Anti-bacterial effect of four extracts from leaves of Dracontomelon dao on Escherichia coli growth using microcalorimetry coupled with principal component analysis

The anti-Escherichia coli activities of four extracts in leaves of Dracontomelon dao, a traditional folk herb in China were investigated and compared by microcalorimetry. The four extracts are PE fraction, CHCl₃ fraction, EtOAc fraction, and n-BuOH fraction. The heat flow power–time (HFP–time) curves of E. coli growth in the presence of the four extracts were measured using an ampoule method. Then the nine thermal kinetic parameters were obtained from the curves. From the result of principal component analysis, it can be seen that parameters k ₁, k ₂, P ₁, and Q _p2 might be the main parameters in evaluating the anti-E. coli effects. In the presence of CHCl₃ fraction, EtOAc fraction, and n-BuOH fraction, k ₂, Q _p2 of E. coli decreased with increasing concentrations of the extracts. The EtOAc fraction was observed to have the strongest anti-bacterial activity with half-inhibitory concentration IC50 of 98.5 μg mL^?1. So, it can be concluded that EtOAc fraction can be further developed as anti-bacterial bioactive fraction of leaves of Dracontomelon dao.     

Influence of anodizing voltage mode on the nanostructure of TiO2 nanotubes

The nanostructure of self-ordered porous anodic TiO₂ nanotubes (PATNTs) has extraordinary influence on their physical and chemical properties. For this reason, extensive attention has been paid on pulse anodization to regulate the nanostructure of PATNT. However, the relationships between the nanostructures and current curves still remain unclear. Based on the traditional potentiostatic and pulse anodizations, five different modes (i.e., potentiostatic, pulse, triangle wave, decrease, and increase step by step) of applied voltage and their influences on the nanostructures of PATNT have been investigated in detail. The growing rates of the nanotubes anodized under five different modes were compared for the first time. The results show that the growing rate of pulse voltage anodization is the fastest, reaching 116.4 nm min^?1. The slowest is triangle wave voltage anodization, only 59.3 nm min^?1. When the applied voltage decreases step-by-step, branched nanotubes can be formed in the bottom of PATNT. Yet, when the applied voltage increases step-by-step, triple-layer nanotubes with different diameters are formed, and the forming mechanism of this special nanostructure is discussed. The present results may be helpful to understand the mechanism of PATNT and facilitate the assembling diverse nanostructures for extensive applications in photocatalysis, dye-sensitized solar cells, and biomedical devices.     

Electrochemical Synthesis of Tetrahexahedral Rhodium Nanocrystals with Extraordinarily High Surface Energy and High Electrocatalytic Activity

Noble metal nanocrystals (NCs) enclosed with high‐index facets hold a high catalytic activity thanks to the high density of low‐coordinated step atoms that they exposed on their surface. Shape‐control synthesis of the metal NCs with high‐index facets presents a big challenge owing to the high surface energy of the NCs, and the shape control for metal Rh is even more difficult because of its extraordinarily high surface energy in comparison with Pt, Pd, and Au. The successful synthesis is presented of tetrahexahedral Rh NCs (THH Rh NCs) enclosed by {830} high‐index facets through the dynamic oxygen adsorption/desorption mediated by square‐wave potential. The results demonstrate that the THH Rh NCs exhibit greatly enhanced catalytic activity over commercial Rh black catalyst for the electrooxidation of ethanol and CO.     

Magnetic Titanium Dioxide Nanocomposites for Surface‐Enhanced Resonance Raman Spectroscopic Determination and Degradation of Toxic Anilines and Phenols

Mesoporous M‐TiO₂ NCs, functionalized by PATP, can capture toxic anilines and phenols by azo coupling. Loading these nanodevices with Ag NPs offers the possibility for a sensitive quantitative determination of target compounds by SERRS spectroscopy, which allows multiplex detection because of the specific vibrational fingerprints. Sensitivity and selectivity can be further enhanced by concentrating the hybrid particles by an external magnet and compound‐specific binding (anilines versus phenols). The bound toxic compounds can be degraded by TiO₂‐assisted photocatalysis after removal of the loaded hybrid particles from the sample solution with an external magnet. The degradation process can be enhanced in the presence of plasmonic Ag nanostructures.     

Visible‐Light‐Induced CS Bond Activation: Facile Access to 1,4‐Diketones from β‐Ketosulfones

A novel method for the synthesis of 1,4‐diketones from β‐ketosulfones was developed by means of a visible light‐induced C?S bond activation process. Symmetrical and unsymmetrical 1,4‐diketones can be easily prepared in moderate to good yields.     

