Structural characterisation of the perovskite series SrxCa1−x−yNdyMnO3: Influence of the Jahn-Teller effect

The crystal structures of the perovskite manganites Sr_xCa_1−x−yNd_yMnO₃ with y=0.1 or 0.2 have been investigated using synchrotron X-ray powder diffraction. At room temperature the structures change from depending on the cation distribution, the different structures exhibiting different tilts of the MnO₆ octahedra. High temperature diffraction measurements demonstrate the presence of, an apparently continuous, isosymmetric I4/mcm to I4/mcm phase transition associated with the removal of long range orbital ordering. Heating the manganites to still higher temperatures results in a continuous transition to the cubic structure. A feature of such transitions is the continuous evolution of the octahedral tilt angle through the I4/mcm to I4/mcm phase transition. The orthorhombic structures do not exhibit orbital ordering and although a first order transition to the tetragonal structure is observed in Sr_0.4Ca_0.5Nd_0.1MnO₃, this high temperature tetragonal structure does not exhibit orbital ordering.     

Ultrasonic-assisted synthesis of Ce doped cubic–hexagonal ZnTiO3 with highly efficient sonocatalytic activity

Ce doped ZnTiO₃ as a novel catalyst with highly efficient and stable sonocatalytic activity was synthesized via an ultrasound-assisted sol–gel method using non-ionic surfactant Pluronic F127 as structure directing agent. Synthesized samples were characterized by using various techniques, such as XRD, TEM, SEM, EDX, ​XRF, BET, DRS, and PL, and their sonocatalytic activity studied toward degradation of p-Nitrophenol as a model organic compound. The synthesized mesoporous Ce/ZnTiO₃ had mixed cubic–hexagonal phase with large surface area (118.2 m² g^–1) and narrow pore size distribution (4.9 nm). The effects of cerium concentration, calcination temperature, and calcination time on the structure and the sonocatalytic activity of Ce/ZnTiO₃ were studied in detail. XRD results were suggested that the relation between the phase structure and the catalytic activity is considerable. Significant decrease in band-gap and PL intensity was observed with increasing the cerium concentration in the ZnTiO₃. It became clear that the Ce/ZnTiO₃ (0.81 mol%) shows high sonocatalytic activity compared with pure ZnTiO₃ and other Ce/ZnTiO₃ samples as well as commercial TiO₂-P25. The possible mechanism for the enhanced sonocatalytic activity of Ce/ZnTiO₃ was discussed in details. The electrical energy consumption was also considered during sonocatalytic experiments.     

不同温度处理的糠醇和聚苯胺树脂碳化产物结构基因变化的红外光谱研究

红外光谱测试结果表明糖醇树脂碳化过程中五员杂环上的碳氧键首先发生断裂,使氧脱出,而剩余的双烯链状结构再进行重排,形成六员稠环结构,并在此基础上发生脱氢反应生成石墨微晶。测试结果还表明聚苯胺树脂中的氮在碳化过程中的稳定性与其相连结的基团结构有密切关系。苯环相连的氮比与苯酚基相连的氮具有更强的抗热解稳定性。聚苯胺碳化产物中的氢主要分为两大类：一类是以碳氢键的形式存在;另一类则是以氮氢键的形式存在。碳化产物中的氢主要是在苯的稠环结构上以碳氢键形式存在。     

Far infrared spectra, conformational equilibria, vibrational assignments, ab initio calculations and structural parameters for 2-bromoethanol

