Photochemically catalyzed reaction of ochratoxin A with D- and L-cysteine

The photolysis (>300 nm) of ochratoxin A (OTA, N-[[(3R)-5-chloro-8-hydroxy-3-methyl-1-oxo-7-isochromanyl]carbonyl]-3-phenyl-L-alanine, 1) in the presence of excess (2 and 12 molar equiv) cysteine (CySH) has been investigated and found to yield sulfur adducts 5 and 6 that are characterized by liquid chromatography-mass spectrometry and 1H-NMR spectroscopy. The adduct 5 was ascribed to the Michael addition conjugate resulting from covalent attachment of CySH to the ochratoxin quinone (4) generated by photooxidation of OTA. This species was also formed by photolysis of a synthetic sample of the hydroquinone of OTA (ochratoxin hydroquinone, 3) in the presence of 12 equiv L-CySH. The conjugate 5 derived from photolysis of 3 with L-CySH was used for 1H-NMR analysis. The sulfur adduct 6 was the major species detected from covalent attachment of CySH to photoactivated OTA, and it resulted from direct displacement of the OTA Cl atom by CySH. The implications of the cysteinyl adducts to the in vivo toxicity of OTA are discussed, with particular emphasis given to conjugate 5, as products from the photooxidative pathway may be of relevance to the nephrotoxic properties of OTA.     

Characterization of the near-surface region of glass implanted with light elements

Ion-implantation of glasses modifies physical properties such as density, refractive index, surface stress, hardness, and chemical durability. Compositional changes can also occur due, e.g., to radiation-enhanced diffusional losses of alkali ions, crystallization, phase separation, and H incursion. Quantitative depth-profiling of the implanted ion distributions and changes in elemental constituent concentrations can be accomplished by means of ion-beam analysis. Elastic recoil detection (ERD) is used for light elements (H to N) while Rutherford backscattering (RBS) is utilized for larger masses. Chemical information from X-ray photoelectron spectroscopy (XPS) supplements the compositional information obtained from ERD and RBS to supply detailed data about the surface region or in-depth after sputter etching. These techniques, have been utilized, in combination with optical spectroscopy, to study the effects of ion-implanted H, Li, B, N, O, and Si on fused silica. Evidence has been obtained for the chemical incorporation of these elements in the silica network. The results allow deeper understanding of the relationship of structure to implant incorporations, as is important for the application of ion implantation wave guide formation in optoelectronic applications.     

EPR Studies of Tl0.5Pb0.5Sr1.6Ba0.4CaCu2?xRuxO7?δ Superconductor

Bulk superconducting samples of type Tl_0.5Pb_0.5Sr_1.6Ba_0.4CaCu_2−x Ru _x O_7−δ, (Tl, Pb)/Sr-1212, with 0.0 ≤ x ≤ 0.525 were prepared by the conventional one-step solid-state reaction technique. The prepared samples were investigated using X-ray powder diffraction, electrical resistivity and electron paramagnetic resonance (EPR) measurements. Enhancement of the phase formation, superconducting transition temperature T _c and hole carriers concentration P was observed up to x = 0.075. For x > 0.075, a reverse trend was observed. EPR spectra were measured at different temperatures (120–290 K) for all prepared samples. The number of spins N participating in the resonance and the paramagnetic susceptibility χ were calculated as a function of both Ru-content and temperature. N and χ increased as the Ru-content increased. A linear relationship between logN and 1/T was established, from which the activation energy E _a was calculated as a function of the Ru-content. The temperature dependence of χ was fitted according to Curie–Weiss type of magnetic behavior. Curie constant C, Curie temperature θ, the effective magnetic moment μ and the electronic specific heat γ were estimated as a function of the Ru-content.     

