Microwave‐Assisted Rapid and Efficient Synthesis of New Series of Chromene‐Based 1,2,4‐Oxadiazole Derivatives and Evaluation of Antibacterial Activity with Molecular Docking Investigation

A new series of novel chromene‐based oxadiazole derivatives were synthesized from a variety of chromene‐based amidoximes with readily available carboxylic acids under conventional oil bath heating as well as under microwave irradiation. The use of commercially available EDCI and HOBt as coupling reagents in DMF combined with microwave heating resulted in high yields and purities of the product 1,2,4‐oxadiazoles in an expeditious manner. This methodology is successfully applied to synthesize 18 numbers of new 2H‐chromene‐substituted 1,2,4‐oxadiazole derivatives in good to high yields. The structure of the product was ascertained by X‐ray crystallographic analysis. All the synthesized compounds were evaluated for their in vitro antibacterial activity against two different pathogenic bacterial strains, that is, Escherichia coli (MTCC614) and Klebsiella pneumoniae (MTCC4031). The obtained results from in vitro antimicrobial assays indicated that 6g and 6h exhibited good antibacterial activity nearer to the standard drug, gentamicin. The molecular docking studies showed that compounds 6g and 6h show hydrogen bonding interaction with the bacterial target DNA gyrase of E. coli.     

Nitroenamines—III: Synthesis of 3,3-diamino-2-nitroacrylonitriles from 1,1-diamino-2-nitroethylenes

A novel fragmentation of an isothiazoline ring is reported. Nitroketene aminals 1 react with benzoyl isothiocyanate to form the adducts 3. These adducts can be converted to the 3,3-diamino-2-nitroacrylonitriles 2 in two discrete steps—first to an isothiazoline (4,7) by oxidation, and then to the nitriles by base-induced fragmentation; alternatively the adducts (3c, 11) can be directly treated with alkaline hydrogen peroxide to provide the nitriles in one step.     

A novel differential scanning calorimetric method to study the complexation of β-cyclodextrin with steroid in solid state

This communication demonstrates that, by simply minotiring the evaporation of water molecules included in β-cyclodextrin cavity, complexation of β-cyclodextrin with steroid in solid state can be studied. The reported method is simple, rapid and novel.     

Geometric features of the mixing of passive scalars at high Schmidt numbers

The mixing of passive scalars of decreasing diffusivity, advected in each case by the same three-dimensional Navier-Stokes turbulence, is studied. The mixing becomes more isotropic with decreasing diffusivity. The local flow in the vicinity of steepest negative and positive scalar gradients is in general different, and its behavior is studied for various values of the scalar diffusivity. Mixing approaches monofractal properties with diminishing diffusivity. We consider these results in the context of possible singularities of scalar dissipation.     

Stabilization effects in flow through helically coiled pipes

When a flow through a straight pipe is passed through a coiled section, two stabilizing effects come into play. First, in a certain Reynolds number range, the flow that is turbulent in the straight pipe becomes completely laminar in the coiled section. Second, the stabilization effect of the coil persists to a certain degree even after the flow downstream of the coil has been allowed to develop in a long straight section. In this paper, we report briefly on aspects related to these two effects.     

Turbulent cascades

Turbulent cascades at high Reynolds numbers are explained briefly in terms of multipliers and multiplier distributions. Two properties of the multipliers ensure the existence of power laws for locally averaged energy dissipation rate: (a) the existence of a multiplier probability density function that is independent of the level of the cascade, and (b) the statistical independence of multipliers at one level on those at previous levels. Under certain conditions described in the paper, the same two properties of multipliers guarantee that velocity increments over inertial-range separation distances also possess power laws. This work is specifically motivated by the need to understand the influence on scaling of the experimental observations that property (a) is true for turbulence, but property (b) is not; and additional motivation is the need to relate cascade models to intermittent vortex stretching (and folding). This effect has been modeled by allowing the multiplier distribution to depend on the magnitude of the local strain rate, and it is demonstrated that this rate-dependent model accounts for the statistical dependence observed in experiments. It is also shown that this model is consistent with the uncorrelated cascade models except for very weak singularity strengths (or for negative moments below a certain order), leading to the conclusion that, for all practical purposes, the uncorrelated level-independent multipliers abstract the essence of the breakdown process in turbulence.     

Spin-trapping studies on the reaction of NO<Subscript>2</Subscript> with <Emphasis Type="Italic">β</Emphasis>-carotene

Absorption spectrophotometric studies indicated that in chloroform -carotene reacted with NO2 with a stoichiometry of 1:2. To understand the reaction mechanism, free radical intermediates produced during their reaction were trapped by spin traps 2-methyl-2-nitroso propane (MNP) and 4-pyridyl-1-oxide-N-1-butyl nitrone (POBN). The resulting stable spin adducts were detected by electron spin resonance (ESR) spectroscopy. NO₂ alone did not interact with spin traps, but introduction of -carotene-generated ESR signals with different nitrogen and hydrogen hyperfine coupling constants (A _N and A _H) characteristsic of the trapped radical. Two possible pathways exist for the reaction of NO₂ with -carotene, viz., electron transfer and addition to the polyene chain. Our ESR results supported an addition mechanism, where formation of carbon-centered [NO₂ · · · -carotene] free radical adduct was observed.