The far infrared spectrum from 370 to 50 cm⁻¹ of gaseous 2-bromoethanol, BrCH₂CH₂OH, was recorded at a resolution of 0.10 cm⁻¹. The fundamental O–H torsion of the more stable gauche (Gg′) conformer, where the capital G refers to internal rotation around the C–C bond and the lower case g to the internal rotation around the C–O bond, was observed as a series of Q-branch transitions beginning at 340 cm⁻¹. The corresponding O–H torsional modes were observed for two of the other high energy conformers, Tg (285 cm⁻¹) and Tt (234 cm⁻¹). The heavy atom asymmetric torsion (rotation around C–C bond) for the Gg′ conformer has been observed at 140 cm⁻¹. Variable temperature (−63 to −100°C) studies of the infrared spectra (4000–400 cm⁻¹) of the sample dissolved in liquid xenon have been recorded. From these data the enthalpy differences have been determined to be 411±40 cm⁻¹ (4.92±0.48 kJ/mol) for the Gg′/Tt and 315±40 cm⁻¹ (3.76±0.48 kJ/mol) for the Gg′/Tg, with the Gg′ conformer the most stable form. Additionally, the infrared spectrum of the gas, and Raman spectrum of the liquid phase are reported. The structural parameters, conformational stabilities, barriers to internal rotation and fundamental frequencies have been obtained from ab initio calculations utilizing different basis sets at the restricted Hartree–Fock or with full electron correlation by the perturbation method to second order. The theoretical results are compared to the experimental results when appropriate. Combining the ab initio calculations with the microwave rotational constants, r₀ adjusted parameters have been obtained for the three 2-haloethanols (F, Cl and Br) for the Gg′ conformers.     

Binary polymorphic cocrystals: an update on the available literature in the Cambridge Structural Database,including a new polymorph of the pharmaceutical 1:1 cocrystal theophylline–3,4‐dihydroxybenzoic acid

An analysis and classification of the 2925 neutral binary organic cocrystals in the Cambridge Structural Database is reported, focusing specifically on those both showing polymorphism and containing an active pharmaceutical ingredient (API). The search was confined to molecules having only C, H, N, O, S and halogens atoms. It was found that 400 out of 2925 cocrystals can be classified as pharmaceutical cocrystals, containing at least one API, and that of those, 56 can be classified as being polymorphic cocrystals. In general, the total number of polymorphic cocrystal systems of any type stands at 125. In addition, a new polymorph of the pharmaceutical cocrystal theophylline–3,4‐dihydroxybenzoic acid (1/1), C₇H₈N₄O₂·C₇H₆O₄, is reported.     

New silicate-germanate Cs2Pb2[(Si0.6Ge0.4)2O7] from the series A2Pb2[B2O7], A = K,Cs, B = Si,Ge with the umbrella-like [PbO3]4- group

New silicate-germanate Cs₂Pb₂[(Si_0.6Ge_0.4)₂O₇] was synthesized in multi-components hydrothermal solution with 20 w.% concentration of Cs₂CO₃ mineralizer, pH = 10. Novel mixed compound belongs to the structure type A₂Pb₂[B₂O₇] previously indicated for powders with A = K, B=Si or Ge. Singe crystal structure determination of Cs₂Pb₂[(Si_0.6Ge_0.4)₂O₇] revealed the need for the correction of the space group of the earlier suggested structural model from P-3 to P-3m1, as well as for the splitting of the Pb-atom position. Umbrella-like groups [PbO₃]^4- are located between [(Si,Ge)O₄]^4- tetrahedra in mica-like honeycomb layers and play the role of tetrahedra with the Pb-lone-pair as the forth apex. Crystal chemical comparison revealed similarities and differences with the classical structure type of α-celsian Ba[Al₂Si₂O₈] with the tetrahedral double layer. Recently investigated nonlinear optical acentric borates Pb₂(BO₃)(NO₃) and Pb₂(BO₃)Cl are both related to this structural type, possessing umbrella-like groups [PbO₃]^4- and honeycomb layers [Pb₂(BO₃)]⁺ with the BO₃-triangles on the tetrahedral positions.     

