Boswellic Acids Show In Vitro Activity against Leishmania donovani

In continuation of our search for leads from medicinal plants against protozoal pathogens, we detected antileishmanial activity in polar fractions of a dichloromethane extract from Boswellia serrata resin. 11-keto-β-boswellic acid (KBA) could be isolated from these fractions and was tested in vitro against Leishmania donovani axenic amastigotes along with five further boswellic acid derivatives. 3-O-acetyl-11-keto-β-boswellic acid (AKBA) showed the strongest activity with an IC₅₀ value of 0.88 µM against axenic amastigotes but was inactive against intracellular amastigotes in murine macrophages     

Niclosamide Is Active In Vitro against Mycetoma Pathogens

Redox-active drugs are the mainstay of parasite chemotherapy. To assess their repurposing potential for eumycetoma, we have tested a set of nitroheterocycles and peroxides in vitro against two isolates of Madurella mycetomatis, the main causative agent of eumycetoma in Sudan. All the tested compounds were inactive except for niclosamide, which had minimal inhibitory concentrations of around 1 µg/mL. Further tests with niclosamide and niclosamide ethanolamine demonstrated in vitro activity not only against M. mycetomatis but also against Actinomadura spp., causative agents of actinomycetoma, with minimal inhibitory concentrations below 1 µg/mL. The experimental compound MMV665807, a related salicylanilide without a nitro group, was as active as niclosamide, indicating that the antimycetomal action of niclosamide is independent of its redox chemistry (which is in agreement with the complete lack of activity in all other nitroheterocyclic drugs tested). Based on these results, we propose to further evaluate the salicylanilides, niclosamide in particular, as drug repurposing candidates for mycetoma.     

Trapping of a Highly Reactive Oxoiron(IV) Complex in the Catalytic Epoxidation of Olefins by Hydrogen Peroxide

The generation of a nonheme oxoiron(IV) intermediate, [(cyclam)Fe^IV(O)(CH₃CN)]²⁺ ( 2 ; cyclam=1,4,8,11‐tetraazacyclotetradecane), is reported in the reactions of [(cyclam)Fe^II]²⁺ with aqueous hydrogen peroxide (H₂O₂) or a soluble iodosylbenzene (sPhIO) as a rare example of an oxoiron(IV) species that shows a preference for epoxidation over allylic oxidation in the oxidation of cyclohexene. Complex 2 is kinetically and catalytically competent to perform the epoxidation of olefins with high stereo‐ and regioselectivity. More importantly, 2 is likely to be the reactive intermediate involved in the catalytic epoxidation of olefins by [(cyclam)Fe^II]²⁺ and H₂O₂. In spite of the predominance of the oxoiron(IV) cores in biology, the present study is a rare example of high‐yield isolation and spectroscopic characterization of a catalytically relevant oxoiron(IV) intermediate in chemical oxidation reactions.     

Erratum on “Probing the kinetics in supramolecular chemistry and molecular assembly by microfluidic-NMR spectroscopy” [Sci.China Chem.,2018,61:1460–1464]

正In the above referenced publication[1],there is a mistake in the Supporting Information.The corrected caption of Figure S2 is:Figure S2 Isothermal titration calorimetry(ITC)data for the titration of 0.125 mM p-CD with 2.5 mM water-soluble viologen derivative(1-dodecyl-1'-methyl-4,4'-bipyridinium bromide iodide,DMV)in an aqueous solution at 25 ℃.Based on the ITC result,4:1 binding stoichiometry     

Undesired Bulk Oxidation of LiMn2O4 Increases Overpotential of Electrocatalytic Water Oxidation in Lithium Hydroxide Electrolytes

Chemical and structural changes preceding electrocatalysis obfuscate the nature of the active state of electrocatalysts for the oxygen evolution reaction (OER), which calls for model systems to gain systematic insight. We investigated the effect of bulk oxidation on the overpotential of ink-casted LiMn₂O₄ electrodes by a rotating ring-disk electrode (RRDE) setup and X-ray absorption spectroscopy (XAS) at the K shell core level of manganese ions (Mn−K edge). The cyclic voltammogram of the RRDE disk shows pronounced redox peaks in lithium hydroxide electrolytes with pH between 12 and 13.5, which we assign to bulk manganese redox based on XAS. The onset of the OER is pH-dependent on the scale of the reversible hydrogen electrode (RHE) with a Nernst slope of −40(4) mV/pH at −5 μA monitored at the RRDE ring. To connect this trend to catalyst changes, we develop a simple model for delithiation of LiMn₂O₄ in LiOH electrolytes, which gives the same Nernst slope of delithiation as our experimental data, i. e., 116(25) mV/pH. From this data, we construct an E^RHE-pH diagram that illustrates robustness of LiMn₂O₄ against oxidation above pH 13.5 as also verified by XAS. We conclude that manganese oxidation is the origin of the increase of the OER overpotential at pH lower than 14 and also of the pH dependence on the RHE scale. Our work highlights that vulnerability to transition metal redox may lead to increased overpotentials, which is important for the design of stable electrocatalysts.     

A mixed crystal of imperatorin and phellopterin,with C—H...O,C—H...π and π–π interactions

The crystal structure of 9‐(3‐methyl­but‐2‐enyl­oxy)­‐7H‐furo­[3,2‐g]­chro­men‐7‐one–4‐methoxy‐9‐(3‐methyl­but‐2‐enyl­oxy)‐7H‐­furo­[3,2‐g]­chromen‐7‐one (0.926/0.074), 0.926C₁₆H₁₄O₄·0.074C₁₇H₁₆O₅, is characterized by two independent imperatorin mol­ecules in the asymmetric unit, which exhibit different side‐chain conformations. A small amount of phellopterin overlaps with one of the two imperatorin mol­ecules. The supramol­ecular structure is supported by C—H...O, C—H...π and π–π interactions.     

Some applications of silica aerogels

Silica aerogels are very highly divided materials which are synthesised through the association of a chemical step, the so-called sol–gel chemistry, with a physical step which is a particular way of drying the wet gel, namely under supercritical conditions with respect to the liquid phase filling its porosity. This drying process preserves the texture of the dry material: in practice it strongly reduces the pore collapse. The resulting hyperporous solids that have bulk densities of the same magnitude as air develop new and very interesting physical and even chemical properties. Owing to their poor chemical reactivity, very large surface areas (of the order of 1,000 m ²/g), unusual porous volumes (greater than 95%), morphologies (monoliths or powders), optical properties (transparent, opaque or translucent), and very low thermal conductivity, they find high added-value applications in the physics of high-energy particles (Cherenkov emitters), transparent and superinsulating double windows, life and space science as well.     

Light-Mediated Formal Radical Deoxyfluorination of Tertiary Alcohols through Selective Single-Electron Oxidation with TEDA2+.

The synthesis of tertiary alkyl fluorides through a formal radical deoxyfluorination process is described herein. This light-mediated, catalyst-free methodology is fast and broadly applicable allowing for the preparation of C−F bonds from (hetero)benzylic, propargylic, and non-activated tertiary alcohol derivatives. Preliminary mechanistic studies support that the key step of the reaction is the single-electron oxidation of cesium oxalates—which are readily available from the corresponding tertiary alcohols—with in situ generated TEDA^2+. (TEDA: N-(chloromethyl)triethylenediamine), a radical cation derived from Selectfluor®.