酞菁铁中N4-Fe2+的氧化还原化学和氧还原性能

准确理解金属大环配合物(如N4-Fe²⁺)体系的氧化还原化学性能,对氧还原反应(ORR)电催化剂的基础研究和合理设计具有重要意义.本文采用微波法将三种不同酞菁铁类金属大环配合物吸附在碳纳米管上,分别记为(NH2)4FePc@CNTs,(t-Bu)4FePc@CNTs和FePc@CNTs,考察了取代基对Fe³⁺/Fe²⁺氧化还原电位的影响,以及碱性介质中的氧还原反应催化活性.结果表明,FePc@CNTs,(t-Bu)4FePc@CNTs和(NH2)4FePc@CNTs的ORR起始电位分别为0.98,0.96和0.96 V,而半波电位(E1/2)由高到低的顺序为FePc@CNTs(E1/2=0.91 V),(t-Bu)4FePc@CNTs(E1/2=0.87 V),(NH2)4FePc@CNTs(E1/2=0.83 V).与20%Pt/C(E1/2=0.85 V)相比,FePc@CNTsFePc@CNTs具有优异的ORR性能.在活性、稳定性和耐甲醇性方面,FePc@CNTs复合材料比其他复合材料表现出更高的ORR性能.研究发现,FePc上的供电子基团可以显著改变N4-Fe²⁺活性位点的电子云密度,增加dz 2轨道(HOMO)的能量,并观察到Fe²⁺/Fe³⁺氧化还原电位显著向阴极方向移动.结果表明,取代基的高电子贡献能力降低了HOMO和LUMO(O2的杂轨道*-轨道)之间的电子耦合,从而降低了氧还原催化活性.因此,FePc框架外围的供电子基团对ORR不利.本文阐明了取代基电子效应-金属大环配合物氧化还原电位与ORR催化性能之间的关系,为ORR催化剂活性中心的构建和调控提供了借鉴.     

Asymmetric,Three‐Component,One‐Pot Synthesis of Spiropyrazolones and 2,5‐Chromenediones from Aldol Condensation/NHC‐Catalyzed Annulation Reactions

A novel one‐pot, three‐component diastereo‐ and enantioselective synthesis of spiropyrazolones has been developed involving the aldol condensation of an enal to generate α,β‐unsaturated pyrazolones, which react with a second equivalent of enal through an N‐heterocyclic carbene (NHC)‐catalyzed [3+2] annulation. The desired spirocyclopentane pyrazolones are obtained in moderate to good yields and good to excellent stereoselectivities. Alternatively, starting from cyclic 1,3‐diketones, 2,5‐chromenediones are available through [2+4] annulation.     

Simultaneous determination of bergenin and gallic acid in Bergenia ligulata wall by high-performance thin-layer chromatography

A simple and reproducible high-performance thin-layer chromatographic method was developed for the simultaneous determination of bergenin and gallic acid in Bergenia ligulata. Water and methanol were used as the extracting solvents. The concentrations of bergenin and gallic acid in both of these solvents were found to be almost the same. The method involves separation of the components by thin-layer chromatography on a precoated Silica Gel 60 F254 plate with a solvent system of ethyl acetate-formic acid-acetic acid-water (100 + 11 + 11 + 27). The sensitivity of the method for bergenin was 0.30 microg, whereas for gallic acid it was 0.25 microg. The proposed method is precise and sensitive and can be used for the detection, monitoring, and simultaneous quantification of bergenin and gallic acid in B. ligulata.     

Facile Hydrolysis of Esters with KOH-Methanol at Ambient Temperature

Summary. A simple, rapid, and efficient method is reported for the hydrolysis of a variety of mono- and diesters of aromatic, aliphatic, fatty, and heterocyclic acids with potassium hydroxide in methanol at ambient temperature (35°C).     

Facile reductive coupling of benzylic halides with ferrous oxalate dihydrate

Facile reductive coupling of benzylic halides is reported with ferrous oxalate dihydrate in DMF or HMPA under nitrogen atmosphere at 155-160 degrees C. The coupling is proposed to proceed by two successive oxidative additions of benzylic halides to ferrous oxalate to give an intermediate organoiron complex which undergoes concerted dimerization to give the corresponding reductively coupled dimers in high yields.     

A multiple focused probe approach for high intensity focused ultrasound based surgery

To produce deep-seated surgical lesions using ultrasound requires high power and intensity levels at the target sites. Conventionally, large transducers are used which require big apertures and so are generally suitable only for extra-corporeal access. Such transducers also result in strong off-focus maxima, where the resulting hot spots can destroy normal tissue whilst deep-seated large tissue volumes are being ablated. This paper describes a new approach in which it is proposed that multiple probes are used simultaneously, each at a relatively low power, to result in an overlapping focused region of high temperature without strong off-focus hot spots. Robotic techniques could be used to move the individual probes in coordination to sweep out the desired region of tissue ablation. Simulation and planning are the key to quality prediction for high intensity focused ultrasound (HIFU). Simplified two-dimensional and three-dimensional models of HIFU probes have been developed to study the characteristics of various multi-probe configurations. Preliminary simulation results show that the multi-probe system can be arranged successfully to minimise off-focus hot spots. Experimental results are presented which validate the modality and confirm this positive finding. Further prediction studies and planning will be necessary to achieve the most appropriate desired treatment, by varying the pulse duration and spacing.     

Applications of Fruit Polyphenols and Their Functionalized Nanoparticles Against Foodborne Bacteria: A Mini Review

The ingestion of contaminated water and food is known to cause food illness. Moreover, on assessing the patients suffering from foodborne disease has revealed the role of microbes in such diseases. Concerning which different methods have been developed for protecting food from microbes, the treatment of food with chemicals has been reported to exhibit an unwanted organoleptic effect while also affecting the nutritional value of food. Owing to these challenges, the demand for natural food preservatives has substantially increased. Therefore, the interest of researchers and food industries has shifted towards fruit polyphenols as potent inhibitors of foodborne bacteria. Recently, numerous fruit polyphenols have been acclaimed for their ability to avert toxin production and biofilm formation. Furthermore, various studies have recommended using fruit polyphenols solely or in combination with chemical disinfectants and food preservatives. Currently, different nanoparticles have been synthesized using fruit polyphenols to curb the growth of pathogenic microbes. Hence, this review intends to summarize the current knowledge about fruit polyphenols as antibacterial agents against foodborne pathogens. Additionally, the application of different fruit extracts in synthesizing functionalized nanoparticles has also been discussed.