chars were determined by X-ray photoelectron spectroscopy (XPS). Additional information about the structure was received from FT-IR, solid-state ¹³C-NMR and, in part, X-ray absorption near edge structure (XANES) spectroscopy. The application of different analytical methods should result in a more reliable classification of the N 1s electron binding energies than is possible by the sole use of XPS. It is interesting to note that the nitrogen in five-membered rings (N-5) of the N-heterocyclic compounds remains in existence in the high temperature products. In the case of the carbazole system it is still the dominant bonding form. The high-temperature char from polyvinylpyridine contains nitrogen in both five- and six-membered rings. It may be concluded that the behaviour of the nitrogen during pyrolysis does not only depend on its functionality but also on its chemical environment. A comprehensible mechanism of the transformation of N-6 into N-5 nitrogen is discussed on the basis of the FT-IR and solid-state ¹³C-NMR spectra of the low temperature chars.     

Structural symmetry breaking of silicon‐containing poly(amide‐imide) oligomers and its relation to electrical conductivity and Raman‐active vibrations

Optically active poly(amide‐imide) oligomers were synthesized by direct polycondensation between an aromatic diamine and a dicarboxylic acid both containing a diphenylsilylene unit. The reaction was carried out using triphenyl phosphite/pyridine in the presence of CaCl₂ and N‐methyl‐2‐pyrrolidone as solvent. Oligomers were obtained in good yields and showed high solubility in common aprotic polar solvents. The precursors, monomers and poly(amide‐imide) oligomers were characterized using elemental analysis and Fourier transform infrared and NMR (¹H, ¹³C, ²⁹Si) spectroscopy. Additionally, the main vibrations of the functional groups (C?O, C?C or N? H) in the oligomers with respect to temperature were characterized using Raman spectroscopy. The glass transition temperature was determined by studying the Raman spectra and corroborated using differential scanning calorimetry. The thermal stability was studied using thermogravimetric analysis. The molecular mass of the compounds was obtained from matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry and their optical properties were analyzed using UV‐visible diode array spectrophotometry. The electronic properties of the oligomers as well as the delocalization of charge carriers within their structures were analyzed using conductance‐voltage curves, which showed that these materials are excellent candidates for integrated optoelectronic applications. Copyright © 2011 Society of Chemical Industry     

<Emphasis Type="Italic">N</Emphasis>-Acylated Bacteriohopanehexol-Mannosamides from the Thermophilic Bacterium <Emphasis Type="Italic">Alicyclobacillus acidoterrestris</Emphasis>

Identification of molecular species of various N-acylated bacteriohopanehexol-mannosamides from the thermophilic bacterium Alicyclobacillus acidoterrestris by semipreparative HPLC and by RP-HPLC with ESI is described. We used triple-quadrupole type mass spectrometer, ¹H and ¹³C NMR for analyzing this complex lipid. CD spectra of two compounds (model compound—7-deoxy-d-glycero-d-allo-heptitol obtained by stereospecific synthesis, and an isolated derivative of hopane) were also measured and the absolute configuration of both compounds was determined. On the basis of all the above methods, we identified the full structure of a new class of bacteriohopanes, represented by various N-acylated bacteriohopanehexol-mannosamides.     

