Solid-state CP/MAS C-NMR analysis of cellulose and tri-O-substituted cellulose ethers

Highly crystalline tri-O-substituted cellulose ethers having ethyl, n-propyl, n-butyl, allyl, and methallyl substituents were prepared from low-molecular weight cellulose (DP = 15). Influences of conformational and packing effects on solid-state ¹³C-NMR spectra were studied by using X-ray diffraction and solid- and solution-state ¹³C-NMR analyses of the cellulose derivatives. Unit-cell sizes tentatively obtained from X-ray diffraction patterns of the cellulose derivatives indicated that conformations and packing states of cellulose chains and alkyl chains of substituents were different between the derivatives. Solid- and solution-state ¹³C-NMR spectra of cellulose allomorphs, and effects of hydrogen bonds present in celluloses I, II, and III on chemical shifts of their solid-state ¹³C-NMR spectra were proposed.     

Structural studies of a mucilage from Abroma augusta root bark

The structure of an acidic polysaccharide isolated from Abroma augusta root bark was determined by sugar and methylation analyses and high resolution ¹H- and ¹³C-NMR spectroscopy. The main chain of the polysaccharide was composed of 1,2-linked - -rhamnopyranose and 1,4- or 1,3-linked - -galacturonic acid residues. The terminal β- -glucuronic acid residue was attached to the 3- and/or 4-position of the - -galacturonic acid residue.     

Distribution of carboxylate groups introduced into cotton linters by the TEMPO-mediated oxidation

The 2,2,6,6-tetramethylpiperidine-1-oxy radial (TEMPO)-mediated oxidation was applied to aqueous slurries of cotton linters. The water-insoluble fibrous fractions thus obtained in the yields of more than 78% were characterized by solid-state ¹³C-NMR, X-ray diffraction and scanning electron microscopic analyses for evaluation of distribution of carboxylate groups formed in the TEMPO-oxidized celluloses. The patterns of solid-state ¹³C-NMR spectra revealed that the oxidation occurred at the C6 primary hydroxyl groups of cellulose. X-ray diffraction and scanning electron microscopic analyses showed that such C6 oxidation took place at the surfaces of cellulose I crystallites without any oxidation at the C6 of inside cellulose I crystallites. Thus, carboxylate and aldehyde groups introduced into the TEMPO-oxidized celluloses are densely present on the surfaces of cellulose I crystallites. In addition, the obtained results revealed that the shoulder signal due to non-crystalline C6 carbons at about 63 ppm in solid-state ¹³C-NMR spectra of native celluloses is ascribed to those of surfaces of cellulose I crystallites or those of cellulose microfibrils.     

胶陀螺光敏毒性成分

食用未经碱处理过的胶陀螺子实体,会出现嘴巴肿胀、暴露在日光下的皮肤灼痛等过敏症状,一直以来困扰着长白山当地居民对这一美食的需求。本文旨在找到胶陀螺Bulgaria inquinans中光敏活性成分。将胶陀螺子实体粉末用丙酮回流提取,浓缩得到浸膏,加吐温-80溶解后灌胃昆明种小鼠,进行光敏活性试验。把出现光敏反应的小鼠处死后,取下红肿的小鼠耳朵用甲醇索式提取得活性组分,进行薄层色谱层析和柱层析,得到一种活性单体化合物,经核磁共振和电子轰击质谱波谱综合解析鉴定该化合物为邻苯二甲酸二异丁酯(DiBP)。结果表明DiBP就是引起胶陀螺光敏中毒反应的活性成分,且经碱水降解后毒性降低。     

Alkaline N-deacetylation of chitin enhanced by flash treatments. Reaction kinetics and structure modifications

A new method for N-deacetylation of chitin is proposed in which a polymer almost free of N-acetyl groups is obtained by flash treatment. The reaction is carried out in 40% NaOH solution for 30–270 s at 140–190°C, using saturated steam.

Flash treatment was found to proceed faster and with a higher activation energy for the deacetylation reaction (E_a = 36 kcal mol⁻¹) compared with the traditional treatment (E_a = 11 kcal mol⁻¹). X-Ray diffractometry, CP-MAS ¹³C-NMR and FTIR spectroscopy show that the flash treatment induces structure modifications; in particular, higher crystallinity indexes and specific area values are observed together with changes in the local and chain conformation.     

