The crucial roles of guest water in a biocompatible coordination network in the catalytic ring-opening polymerization of cyclic esters: a new mechanistic perspective

The ring-opening polymerization (ROP) of cyclic esters/carbonates is a crucial approach for the synthesis of biocompatible and biodegradable polyesters. Even though numerous efficient ROP catalysts have been well established, their toxicity heavily limits the biomedical applications of polyester products. To solve the toxicity issues relating to ROP catalysts, we report herein a biocompatible coordination network, CZU-1, consisting of Zn₄(μ₄-O)(COO)₆ secondary building units (SBUs), biomedicine-relevant organic linkers and guest water, which demonstrates high potential for use in the catalytic ROP synthesis of biomedicine-applicable polyesters. Both experimental and computational results reveal that the guest water in CZU-1 plays crucial roles in the activation of the Zn₄(μ₄-O)(COO)₆ SBUs by generating μ₄-OH Brønsted acid centers and Zn–OH Lewis acid centers, having a synergistic effect on the catalytic ROP of cyclic esters. Different to the mechanism reported in the literature, we propose a new reaction pathway for the catalytic ROP reaction, which has been confirmed using density functional theory (DFT) calculations, in situ diffuse reflectance IR Fourier transform spectroscopy (DRIFTS), and matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF MS). Additionally, the hydroxyl end groups allow the polyester products to be easily post-modified with different functional moieties to tune their properties for practical applications. We particularly expect that the proposed catalytic ROP mechanism and the developed catalyst design principle will be generally applicable for the controlled synthesis of biomedicine-applicable polymeric materials.

A new ring-opening polymerization mechanism is unveiled based on synergistic catalysis involving Brønsted and Lewis acid centers in a coordination framework.     

Long-duration transcutaneous electric acupoint stimulation alters small-world brain functional networks

Acupuncture, which is recognized as an alternative and complementary treatment in Western medicine, has long shown efficiencies in chronic pain relief, drug addiction treatment, stroke rehabilitation and other clinical practices. The neural mechanism underlying acupuncture, however, is still unclear. Many studies have focused on the sustained effects of acupuncture on healthy subjects, yet there are very few on the topological organization of functional networks in the whole brain in response to long-duration acupuncture (longer than 20 min). This paper presents a novel study on the effects of long-duration transcutaneous electric acupoint stimulation (TEAS) on the small-world properties of brain functional networks. Functional magnetic resonance imaging was used to construct brain functional networks of 18 healthy subjects (9 males and 9 females) during the resting state. All subjects received both TEAS and minimal TEAS (MTEAS) and were scanned before and after each stimulation. An altered functional network was found with lower local efficiency and no significant change in global efficiency for healthy subjects after TEAS, while no significant difference was observed after MTEAS. The experiments also showed that the nodal efficiencies in several paralimbic/limbic regions were altered by TEAS, and those in middle frontal gyrus and other regions by MTEAS. To remove the psychological effects and the baseline, we compared the difference between diffTEAS (difference between after and before TEAS) and diffMTEAS (difference between after and before MTEAS). The results showed that the local efficiency was decreased and that the nodal efficiencies in frontal gyrus, orbitofrontal cortex, anterior cingulate gyrus and hippocampus gyrus were changed. Based on those observations, we conclude that long-duration TEAS may modulate the short-range connections of brain functional networks and also the limbic system.     

钾改性Mn/Ce0.65Zr0.35O2催化剂催化氧化甲苯

Volatile organic compounds (VOCs) are both harmful to human health and the environment; however, catalytic combustion offers a promising method for VOC purification because of its high efficiency without secondary pollution. Although manganese-based catalysts have been well studied for VOC catalytic oxidation, their catalytic activity at low temperature must be improved. Alkali metals as promoters have the potential to modulate the electronic and structural properties of the catalysts, improving their catalytic activity. Herein, a Ce_0.65Zr_0.35O₂ support was prepared by co-precipitation and MnO_x/Ce_0.65Zr_0.35O₂ catalysts were obtained through the incipient-wetness impregnation method. The catalytic properties of K-modified MnO_x/Ce_0.65Zr_0.35O₂ for toluene oxidation with different molar ratios of K/Mn were investigated. In addition, the catalysts were characterized by XRD, UV/visible Raman, Hydrogen temperature program reduction (H₂-TPR), Oxygen temperature programmed desorption (O₂-TPD), X-ray photoelectron spectroscopy (XPS) and in situ diffuse reflectance FTIR spectroscopy (DRIFTS) experiments. The results showed that alkali metal doping with K significantly improved the catalytic activity. In particular, when the molar ratio of K/Mn was 0.2, the monolith catalyst Mn/Ce_0.65Zr_0.35O₂-K-0.2 exhibited the best performance with the lowest complete conversion temperature T₉₀ of 242 ℃ at a GHSV of 12000 h⁻¹. The XRD results suggested that MnO_x was uniformly distributed on the surface of the catalyst and that Mn⁴⁺ partially reduced to Mn³⁺ on the addition of K. The Raman spectrum demonstrated that with increasing K content, both the β- and α-MnO₂ phases coexisted on the Mn/Ce_0.65Zr_0.35O₂-K-0.2 catalyst, increasing the number of surface defect sites. The H₂-TPR experiment results confirmed that Mn/Ce_0.65Zr_0.35O₂-K-0.2 exhibited the lowest reduction temperature and good reducibility. From the O₂-TPD experiments, it was clear that Mn/Ce_0.65Zr_0.35O₂-K-0.2 contained the most surface adsorbed oxygen species and excellent lattice oxygen mobility, which benefitted the toluene oxidation activity. In addition, the XPS results suggested that the content of surface adsorbed oxygen species of the Mn/Ce_0.65Zr_0.35O₂-K-0.2 catalyst was the highest among all the tested samples. In addition, toluene-TPSR in N₂ as measured by in situ DRIFTs analysis demonstrated that available lattice oxygen was present in the Mn/Ce_0.65Zr_0.35O₂-K-0.2 catalyst. Therefore, the Mn/Ce_0.65Zr_0.35O₂-K-0.2 catalyst exhibited the best redox properties and oxygen mobility of the prepared samples and showed excellent activity toward toluene oxidation. Therefore, it was concluded that the addition of an appropriate amount of K improved the redox performance of the catalyst and increased the number of surface defect sites and mobility of the lattice oxygen of the catalyst as well as the concentration of the surface active oxygen species, thereby significantly improving catalytic ability.     