Effect of IR laser radiation on the structure and optical properties of PC-PBT/Pd polymer nanocomposite films

ABSTRACT

Bayfol (PC-PBT blend ?lm) is a class of polymeric solid-state nuclear track detector which has a lot of applications in several radiation detection ?elds. It is a bisphenol-A polycarbonate PC blended with polybutylene terephthalate PBT. Bayfol/Palladium (PC-PBT/Pd) nanocomposite films have been deposited using the molding technique. It is worth mentioning that this report is almost the first one dealing with the topic of the changes of physical properties of Bayfol/Pd nanocomposite due to laser exposure. Samples from PC-PBT/Pd (5?wt%) nanocomposite were exposed to IR-pulsed laser of 5-W power, capable of producing 2000 pulses per second with pulse duration of 200?ns at 904?nm. The laser fluences were in the range 2–25?J/cm². The resultant modi?cations in the exposed nanocomposite samples have been studied as a function of fluence using different characterization techniques such as X-ray diffraction (XRD), UV spectroscopy and color difference studies. The results indicate the proper dispersion of Pd nanoparticles in the PC-PBT matrix that causes a strong intermolecular interaction between Pd and PC-PBT, resulted in an increase in refractive index and the amorphous phase. Also, it is found that the laser exposure reduces the optical energy gap that could be attributed to the increase in structural disorder of the exposed PC-PBT/Pd nanocomposites due to crosslinking. Further, the color intensity ΔE, which is the color difference between the exposed samples and the non-exposed one, was increased with increasing the laser fluence, convoyed by a significant increase in the green and yellow color components.     

Structure of potassium germanophosphate glasses by X-ray and neutron diffraction. Part 1: Short-range order

It has been reported that the addition of K₂O or P₂O₅ to binary germanate glasses increases the Ge−O coordination numbers (N_GeO). The present work describes X-ray and neutron diffraction studies aimed at clarifying the concomitant effects of both oxides on the structures of ternary K₂O-GeO₂-P₂O₅ glasses. The Ge−O coordination numbers obtained range from 4.2 to 5.1, less than what is predicted according to a model which assumes all oxygen atoms form network bridges similar to those found in the related crystal structures. This implies that the glass structures must include terminal oxygen sites, likely associated with the PO₄ tetrahedra, that are neutralized by coordinating K⁺ ions. The shapes of the high resolution first-neighbor diffraction peaks do not indicate distinctly different species of P−O and Ge−O bonds. The model for the increase of N_GeO which is based on an increase of the fraction of GeO₆ units, at the expense of GeO₄ units, is supported by the analysis of the two main components of the Ge−O peak used in the fits. However, the existence of a GeO₅ fraction cannot be excluded from the present data sets. A linear relation between the total Ge−O coordination numbers and mean Ge−O distances exists, assuming end members of units GeO₄ and GeO₆ with bond lengths of ∼0.175 and ∼0.190 nm, respectively.     

昆虫信息素研究III: 拟蚜虫警戒素的研究

合成了一系列碳数为十五和十四的倍半萜类蚜虫警戒素,并进行了生物活性测定,从中筛选有效化合物.     

Properties and structure of cesium phosphate glasses

A series of Cs-phosphate glasses, xCs₂O(1−x)P₂O₅, where 0?x?0.60, were prepared. The glass transition temperature (T_g) decreases with the initial addition of Cs₂O to P₂O₅, from 637 K at x=0 to 472 K at x=0.16. There is little change in T_g with further additions of Cs₂O up to x=0.60. The ³¹P magic angle spinning nuclear magnetic resonance (MAS NMR) spectra show that Cs₂O additions systematically convert the cross-linked ultraphosphate network of ν-P₂O₅ to a chain-like metaphosphate structure as x approaches 0.50. The ¹³³Cs MAS NMR spectra show a 90 ppm increase in isotropic chemical shift (δ_iso) with increasing Cs₂O content, which indicates a decrease in the average electron density around the Cs⁺ ions, more covalent Cs-O bonding, and a shorter average Cs-O bond length. The physical properties and spectroscopic results are interpreted using a structural model that considers the effects of composition on the average coordination environment of Cs⁺ ions.     

羧甲基纤维素钠水凝胶的制备及其生物降解性研究

用羧甲基纤维素钠(CMC—Na)制得了含水量高达98％的水凝胶，考察了防腐剂、交联剂、无机态氮素、有机态氮素、碳水化合物的加入量以及环境中pH值等因素对生物降解性的影响。结果表明：制备条件不同，水凝胶的生物降解性不同；环境中一定量铵根离子的存在有利于水凝胶的生物降解；在pH=5．2的环境中纤维素酶活性最高，降解程度最大。