The latest research progress on the prevention of storage pests by natural products: Species,mechanisms, and sources of inspiration

The quality of grains is influenced by storage pests, which are not only spoilers of stored grain, but also vectors of human and animal diseases. Chemical pesticides play an essential role in the cultivation and storage of cereals, however, due to the low degradability and residual toxicity of synthetic pesticides on the environment and non-target organisms, as well as the increasing resistance of target organisms to them, consideration should be given to the development of alternative pest control agents. Compounds isolated from natural sources have emerged as preferred targets for the development of novel insecticidal agents because of their eco-friendliness, safety, and effectiveness. In this review, we primarily focus on the natural product (NPs) control of storage pests. The effective monomer components of NPs and their anti-insect mechanisms were discussed, and natural sources of inspiration and models for insect repellents are described. This review aimed to provide guidelines for the exploitation and utilization of green and efficient natural insecticides.     

Fluorine-Containing Drugs Approved by the FDA in 2018

Over the last two decades, fluorine substitution has become one of the essential structural traits in modern pharmaceuticals. Thus, about half of the most successful drugs (blockbuster drugs) contain fluorine atoms. In this review, we profile 17 fluorine-containing drugs approved by the food and drug administration (FDA) in 2018. The newly approved pharmaceuticals feature several types of aromatic F and CF₃, as well as aliphatic (CF₂) substitution, offering advances in the treatment of various diseases, including cancer, HIV, malarial and smallpox infections.     

VITALAB21型半自动生化分析仪常见故障及故障排除方法

介绍VITALAB21型半自动生化分析仪常见故障、故障原因及故障排除方法。     

Development of a multi-class method for the quantification of veterinary drug residues in feedingstuffs by liquid chromatography-tandem mass spectrometry

A simple multi-residue method was developed for detecting and quantifying 33 analytes from 13 classes of antibiotics (tetracyclines (3), quinolones (7), penicillins (3), ionophore coccidiostats (7), macrolides (3), sulfonamides (1), quinoxalines (2), phenicols (2), lincosamides (1), diaminopyrimidines (1), polypeptides (1), streptogramins (1) and pleuromutilins (1)) in animal feeds. Extraction and clean-up procedures were optimized with spiked piglet feed. Samples were extracted by ultrasonic-assisted extraction with a mixture of methanol/acetonitrile/McIlvaine buffer at pH 4.6 (37.5/37.5/25, v/v/v) containing 0.3% of EDTA-Na₂, followed by a clean up using a dispersive solid-phase extraction (d-SPE) with PSA (primary secondary amine). Detection of antibiotics was achieved by liquid chromatography-electrospray tandem mass spectrometry (LC–ESI-MS/MS) within 28 min using both positive and negative ESI mode. Average recoveries ranged from 51% (oxytetracycline) to 116% (tilmicosin) with associated relative standard deviations of 7.3% and 9.0% and an overall mean of 87%. Limits of quantification ranged from 3.8 ng g⁻¹ (lincomycin) to 65.0 ng g⁻¹ (bacitracin). Following optimization, the method was further verified for bovine and lamb feedingstuffs; negative matrix effects were evaluated and overcome by a standard addition method.     

The Biochemical Reactions of Organometallics with Enzymes and Proteins

Most specialists doing organometallic chemistry have little understanding of what modern biochemistry is. On the other hand, most biochemists believe that organometallic chemistry stands much apart from the problems they study. But the real distance, if any, between these magnificent pyramids of modern science is progressively decreasing. Their interaction has given birth to a new branch of science, organometallic biochemistry, the general aspects of which are discussed here.     

E面和H面方向图等化的双模圆锥喇叭设计

 介绍用于Φ7.3 m Cassegrain天线的高功率馈源喇叭的设计。为使E面和H面方向图在照射区域内具有高的等化度,选择双模圆锥喇叭作为馈源的结构形式。由于高功率源采用BJ-32波导输出信号,故馈源系统中还应包含一个矩形到圆形的模式转换器,将TE10模转换为TE11模。设计了双模圆锥喇叭和模式转换器,并进行了功率容量估算。测试结果表明,所设计的馈源达到了设计要求,理论计算结果和实验测试数据吻合良好。     

Enzyme-catalysed Transformations of Compounds Containing the –CH2-AsO3H2 Group

Enzymes that act on substrates R–O–PO₃H₂ often work on substrate analogues R–O–AsO₃H₂; such substrates are unstable, since esters of H₃AsO₄ hydrolyse easily. They also form easily, so that an enzyme that acts on R–O–PO₃H₂ often acts on a mixture of R–OH and arsenate via an ester that forms at the active site. Similarly coenzyme analogues may be formed; for example, a stable and active aspartate aminotransferase forms from the apoenzyme with free pyridoxal and arsenate. Enzymes that convert R–O–PO₃H₂ into a diester often act on R–CH₂–AsO₃H₂, a stable substrate analogue; then the product is unstable and hydrolyses to re-form the analogue, giving a futile cycle. For example, RNA polymerase acquires exonuclease activity in the presence of H₂O₃P–CH₂–AsO₃H₂; adenylate kinase acquires ATPase activity in the presence of the arsonomethyl analogue of AMP. A recent observation is that HO–CH₂–CHOH–CH₂–CH₂–AsO₃H₂ is a good substrate for glycerol-3-phosphate dehydrogenase. The product is unstable and eliminates arsenite, sharing this ability with other 3-oxoalkylarsonates. Thus this enzyme–catalysed oxidation is a lethal synthesis, in view of the toxicity of arsenite. Another unusual biochemical reaction of an arsonic acid is seen in the ability of a bacterium to use arsonoacetate as its sole source of carbon and energy. In contrast with the elimination of arsenite by 3-oxoalylarsonic acids, 3-oxoalkylphosphonic acids, R–CO–CH₂–CH₂–PO₃H₂, are stable. 2-Oxoalkylphosphonic acids, R–CO–CH₂–PO₃H₂, however, are moderately unstable to hydrolysis, yielding phosphate and R–CO–CH₃. 2-Oxoalkylarsonic acids, R–CO–CH₂–AsO₃H₂, decompose in the same way, but much more readily, yielding arsenate. © 1997 by John Wiley & Sons, Ltd.