Two-dimensional n.m.r. studies of polybutadiene adducts with dihalocarbenes

A variety of two-dimensional (2D) n.m.r. experiments were performed on the adducts of 1,4-polybutadienes (PBD) with difluorocarbene (:CF₂) and fluorochlorocarbene (:CFC1) to assign stereochemical microstructure, carbon types, and syn and anti isomers. A 2D homonuclear ¹⁹F J-correlated (COSY) spectrum of the trans-PBD:CF₂ adducts at complete conversion showed that the geminal fluorines were equivalent in the isotactic and syndiotactic stereochemical triads (AA' singlets), but nonequivalent in the heterotactic triad (AB quartet). The 2D homonuclear ¹⁹F J-resolved experiment confirmed this finding and gave a geminal coupling constant of 160 Hz. Pentad stereosequence fine structure was observed in the 2D spectra but not in the 1D spectra. Editing of carbon types proved difficult by the distortionless enhancement by polarization transfer (d.e.p.t.) pulse sequence (Doddrell, D. M., Pegg, D. T. & Bendall, M. R., J. Magn. Reson., 1982, 48 , 323) for PBD:CFC1 adducts, owing in part to different magnitudes of the ¹J₁₃ scalar coupling constant. A 2D heteronuclear ¹³C-¹H J-resolved experiment was superior and also provided the coupling constants, which ranged from 130 Hz (acyclic methylenes) to 167 Hz (cyclopropyl methines). The identity of syn and anti structures in cis-PBD:CFC1 adducts was rigorously established by a 2D heterocorrelated ¹⁹F-¹H nuclear Overhauser experiment (NOESY). It is noteworthy that the more hindered structure with chlorine syn to the alkyl groups is preferred by 1·65:1. Analysis of a model compound obtained from cis-5-decene gave ³J couplings of 20 and ≤ 3 Hz for the syn and anti compounds, respectively. These couplings were obscured in the 1D polymer spectrum by stereosequence broadening, but their values could be extracted by 2D ¹⁹F-¹H J-resolved spectroscopy.     

C60-polymer nanocomposites: evidence for interface interaction

Polyaniline-fullerene (PA-C₆₀) composites have been studied by Surface Enhanced Raman scattering (SERS) spectroscopy and X-ray diffraction. They were obtained by mixing solutions of polyaniline-emeraldine base (PA-EB) and C₆₀, as well as by chemical synthesis from aniline, sulfuric acid and potassium dichromate, with addition of C₆₀. The Raman bands peaking at 1330-1370 cm⁻¹, associated with a protonated structure were used as indicative for changes of the PA-EB phonon spectrum resulting from C₆₀ doping. The two types of compounds show different SERS spectra, also dependent on the metallic support used (Au or Ag). Variation of the SERS spectra with the type of metallic support is related to a chemical interface interaction between composite and metal. In mixture samples, a doped polymeric chain (with ionically attached C₆₀⁻) was evidenced by an increased fraction of quinoid rings. The SERS spectra of the chemically synthesized PA-C₆₀ reveals the existence of two polymeric structures: a doped PA (doped with C₆₀⁻ ions) and an undoped one, the latter with a structure of ‘pendant chain’ type. Structural (XRD) data reveal the presence of C₆₀ nano-zones, with a lattice parameter increase of 0.3-0.6%, attributed to slight oxidation. Detailed analysis of the fcc(111) line asymmetry suggests, in mixture samples, a boundary zone with an ‘expanded’ lattice, induced by ionic interface effects.     

On the structure of glasses in the Ge-S-Br and Ge-Se-Br systems

The structure of the vitreous GeSBr₂ and GeSeBr₂ compounds has been investigated using Raman scattering spectroscopy. The Raman spectra of the GeSBr₂ compound contain bands at 235 and 113 cm⁻¹, which are attributed to vibrations in the GeBr₄ molecule, and bands at 288, 254, 161, and 147 cm⁻¹, which are absent in the Raman spectra of binary compounds. The Raman spectrum of the GeSeBr₂ glass has common features with the spectra of the GeSe₂ and GeBr₄ compounds but also involves a number of new bands intermediate in position between the bands at 265 cm⁻¹ for the GeSe₂ compound and the bands at 325 cm⁻¹ for the GeBr₄ compound. The spectra obtained confirm the existence of equilibria between the formation and dissociation of ternary structural units in melts of the thiobromide and selenobromide systems.     