TiO2掺杂调控聚苯乙烯微球折射率及胶体光子晶体结构色

胶体光子晶体由于其可调变的结构色在绿色印刷、印染等领域备受关注,而其光子带隙的宽度和位置由光子晶体的晶格参数(晶面间距,通常受胶体微球尺寸影响)和介质的折射率决定。现有人工胶体光子晶体主要基于SiO_2和高分子(如聚苯乙烯(PS)等)微球的组装制备,由于胶体微球材质种类有限,折射率调控受限,因而目前调控胶体光子晶体结构色主要靠改变胶体微球的尺寸来实现。本文首先制备高折射率(2.6)的TiO_2纳米晶,在乳液聚合制备单分散的PS(折射率1.6)微球过程中,将所制备的TiO_2纳米晶掺杂于PS微球中,通过TiO_2的掺杂量有效调控胶体微球的折射率,进而实现胶体光子晶体的结构色调控。以多色胶体光子晶体微球的水溶液为墨水,采用彩色喷墨打印技术打印了电脑设计的光子晶体彩画。本文发展的光子晶体结构色调控新技术拓展了胶体光子晶体的应用。     

Synthesis,X-ray crystal structure and DFT studies of cobalt(II) and vanadium(V) complexes with N,N,O-tridentate aroyl-hydrazone based ligand

A new aroyl-hydrazone, 2-pyridine carboxaldehyde-derived hydrazone ligand and its cobalt(II) (1) and vanadium(V) (2) complexes were prepared. The structures of these compounds were investigated using elemental analysis, spectral (IR, UV), and X-ray diffraction measurements. The electrochemical properties of the complexes were studied by cyclic voltammetry. The hydrazone ligand acted as tridentate and coordinated to vanadium and cobalt via N-imine, N-pyridine, and O-benzohydrazide atoms. The Co(II) complex crystallizes in the monoclinic system, space group P2₁/c, and has a binuclear structure. Chloride ions behave as the linking bridge and a tridentate hydrazine ligand HL and water as the terminal capping ligands. The central Co(II) ion has distorted octahedral geometry. The vanadium(V) complex crystallizes in the monoclinic crystal system, space group P2₁/n, and can be described as having highly distorted trigonal-bipyramidal coordination. The geometries and electronic properties of the complexes were also obtained using DFT and TD-DFT calculations.     

Studies on chemistry and immuno‐ modulating mechanism of a glycoconjugate from Lycium barbarum L.

The detailed structure of an O‐glycan derived from the fruit of Lycium barbarum L. was elucidated based on glycosidic linkage analysis, complete and partial acid hydrolysis, ¹H‐NMR and ¹³C NMR spectroscopy. According to the experiments, the carbohydrate was in the form of polysacchride (arabinogalactan) chains with highly branched 3, 4‐galactans and terminal arabinofuranosyl substituents. The immuno‐modulating mechanism of glycoconjugate and its glycan were investigated using tritium thymidine incorporation assay, flow cytometry assay and electrophoretical mobility shift assay (EMSA). The results suggested that the immunoactive components of the fruit of Lycium barbarum L. could enhance the splenocyte proliferation in normal mice and the effects of glycan chain were stronger than those of glycoconjugate. The target cell was most likely to be B‐lymphocyte, on which existed receptor binding site acting with the glycan. In addition, the immuno‐stimulatory effect of glycoconjugate (LbGp4) and its glycan (LbGp4‐OL) was associated with activating the expression of nuclear factor KB (NF‐KB) and activator protein 1 (AP‐1).     

The first total synthesis and structural determination of antibiotics K1115 B1s (alnumycins)

K1115 B₁, isolated from the broth of Streptomyces species, was found to be a mixture of stereoisomers. Authors synthesized all stereoisomers of K1115 B₁ by convergent synthesis coupling a rhamnose derivative, an isobenzofuranone, and a chiral tetraol. Comparison of ¹H NMR spectra and optical rotations made it clear that the absolute structures of K1115 B_1α (the major isomer) and K1115 B_1β (the minor isomer) were (1R, 17S)- and (1R, 17R)-configurations, respectively. The optical rotations of the stereoisomers revealed that alnumycin, reported as the identical structure with K1115 B₁, might be another mixture of stereoisomers.