稻秆木素侧链13C同位素示踪及固体13CNMR分析

在水稻(Oryza sativa L.)生长过程中,向其茎秆部节间的空腔分别注入在侧链α,β,γ位带有¹³C标记的松柏醇葡萄糖甙,得到¹³C标记的稻秆木素,用高分辨率固体核磁¹³CNMR对其组织进行分析,发现外源性的松柏醇葡萄糖甙并不影响水稻中木素的正常合成.证明了β-O-4,β-β,β-5和β-1结构是稻秆原本木素中的主要结构,另外还有少量的松柏醇和阿魏酸类结构,并证实木素在α位与糖类等组分有共价键形成.     

Polymorphism of phenylpyruvic acid studied by IR, Raman and solid state C NMR spectroscopy

Polymorphs I and II of phenylpyruvic acid are obtained as mixtures of both crystal forms or relatively pure crystals, from different solvents. Polymorph I is more stable than polymorph II at room temperature. Spectral characteristics of these polymorphs are discussed on the basis of IR, Raman and solid state ¹³C NMR spectra. Also, the assignment of the IR features observed in the 1600–1700 cm⁻¹ region is re-investigated by referring to the spectra of heavy-atom substituted derivatives. It is suggested that the C=O stretching band is split by the crystal field for both polymorphs.     

Characterization of milled wood lignin and ethanol organosolv lignin from miscanthus

Ethanol organosolv lignin extracted from Miscanthus × giganteus (using the following conditions: T = 190 °C, t = 60 min, sulfuric acid = 1.2% w/w, EtOH/H₂O = 0.65) and milled wood lignin from Miscanthus × giganteus were subjected to a comprehensive structural characterization by ¹³C, ³¹P NMR, FTIR, UV spectroscopies and size exclusion chromatography. The results showed that Miscanthus lignin is an H/G/S type (4%, 52%, 44% respectively) with ∼0.41 β-O-4 linkage per aromatic ring and contains coumarylate linkages (0.1/Ar). It was shown that during organosolv treatment, cleavage of β-O-4 linkages and of ester bond (acetyl and coumaryl residues) was the major mechanisms of lignin breakdown but the process did not significantly change the core of the lignin structure.     

Investigation of the chemical modifications of beech wood lignin during heat treatment

Holocellulose, Klason lignin and milled wood lignin (MWL) of beech wood were extracted before and after heat treatment and analysed using CP MAS ¹³C NMR, ¹³C NMR, ³¹P NMR and size exclusion chromatography (SEC). Experimental results showed that the thermal treatment degrades hemicelluloses and affects lignin polymer through depolymerisation due mainly to cleavage of β-aryl-ether linkages and recondensation reactions. The spectroscopic analysis of MWL demonstrated that these recondensation reactions involved mainly guaiacyl units through formation of 5,5′-biphenolic and diarylmethane structures.Analysis of molecular weight distribution of MWL by SEC indicated that average molecular weights of heat treated milled wood lignin were lower than those of native milled wood lignin.     

Use of steam explosion liquor from sugar cane bagasse for lignin peroxidase production by Phanerochaete chrysosporium

The possibility of using two by-products of the sugar cane industry, molasses and bagasse steam explosion liquor (SEL), for lignin peroxidase (LiP) production by Phanerochaete chrysosporium was investigated. For comparison, the fungus was initially cultivated in synthetic media containing either glucose, sucrose, xylose, or xylan as sole carbon sources. The effect of veratryl alcohol (VA) was also investigated in relation to the enzyme activity levels. Results showed that sucrose was not metabolized by this fungus, which precluded the use of molasses as a carbon source. Glucose, xylose, and xylan promoted equivalent cell growth. Enzyme levels in the absence of VA were lower than 28 UI/L and in the presence of VA reached 109 IU/L with glucose and 85 IU/L with xylose or xylan. SEL was adequate for P. chrysosporium LiP production as LiP activity reached 90 IU/L. When VA was added to this medium, enzyme concentration increased to 155 IU/L.     