Hydroperoxide formation during autoxidation of conjugated linoleic acid methyl ester

The aim of this study was to investigate whether hydroperoxides are formed in the autoxidation of conjugated linoleic acid (CLA) methyl ester both in the presence and absence of α‐tocopherol. The existence of hydroperoxide protons was confirmed by D₂O exchange and by chemoselective reduction of the hydroperoxide groups into hydroxyl groups using NaBH₄. These experiments were followed by nuclear magnetic resonance (NMR) spectroscopy. The ¹³C and ¹HNMR spectra of a mixture of 9‐hydroper‐oxy‐10‐trans,12‐cis‐octadecadienoic acid methyl ester (9‐OOH) and 13‐hydroperoxy‐9‐cis, 11‐trans‐octadecadienoic acid methyl ester (13‐OOH), which are formed during the autoxidation of methyl linoleate, were studied in detail to allow the comparison between the two linoleate hydroperoxides and the CLA methyl ester hydroperoxides. The ¹³CNMR spectra of samples enriched with one of the two linoleate hydroperoxide isomers were assigned using 2D NMR techniques, namely Correlated Spectroscopy (COSY), gradient Heteronuclear Multiple Bond Correlation (gHMBC), and gradient Heteronuclear Single Quantum Correlation (gHSQC). The ¹³C and ¹H NMR experiments performed in this study show that hydroperoxides are formed during the autoxidation of CLA methyl ester both in the presence and absence of α‐tocopherol and that the major isomers of CLA methyl ester hydroperoxides have a conjugated monohydroperoxydiene structure similar to that in linoleate hydroperoxides.     

Synthesis,X-ray crystal structure and optical properties of novel 2,5-diaryl-1,3,4-oxadiazole derivatives containing substituted pyrazolo[1,5-a]pyridine units

A series of pyrazolo[1,5-a]pyridine-containing 2,5-diaryl-1,3,4-oxadiazole derivatives were synthesized and their structures were characterized by IR, ¹H NMR and HRMS spectra. The crystal structure of 3a was determined using single crystal X-ray crystallography. Its spatial structure was found to be monoclinic, and all aromatic rings were approximately coplanar, which allowed conjugation. The absorption results showed that compounds 1a–f presented their absorption peaks ranging from 264 nm to 290 nm, while compounds 3a–f with a larger conjugation system exhibited red-shifted absorption character (absorption maxima between 283 nm and 303 nm) compared to the corresponding absorption of 1a–f. Fluorescence spectra revealed that these compounds exhibited blue fluorescence (421–444 nm) in dilute solutions and showed quantum yields of fluorescence between 0.32 and 0.83 in dichloromethane.     

Electropolymerization of chlorinated phenols on a Pt electrode in alkaline solution. Part IV: A gas chromatography mass spectrometry study

The electropolymerization of phenol and chlorinated phenols (monochlorophenols, dichlorophenols, 2,3,6-, 2,4,6-, 2,4,5-trichlorophenols and pentachlorophenol) was studied on a platinum electrode at 0.78 V vs SHE in alkaline 1 M NaOH aqueous solutions containing 0.1 M of the phenols. The low molecular weight reaction products were investigated by means of gas chromatography mass spectrometry (GCMS). Product analyses show that oligomers (dimers, trimers and tetramers) are present in the polymer mixtures formed. The MS spectra reveal the ether-linked nature of the oligomers formed during the electrooxidation-electropolymerization of the phenolic compounds. The mass spectra of the low molecular weight substances formed suggest that the oxidation–polymerization of phenols proceeds following two different mechanisms: (i) through the quinol-ether route (without chlorine elimination) and (ii) via the nucleophilic-radical substitution (S_RN1) route (with some elimination of chlorine from ortho and/or para positions).     

