Exploring the Chemistry of Non-sticky Sugars: Synthesis of Polyfluorinated Carbohydrate Analogues of d-Allopyranose

There is a growing interest in the preparation of polyfluorinated carbohydrates. A limited number of fluorohexopyranosides have been used in biological investigations because of the synthetic challenge they present. Hence, we report the synthesis of fluorinated homodimer, fluorodisaccharides, C-terminal fluoroglycopeptides, lipoic acid fluoroglycoconjugate and trifluoroallopyranoside derivatives functionalized at C-6. Our strategy uses levoglucosan as inexpensive starting material and facilitates an approach to complex carbohydrate analogues with multiple C−F bonds. The challenge of our synthetic route centered around an efficient preparation of crucial 1,6-anhydro-2,4-dideoxy-difluoroglucopyranose and focused on achieving a difficult glycosylation of the trifluoroallopyranose donor. The results clearly highlight challenges related to the preparation of polyhalogenated complex organic molecules and pave the way to access novel medically relevant tools.     

Stable complex formation with boric acid in pyrolysis of levoglucosan in acidic media

The influence of boric acid or phenylboronic acid on thermal conversion of levoglucosan in acidic sulfolane was studied. Although levoglucosan was converted to levoglucosenone, furfural and 5-hydroxymethyl furfural (total yield: 40 mol%) at 200 °C in sulfolane containing 0.1 wt% H₂SO₄, addition of boric acid enormously lowered the yields of these, and instead caused the formation of a stable complex in more than 70 mol% yield. Thus, boric acid substantially suppressed the acid-catalyzed dehydration and formation of furfurals from levoglucosan through complex formation. From the ¹H NMR spectrum, the chemical structure of this complex was confirmed as -d-glucofuranose cyclic 1,2:3,5-bisborate, which was readily hydrolyzed quantitatively to glucose by the addition of water. Phenylboronic acid also exhibited similar influences.     

High-performance anion-exchange chromatography–mass spectrometry method for determination of levoglucosan, mannosan, and galactosan in atmospheric fine particulate matter

Biomass burning has a strong influence on the atmospheric aerosol composition through particulate organic, inorganic, and soot emissions. When biomass burns, cellulose and hemicelluloses degrade, producing monosaccharide anhydrides (MAs) such as levoglucosan, mannosan, and galactosan. Therefore, these compounds have been commonly used as tracers for biomass burning. In this study, a fast water-based method was developed for the routine analysis of MAs, based on high-performance anion-exchange chromatography with electrospray ionization mass spectrometry detection. This method combines simple sample preparation, fast separation, and the advantages of the selective detection with MS. Analysis run was optimized to the maximum separation of levoglucosan, mannosan, and galactosan with 15-min analysis. The validation results indicated that the method showed good applicability for determination of MA isomer concentrations in ambient samples. The limit of detection was 100 pg for levoglucosan and 50 pg for mannosan and galactosan. Wide determination ranges enabled the analysis of samples of different concentration levels. The method showed good precision, both for standard solutions (3.9–5.9% RSD) and for fine particle samples (4.3–8.5% RSD). Co-elution of internal standard (carbon-13-labeled levoglucosan) and sugar alcohols with levoglucosan decreased the sensitivity of levoglucosan determination. The method was used to determine the MA concentrations in ambient fine particle samples from urban background (Helsinki) and rural background (Hyytiälä) in Finland. The average levoglucosan, mannosan, and galactosan concentrations were 77, 8.8, and 4.2 ng?m^?3 in Helsinki (winter 2008–2009) and 17, 2.3, and 1.4 ng?m^?3 in Hyytiälä (spring 2007), respectively. The interrelation of the three MA isomers was fairly constant in the ambient fine particle samples.     

