高效液相色谱-电感耦合等离子体质谱法测定烟草中砷的形态

应用高效液相色谱-电感耦合等离子体质谱联用技术(HPLC-ICP-MS)建立了烟草中As(Ⅲ)、As(V)、一甲基砷酸(MMA)和二甲基砷酸(DMA)4种砷形态的检测方法。研究了不同提取液、提取液体积以及提取时间对提取效果的影响,并对色谱条件进行优化。以15 mL甲醇-水(1∶1)混合液为提取液,30℃超声提取20 min,以(NH4)2HPO4(pH 6.0)为流动相,采用PRP-X100阴离子交换柱对砷形态进行分离。在0.1～25μg/L质量浓度范围内,4种砷形态的线性系数均不小于0.997,日内(n=5)和日间(n=3)RSD均不大于4.2%,仪器检出限为0.1～0.2μg/L,定量下限为0.2～0.5μg/L。在低、中、高3个加标水平下,砷的回收率均为83%～115%,方法稳定性较好,RSD不大于5.7%。采用该方法对国内外8种烟草中的4种砷形态含量进行分析,其含量从高到低依次为As(Ⅴ)、MMA、As(Ⅲ)和DMA。该方法准确、灵敏、方便,适用于烟草中砷形态的测定。     

Bioorganic Chemistry of Hypothiocyanite

Abstract

Hypothiocyanite (OSCN^?) plays an important role in the human host defense system as a nonimmunological antimicrobial agent. Although many conjugate reactions of proteins have been attributed to OSCN^?, there is little precedence for such reactions in small-molecule chemistry. We will discuss the derivative species that are in equilibrium with OSCN^?, including hypothiocyanous acid (HOSCN), thiocyanogen [(SCN) ₂ ], and trithiocyanate [(SCN) ₃ ^?], the first organic derivatives of this mixture to be fully characterized, and we will describe a new method of synthesizing hypothiocyanite.     

Alkaloid-rich plant Tylophora indica; current trends in isolation strategies,chemical profiling and medicinal applications

Tylophora indica, a threatened medicinal plant of family Asclepiadaceae, grows profoundly in Asia, Africa, Australia, Oceanic Islands, Ceylon, Malay island, and Borneo. The plant is a twinning herb that is excessively used in folk medicine as a substitute of ipecac, an expectorant. Different parts of the plant are accredited for the anti-asthmatic, antibacterial, anti–psoriasis, antimicrobial, antiulcer, antiallergic, antidiarrhoeal, hypolipidemic, and anxiolytic properties. Antidiabetic, hepatoprotective, antiangiogenic, anti-tumor, antioxidant, anticonvulsant, anti-rheumatic, and diuretic activities are also attributed to the magnificent medicinal plant owing to the occurrence of various active phytochemicals such as alkaloids, saponins, phytosterols, tannins, and primary metabolites. The plant has been exploited by the ethnic people due to the immense medicinal importance, leading to the endangerment of the plant species. The review brings to light the important pharmacological attributes, folk medicinal uses, and biotechnological approaches that must be followed to save the plant from extinction.     

Diesel Soot Combustion over Mn2O3 Catalysts with Different Morphologies: Elucidating the Role of Active Oxygen Species in Soot Combustion

Catalytic diesel soot combustion was examined using a series of Mn₂O₃ catalysts with different morphologies, including plate, prism, hollow spheres and powders. The plate‐shaped Mn₂O₃ (Mn₂O₃‐plate) exhibited superior carbon soot combustion activity compared to the prism‐shaped, hollow‐structured and powdery Mn₂O₃ under both tight and loose contact modes at soot combustion temperatures (T₅₀) of 327 °C and 457 °C, respectively. Comprehensive characterization studies using scanning electron microscopy, scanning transmission electron microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, temperature‐programmed reduction and oxygen release measurements, revealed that the improved activity of Mn₂O₃‐plate was mainly attributed to the high oxygen release rate of surface‐adsorbed active oxygen species, which originated from oxygen vacancy sites introduced during the catalyst preparation, rather than specific surface‐exposed planes. The study provides new insights for the design and synthesis of efficient oxidation catalysts for carbon soot combustion as well as for other oxidation reactions of harmful hydrocarbon compounds.     

