A rare porous zinc phosphonocarboxylate framework with high thermal stability and interesting structural transformation

A rare porous metal-phosphonocarboxylate framework with ultrahigh thermal stability over 500℃ was obtained, which can be transformed into three different cluster-based frameworks with the same CaF₂-type topology.     

NMR characterization of α- and β-mannopyranurono-2,6-lactones

Determining the stereochemistry at the anomeric position of glycosides is imperative in chemical synthesis. As for 1,2-cis-β-glycosides such as β-mannosides, ¹³C-¹H coupling constants, ¹J_CHs, are conventionally used when glycosides are in an ordinary chair conformation. In this work, we searched for appropriate criteria to determine the stereochemistry of products in a recently developed glycosylation reaction using 2,6-lactones. As a result, we found that α-glycosides exhibited vicinal coupling constants of around 3.0?Hz?at the anomeric proton, as well as a long-range coupling between protons at C-1 and C-5, whereas β-glycosides had coupling constants of 1.2?Hz?at most. These figures are expected to be useful for future assignments. In addition, the observations obtained from this study revealed the conformation of glycosides with a 2,6-lactone moiety.     

Anti-MRSA actinomycins D1-D4 from the marine sponge-associated Streptomyces sp. LHW52447

Actinomycins D₁?D₄ (1–4), four new D-type actinomycin analogues, were isolated from the fermentation broth of a strain of marine sponge-associated Streptomyces sp. LHW52447, together with actinomycin D (5). The structures of 1?4 were determined by a combination analysis of HRMS and NMR spectroscopic methods, and their absolute configurations of amino acids were determined by Marfey's analysis. Actinomycins D₁ (1) and D₂ (2) are the first two naturally occurring actinomycins with incorporation an oxazole unit into the central phenoxazinone chromophore. Both 1 and 2 showed more potent antibacterial activities against three strains of pathogenic methicillin-resistant Staphylococcus aureus (MRSA) with MIC values of 0.125–0.25?μg/mL than those of 3?5 with MIC values of 0.5–1.0?μg/mL, which suggested that the anti-MRSA activity might be enhanced by the incorporation of an additional oxazole unit. In addition, the cytotoxicity evaluation against WI-38 human diploid lung fibroblasts revealed that the incorporation of oxazole unit could decrease the cytotoxicity of actinomycins on human normal cells.     

Structural diversity in dinickel(II) complexes of thiosemicarbazones

2,6-Diformyl-p-cresol serves as a starting point for the generation of multidentate N/O/S chelating agents. Condensation with 4-(X-phenyl) thiosemicarbazide yields the pentadentate ligand having SNONS donor sequences, capable of holding two metal ions in close proximity. The ligands behave as mono/di/tri basic depending on the pH of the medium. Stereochemical diversity in the reaction product of such ligands with nickel(II) chloride at different pH is observed. Sterically demanding substituted ligands in association with various exogenous bridges dictate the geometry and coordination number of such complexes. The compounds were investigated by elemental analysis, molar conductivities, electronic spectra, IR, NMR, FAB mass spectra, TG-DTG, magnetic susceptibility measurements. Varieties of geometries such as square planar, square pyramidal, octahedral and square planar–square pyramidal are observed. Cryomagnetic data for the complexes (79–296 K) can be reproduced by an equation based on the Heisenberg model (H=−2JS₁S₂, S₁=S₂=1). The singlet–triplet splitting, J varies systematically with the coordination geometry about the Ni₂(SNONS) core, with the hydroxo bridged complex exhibiting the greatest degree of antiferromagnetic coupling. The coupling is somewhat weaker for the chloro-bridged complexes. None of the complexes have shown any appreciable antimicrobial activity.     