左旋葡聚糖的制备与在生物技术领域的应用

左旋葡聚糖(LGA)作为一种极具潜力的新糖源,既可以加酸水解为葡萄糖后间接用于微生物发酵,也可以被真菌或细菌甚至构造的基因工程菌直接代谢,目前已经在发酵上展现出良好的应用前景。此外,LGA还可作为碳源,生产生物乙醇、丁二酸等。目前制备LGA普遍采用生物质热解法,该方法存在能耗高、产率低、产物难以提取等缺点,应努力发展在溶剂体系中分解纤维素制备LGA的方法以提高产率。今后的研究应致力于开发微生物代谢LGA的新过程、新方法、新菌种,为LGA的高效利用提供坚实基础。     

Quantitative Determination of Carbohydrates in Solution via a Reduction/Permethylation Technique

Abstract

A reduction/permethylation technique has been developed for the quantitative gas Chromatographie analysis of anhydrosugars, monosaccharides, and disaccharides. All derivatizations are carried out in the same vial, and transfers are not necessary until recovery of the permethylated derivatives. The reaction scheme is extremely simple and offers improved accuracy over standard GC carbohydrate analysis protocols. Emphasis is placed on quantitative compound recovery, and relative response factors are presented for several carbohydrates. The sodium hydroxide/methyl iodide permethylation reaction has also been shown to be a viable replacement for standard dimsyl anion procedures utilized for methylation analysis of polysaccharides. Application of the reduction/permethylation sequence to the analysis of the hydrolyzate resulting from the dilute sulfuric acid hydrolysis of cellulose demonstrates that reversion products account for a considerable amount of the glucose losses, with levoglucosan, 1, 6-anhydro-β-D-glucofuranose, isomaltose, and gentiobiose predominating.     

High performance thin layer chromatography determination of cellobiosan and levoglucosan in bio-oil obtained by fast pyrolysis of sawdust

In this work, high performance thin layer liquid chromatography (HTPLC) is applied to the determination of sugars in fast pyrolysis liquids (bio-oil) and fractions thereof. The proposed procedure allows the separation of anhydrosugar levoglucosan and cellobiosan, as well as glucose, arabinose, xylose and cellobiose. Pre-treatment and derivatization of samples are not necessary and volatile compounds present in bio-oil do not interfere with sugar analysis. The detrimental effect of the complex bio-oil matrix on columns and detector lifetime is avoided by using disposable HTPLC plates. Prior screening of glucose, present especially in aged and aqueous bio-oil fractions, is required to quantify cellobiosan without interference. Concentrations of levoglucosan and cellobiosan in bio-oil samples obtained from Pinus radiata sawdust were ranged between 1.27-2.26% and 0.98-1.96% respectively, while a bio-oil sample obtained from native wood contained a higher levoglucosan concentration.     

Zirconium(IV) chloride catalyzed new and efficient protocol for the selective cleavage of p-methoxybenzyl ethers

A highly selective and efficient method for the unmasking of p-methoxybenzyl (PMB) ethers and esters has been developed by use of 20 mol % of zirconium(IV) chloride as Lewis acid in acetonitrile. The present method is very fast, and the conditions are tolerable to a variety of acid/base-sensitive protecting groups and substrates such as carbohydrates, terpenes, and amino acids. The products are obtained in good to high yields.     

Flame retarding of wood by impregnation with boric acid - Pyrolysis products and char oxidation rates

The pyrolysis of fir wood impregnated with boric acid (0-5.4%) has been investigated for heating temperatures of 650 and 800 K by examining the yields of char, water, permanent gases (CO₂, CO, CH₄) and total organic products (together with 32 compounds). The yields of the last product class continuously decrease to the advantage of char and water, but the most significant modifications occur for acid contents below 2%. The formation of levoglucosan (with 2-acetylfuran, 5-methyl-2-furaldehyde and other minor species) first and levoglucosenone (with 2-furaldehyde) afterwards is favoured, whereas other compounds generated from the holocellulosic (hydroxyacetaldehyde, hydroxypropanone, acetic acid and minor carbohydrates) and lignin (phenols, cresols) fractions generally decline. Conversion times become longer and volatilization rates are reduced. The oxidation characteristics of char have been studied by means of thermogravimetric analysis and interpreted according to a three-step reaction mechanism. The boric acid treatment lowers the activation energy and reaction order of the most important step (145 versus 226 kJ/mol and 1.2 versus 0.86, respectively) which also shows lower rates and is slightly delayed.     

