乙酰化淀粉的塑化和性能研究

以乙酰化改性淀粉为基体,甘油为增塑剂,利用哈克旋转流变仪密炼制备热塑性乙酰化淀粉.实验结果表明制备热塑性乙酰化淀粉的甘油/乙酰化淀粉配比应大于30/100(W/W),且随甘油含量增加,热塑性乙酰化淀粉的脆性降低.动态机械热分析(DMTA)显示热塑性乙酰化淀粉包含富甘油和富淀粉两相,乙酰化淀粉和甘油为部分互溶.流变学分析显示淀粉分子间作用力非常强,表现为类固态行为.同时本文对材料的热稳定性进行了初步研究.     

Sorption of spruce O-acetylated galactoglucomannans onto different pulp fibres

Sorption of spruce acetylated galactoglucomannans (GGM) onto different pulps, among which unbleached and peroxide-bleached mechanical pulps, and unbleached and bleached kraft (BK) pulps, was studied as a means of understanding the retention of acetylated GGMs in mechanical pulping and papermaking. The fibre surface coverage of lignin and carbohydrates was estimated by X-ray photoelectron spectroscopy (XPS) or electron spectroscopy for chemical analysis (ESCA). GGM sorption was clearly favoured on kraft pulps. Hardly any differences in sorption were, however, observed between unbleached and BK pulps, even if the surface coverage of lignin was lower on the bleached pulp. Neither thermomechanical pulp (TMP) nor chemithermomechanical pulp (CTMP) manufactured from spruce sorbed any acetylated GGMs. Peroxide bleaching of the pulp did not increase sorption. Only CTMP produced from aspen sorbed some GGMs. The anionic charge of neither chemical nor mechanical pulps influenced GGM sorption.     

Specificity of an Aspergillus Niger Esterase Deacetylating Cellulose Acetate

A purified acetyl esterase (AE), isolated from a commercial enzyme preparation, released acetic acid from water-soluble and water-insoluble cellulose acetates (CAs), native and chemically acetylated xylan as well as acetylated starch. The AE specifically cleaved off the acetyl substituents from the C₂- and C₃-positions from CAs of DS <1.8 and left the acetyl substituents at the C₆-positions intact without degrading the polysaccharide. The activity of endoglucanase was enhanced by the presence of acetyl esterase, while the acetyl esterase derived no advantage from the presence of the endoglucanase; it was able to function independently.     

秸秆稀酸水解液的气相色谱／质谱法研究

在秸秆两步稀酸水解工艺中,用气相色谱/质谱(GC/MS)法对其水解液中的单糖成分进行测定,采用2%硼氢化钠的氨溶液将稀酸水解液中的单糖还原成糖醇,然后在甲基咪唑催化剂的作用下和乙酸酐在水相中直接反应生成乙酰化的糖醇,用二氯甲烷萃取后进行GC/MS测定.研究结果表明:秸秆稀酸水解液中有五种单糖,主要是木糖和葡萄糖,其次是阿拉伯糖、半乳糖和少量的甘露糖;利用此方法测定了一批秸秆稀酸水解液,得到了该秸秆稀酸水解过程的最佳的反应时间.该方法可快速、准确测定秸秆稀酸水解液中单糖的浓度,为水解工艺的研究提供一种有效的分析方法.     

Gold Nanoparticle Based Fluorescence Resonance Energy Transfer Immunoassay for the Detection of the Histone Deacetylase Activity using a Fluorescent Peptide Probe

A novel platform for detection of histone deacetylase (HDAC) activity has been developed using a gold nanoparticle based fluorescence resonance energy transfer (FRET) immunoassay. This strategy combined the acetylated fluorescent peptide probe with the anti-acetyl antibody functionalized Au NPs to measure the deacetylation activity of histone deacetylase sirtuin2. Enzymatic deacetylation of the acetylated peptide substrate was detected by a gold nanoparticle labeled anti-acetyl peptide antibody with the formation of the immunocomplex resulting in energy transfer between the fluorescent dyes and the nanoparticles. Due to the highly efficient fluorescence quenching of the gold nanoparticles, the proposed method shows a low background and favorable sensitivity. In addition, this approach can be applied to the evaluation of HDAC inhibitor activity. The proposed platform should facilitate the development of new assays for HDAC activity and other histone modifications.     