CHEMISTRY, PROPERTIES, AND PHYLOGENETIC IMPLICATIONS OF THE METHYLATED CARRAGEENANS FROM RED ALGAE OF THE GENUS ARESCHOUGIA (ARESCHOUGIACEAE, GIGARTINALES, RHODOPHYTA)

The three Australian-endemic species comprising the genus Areschougia have been examined to determine the structure of their nonfibrillar wall components. The polysaccharide extracted from the most widely distributed species, A. congesta (Turner) J. Agardh, was shown by compositional analyses, Fourier transform infrared (FTIR) spectroscopy, linkage analysis, and ¹³C-NMR spectroscopy to be a carrageenan composed predominantly of the repeating disaccharides 6'- O -meth- ylcarrabiose 2,4'-disulfate, carrabiose 2,4'-disulfate (the repeating unit of ι-carrageenan), 4',6'- O -(1-carboxyethylidene)carrabiose 2-sulfate, and 6'- O -methylcarrabiose 2-sulfate. The carrageenan also contained small amounts of 4-linked Gal p residues, some bearing methyl ether substitution at O-3 and some possibly bearing sulfate ester and/or glycosyl substitutions at O-3. The A. congesta carrageenan had unique rheological properties, its gels having some similarities to those of commercial ι-carrageenan but with the viscosity of commercial λ-carrageenan. Polysaccharides from A. ligulata Harvey ex J. Agardh and A. stuartii Harvey were shown by constituent sugar and FTIR analyses to be sulfated galactans rich in mono- O -methylgalactose. The carrageenan structures of Areschougia spp. were consistent with those of the genera Rhabdonia , Erythroclonium , and Austroclonium , the other genera constituting the family Areschougiaceae.     

Amylose conformational transitions in binary DMSO/water mixtures

The effects on amylose conformation of percentage water in dimethyl sulfoxide (DMSO)/water mixtures were measured by following changes in specific optical rotation, limiting viscosity number, and ¹³C-NMR chemical shifts. The temperature dependence of specific optical rotation showed differences in amylose conformation at four chosen ratios of dimethyl sulfoxide/water. An amylose conformational change was also deduced from ¹³C-NMR chemical shift data. Changes in limiting viscosity of amylose in different proportions of DMSO/water, and the effect of tetramethylurea on the specific rotation of amylose, indicate that intramolecular hydrogen bonding decreases with increased water content. 66.6% DMSO appears to be a crossover concentration, below which the helical conformation is progressively lost as water is added. When water content is over 60%, transition to a conformation which allows iodine complexation to take place is complete. A transition of amylose conformation from helix to loose helix to random coil with increasing water content was deduced from the experimental results.     

NMR analyses of polysaccharide derivatives containing amine groups

Amylose, amylopectin, hydroxyethylcellulose, methylcellulose, and cellulose were reacted with diethylaminoethyl chloride HCl salt and 3-chloro-2-hydroxy-propyltrimethylammonium chloride under aqueous alkaline conditions in order to introduce tertiary amine and quaternary ammonium groups into polysaccharides. Degrees of substitution were obtained from ¹H- or ¹³C-NMR spectra of hydrolyzates, and distributions of diethylaminoethyl groups in polysaccharides were measured by ¹³C-NMR. Since amylose, amylopectin, and hydroxyethylcellulose were soluble in the reaction media, these three polysaccharides had higher reactivity for etherifications than cellulose. Methyl-cellulose, which has hydrophobic methyl groups, had as much reactivity as cellulose. Primary hydroxyl groups, C-6, of polysaccharides had the highest reactivity for diethylaminoethylation.     

Structural characteristics of the cold-water-soluble arabinoxylans from the white flour of the soft wheat variety Kadet

Cold-water-soluble arabinoxylan polymers from the soft wheat variety Kadet were isolated by a stepwise (NH₄)₂SO₄ precipitation and freed from co-precipitating proteins by pronase digestion. The purified arabinoxylans, representing 0·5% of the dry weight of the white flour, were fractionated by graded precipitation with ethanol. Monosaccharide analysis revealed the major carbohydrate fractions to contain arabinoxylans only. The arabinoxylans are heterogeneous in molecular size. Determination of the carbohydrate composition in conjunction with methylation analysis and ¹³C-NMR spectroscopy, indicated that they can be divided into specific groups, based on characteristic differences with respect to -xylopyranose to -arabinofuranose ratio and in 2,3,4-tri-:3,4-di-:4-mono-substituted -xylopyranose ratio.     