Synthesis, X-ray crystal structure and optical properties of novel 2,5-diaryl-1,3,4-oxadiazole derivatives containing substituted pyrazolo[1,5-a]pyridine units

A series of pyrazolo[1,5-a]pyridine-containing 2,5-diaryl-1,3,4-oxadiazole derivatives were synthesized and their structures were characterized by IR, ¹H NMR and HRMS spectra. The crystal structure of 3a was determined using single crystal X-ray crystallography. Its spatial structure was found to be monoclinic, and all aromatic rings were approximately coplanar, which allowed conjugation. The absorption results showed that compounds 1a-f presented their absorption peaks ranging from 264 nm to 290 nm, while compounds 3a-f with a larger conjugation system exhibited red-shifted absorption character (absorption maxima between 283 nm and 303 nm) compared to the corresponding absorption of 1a-f. Fluorescence spectra revealed that these compounds exhibited blue fluorescence (421-444 nm) in dilute solutions and showed quantum yields of fluorescence between 0.32 and 0.83 in dichloromethane.     

Development of whey protein isolate/polyaniline smart packaging: Morphological,structural, thermal,and electrical properties

Development of smart packaging from biodegradable polymers that allow monitoring food exposure conditions is important to reduce food and material packaging waste. The objective of this article is to evaluate the conductivity of polyaniline (PANI) in its doped form with dodecylbenzene sulfonic acid on morphological, structure, thermal, and electrical (Hall effect) properties of whey protein isolate (films. Films show immiscible with 10⁻³ S cm⁻¹ conductivity and semiconductor behavior due to a phase separation that is observed (scanning electron microscopy and thermogravimetric analysis). Fourier transform infrared and Raman spectra do not present changes in relation to control samples, suggesting no chemical interaction with polymers. This result is probably due to deprotonation of PANI. No significant differences are observed for conductivity of film made above 60 mg mL⁻¹ of PANI. Films showed semiconducting properties that allow a new application on smart packaging to help monitor electrical properties of foods in processes of degradable. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47316.     

Synthesis of thermoreactive polysiloxanes with cyclic fragments in the side chain

The synthesis of polysiloxanes with pendant unsaturated cyclic fragments have been successfully performed by hydrosilylation reactions of polymethylhydrosiloxane with 4‐vinyl‐1‐cyclohexene in the presence of platinum hydrochloric acid (0.1 M solution in THF), Karstedt's catalyst (Pt₂[(VinSiMe₂)₂O]₃) and platinum on the charcoal (5%). Reactions were carried out at various temperatures with different ratios of initial compounds. It was shown, that not all active ≡Si? H groups take part in the hydrosilylation reaction. Some kinetic parameters of reactions were studied. The synthesized oligomers were characterized by FTIR, ¹H, ¹³C, H,H‐COSY, and C,H‐correlation NMR spectroscopy. Calculations using the quantum‐chemical semi empirical AM1 method for modeling reactions between methyldimethoxysilane [Me(MeO)₂SiH] and 4‐vinyl‐1‐cyclohexene were performed to evaluate possible reaction paths. Synthesized oligomers were characterized by gel‐permeation chromatography, differential scanning calorimetric, thermogravimetric, and wide‐angle X‐ray analyses. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Rational Design of Domain‐Swapping‐Based c‐Type Cytochrome Heterodimers by Using Chimeric Proteins

The design of protein oligomers with multiple active sites has been gaining interest, owing to their potential use for biomaterials, which has encouraged researchers to develop a new design method. Three‐dimensional domain swapping is the unique phenomenon in which protein molecules exchange the same structural region between each other. Herein, to construct oligomeric heme proteins with different active sites by utilizing domain swapping, two c‐type cytochrome‐based chimeric proteins have been constructed and the domains swapped. According to X‐ray crystallographic analysis, the two chimeric proteins formed a domain‐swapped dimer with two His/Met coordinated hemes. By mutating the heme coordination structure of one of the two chimeric proteins, a domainswapped heterodimer with His/Met and His/H₂O coordinated hemes was formed. Binding of an oxygen molecule to the His/H₂O site of the heterodimer was confirmed by resonance Raman spectroscopy, in which the Fe?O₂ stretching band was observed at 580 cm^?1 for the reduced/oxygenated heterodimer (at 554 cm^?1 under an ¹⁸O₂ atmosphere). These results show that domain swapping is a useful method to design multiheme proteins.     

