Synthesis and Antifungal Screening of 2‐(2‐Aryl‐4‐methyl‐thiazol‐5‐yl)‐5‐((2‐aryl/benzylthiazol‐4‐yl)methyl)‐1,3,4‐oxadiazole Derivatives

A new series of synthesis and biological screening of 2‐(2‐aryl‐4‐methyl‐thiazol‐5‐yl)‐5‐((2‐aryl/benzylthiazol‐4‐yl)methyl)‐1,3,4‐oxadiazole derivatives 5a , 5b , 5c , 5d , 5e , 5f , 5g , 5h , 5i was achieved by condensation of 2‐(2‐aryl/benzylthiazol‐4‐yl)acetohydrazide 2a , 2b , 2c with 4‐methyl‐2‐arylthiazole‐5‐carbaldehyde 3a , 3b , 3c followed by oxidative cyclization of N'‐((4‐methyl‐2‐arylthiazol‐5‐yl)methylene)‐2‐(2‐aryl/benzylthiazol‐4‐yl)acetohydrazide 4a , 4b , 4c , 4d , 4e , 4f , 4g , 4h , 4i using iodobenzene diacetate as oxidizing agent. All the synthesized compounds were screened for their in vitro antifungal activity against Candida albicans, Candida tropicalis, Aspergillus niger, and Aspergillus flavus. Some of the synthesized compounds showed good antifungal activity.     

Transition Metal‐Catalyzed Carbonylative CH Bond Functionalization of Arenes and C(sp3)H Bond of Alkanes

In this article, we present the progress made in the area of carbonylative C? H functionalization, with special emphasis on arenes and alkanes. The importance of directing group assistance and C? H functionalization using CO surrogates is also included. The budding development in the area of transition metal‐catalyzed C(sp³)? H activation makes us feel it necessary to file a summary on the past, as well as current, contributions and a prospective outlook on the transition metal‐catalyzed carbonylative transformation of C? H bonds, which is the focus of this review.     

Adverse and favorable mixed convection heat transfer in a two-side heated square channel

Experimental heat transfer measurements and analysis for mixed convection in a vertical square channel are presented. Water flow directions are selected such that buoyancy assists or opposes the bulk flow pressure gradient. Unlike most previous experiments with symmetrically heated circular tubes, the present configuration uses an asymmetric heating condition (two sides heated and two sides insulated) and shows significant increase in the Nusselt number for both assisted and opposed flow conditions. Observed heat transfer coefficient distributions are different from the symmetrically heated channels; and this difference in heat transfer coefficient is attributed to the formation of buoyancy driven large-scale flow structures. In general, opposed flow shows higher heat transfer coefficients, and the Nusselt number ratio is observed to increase as Gr/Re or Gr/Re² ratios increase for both assisted and opposed flow conditions. A correlation based on the buoyancy parameter predicts the heat transfer pattern well in both assisted and opposed mixed convection. The range of Reynolds numbers discussed (Re=400–10,000) is of importance for direct numerical simulations and the details provided here can serve as the benchmark data required for complicated buoyancy affected turbulence simulations.     

Spectrophotometric determination of Fe(III) by using casein-functionalized gold nanoparticles

The preparation and application of casein-capped gold nanoparticles (AuNPs) as a specific probe for ferric ions Fe(III) is reported. The functionalized AuNPs exhibit narrow size distribution and form stable dispersions in water of different ionic strengths and basicity. The presence of diverse functional groups from the side chain of peptides warrants colloidal stability of AuNPs and also assists recognition of Fe(III) in versatile conditions. Fe(III) ion reportedly causes the aggregation of AuNPs and a red-shift in absorbance toward longer wavelength (660 nm). A spectrophotometric method is appropriate for selective detection of Fe(III) and the spectral shift is also accompanied by a color change from red to blue. The aggregation of AuNPs is not suppressed after the addition of NaOH or at moderate ionic strength. The resulting spectrophotometric method works for Fe(III) in the concentration range of 0.1 to 0.9 μM and has a detection limit of 450 nM. The AuNP probe can also detect Fe(III) ion content in real samples at the same detection limit, which is much lower than the maximum contaminant level allowed for Fe(III) in drinking water (5.37 μM) by the U.S. Environmental Protection Agency.