Structure analysis and degree of substitution of chitin, chitosan and dibutyrylchitin by FT-IR spectroscopy and solid state C NMR

Chitin, an important constituent of the exoskeleton of many organisms such as crustacea and insects, and its derivates promote the ordered healing of tissues and are therefore very suitable for use in wound dressings. The degree of substitution (DS) is an important parameter when assessing the conversion of chitin into one of its derivates. The degree of acetylation of chitin and chitosan and the degree of butyrylation of dibutyrylchitin was evaluated. It is found that FT-IR spectroscopy is a relatively easy but indirect way of determining the DS. FT-IR spectroscopy proved to be very useful for comparing the degrees of conversion and -substitution, as well as for differentiating between different chitin types. Absolute DS determinations by FT-IR however are only reliable when a calibration, using a direct technique such as ¹³C-NMR, is made.     

The confromational behaviour of the cardiac glycoside digoxin as indicated by NMR spectroscopy and molecular dynamics calculations

The ¹H- and ¹³C-NMR spectra of dogoxin in solution in Me₂So-d₆ have been assigned completely. Measurement of the ³J_C,H values has enabled estimation of the torsional angles involving the bonds linking the digitoxose residues, between the inner digitoxose and the genin unit, and for the unsaturated γ-lactone ring. These values have been supplemented by ¹H---¹H NOE data. In general, there is good agreement between the conformations in solution (NMR data) and the solid state (X-ray data), and that derived from theological modelling which shows evidence of conformational flexibility. The major difference occurs for the torsion between the genin and the innermost digitoxose residue where molecular dynamics predict the presence of two conformations, one similar to that seen by NMR and the other similar to the X-ray structure.     

Synthesis and analysis of DNA adducts of arylamines

Atylamines and nitroarenes are very important environmental and occupational pollutants. Genotoxic effects of arylamines are believed to be initiated by the formation of DNA adducts. DNA adducts of arylamines have been found in experimental animals and in exposed humans, and are predominantly formed with the carbon 8 of 2'-deoxyguanosine. Reference standards are necessary to develop methods for the quantification of DNA-adducts. Therefore, we have synthesized the 2'-deoxyguanosin-8-yI adducts of 2-methylaniline, 2-chloroaniline, 4-chloroaniline, 2,4dimethylaniline, and 2,6-dimethylaniline. The products were characterized by ¹H-NMR, ¹³C-NMR, MS and UV. The corresponding 2'-deoxyguanosine-3' -monophosphate adducts were synthesized for the quantification of DNA adducts by the ³²P-postlabelling technique. A GC-MS method was developed for the analysis of the new adducts as an alternative to the ³²P-postlabelling. DNA was spiked with the synthesized adducts and treated with 0.3 m NaOH overnight at 110 °C in the presence of a deuterated internal standard. We observed up to 80% recovery from about 1 adduct in 10⁸ to 1 in 10⁵ nucleotides.     

The molecular characterization of the polysaccharide gum from Laguncularia racemosa

A polysaccharide isolated from the exudate of Laguncularia racemosa, (Combreta-ceae) has been investigated using Smith-degradation, methylation analysis, hydrolysis, and ¹³C-NMR spectroscopy. The backbone of the structure is constituted of uronic acids, galactose and rhamnose. A complex pentasaccharide, constituted of these sugars, was isolated from the original gum and degradation products. This oligosaccharide is, probably, the main structural feature of the investigated polysaccharide. On the other hand, according to chemical and spectral evidence rhamnose is present, predominantly as internal residues. Arabinosyl (pyranosyl and furanosyl) residues and some galactosyl, glucuronic acid and 4-0-methyl--D-glucuronic acid residues are located in branches.     

Microscopic and chemical studies of a gelling polysaccharide from Lactobacillus hilgardii

The bacterium Lactobacillus hilgardii (previously named L. brevis), isolated from sugary kefir grains, has been found to produce a gelling extracellular polysaccharide. Methylation analysis and ¹H- and ¹³C-NMR analysis revealed a dextran-like structure for the polysaccharide. A high proportion of -(1,6)-Glc and small proportions of -(1,3,6)-Glc, -(1,4,6)-Glc and terminal -Glc were detected. The L. hilgardii polysaccharide differed from normal dextrans in containing a small proportion of -(1,3)-Glc. The structure of the polysaccharide was found to be independent of harvesting time and unaffected by changes in the growth medium. The development of the gel structure has been followed by transmission electron microscopy.     