Oxidative cracking of precipitated hardwood lignin by hydrogen peroxide

Precipitated hardwood lignin (PHL) is a major byproduct in the biomassto-ethanol process. Oxidativecracking of PHL by hydrogen peroxide in aqueous medium was investigated as a means to produce potentially useful chemicals. The cracking reaction takes place at moderate temperatures (80–160°C), giving mono-and dicarboxylic acids as the main products. The yields of these products are in the range of 30–50% of initial lignin. The reaction mechanism and the product distribution are dependent upon the reaction conditions, especially the pH. The reaction under strong alkaline condition proceeds well even at low reaction temperatures (80–90°C). Under acidic conditions, higher temperatures (130–160°C) are required to attain the same degrees of cracking. The reaction patterns of the oxidative cracking reaction involve the cleavage of lignin ring, aryl ether bond, or other linkages within lignin. By using the findings of this investigation and those of previous work, we have illustrated the reaction pathways for degradation of PHL under alkaline and acidic conditions. Aldehydes and aromatic acids are interm ediate products in the oxidative degradation of lignin. However, they were produced only in trace amounts owing to rapid degradation induced by hydrogen peroxide. Presented at the 21st Symposium on Biotechnology for Fuels and Chemicals, Fort Collins, CO, May 1999.     

Oxidation of C-labeled ethyl linoleate monitored and quantitatively analyzed by C NMR

The oxidation of ¹³C-labeled ethyl linoleate (¹³C-EL), a model compound for alkyd resins, was investigated by ¹³C NMR in the presence of Co(II)-2-ethylhexanoate (Co-EH), Mn(acac)₃ (acac = acetylacetonate), and Mn(acac)₃ in combination with 2,2′-bipyridine (bpy), respectively. The use of ¹³C-EL allows us, in an unprecedented way, to reveal the individual evolution of hydroperoxides (ROOH) and peroxy (ROOR) links by ¹³C NMR and to quantify the oxidation intermediates during the oxidation. Mn(acac)₃ appeared to be less effective in decomposing ROOH than Co-EH and the Mn(acac)₃/bpy combination. Quantitative analyses were attempted for a few major ¹³C peaks.     

Evidence of char formation during wood heat treatment by mild pyrolysis

The behaviour of wood polymers during heat treatment carried out under inert atmosphere at 240 °C has been reinvestigated to understand the important decrease of the O/C ratio observed in a previous study using X-ray photoelectron spectroscopy (XPS). Heat treatment was performed not only on beech sawdust but also on its lignin and holocellulose fractions obtained after acidic hydrolysis of polysaccharides or delignification with sodium chlorite. CP/MAS ¹³C NMR spectra indicate as previously reported an important degradation of hemicelluloses after thermal treatment. However, assignments of the signals appearing in the range of 125-135 ppm and 35 ppm attributed up to now to thermal crosslinking of lignin and formation of methylene bridges should be reconsidered. Indeed, heat treatment of the holocellulose fraction indicates quite similar signals showing that these latter are not due to lignin modification. According to the literature, these new signals have been attributed to the beginning of char formation. Determination of Klason lignin and HPLC analysis of the sugars contained in the hydrolysate support the hypothesis of formation of carbonaceous materials within the wood structure during heat treatment by mild pyrolysis.     

Sequence Distribution of Poly(methyl acrylate) by Incremental Calculation

The carbonyl signal in the 100 MHz ¹³C NMR spectra of poly(methyl acrylate) (PMA) recorded in benzene-d₆ exhibits configurational sensitivity up to pentads, and the signal of backbone β-CH₂ carbons shows splitting up to configurational hexads with traces of octads. Assignment of the sequences to respective signals was confirmed by computer simulation of both carbonyl and methylene signals applying a method of incremental calculation of chemical shifts of individual sequences and second-order Markov statistics for sequence probabilities.     

Characterization of Acacia mangium polyflavonoid tannins by MALDI-TOF mass spectrometry and CP-MAS C NMR