Structural phase transitions in BaV6O11

BaV₆O₁₁ was synthesized under high pressures and crystallizes in a structure closely related to magnetoplumbite. [V(1)O₆]-octahedra share common edges and form a Kagomé lattice normal to the hexagonal [0 0 1] direction. The layers are connected in the direction of c via trigonal [V(3)O₅]-bipyramids and [V(2)O₆]-octahedra, which share common faces. The Ba-atoms are incorporated into cavities of the vanadium oxide framework and are coordinated by 12 oxygen atoms in the shape of a dodecahedron.Three magnetic anomalies at approximately 250, 115 and 75 K were detected in this compound. All of them are accompanied by anomalies in the specific heat measurement. To characterize possible structural transitions and determine the response of the structure to the magnetic anomalies, single crystal X-ray diffraction studies were carried out in the temperature range from 293 to 80 K. At 250 K the compound undergoes a structural phase transition. The space group above the transition temperature is P6₃/mmc, at lower temperature the symmetry reduces to P6₃mc. For the refinements in P6₃mc an inversion twin model was used, this way accounting for the loss of the center of symmetry. The structural phase transition is characterized by a small displacement of the V(1)-atom (forming the Kagomé lattice) out of its central position in the octahedra. As a consequence part of the octahedral edges/angles are increased, while the opposite ones are decreased. One limiting surface of the octahedral sheet is corrugated, while the other one is smoothened with respect to the high-temperature structure. This deformation of the octahedral sheets leads to the corresponding geometrical changes in the other coordination polyhedra.The structural response to the magnetic anomaly at 115 K is weak and mainly observable in the geometric parameters concerning the [V(1)O₆]-octahedra and [V(3)O₅]-bipyramids. This may serve as a first indication that the corresponding central atoms play an important role in the mechanism of the magnetic phase transition.     

序列结构对液晶共聚酯性能的影响

本文通过熔融酯交换和Schottern-Baumann缩聚反应合成了两类组成相同而序列结构不同的基于对羟基苯甲酸、对苯二甲酸和二元酚的三元共聚酯,用热台偏光显微镜、DSC和X-射线衍射,较详细地研究了序列结构对液晶相类型、转变温度和固态结构等的影响。结果表明,无规共聚酯较规则共聚酯的熔化温度普遍降低;但序列结构的差异并不改变液晶相类型,规则共聚酯和无规共聚酯均为热致向列型液晶,两类共聚酯固态结构的差异可用结构单元的相似性进行解释。     

用核磁共振方法研究聚硅氧烷类液晶侧链的结构异构

<正> 近十多年来,侧链型液晶聚合物的研究日益活跃。研究结果表明,这类聚合物将作为新的功能材料,在化合物分离、信息存储和显示装置上得到实际应用。聚硅氧烷类侧链型液晶是迄今研究得最多,很有潜在实用价值的一种侧链型高分子液晶。它通常是用含中介基团的烯烃与聚甲基氢硅氧烷通过硅氢化反应制得的。文献中给出的反应式都可表示为:     

Structural Chemistry of Borophosphates,Metalloborophosphates, and Related Compounds

A concept for the classification of crystalline (metallo)borophosphates in terms of structural chemistry is proposed and the compounds known to date are classified in an overview. Similarities and differences with (alumo)silicates and Liebau's classification are discussed with respect to the observation that the different borate and phosphate complexes are not interconnected arbitrarily in borophosphates. By combination and extension of existing concepts for silicates and borates a hierarchical system based on oligomeric building units has been developed. The observed connection rules are rationalized and the strong influence of the composition on dimensionality and structural motifs of the formed anions is pointed out. Likewise the effect of OH groups is taken into account by grading anions according to the degree of protonation (ratio O:OH). A general distinction is made between tetrahedral and mixed coordinated borophosphates. Metalloborophosphates are treated separately as special cases of borophosphates. Finally, anion‐substituted compounds, border cases, and borate‐phosphates complete the overview.     

Isolation,purification and structural characterization of a water-soluble polysaccharide HM41 from Halenia elliptica D. Don

A water-soluble polysaccharide, HM_(41), was obtained from Halenia elliptica D. Don by acidic ethanol fractionation and gel filtration. Its homogeneity was confirmed by chromatography using multiple systems. HM_(41) was composed of rhamnose(Rha), arabinose(Ara), xylose(Xyl), mannose(Man),galactose(Gal), glucose(Glc) with a molar ratio of 1.0:5.5:1.8:3.0:9.4:21. The average molecular weight of HM_(41) was approximately 1.17 * 10~4. Periodate oxidation, Smith degradation, methylation and GC, IR,NMR, XRD, GC–MS analysis were used for the structural analysis of HM_(41). Its main chain was composed mainly of β-(1→4)Gal, β-(1→4)Glc and β-(1→6)Glc. β-(1 →4)Gal were substituted at 6-O and on average there were 14 branches among 23 main chain residues;(1→ 4)Glc had no branch;(1→6)Glc were substituted at 3-O and on average there were 9 branches among 14 main chain residues. The side chain was composed of(1→3,6)-Rha,(1→4)/(1→5)-Ara,(1 →4)/(1→5)-Xyl,(1→4,6)-Man and(1→2)-Glc. The terminal residue was composed of Ara, Xyl, Man, Gal, and Glc. Then, we demonstrated that HM and HM_(41) had strong scavenging activities in vitro hydroxyl. Overall, HM and HM_(41) may have potential applications in the antioxidants for medical and food industry.