Solid-phase oligosaccharide synthesis of a small library of N-glycans

Solid-phase oligosaccharide synthesis is based on a hydroxymethylbenzyl benzoate spacer linker which is connected to the Merrifield resin (1 P). Glycosylation was performed with O-glycosyl trichloroacetimidates of glucosamine, mannose, and galactose permitting chain extension (2e, 5e), branching (4b, 7b, 8b), and chain termination (3t, 6t, 9t) with the use of O-benzyl, O-benzoyl, and N-dimethylmaleoyl as permanent and O-fluorenylmethoxycarbonyl (Fmoc) and O-phenoxyacetyl (PA) as temporary protecting groups. The steps required on solid phase are i) glycosylation under TMSOTf catalysis, ii) selective cleavage of the temporary protecting groups, Fmoc with NEt3 and PA with 0.5 equivalents of NaOMe in CH2Cl2/MeOH, and iii) product cleavage from the resin with 4.0 equivalents of NaOMe in CH2Cl2/MeOH and following O-acetylation for convenient product isolation. Thus a highly successful synthesis of a small library of seventeen N-glycan structures was made possible comprising the N-glycan pentasaccharide core structure 53 and two further chain extended hexa- and heptasaccharide N-glycans with a glucosamine or a lactosamine residue, respectively, which is attached to one of the mannose residues of the core structure (56 and 59).     

Unexpected reactions of ferrocene acetal derived from tartaric acid with alkyllithium: competition between proton abstraction and nucleophilic attack

We wished to prepare planar chiral compounds by the lithiation of acetal 2-ferrocenyl-(4S,5S)-bis(methoxymethyl)-1,3-dioxolane (1) with butyllithium followed by the reaction with an electrophile. However, the desired products were not observed and two unexpected products, 1-ferrocenyl-1-pentanol (4) of the nucleophilic attack product and 2-ferrocenyl-4,5-dimethylene-1,3-dioxolane (5) of the proton abstraction product, were isolated. Because the nucleophilic attack on acetal carbon is rarely reported so far and both products 4 and 5 may have some potential uses in organic synthesis, these unexpected reactions are investigated in detail. The mechanisms of these reactions are discussed.     

Studies into the Early Degradation Stages of Cellulose by Different Iron Gall Ink Components

Selective fluorescence labelling of oxidized cellulose functionalities followed by GPC-MALLS was used to get a deeper insight into ink-induced degradation processes. As the method is very sensitive towards oxidation and molecular weight changes, slight variations at the very beginning of aging processes, e.g. during ink corrosion of cellulose, can be studied. Five different ink modifications were applied on model papers and underwent mild accelerated aging at 55 °C and cycling humidity (7 days) followed by a short period of static humid aging at 80 °C (2 days). Pure ink constituents like tannic acid or iron sulphate do not result in the same degree of oxidation or chain scission as complete inks. Balanced ink degrades paper more than single compounds, but less than unbalanced inks. Interestingly, some degradation occurs already during or shortly after the application process of unbalanced inks on paper. It could be demonstrated that this oxidation proceeded in a rather high Mw area, while the subsequent aging steps affected predominantly regions of shorter cellulose chains.     

Numerical Schemes for Linear and Non-Linear Enhancement of DW-MRI

We consider the linear and non-linear enhancement of diffusion weighted magnetic resonance images (DW-MRI) to use contextual information in denoising and inferring fiber crossings. We describe the space of DW-MRI images in a moving frame of reference, attached to fiber fragments which allows for convection-diffusion along the fibers. Because of this approach, our method is naturally able to handle crossings in data. We will perform experiments showing the ability of the enhancement to infer information about crossing structures, even in diffusion tensor images (DTI) which are incapable of representing crossings themselves. We will present a novel non-linear enhancement technique which performs better than linear methods in areas around ventricles, thereby eliminating the need for additional preprocessing steps to segment out the ventricles. We pay special attention to the details of implementation of the various numerical schemes.     