Simplification and assignment of proton and two-dimensional hetero-correlated NMR spectra of petroleum fractions using gradient selected editing pulse sequences

In this paper, gradient selected (gs) NMR experiments are presented for editing the proton, and two-dimensional (2D) ¹H-¹³C-correlation spectra of different fractions of the petroleum according to the carbon multiplicity. The state of the art experiments allow the much sought after simplification and resolution of the proton, and 2D ¹H-¹³C correlated NMR spectra of such fractions in considerably reduced acquisition times. The proton-edited experiments offer a new and much convenient way of unambiguous estimation of cut-off points between signals from α-methyl and α-methylene protons in ¹H NMR spectra of petroleum fractions. The gs edited 2D ¹H-¹³C correlated spectra of the fractions provide carbon multiplicity information and hetero-nuclear correlation with improved sensitivity in a single experiment leading to complete spectral assignment. These experiments have been applied to complex petroleum fractions for the first time, and show lot of potential to resolve various hitherto unanswered issues concerning the interpretation of the complex NMR spectra of the petroleum products.     

C NMR study of C-enriched single-wall carbon nanotubes synthesized by catalytic decomposition of methane

¹³C NMR spectra and spin-lattice relaxation times were measured for single-wall carbon nanotubes with 99.9 and 50.0% ¹³C enrichments and natural abundance (1.1% ¹³C) prepared by catalytic decomposition of CH₄. The ¹³C isotropic shift is about 116 ppm from tetramethylsilane, being estimated from magic-angle-spinning (MAS) spectra. The value does not depend on the degree of the ¹³C enrichment. The ¹³C MAS NMR spectra show two additional small peaks at 171 and 152 ppm, which are ascribed to carbon species at defects or edges. The line widths of the main isotropic peak in MAS spectra are about 30 ppm, the origin of which is mostly chemical shift dispersion, reflecting a distribution of diameter and helicity. The line width in the ¹³C static spectra originates from chemical shift dispersion, chemical shift anisotropy and dipole–dipole interactions between ¹³C spins as well as between ¹³C and ¹H spins at defects or edges. ¹H NMR spectra confirm the presence of H-containing species. The ¹³C spin-lattice relaxation is dominated presumably by interaction with magnetic impurities.     

Structural analysis of oriented poly(ε‐caprolactone) including CaCO3 particles with 13C solid‐state NMR

The results of a study of the relation between the oriented structure and drawn Poly(ε‐caprolactone) specimens including CaCO₃ particles and their dynamic mechanical properties are presented. The loss elasticity, E″, showed almost the same curve for both undrawn sheets and drawn sheets as a function of CaCO₃ content. On the other hand, the storage modulus, E′, of drawn sheets increased nonlinearly with increasing CaCO₃ content, and their curve showed lower E′ values than those of undrawn sheets. By simulation of ¹³C CP NMR spectra of drawn PCL/CaCO₃ sheets, both oriented and unoriented components were observed. The distribution parameter, p, of drawn PCL/CaCO₃ sheets was 13°, which was larger than those (8°) of drawn PCL. Further, the fraction of the unoriented component increased with increasing CaCO₃ content. Thus, adding CaCO₃ particles into the PCL, the arrangement of the oriented component was disturbed and decreased. In addition, from the line shape analyses of ¹³C CP MAS NMR spectra, four peaks were obtained in not only undrawn sheets but also in drawn sheets of both PCL and PCL/CaCO₃ compounds. Besides, structural change occurred at only drawn PCL/CaCO₃ sheets. Therefore, the change in dynamic mechanical properties observed only for drawn PCL/CaCO₃ sheets were strongly dependent on the orientational structure, which was formed under shear stress of the stretching drawn process. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2376–2382, 2001     

Assignment of13C nuclear magnetic resonance signals in fatty compounds with allylic hydroxy groups