Bio‐inspired Nonheme Iron Oxidation Catalysis: Involvement of Oxoiron(V) Oxidants in Cleaving Strong C−H Bonds

Nonheme iron enzymes generate powerful and versatile oxidants that perform a wide range of oxidation reactions, including the functionalization of inert C?H bonds, which is a major challenge for chemists. The oxidative abilities of these enzymes have inspired bioinorganic chemists to design synthetic models to mimic their ability to perform some of the most difficult oxidation reactions and study the mechanisms of such transformations. Iron‐oxygen intermediates like iron(III)‐hydroperoxo and high‐valent iron‐oxo species have been trapped and identified in investigations of these bio‐inspired catalytic systems, with the latter proposed to be the active oxidant for most of these systems. In this Review, we highlight the recent spectroscopic and mechanistic advances that have shed light on the various pathways that can be accessed by bio‐inspired nonheme iron systems to form the high‐valent iron‐oxo intermediates.     

Fabrication of Z-Scheme WO3/KNbO3 Photocatalyst with Enhanced Separation of Charge Carriers

Z-Scheme photocatalysts as a research focus perform strong redox capability and high photocatalytic performance. WO₃/KNbO₃ photocatalysts were fabricated by ball milling method, and performed higher photocatalytic activity in liquid degradation(rhodamine B, methylene blue and bisphenol A), compared with WO₃ or KNbO₃ monomer. This is due to that Z-scheme heterojunction is formed between WO₃ and KNbO₃, and the holes photo-excited in valence band of KNbO₃ are quickly combined with the electrons in conduction band of WO₃. The electrons accumulated in conduction band of KNbO₃ show high reducibility, thereby reducing O₂ to ^·O₂^-, and the holes in valence band of WO₃ show high oxidative to oxidize H₂O to ^·OH, respectively. Furthermore, it is proved by means of electron spin resonance(ESR) spectra, terephthalic acid photoluminescence probing technique(TA-PL), and UV-Vis absorption spectra of nitroblue tetrazolium. This work indicates that the fabrication of Z-scheme structure can improve the photocatalytic activity by efficiently separating the photogenerated electrons and holes in the photocatalytic reaction system, which is helpful to deeply understand the migration mechanism of photoexcited carrier(band-band transfer and Z-scheme transfer) in heterojunction photocatalysts.     

C−H Oxygenation Reactions Enabled by Dual Catalysis with Electrogenerated Hypervalent Iodine Species and Ruthenium Complexes

The catalytic generation of hypervalent iodine(III) reagents by anodic electrooxidation was orchestrated towards an unprecedented electrocatalytic C?H oxygenation of weakly coordinating aromatic amides and ketones. Thus, catalytic quantities of iodoarenes in concert with catalytic amounts of ruthenium(II) complexes set the stage for versatile C?H activations with ample scope and high functional group tolerance. Detailed mechanistic studies by experiment and computation substantiate the role of the iodoarene as the electrochemically relevant species towards C?H oxygenations with electricity as a sustainable oxidant and molecular hydrogen as the sole by‐product. para‐Selective C?H oxygenations likewise proved viable in the absence of directing groups.     

Self‐Amplified Photodynamic Therapy through the 1O2‐Mediated Internalization of Photosensitizers from a Ppa‐Bearing Block Copolymer

Nanocarriers are employed to deliver photosensitizers for photodynamic therapy (PDT) through the enhanced penetration and retention effect, but disadvantages including the premature leakage and non‐selective release of photosensitizers still exist. Herein, we report a ¹O₂‐responsive block copolymer (POEGMA‐b‐P(MAA‐co‐VSPpaMA) to enhance PDT via the controllable release of photosensitizers. Once nanoparticles formed by the block copolymer have accumulated in a tumor and have been taken up by cancer cells, pyropheophorbide a (Ppa) could be controllably released by singlet oxygen (¹O₂) generated by light irradiation, enhancing the photosensitization. This was demonstrated by confocal laser scanning microscopy and in vivo fluorescence imaging. The ¹O₂‐responsiveness of POEGMA‐b‐P(MAA‐co‐VSPpaMA) block copolymer enabled the realization of self‐amplified photodynamic therapy by the regulation of Ppa release using NIR illumination. This may provide a new insight into the design of precise PDT.     

An Innovative Hydrogen Peroxide-Sensing Scaffold and Insight Towards its Potential as an ROS-Activated Persulfide Donor

Reactive sulfur species, such as hydrogen sulfide, persulfides, and polysulfides, have recently emerged as key signaling molecules and important physiological mediators within mammalian systems. To better assess the therapeutic potential of their exogenous administration, we report on the development of a unique hydrogen peroxide (H₂O₂)-sensing motif and its capacity for providing cellular protection against oxidative stress while serving as a reactive oxygen species (ROS)-activated persulfide donor. With the strategic implementation of a gem-dimethyl group to promote both stability and cyclization, we found the initial rate of payload release from this newly derived scaffold to be directly proportional to the concentration of H₂O₂ and to proceed via an unprecedented pathway that avoids the production of electrophilic byproducts, a severe limitation that has plagued the physiological application of previous designs.