Improved synthesis of disaccharides with Escherichia coli β-galactosidase using bio-solvents derived from glycerol

A noticeably increase in activity, keeping total regioselectivity was found in the synthetic behaviour of Escherichia coli β-galactosidase in glycerol-based solvents using a 1:7 molar ratio of donor (pNP-β-Gal): acceptor (GlcNAc). Yields of up to 97% of β(1→6) with different solvents were found. These reactions take place without noticeable hydrolytic activity and with total regioselectivity, representing a considerable improvement over the use of aqueous buffer or conventional organic solvents. There is a clear dependence of the catalytic results on the solvent structure, which is analysed in terms of polarity and hydrophobicity.     

Selective recognition of the ditopic trimethylammonium cations by water-soluble aminocalix[4]arene

In this Letter, the role of the depth of the cavity in the recognition processes of the guests by the hosts has been investigated. The hosts 2, 3 interact with both the cationic function and the aromatic moiety in the guests 5, 6 but with a slight preference for the cationic functions. The host 4 selectively recognizes the trimethylammonium functions of the guests 5 and 6. However, the host 1 selectively recognizes the aromatic moiety of the ditopic trimethylammonium guests 5 and 6. The recognition and orientation of the guest in the cavity of the host are directly dependent on the depth of the hydrophobic cavity of the host.     

Optical and electrochemical DNA nanobiosensors

In the past two decades, nanoscale advanced materials have been explored for biosensing molecules, so new horizons have opened up for identifying and quantifying biomolecules, and possible early diagnosis of diseases.DNA nanobiosensors show promise. This article provides an overview on their optical and electrochemical aspects. We discuss recent progress in this field, describing basic concepts of molecular beacons and quantum dots as optical nano-imaging systems. Also, carbon nanotubes provide a platform for development and advancement of electrochemical DNA nanobiosensors, which are increasingly being implemented as robust tools for detection in biomedical sciences.     

Recent developments in synchrotron vacuum ultraviolet photoionization coupled to mass spectrometry

In recent years, increasing attention has been paid to “soft” photoionization (PI), which will potentially become a standard, universal ionization method. Tunable synchrotron vacuum ultraviolet (SVUV) light, a quasi-continuous light with good energy resolution and high photon flux, has proved an ideal source for “soft” PI in various research fields (e.g., combustion chemistry and molecular imaging).This review focuses on combinations of SVUV light with commonly used techniques (e.g., molecular-beam sampling, laser desorption, ion desorption, and thermal vaporization). These couplings have successful applications in flame chemistry, organic analysis, chemical imaging and aerosol mass spectrometry.     

Pervaporation for separating benzene/cyclohexane mixture by P(AA-MA) copolymer membranes

P(AA-MA)copolymers composed of acrylic acid and methyl acrylate with different molecular weights and sequence structures were synthesized by combination of ATRP and selective hydrolysis.These copolymers were used as membrane materials to separate benzene/cyclohexane mixture by pervaporation.The effects of molecular weight and sequence structure of the copolymers on the pervaporation performance were investigated in detail.For the random copolymers,the permeate flux decreased rapidly with the increasing of molecular weight.The separation factor was also influenced by the molecular weight,which was changed from no selectivity to cyclohexane selectivity with increasing the molecular weight.Contrarily,the block copolymer membrane showed good benzene selectivity with separation factor of 4.3 and permeate flux of 157 g/(m~2h)to 50 wt%benzene/cyclohexane mixture.     

Structural phase transition and magnetic properties of layered organic-inorganic hybrid compounds: p-Haloanilinium tetrachlorocuparate(II)

Compounds of the general formula A₂CuCl₄, (where A = 4-fluoroanilinium (1) and 4-chloroanilinium (2)) were prepared, structurally characterized and their thermal and magnetic properties studied. These compounds have a layered structure, distorted perovskite, where layers of CuCl₄²⁻ are sandwiched between a 4-haloanilinium cation bilayer. A single crystal X-ray diffraction study on (4-fluoroanilinium)₂CuCl₄, (1), shows that it crystallizes in the monoclinic P2₁/c space group with cell dimensions a = 15.5113(5) Å, b = 7.3788(2) Å, c = 7.0929(2) Å, β = 99.004(2)°, volume 801.81(4) Å³ at 150 K. Compound 2, (4-chloroanilinium)₂CuCl₄, crystallizes isostructurally to 1 at RT, but at 150 K it adopts the Pccn space group. This structural transition for 2 is reversible, and has been observed using Differential Scanning Calorimetric (DSC) measurements. The dc-magnetic studies using a SQUID magnetometer suggest that both compounds are soft ferromagnets and show an onset of long range magnetic ordering below 9 K. The ac-susceptibility measurements confirm the presence of this ferromagnetic ordering in both the compounds.     

二芳基三嗪类HIV-1逆转录酶抑制剂的分子对接及3D-QSAR研究

对40个二芳基三嗪类HIV-1逆转录酶抑制剂进行了分子对接研究,结果表明,2个疏水性芳香取代基团与结合口袋底部形成的疏水和范德华相互作用、三嗪环母核及其R4取代基与结合位点产生的氢键和静电作用以及R4取代基与袋口形成的空间位阻效应是影响该系列化合物活性的重要因素.根据对接优势构象进行分子叠合和比较分子相似性指数分析(C...     

Feasibility of high-resolution continuum source molecular absorption spectrometry in flame and furnace for sulphur determination in petroleum products

For the first time, high-resolution molecular absorption spectrometry with a high-intensity xenon lamp as radiation source has been applied for the determination of sulphur in crude oil and petroleum products. The samples were analysed as xylene solutions using vaporisation in acetylene-air flame or in an electrothermally heated graphite furnace. The sensitive rotational lines of the CS molecule, belonging to the ?ν = 0 vibrational sequence within the electronic transition X¹∑⁺ → A¹П, were applied. For graphite furnace molecular absorption spectrometry, the Pd + Mg organic modifier was selected. Strong interactions with Pd atoms enable easier decomposition of sulphur-containing compounds, likely through the temporal formation of Pd_xS_y molecules. At the 258.056 nm line, with the wavelength range covering central pixel ± 5 pixels and with application of interactive background correction, the detection limit was 14 ng in graphite furnace molecular absorption spectrometry and 18 mg kg⁻¹ in flame molecular absorption spectrometry. Meanwhile, application of 2-points background correction found a characteristic mass of 12 ng in graphite furnace molecular absorption spectrometry and a characteristic concentration of 104 mg kg⁻¹ in flame molecular absorption spectrometry.The range of application of the proposed methods turned out to be significantly limited by the properties of the sulphur compounds of interest. In the case of volatile sulphur compounds, which can be present in light petroleum products, severe difficulties were encountered. On the contrary, heavy oils and residues from distillation as well as crude oil could be analysed using both flame and graphite furnace vaporisation. The good accuracy of the proposed methods for these samples was confirmed by their mutual consistency and the results from analysis of reference samples (certified reference materials and home reference materials with sulphur content determined by X-ray fluorescence spectrometry).     

分子氧无溶剂催化氧化法合成对叔丁基苯甲酸

在常压、无溶剂条件下,以氧气为氧化剂,醋酸钴为催化剂,研究了催化氧化对叔丁基甲苯(PTBT)合成对叔丁基苯甲酸(PTBA)的反应.考察了催化剂与PTBT质量比、促进剂类型、促进剂用量、氧气流速、反应温度、反应时间等因素对反应的影响,确定了优化的反应条件.在PTBT用量30mL、催化剂用量0.7g、乙醛促进剂用量0.3m...