三氟丙基修饰的有机-无机杂化二氧化硅膜制备、氢气分离及水热稳定性能

以三氟丙基三甲氧基硅烷(TFPTMS)和1,2-双(三乙氧基硅基)乙烷(BTESE)为前驱体, 通过溶胶-凝胶法在酸性条件下制备三氟丙基修饰的有机-无机杂化SiO₂膜材料, 并深入研究三氟丙基修饰对溶胶粒径和疏水性能的影响以及膜材料的氢气渗透分离性能和长期水热稳定性. 结果表明三氟丙基已成功修饰到有机-无机杂化SiO₂膜材料中, 且随着TFPTMS修饰量的增加, 溶胶粒径有减小趋势, 膜材料的疏水性能逐渐提高. 当n(TFPTMS)/n(BTESE)＝0.6时, 溶胶平均粒径为2.11 nm, 膜材料对水的接触角达到111.6°±0.7°. H₂在修饰后膜材料中的输运主要遵循微孔扩散机理, 300 ℃时H₂的渗透率为8.86×10^-7 mol·m^-2·s^-1·Pa^-1, H₂/CO₂的理想分离系数达到5.4, 且当进气摩尔比例为1∶1时H₂/CO₂的双组分气体分离系数达到了4.82, 均高于Knudsen扩散分离因子(H₂/CO₂＝4.69), 膜材料呈现出良好的分子筛分性能. 膜材料在250 ℃及水蒸气摩尔含量为5%的水热环境中能稳定工作300 h以上.     

Finite groups with some pronormal subgroups

A subgroup H of finite group G is called pronormal in G if for every element x of G, H is conjugate to H ^x in 〈H, H ^x 〉. A finite group G is called PRN-group if every cyclic subgroup of G of prime order or order 4 is pronormal in G. In this paper, we find all PRN-groups and classify minimal non-PRN-groups (non-PRN-group all of whose proper subgroups are PRN-groups). At the end of the paper, we also classify the finite group G, all of whose second maximal subgroups are PRN-groups.     

染料分子固定基团-CN,-NH2,-OH,-COOH,-SH在ZnO(10-1 0表面吸附

采用基于第一性原理的密度泛函理论系统研究了染料分子中的-CN, -NH2, -OH, -COOH和-SH等5种固定基团在ZnO 表面的吸附, 分析了它们在ZnO 表面上的吸附机制. 结果表明：5种基团在ZnO 表面都发生了化学吸附, 其中-CN、-NH2和-OH发生了非解离吸附, -COOH和-SH则是表面解离吸附. 5种固定基团的吸附能分别是：-0.64 eV, -1.28 eV, -1.03eV, -1.21eV(-1.40 eV)和-1.14 eV. 综上所述, 以-COOH为固定基团的染料分子制备的染料敏化太阳能电池(DSSCs)具有更稳定的性能, 这为ZnO染料敏化太阳能电池的设计和应用提供了理论基础.     

Synthesis and Properties of New Fluorinated Polyimides Derived from an Unsymmetrical and Noncoplanar Diamine

A new unsymmetrical and noncoplanar diamine containing trifluoromethyl and trimethyl groups, 1,4‐bis(4‐amino‐2‐trifluoromethylphenoxy)‐2,3,5‐trimethylbenzene ( 2 ), was synthesized using 2,3,5‐trimethylhydroquinone and 2‐chloro‐5‐nitrobenzotrifluoride as starting materials. A series of fluorinated poly(ether imide)s (PEIs) ( 4a–4d ) were prepared from diamine 2 with four aromatic dianhydrides via a one‐step high‐temperature polycondensation procedure. The obtained PEIs were readily soluble in most organic solvents and could be solution‐cast into flexible and strong films. The resulting thin films exhibited light color and good optical transparency with a cutoff wavelength of 356–376 nm. They also displayed good thermal stability with glass transition temperatures (T_g) above 281°C, 10% weight loss temperatures in the range of 482–486°C, and the weight residue more than 55% at 800°C in nitrogen. Moreover, they revealed low dielectric constants (2.77–2.93 at 1 MHz) and low moisture absorptions (0.41%–0.57%).