The MALDI-TOF mass spectrometry (MS) and solid state CP-MAS ¹³C Nuclear Magnetic Resonance (NMR) spectroscopic technique were introduced to characterize Acacia mangium tannin (condensed tannins). The MALDI-TOF MS illustrated a series of peaks corresponding to oligomers of condensed tannins of up to 11 flavonoid units (3200 Da). A. mangium condensed tannins were found to consist predominantly of prorobinetinidin combined with profisetinidin and prodelphinidin. Both the MALDI-TOF mass spectra and the solid state CP-MAS ¹³C NMR indicated that the A. mangium tannins obtained from Kudat, had an almost completely linear structure; In addition, Lembah Beringin, consist of “angular” polymer structure; and Tawau, has included “twice-angular” polymer structures present in oligomers type of up to 7 flavonoid units. The high degree of polymerization of linear, angular type, twice-angular structures and longer oligomer (3200 Da) chains have not been observed in previous studies of condensed tannins. The spectra also indicated that A. mangium tannins are more heavily branched and have higher degree of polymerization (>7.0) compared to commercial mimosa (A. mearnsii) tannin (4.9). Because tannins are phenolic, it was expected that they can be used to replace phenol-formaldehyde (PF) adhesives.     

The effect of silica nanoparticles on the morphology, mechanical properties and thermal degradation kinetics of PMMA

Silica-PMMA nanocomposites with different silica quantities were prepared by a melt compounding method. The effect of silica amount, in the range 1-5 wt.%, on the morphology, mechanical properties and thermal degradation kinetics of PMMA was investigated by means of transmission electron microscopy (TEM), X-ray diffractometry (XRD), dynamic mechanical analysis (DMA), thermogravimetric analyses (TGA), Fourier-transform infrared spectroscopy (FTIR), ¹³C cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy (¹³C{¹H} CP-MAS NMR) and measures of proton spin-lattice relaxation time in the rotating frame (T_1ρ(H)), in the laboratory frame (T₁(H)) and cross-polarization times (T_CH). Results showed that silica nanoparticles are well dispersed in the polymeric matrix whose structure remains amorphous. The degradation of the polymer occurs at higher temperature in the presence of silica because of the interaction between the two components.     

Maximizing the xylitol production from sugar cane bagasse hydrolysate by controlling the aeration rate

Batch fermentations of sugar cane bagasse hemicellulosic hydrolysate treated for removing the inhibitors of the fermentation were performed byCandida guilliermondii FTI20037 for xylitol production. The fermentative parameters agitation and aeration rate were studied aiming the maximization of xylitol production from this agroindustrial residue. The maximal xylitol volumetric productivity (0.87 g/L h) and yield (0.67 g/g) were attained at 400/min and 0.45 v.v.m. (K_La 27/h). According to the results, a suitable control of the oxygen input permitting the xylitol formation from sugar cane bagasse hydrolysate is required for the development of an efficient fermentation process for large-scale applications.     

Enzymatically Synthesized Conducting Polyaniline Nanocomposites: A Solid‐State NMR Study

Abstract

The chiral conducting polyaniline (PANI) nanocomposites [polyacrylic acid/polyaniline/(?) camphorsulphonic acid (CSA)] were synthesized using enzyme, horseradish peroxidase (HRP) in the aqueous buffer solution at pH 4.3. It appears that the enzyme HRP apart being a biocatalyst, plays an important role during the polymerization, which allows PANI to prefer a specific helical conformation whether the induced chirality in the monomer‐CSA complex is either by (+)CSA or (?)CSA. In this paper, we report, the structural characterization of these nanocomposites by solid‐state ¹³C cross‐polarization with magic angle spinning (CP/MAS) NMR techniques. The structural features of PANI in the conducting form of nanocomposite (as‐synthesized) are similar to that of enzymatically and chemically synthesized PANI. Preliminary data also suggest that some portion of nanocomposite samples are not completely doped. Dedoping of as‐synthesized PANI nanocomposite with aqueous NH₄OH shows the spectral features that of the emeraldine base form. Solid‐state ¹³C NMR data suggest that it is possible to detach PAA and CSA from PANI in the nanocomposite material.     