Product distribution from fast pyrolysis of glucose-based carbohydrates

Carbohydrates are the major constituents of biomass. With the growing interest in utilizing bio-oil obtained from fast pyrolysis of biomass for fuels and chemicals, understanding the carbohydrate pyrolysis behavior has gained particular importance. The chemical composition of the bio-oil is an important consideration for its upstream and/or downstream processing. Though the classification of pyrolysis products into overall tar, char and gaseous fraction has evolved as a standard; detailed knowledge of the chemical constituents that determine the quality of bio-oil has received little attention. Furthermore, the speciation arising from primary and secondary reactions has been rarely distinguished. In this study the product distribution arising from the primary reactions during 500 °C fast pyrolysis of several mono-, di- and polysaccharides is studied with the help of micro-pyrolyzer. The study suggests that levoglucosan and the low molecular weight compounds are formed through competitive pyrolysis reactions rather than sequential pyrolysis reactions. It is also shown that the orientation or the position of glycosidic linkages does not significantly influence the product distribution except with 1,6-linked polysaccharide, which showed considerably less formation of levoglucosan than other polysaccharides.     

微机模拟计算各种类型酸的滴定曲线以及滴定误差

本文对三元酸滴定曲线的精确计算公式加以改进,设计出适合各种类型酸的滴定曲线和滴定误差的模拟计算程序,通过在Rainbow-100机上运行,计算结果与文献报道相符。此法简单、快速,对选择滴定条件,优化实验方法具有很重要的应用价值。     

Improved production of levoglucosan and levoglucosenone from acid-impregnated cellulose via fast pyrolysis

Cellulose - In this research, the production of levoglucosan (LG) and levoglucosenone (LGO) was improved from acid-impregnated cellulose via fast pyrolysis. Thermogravimetric and kinetic analysis...     

Recognition of anionic carbohydrates by an artificial receptor in water

A tris-cationic artificial receptor 1 efficiently binds anionic carbohydrates even in aqueous solution as shown by NMR and UV titration experiments. Complex formation involves both ion pair formation and H-bonds to the sugar, explaining the preference for saccharides compared to simple anions and the observed selectivities among different sugars. [structure: see text]     

电位质子滴定与NEXAFS和XPS表征功能化多壁碳纳米管比较(英文)

Since the discovery of carbon nanotubes (CNT), this material has been recognized as an attractive catalyst support. CNT must be functionalized before use as a catalyst support and typically this involves oxidation. However, the functional group distribution on the CNT is very complex mixture of groups and varies with oxidation agent used. Here a simple acid-base titration is introduced to characterize the oxygen functionalized CNT. By comparing characterization with near-edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS) for both at the C and O K-edges, it can be demonstrated that potentiometric proton titration can be a fast and quantitative analysis for Brnsted acid functional groups on CNT.     

Determination of some carbohydrates with N-bromophthalimide and N-bromosaccharin

Two better titrimetric methods have been developed for determination of carbohydrates such as glucose, fructose, lactose and sucrose, and sugars present in honey and milk. They involve reduction of Cu(II) to Cu(I) by the carbohydrate concerned, and oxidative titration of the Cu(I) with a standard solution of N-bromophthalimide or N-bromosaccharin.     

Phosphate rock treatment with citric acid for the rapid potentiometric determination of fluoride with ion-selective electrode

A fast method for sample treatment of phosphate rock has been developed for the purpose of quantitative leaching (98-100%) of fluoride but less of the interfering cations such as iron and aluminum. Citric acid (0.5 M) was used to extract fluoride in 15-45 min. Leaching of iron and aluminum is minimal, and these ions are complexed with citric acid. The leaching method was optimized with respect to sample size, citric acid concentration, leaching time and temperature. The analysis was completed by the rapid determination of fluoride with ion-selective electrode. The proposed treatment method was applied to phosphate rock samples from Jordan and Morocco and yielded accurate results as compared to the standard steam distillation from strong acid solution followed by thorium nitrate titration.     