¹³C Nuclear magnetic resonance (NMR) signals in several fatty compounds with allylic mono- and dihydroxy groups were assigned by comparing compounds with and without other functional groups (allylic hydroxy, carboxylic acid, respectively, methyl ester at C₁). The simple¹³C NMR spectra of hydroxylated compounds derived from symmetrical alkenes are particularly useful in making assignments. The compounds whose signals were partially assigned are 8-hydroxy-9(E)-octadecenoic acid, 11-hydroxy-9(E)-octadecenoic acid, 8, 11-dihydroxy-9(E)-octadecenoic acid, 9(E)-octadecen-8-ol, and 9(E)-octadecene-8, 11-diol. The present evaluation can be used for assigning signals in other fatty compounds.     

Enzymatic hydrolysis of autohydrolyzed barley husks

BACKGROUND: Barley husks were subjected to non‐isothermal autohydrolysis of different severities, yielding a liquid phase rich in hemicellulose‐derived compounds and a solid phase, composed mainly of cellulose and lignin. This solid phase was subjected to enzymatic hydrolysis in order to assess the effects of severity on the susceptibility of substrates to enzymatic hydrolysis. The effects of the liquid to solid ratio (LSR, in the range 6 to 18 g g^?1) and cellulase to substrate ratio (CSR, in the range 3.3 to 8.2 FPU g^?1) on the enzymatic hydrolysis were assessed. RESULTS: Up to 25.8 g oligomers per 100 g raw material were present in liquors from the hydrothermal processing. Enzymatic hydrolysis of solid phases obtained under selected conditions (log Ro = 4.14, LSR = 6 g g^?1 and CSR = 5.8 FPU g^?1) yielded glucose concentrations up to 67 g L^?1 (corresponding to cellulose to glucose conversions close to 100%). CONCLUSION: It was shown that autohydrolysis is an effective method for improving the enzymatic susceptibility of barley husks. High cellulose conversions resulting in high glucose yields were achieved by enzymatic hydrolysis at low LSR and CSR. The liquid fraction obtained upon autohydrolysis contained large amounts of hemicellulose‐derived compounds. Copyright © 2010 Society of Chemical Industry     

EPR study of compounds in the LaAlO<Subscript>3</Subscript>-La<Subscript>0.67</Subscript>Sr<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript> system

The EPR spectra of compounds in the LaAlO₃-La_0.67Sr_0.33Mn _y O₃ system at a frequency of 9.4 GHz have been investigated at the temperatures T = 77 and 300 K as a function of the manganese concentration y (y = 0.015, 0.030, 0.080). It has been revealed that, in the paramagnetic state at y = 0.015, there exist isolated Mn²⁺ and Mn⁴⁺ ions, which has been confirmed by simulating the EPR spectra. The parameters of the EPR spectra have been determined. The effective magnetic moments μ_eff of the Mn²⁺ and Mn⁴⁺ ions have been calculated from the EPR spectra. It has been demonstrated that an increase in the Mn concentration leads to a decrease in the number of isolated ions and to the formation of new spin clusters. This manifests itself in the predominance of a broad line with weak traces of the hyperfine structure due to the isolated manganese ions.     

X-ray absorption fine structure study on residue bromine in carbons with different degrees of graphitization

The structure of bromine residue compounds was investigated by X-ray absorption fine structure (XAFS) in order to interpret where and how bromine is present in carbons with different degrees of graphitization. The residue compounds can be classified into three groups, as obtained from X-ray absorption near edge structure (XANES) spectra and the values of the intramolecular distance r_Br–Br determined by extended X-ray absorption fine structure (EXAFS). In Group I, prepared from the host carbons heat treated at temperatures higher than 1900 °C, bromine exists in the interlayer space of graphite in the form of Br₂ molecules with interaction of the π electrons of graphite. In Group III, from carbon heat treated at 1000 °C, most of the bromine probably reacts with carbon atoms having a dangling bond or functional groups. For Group II, where the host carbons are heat treated at intermediate temperatures, it is likely that bromine exists in undeveloped defects with a unique electronic state.