矿物油样品采集及计算公式的探讨

针对矿物油在水体中特殊的存在形态，结合实践，从采集矿物油样品的目的，装置及分析结果表达式三个方面，就如何统一，规范地采集具有代表性的矿物油样品，以及合理地进行分析，提出了初步的看法。     

EXISTENCE AND STABILITY OF PERIODIC ORBITS FOR A PERTURBED FOUR-DIMENSIONAL SYSTEM

The purpose of this paper is to study periodic orbits of a perturbed four- dimensional system.Using bifurcation methods and the integral manifold theory,sufficient conditions for the existence and stability of periodic orbits of the perturbed four-dimensional system are obtained.     

Dereplication and targeted isolation of bioactive sulphur compound from bacteria isolated from a hydrothermal field

Marine micro-organisms in the deep-sea hydrothermal vent systems are considered as potential sources of bioactive natural products. Sixteen bacterial strains were isolated from a deep-sea hydrothermal field and screened for bioactive metabolism studies. After the strains were subjected to bioactive testing at different culture media, chemical dereplication by HPLC coupled to high-resolution mass spectrometer was performed to analyse or determine the main secondary metabolisms in those strains. Strain 06204 was large-scale fermented with relative optimal media, for isolating the desired sulphur compound. Butyrolactone I 3-sulphate was isolated and structurally identified from the extract, guided by dereplication and showed moderate antivirus activities against H3N2 and EV71 viruses. Our study suggests that deep-sea hydrothermal bacteria are good sources of sulphur natural products. Meanwhile, the described approach, mainly bioactive screening, dereplication and targeted isolation, is effective and efficient to discover interesting bioactive compounds in hydrothermal bacteria.     

Potassium sodium tin selenide,K3NaSn3Se8

The title compound, tripotassium sodium tritin octaselenide, K₃NaSn₃Se₈, has a molecular (zero‐dimensional) structure containing trimeric [Sn₃Se₈]^4? units which consist of three edge‐sharing SnSe₄ tetrahedra. The [Sn₃Se₈]^4? anions and the tetrahedrally coordinated Na⁺ cations are arranged in an alternating fashion along the c axis to form SiS₂‐like chains, which are then separated by eight‐coordinate K⁺ cations. The Sn—Se bond distances are normal, being in the range 2.477 (1)–2.612 (1) Å.     

Seasonal Variation in Chemical Compositions of Essential Oils Extracted from Lavandin Flowers in the Yun-Gui Plateau of China

Lavandin, as an important cash crop, is cultivated in Kunming, Yun-Gui Plateau of China. For the special growing environment, Lavandin was grown here and used to investigate the changes in the yield and chemical compositions of essential oils extracted from the flowers in different seasons. The essential oils were extracted by hydro-distillation and analysis by gas chromatography-mass spectrometry (GC-MS). Results indicated great changes in chemical composition depending on the season of harvesting. The yields of essential oils ranged from 2.0% to 3.8% among the seasons, and the highest yield was in the summer. Chemical composition data showed that the extracted oils were rich in oxygenated monoterpenes (55.4–81.4%), eucalyptol (38.7–49.8%), camphor (8.41–14.26%), α-bisabolol (6.6–25.5%), and linalool (4.6–12.5%). The contents of eucalyptol and α-bisabolol changed in a contrary trend with seasonal variations. The results provided new insight for Chinese Lavandin germplasm to be used in application and development, and reference to the researcher, the farmer, and investor for sustainable industrialization of the plant grown in the Yun-Gui Plateau of China, but also the similar plateau area of the sustainable developments.     

基于BP算法和ACO算法的故障诊断推理研究

BP算法在故障诊断领域已取得广泛应用,但其存在收敛速度慢且容易陷入局部最小值的缺陷,限制了其进一步的发展;ACO(Ant colony optimization)算法是一种模拟进化算法,已很好地应用于解决旅行商和资源两次分配等经典的优化问题,具有启发式收敛、正反馈以及分布式计算等优点;为此,将ACO算法引入BP算法故障诊断方法中,使用ACO算法对BP网络中的参数即权值、阈值以及学习率等进行优化,定义了一种结合ACO算法和BP算法能对故障进行诊断的新算法,并将其应用于具体的故障诊断实例中,最后,通过100组样本中的95组进行训练,并对剩余5组进行故障诊断,实验证明结合ACO算法和BP算法的新算法较传统的仅使用BP算法的诊断方法具有收敛速度快、诊断精确高以及训练性能好的优点。