Preparation of linear oligosaccharides by a simple monoprotective chemo-enzymatic approach

A monoprotective approach, involving acetyl ester as unique protective group in oligosaccharides synthesis, has been developed. Starting from peracetylated monosaccharides and glycals, by using an efficient and selective chemo-enzymatic ‘one-pot’ strategy (a regioselective hydrolysis catalyzed by immobilized lipases followed by a chemical acyl migration), different carbohydrate acceptors, only protected with acetyl ester, can be achieved. If combined with the use of an acetylated glycosyl donor, the glycosylation reaction with these glycosyl acceptors leads to peracetylated oligosaccharides. These compounds can be directly used as intermediates for the synthesis of glycopeptides used as antitumoral vaccines and, at the end of the process, can be easily fully deprotected in only one step. Thus, these key building blocks have been successfully used in glycosylation reactions for an efficient construction of peracetylated disaccharides, such as the biological relevant lactosamine, in multigram scale. Subsequently, glycosylation with the 3OH-tetraacetyl-α-d-galactose, used as carbohydrate acceptor, allowed the synthesis of a peracetylated N-trisaccharidic precursor of the lacto-N-neo-tetraose antigen. Extending this strategy to a 3OH-di-acetyl galactal, one peracetylated precursor of the T tumor-associated carbohydrate antigen has been synthesized.This efficient approach, characterized by the use of the acetyl ester as only protecting group during all the synthetical steps expected, represents an easy and efficient alternative to the classical synthetic methods in carbohydrate chemistry that involve several protecting group manipulation.     

Novel ring A rearranged isomers with γ-lactone from the fruits of Aphanamixis grandifolia

Aphagranols A (1) and B (2), a pair of isomers with a novel limonoid carbon skeleton, were isolated from the fruits of Aphanamixis grandifolia. Their structures were determined by spectroscopic analyses and further confirmed by their unique acetylated derivative aphagranol C (3). The possible equilibrium system of the enol interconversion was presented using the polarizable continuum model (PCM). The absolute configuration of 3 was established via experimental and calculated ECD spectra comparison. The γ-lactone moiety in ring A system was first found in this class of limonoids.     

Preparative separation of minor saponins from Platycodi Radix by high-speed counter-current chromatography

Platycosides (PSs), the saponins found in the root of Platycodon grandiflorum (Jacq.) A. DC. (Platycodi Radix), are typically composed of oleanene backbones with two side chains; one is a 3-O-glucose linked by a glycosidic bond, and the other is a 28-O-arabinose-rhamnose-xylose-apiose linked by an ester bond. Minor saponins, acetylated isomers of the major saponin on either the 2' or 3' position of rhamnose, were isolated from Platycodi Radix using a multi-step process including high-speed counter-current chromatography (HSCCC) and preparative reversed-phase high-performance liquid chromatography (RP-HPLC). After the separation of the major components, the enriched minor saponin fraction was used for this study. A two-phase solvent system consisting of chloroform-methanol-isopropanol-water (3:2:2:3, v/v) was used for HSCCC. HSCCC separation of the enriched minor saponin fraction yielded 2'-O-acetylplatycodin D, 3'-O-acetylpolygalacin D, 2'-O-acetylpolygalacin and a mixture of 3'-O-acetylplatycodin D and polygalacin D. The mixture fraction from HSCCC separation was further purified by preparative RP-HPLC, giving 3'-O-acetylplatycodin D and polygalacin D at a purity of over 98.9%. The developed method provides the preparative and rapid separation of minor saponins in the crude extract of Platycodi Radix. To the best of our knowledge, this is the first on the separation of acetylated PSs by HSCCC.     

New Acetylated Flavonol Glycosides from Knoxia corymbosa

Two new diacetylated flavonol glycosides, kampferol-3-O-β-3“, 6“-diacetylglucopyrano-side and quercetin-3-O-β-3“, 6“-diacetylglucopyranoside were isolated from knoxia corymbosa. Their structures were elucidated by spectroscopic evidents.     

Mass Spectrometric Study of Acetylated Glycopyranosyl Azides

Introduction Glycosyl azides are useful, versatile intermediates for the synthesis of N-glyeosyl derivatives and other biologically important non-carbohydrate derivatives since the azido group can be introduced readily into aliphatic, aromatic and heterocyclic systems, and can be transformed into other functional groups and utilized for the synthesis of hetero-