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Graphical abstract Casein peptide functionalized gold nanoparticles: synthesis, characterization, and their application to the visual detection of Fe(III).

     

A pot-economical and green synthesis of novel (benzo[d]imidazo[2,1-b]thiazol-3-yl)-2H-chromen-2-one in ethanol–PEG-600 under catalyst-free conditions

A catalyst-free, environmentally benign, and simple one-pot multi-component protocol has been developed for the efficient synthesis of novel (benzo[d]imidazo[2,1-b]thiazol-3-yl)-2H-chromen-2-one derivatives in excellent yields using ethanol-PEG-600. This novel and green protocol have the advantages of shorter reaction times, high conversions, and follow the group-assisted-purification (GAP) chemistry process, which can avoid traditional purifications, chromatography and recrystallization. This is the first report for the synthesis of benzo[d]imidazo[2,1-b]thiazol-3-yl)-2H-chromen-2-one.     

Macrocyclic Pd(II) dithiolate complexes as catalysts in Heck reactions

The supramolecular palladium dithiolate complexes, [Pd₂(dppe)₂{S(C₆H₄)_nS}]₂(OTf)₄ and [Pd₂(dppe)₂(SCH₂C₆H₄CH₂S)]₄(OTf)₈ (dppe = 1,2-bis(diphenylphosphino)ethane) has been investigated as highly stable and robust catalysts in Heck C-C coupling reactions. The arylation of butyl acrylate and styrene with various aryl bromides under optimized catalytic systems, showed excellent yield and turnover number (410,000) of the products. The tetranuclear complexes showed slightly higher catalytic activity than the octanuclear complex.     

Dual Reactivity of 1,2,3,4‐Tetrazole: Manganese‐Catalyzed Click Reaction and Denitrogenative Annulation

A general catalytic method using a Mn‐porphyrin‐based catalytic system is reported that enables two different reactions (click reaction and denitrogenative annulation) and affords two different classes of nitrogen heterocycles, 1,5‐disubstituted 1,2,3‐triazoles (with a pyridyl motif) and 1,2,4‐triazolo‐pyridines. Mechanistic investigations suggest that although the click reaction likely proceeds through an ionic mechanism, which is different from the traditional click reaction, the denitrogenative annulation reaction likely proceeds via an electrophilic metallonitrene intermediate rather than a metalloradical intermediate. Collectively, this method is highly efficient and offers several advantages over other methods. For example, this method excludes a multi‐step synthesis of the N‐heterocyclic molecules described and produces only environmentally benign N₂ gas a by‐product.     

Substituent Effects in BODIPY in Live Cell Imaging

Small‐molecule organoselenium‐based fluorescent probes possess great capacity in understanding biological processes through the detection of various analytes such as reactive oxygen/nitrogen species (ROS/RNS), biothiols (cysteine, homocysteine and glutathione), lipid droplets, etc. Herein, we present how substituents on the BODIPY system play a significant part in the detection of biologically important analytes for in vitro conditions and live cell imaging studies. The fluorescence of the probe was quenched by 2‐chloro and 6‐phenyl selenium groups; the probe shows high selectivity with NaOCl among other ROS/RNS, and gives a turn‐on response. The maximum fluorescence intensity is attained within ≈1–2 min with a low detection limit (19.6 nm ), and shows a ≈110‐fold fluorescence enhancement compared to signals generated for other ROS/RNS. Surprisingly, in live cell experiments, the probe specifically located and accumulated in lipid droplets, and showed a fluorescence turn‐on response. We believe this turn‐on response occurred because of aggregation‐induced emission (AIE), which surprisingly occurred only by introducing one lipophilic mesityl group at the meso position of the BODIPY.