The Photo‐Nazarov Reaction: Scope and Application

The reaction conditions and scope of the photo‐Nazarov reaction of aryl vinyl ketones were investigated. In contrast to the conventional acid‐catalyzed methods, this photolytic electrocyclization proceeds in the neutral or basic conditions. Irradiating substrates bearing various aromatic rings, acid‐sensitive groups, cyclohexenyl, cycloheptenyl, and unsaturated pyran with UV‐light (254 nm) smoothly yielded hexahydrofluorenones and related structures. This photo‐Nazarov reaction could also be applicable to the substrates carrying β‐alkyl groups on the enone, which gave corresponding polycyclic rings containing quaternary centers. These photo‐electrocyclized products may prove useful for synthesizing a variety of natural products and their derivatives. Further application of this mild photo‐Nazarov reaction in the synthesis of taiwaniaquinol B was achieved.     

Photochemically Engineering the Metal–Semiconductor Interface for Room‐Temperature Transfer Hydrogenation of Nitroarenes with Formic Acid

A mild photochemical approach was applied to construct highly coupled metal–semiconductor dyads, which were found to efficiently facilitate the hydrogenation of nitrobenzene. Aniline was produced in excellent yield (>99 %, TOF: 1183) using formic acid as hydrogen source and water as solvent at room temperature. This general and green catalytic process is applicable to a wide range of nitroarenes without the involvement of high‐pressure gases or sacrificial additives.     

Direct X‐ray Observation of Trapped CO2 in a Predesigned Porphyrinic Metal–Organic Framework

Metal–organic frameworks (MOFs) are emerging microporous materials that are promising for capture and sequestration of CO₂ due to their tailorable binding properties. However, it remains a grand challenge to pre‐design a MOF with a precise, multivalent binding environment at the molecular level to enhance CO₂ capture. Here, we report the design, synthesis, and direct X‐ray crystallographic observation of a porphyrinic MOF, UNLPF‐2, that contains CO₂‐specific single molecular traps. Assembled from an octatopic porphyrin ligand with [Co₂(COO)₄] paddlewheel clusters, UNLPF‐2 provides an appropriate distance between the coordinatively unsaturated metal centers, which serve as the ideal binding sites for in situ generated CO₂. The coordination of Co^II in the porphyrin macrocycle is crucial and responsible for the formation of the required topology to trap CO₂. By repeatedly releasing and recapturing CO₂, UNLPL‐2 also exhibits recyclability.     

Chemical and Toxicological Investigations of a Previously Unknown Poisonous European Mushroom Tricholoma terreum

The established tradition of consuming and marketing wild mushrooms has focused attention on mycotoxicity, which has become a global issue. In the present study, we describe the toxins found in a previously unknown poisonous European mushroom Tricholoma terreum. Fifteen new triterpenoids terreolides A–F ( 1 – 6 ) and saponaceolides H–P ( 8 – 16 ) were isolated from the fruiting bodies of the toxic mushroom T. terreum. Terreolides A–C ( 1 – 3 ) possessed a unique 5/6/7 trioxaspiroketal system, whereas terreolides D–F ( 4 – 6 ) possessed an unprecedented carbon skeleton. Two abundant compounds in the mushroom, saponaceolide B ( 7 ) and saponaceolide M ( 13 ), displayed acute toxicity, with LD₅₀ values of 88.3 and 63.7 mg kg^?1 when administered orally in mice. Both compounds were found to increase serum creatine kinase levels in mice, indicating that T. terreum may be the cause of mushroom poisoning ultimately leading to rhabdomyolysis.     

Nucleophilic Difluoromethylation of Epoxides with PhSO(NTBS)CF2H by a Preorganization Strategy

Unlike the facile synthesis of β‐monofluoromethyl alcohols by nucleophilic monofluoromethylation of epoxides, the synthesis of β‐difluoromethyl alcohols by nucleophilic difluoromethylation of epoxides still remains a challenge. Herein, studies on tackling this problem with PhSO(NTBS)CF₂H ( 2 ; TBS=tert‐butyldimethylsilyl) are reported. The preorganization of 2 and epoxides with BF₃ ? Et₂O was found to be crucial for the reaction. The reaction shows excellent regioselectivity and has a broad substrate scope. The facile transformation of the ring‐opened products to β‐difluoromethyl, γ‐difluoromethyl, and β‐difluoromethylenyl alcohols demonstrates the synthetic utility of the reaction.