Synthesis of sulfated derivatives of curdlan and their anti-HIV activity

Sulfopropyl curdlan was synthesized, its structure was determined, and the anti-HIV activity was compared with that of standard curdlan sulfates obtained with piperidine N-sulfonic acid in dimethyl sulfoxide. It was shown that sulfopropyl curdlan exhibits weaker anti-HIV activity than curdlan sulfate. Curdlan sulfates were synthesized with a SO₃-pyridine complex in a heterogeneous phase. It was shown from ¹³C-NMR spectra of acetylated curdlan sulfates that they had a different substituent distribution from standard curdlan sulfate. The cytotoxicity of the curdlan sulfates was attributed to their heterogeneous structure.     

Structural characterization of a galactomannan from the cyanolichen Leptogium azureum

A galactomannan was isolated from the cyanolichen Leptogium azureum via successive alkaline extraction and precipitation with Fehling solution. The structure of the polysaccharide was investigated using NMR spectroscopy, methylation analysis, Smith degradation, and HPSEC-MALLS. As galactomannans from other lichens species, the polymer obtained presents a (1→6)-linked main chain of -mannopyranose, substituted preferentially at O-2 by -Manp or β-Galp non-reducing ends. As observed in previous investigations, the C-1 region of the ¹³C-NMR of these heteropolysaccharides are typical of some lichens species, and can be used as fingerprints in chemotaxonomy. However, in despite of the general structure in common, the substitution level of this structure and their content of mannose is higher than of the others galactomannans obtained of lichenized fungi contained the green alga of the genus Trebouxia.     

Lanthanide induced shift as a tool for isomer assignment in esters of unsaturated fatty acids

Addition of Yb(fod)₃ to methyl oleate (cis) and methyl elaidate (trans) shifts the carboxylic lines of their ¹³C-NMR spectra to different extents; that of the cis isomer less than that of the trans isomer, as is to be expected.

On the same theoretical ground it can be anticipated that the opposite will occur for C-17: an effect that has been confirmed experimentally. The method is thus proposed as a means of aiding in the assignment of the cis and trans configuration in esters of fatty acids with one double bond.     

A Regioselective, Chemoenzymatic Synthesis of Sucrose- 1'-Methacrylate

Pure sucrose is inexpensive and readily available, making this disaccharide a highly desirable starting material for new polymers. In order to achieve a clean polymerization, the disaccharide must be regioselectively monofunctionalized in good yield. This paper describes the practical, enzyme-mediated synthesis of sucrose-1 '-methacrylate 2 from sucrose and vinyl methacrylate using subtilisin Carlsberg (Sigma, Protease VIII), a readily available bacterial serine protease. A key aspect of this process, ascertaining the positional selectivity of acylation, was unambiguously accomplished using ¹H-detected (¹H, ¹³C) one-bond shift correlation (HMQC) spectroscopy and¹H-detected (¹H, ¹³C) multiple bond correlation (HMBC) spectroscopy.     

蛇足石杉内生真菌无柄盘菌Pezicula sp. JR14中抑制乙酰胆碱酯酶的次级代谢产物分离

采用形态学及ITS-rDNA序列分析法,对具有抑制乙酰胆碱酯酶活性的蛇足石杉内生菌株JR14进行鉴定,确定为无柄盘菌Pezicula sp.。开展了乙酰胆碱酯酶抑制活性化合物的分离,从Pezicula sp. JR14乙酸乙酯提取物中分离到4个化合物,利用核磁共振及质谱技术将其鉴定为behenic acid (1)、himeic acid B (2)、secalonic acid A (3)和palmitic acid (4)。采用改进的Ellman比色法对分离的化合物进行活性检测,结果表明,himeic acid B (2)具有较强的乙酰胆碱酯酶抑制活性,其IC₅₀为205μg/mL（0.64mmol/L）。     

Comparison of two Pithecellobium gum exudates

Pithecellobium saman and Pithecellobium mangense exudate a yellow clear gum. The gums are both dextrorotatory. The acidity of these gums is very similar. Galactose and arabinose are the major neutral sugar constituents. The high content of rhamnose in P. saman gums contrasts with the absence of this methyl pentose in P. mangense gum. ¹³C-NMR spectra of the gums studied showed interesting structural features of these complex polymers.