Differential electrolytic potentiometric titration method for the determination of ciprofloxacin in drug formulations

A simple and rapid differential electrolytic potentiometric titration method for the determination of ciprofloxacin was developed. The work is based on the fast complexation reaction between iron(III) and ciprofloxacin in a ratio of 1:3, respectively, in sulfuric acid media of 0.09 mol dm⁻³. Among the electrodes tested silver amalgam electrodes were found to be a suitable indicating system. By applying a current density of 0.5 μA cm⁻² to these electrodes and using iron(III) solution of 0.097 mol dm⁻³ as a titrant, normal titration curves were obtained. The method was successfully applied for the determination of ciprofloxacin in drug formulations as low as 4.0 ppm.     

Mass spectrometric behavior of levoglucosan under different ionization conditions and implications for studies of cellulose pyrolysis

Pyrolysis-mass spectrometric studies of cellulose indicate low abundances of levoglucosan in the product spectrum compared to the yield values determined in more conventional types of pyrolysis studies. To examine the reason for these conflicting observation, levoglucosan was examined under different ion source conditions and ionization modes to ascertain the relative contributions of thermal degradation and ionization fragmention to the low abundances of the levoglucosan molecular ion. Low-energy electron ionization using conventional sample volatilization and molecular-beam sampling is compared to chemical ionization using methane, isobutane, and ammonia as reagent gases, and to field ionization and desorption. The mass spectrometric fragmentation patterns under the various systems indicate that studies of cellulose pyrolysis underestimate the amount of levoglucosan formed due to ionization fragmentation and thermal rearrangement reactions in the ion source. Several peaks, including m/z 126 and 144, are dominated by the contribution from the fragmentation of levoglucosan.     

Determination of chloride in sulphuric acid by potentiometric mercurometric titration

The chloride content of concentrated sulphuric acid is determined by mercurometric titration in 80% v/v methanol medium, with a mercury pool as indicator electrode. The method is simple, fast, accurate and reasonably sensitive (limit of detection 4.5 μg/ml), and suitable for routine application.     

Rapid determination of magnesium in the presence of calcium and phosphate by titration with cdta

A method is presented for the accurate determination of magnesium in phosphate rock and phosphoric acid down to 0.03% magnesium oxide in the presence of 0–70% phosphorus pentoxide by titration with cyclohexanediaminetetraacetic acid (CDTA). Interference from heavy metals for which inaccurate empirical corrections have previously been made in the combined magnesium and calcium titration are linearly and unequivocally determined and subtracted from the combined titration. Magnesium oxide is determined in less than 20 min after sample digestion for Ca: Mg ratios from 1:9 to 850:1.     

用氟钽酸根指示电位滴定钽的新方法

A new potentiometric titration method for the determination of tantalum in sulfuric acid and hydrofluoric acid media is described. EMF's were monitored with a double-junction reference electrode and a flurortantalate ion selective indicator electrode made in this laboratory previously. Five titrants have been evaluated for the precipitation titration. CPC, BDTAC and TPA yield the highest precision and largest potentiometric breaks, then rank CETAB and Hyamine 1622 in turn. CPC is considered to be the most satisfactory owing to the most sharp end-point break yielded when 10^-^4M of Ta is titrated with it. The concentration of H2SO4 suitable for the titration is 0.18 to 1.8M and that of HF is 0.23 to 1.7M. The method is suitable for Ta content in the range of 0.5 to 150 mg with a coefficient of variation of 0.15% (9 results) for 20 mg of Ta. HCl, H3PO4, tartaric acid and (NH4)2C2O4 as wellas a large amount of Fe^3^+, Ni^2^+, Cr^3^+, WO2^-^4, Zr^4^+, La^3^+, Al^3^+, MoO2^-^4 and Nb^5^+ do not interfere, while ClO^-^4, H2O2 and BF^-^4 must be avoided. The method has been found to be very useful for the determination of Ta in steels and crystalline lithium tantalate. The results obtained are in good agreement with those of comparable methods. This method is very simple and provides a fast determination process.