Synthesis of regioselectively O-labelled chlorophyll derivatives at the 3- and/or 13-positions through one-pot exchange of carbonyl oxygen atoms

3¹- and/or 13¹-¹⁸O-oxo-labelled methyl pyropheophorbides (84-90% ¹⁸O atoms at each position) were prepared by exchanging carbonyl oxygen atoms under biphasic conditions of acidic H₂¹⁸O (ca. 95% ¹⁸O) and dichloromethane. The (un)labelling occurred more rapidly at less sterically hindered (13-CO possessing 13²-COOCH₃>13-CO lacking it) or more reactive carbonyl groups (formyl>keto group), and not at any hydroxy groups. Reduction of a carbonyl to carbinol group was useful for preparation of regioselectively ¹⁸O-labelled chlorophyll derivatives. Following the labelling procedure, 13¹-¹⁸O-pheophytin-a and 3¹-¹⁸O-pheophytin-d were obtained. All the synthetic ¹⁸O-labelled compounds were characterized by their FAB-mass, ¹³C NMR and IR spectra. Especially, ¹⁸O-labelling induced 0.02 (¹³C-O) and 0.04-0.05 ppm high field shifts (¹³CO) in ¹⁸O-attached carbon resonances and about 30 cm⁻¹ down-shifts in ¹⁸O-labelled carbonyl stretching vibrational bands.     

Optical properties of a polyethylene dispersion with a luminescent silica prepared by surface grafting of a perylene derivative

A micrometric silica modified with perylene derivative (SiO₂–TES) has been prepared by hydrolysis–condensation reactions between silica and N,N’-bis-(3-triethoxysilylpropyl)-perylene-tetracarboxyldiimide (P-TES) and utilized as filler in LLDPE films together with a compatibilizer. Spectroscopic analyses on SiO₂–TES confirmed the grafting of P-TES on silica, while its amount was determined by thermogravimetric analysis. Solid state NMR provided information about the structure of silicon atoms involved in the condensation of SiO₂ and P-TES that resulted mainly in silicon atoms grafted with bi-dentate anchorages.UV–Vis and fluorescence analyses carried out on P-TES showed the ability of the dye to generate J-type aggregates in apolar solvents. The same analyses on SiO₂–TES revealed the presence of both isolated and aggregated dye molecules grafted on silica surface, while on polymeric dispersions of SiO₂–TES, they have shown only the presence of P-TES aggregates grafted to silica.Thanks to the direct correlation between optical properties (obtained both by UV–Vis and by fluorescence analyses) and the chemical environment of composites, the luminescent silica SiO₂–TES could be used to estimate the filler dispersion extent in different microcomposite polymer materials.     

Reactive processing of polymers: Structural characterisation of products by H and C NMR spectroscopy for glycidyl methacrylate grafting onto EPR in the absence and presence of a reactive comonomer

Grafted GMA on EPR samples were prepared in a Thermo-Haake internal mixer by free radical melt grafting reactions in the absence (conventional system; EPR-g-GMA_CONV) and presence of the reactive comonomer divinyl benzene, DVB (EPR-g-GMA_DVB). The GMA-homopolymer (poly-GMA), a major side reaction product in the conventional system, was almost completely absent in the DVB-containing system, the latter also resulted in a much higher level of GMA grafting. A comprehensive microstructure analysis of the formed poly-GMA was performed based on one-dimensional ¹H and ¹³C NMR spectroscopy and the complete spectral assignments were supported by two-dimensional NMR techniques based on long range two and three bond order carbon-proton couplings from HMBC (Heteronuclear Multiple Bond Coherence) and that of one bond carbon-proton couplings from HSQC (Heteronuclear Single Quantum Coherence), as well as the use of Distortionless Enhancement by Polarization Transfer (DEPT) NMR spectroscopy. The unambiguous analysis of the stereochemical configuration of poly-GMA was further used to help understand the microstructures of the GMA-grafts obtained in the two different free radical melt grafting reactions, the conventional and comonomer-containing systems. In the grafted GMA, in the conventional system (EPR-g-GMA_CONV), the methylene protons of the GMA were found to be sensitive to tetrad configurational sequences and the results showed that 56% of the GMA sequence in the graft is in atactic configuration and 42% is in syndiotactic configuration whereas the poly-GMA was predominantly syndiotactic. The differences in the microstructures of the graft in the conventional EPR-g-GMA_CONV and the DVB-containing (EPR-g-GMA_DVB) systems is also reported     

The stereochemistry of a nine-membered ring analogue of nefopam,a nonnarcotic analgesic drug

The solid-state structure of a (±)-homonefopam hydrogenfumarate salt having an-O(CH₂)₃N-fragment was determined by single-crystal X-ray diffraction analysis. Homonefopam hydrogenfumarate gave crystals belonging to the monoclinicP2₁/c space group, and at ambient temperaturea=10.220(1),b=18.187(2),c=10.687(2)A,=94.43(1),V=1980.5(5)å³ Z=4,R(F)=0.039,R _w =0.039,R _W (F)=0.025. The¹H NMR spectrum of homonefopam hydrochloride in CD₂Cl₂ solution showed two species (7:1 ratio) at the prototropic shift-nitrogen inversion slow exchange limit. The solution-state major species has the same conformation andtrans-to-phenyl axial N-methyl disposition found in the crystal as evidenced by three antiperiplanar vicinal³ J (HH) coupling constants in the oxytrimethyleneamino fragment and vicinal coupling constants involving theN-H proton. TheR-ratio method was used to estimate 64(2) O-C(3)-C(4)-C(5) and 75(3) C(3)-C(4)-C(5)-N(6) dihedral angles for the major species in CD₂Cl₂ solution in accord with its proposed structure. The finding of C(3)-C(4) bond time-averaged magnitude³ J (HH) values and severe broadening of signals from other minor species protons suggests conformational heterogeneity for the solution-state minor species.     

Solid-state vibrational spectra and theoretical study of alaninamide acetate

Solid-state IR and Raman spectroscopic elucidation of alaninamide acetate is preformed by means of the possibilities of linear-polarized IR and Raman methods. The experimental assignment is compared with theoretical vibrational analysis with the intention to explain the influence of intermolecular interactions in solid phase on the spectroscopic properties of the compound studied. The 1H and ¹³C NMR spectra in solution are compared with the corresponding ones of alanine, studying the amidation effect on the chemical shift signals in the alanine moieties.     

Pretreatment of sugar cane bagasse hemicellulose hydrolyzate for ethanol production by yeast

The cellulase system ofBacillus circulans F-2 effectively hydrolyzed carboxymethyl cellulose (CMC), xylan, avicel, cellobiose, filter paper, cotton, andp-nitrophenyl-Β-D-cellobioside, and the crude enzyme produced mainly glucose from digestion of avicel. Two major and one minor peaks of enzyme activities were eluted on DEAE ion-exchange chromatography, and designated cellulase complex I(C-I) and complex II(C-II) for the two major peaks, and cellulase-III for a minor peak. C-I and C-II were further purified on gel filtration column of a TSK-Gel SW G3000 ×L. The molecular masses of C-I and C-II were estimated to be about 669 and 443 kDa, respectively. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of the C-I and C-II complexes showed that the C-I complex was present as a multiple protein complex, consisting of at least five CMCases and two xylanases, and that the C-II complex was consisted of at least three CMCase and four xylan ases. C-I showed high activities of cellohydrolase, CMCase, xylanase, and Β-glucosidase, whereas C-II showed high activities of CMCase, xylanase, avicelase, and Β-glucosidase. The outstanding property of the C-II was its high hydrolytic activity toward filter paper, a highly resistant substrate against enzymatic degradation. However, cellulaseIII showed only strong avicelase activity. These results indicated that the cellulase system of the strain exists as multiple complex forms.     

A multi-analytical study of degradation of lignin in archaeological waterlogged wood

Historical or archaeological wooden objects are generally better conserved in wet environments than in other contexts. Nevertheless, anaerobic erosion bacteria can slowly degrade waterlogged wood, causing a loss of cellulose and hemicellulose and leading to the formation of water-filled cavities. During this process, lignin can also be altered. The result is a porous and fragile structure, poor in polysaccharides and mainly composed of residual lignin, which can easily collapse during drying and needs specific consolidation treatments. For this reason, the chemical characterization of archaeological lignin is of primary importance in the diagnosis and conservation of waterlogged wood artifacts. Current knowledge of the lignin degradation processes in historical and archaeological wood is extremely inadequate. In this study lignin extracted from archaeological waterlogged wood was examined using both Py-GC/MS, NMR spectroscopy and GPC analysis. The samples were collected from the Site of the Ancient Ships of San Rossore (Pisa, Italy), where since 1998 31 shipwrecks, dating from 2nd century BC to 5th century AD, have been discovered. The results, integrated by GPC analysis, highlight the depolymerization of lignin with cleavage of ether bonds, leading to an higher amount of free phenol units in the lignin from archaeological waterlogged wood, compared to sound lignin from reference wood of the same species.