Kinetics and mechanism of palladium(II) catalysed oxidation of amines and aminoalcohols by N-bromosuccinimide in perchloric acid

Summary The kinetics of oxidation of amines (EtNH₂, Et₂NH, Et₃N) and aminoalcohols [H₂NCH₂CH₂OH, H₂N(CH₂)₃OH, (CH₂CH₂OH)₂NH, (CH₂CH₂OH)₃N] by N-bromosuccinimide (NBS) have been studied in aqueous HClO₄ with PdCl₂ as catalyst, and in the presence of Hg(OAc)₂ to ensure oxidation by pure NBS. The order of reaction with respect to NBS was unity, however, an increase in [NBS]₀ resulted in a decrease in the rate constant. The rate was directly proportional to [Pd^II] for the aminoalcohols while for EtNH₂ the rate was proportional to k + k[Pd^II] (where k and k are rate constants for the uncatalysed and catalysed paths, respectively). Retarding effects for HClO₄, succinimide, Cl^– and AcOH on the rate of oxidation were observed. The kinetic data support the formation of [Pd^II-A] and [Pd^II-(A)₂] complexes (where A represents amine or aminoalcohol). A mechanism, consistent with the observed kinetic data, is proposed.     

Effect of ultraviolet light absorbers on photostabilization of azadirachtin-A in solution (part: II)

The effect of photostabilization of azadirachtin-A (Aza-A) was examined in solutions when exposed to UV radiation, in the presence of four structurally different UV absorbers namely, p-aminobenzoic acid, 2,4-dihydroxybenzophenone, 4,4'-dihydroxybenzophenone and phenyl salicylate. The percentages of Aza-A recovered from the solutions after 6 h exposed to UV radiation in the presence and absence of UV absorbers indicated that the order of stabilization of Aza-A by these absorbers was similar to that obtained in the solid phase experiments in accordance with our previous observations. It is observed that the addition of phenyl salicylate in Aza-A (in 1:1 mole ratio) provides the excellent photostabilization of Aza-A molecule in solid phase as well as in solution among the four absorbers studied.     

Complexes of quinolone drugs norfloxacin and ciprofloxacin with alkaline earth metal perchlorates

The interaction of quinolone drugs Norfloxacin (NR) and Ciprofloxacin (CP) with magnesium, calcium and barium perchlorates was investigated. Solid complexes, obtained as products of this interaction, were isolated and characterized by elemental and thermal analysis, FT-IR spectral and electrical conductivity measurements. The spectral studies of the isolated complexes suggest that NR and CP act as bidentate ligands that bind through one carboxylic oxygen atom and the exocyclic carbonyl oxygen atom. The obtained results indicate the formation of the complexes of the following formulas: [M(CP)₂](ClO₄)₂·xH₂O and [M(NR)₂](ClO₄)₂·xH₂O, where M = Mg(II), Ca(II), and Ba(II).     

Ultrasound promoted greener synthesis of spiro[indole-3,5′-[1,3]oxathiolanes in water

An aqueous mediated novel synthesis of substituted 2′amino-4′benzoyl-2′-methyl spiro[indole 3,5′-[1,3]oxathiolane]-2(1H)-ones (2a–f) was carried out from the reaction of spiro [indole-3,2′-oxiranes] (1a–f) with thioacetamide in the presence of LiBr as catalyst. The reaction was carried out under both microwaves and sonication and results were also compared with conventional method. In general, improvement in rate and yields observed when reaction was carried out under sonication as compared to microwave irradiation and conventional method.     

Carbon-SO3H catalyzed expedient synthesis of new spiro-[indeno[1,2-b]quinoxaline-[11,2′]-thiazolidine]-4′-ones as biologically important scaffold

In this report, we have described a convenient and eco-compatible approach for synthesis of new hybrid spiro[indeno[1,2-b]quinoxaline-[11,2′]-thiazolidine]-4′-ones (4a–k) via multi-component reaction of indeno[1,2-b]quinoxalinone, α-mercaptocarboxylic acids and various types of amines using urea-choline chloride as green deep eutectic solvent and carbon-SO₃H as a solid acid catalyst. This new protocol produces a thiazolidine ring attached to indeno[1,2-b]quinoxaline through spiro carbon in good to excellent yields. The advantages of this protocol are avoidance of toxic and harmful catalyst and solvents further both catalyst and DES were recovered from the reaction mixture quantitatively and reused several times. Synthesized compounds were characterized on the basis of spectral and single crystal X-ray analysis. The prepared catalyst was characterized by FT-IR, SEM, and X-ray diffraction method.     

Thermal and oxidative stability assessment of synergistic blends of sunflower and sesame oils tailored for nutritionally stable composition of omega fatty acids

The thermal stability of ω-6 fatty acid-rich oils is a bewildering problem. The synergistic blends of sunflower (SO) (50–80%) and sesame oil (SEO) (20–50%) were optimized for improved thermal stability, better retention of antioxidants, and balanced ratio of ω-fatty acids (ω-6 and 9). The oil blends were thermally oxidized by Rancimat (temperature 100, 110, 120, and 130 °C; airflow rate 20 L h⁻¹) for estimating the induction period (IP) and kinetic rate constant (k) of lipid oxidation. The oils were exhaustively characterized for thermal stability by thermogravimetry and differential scanning calorimetry. The temperature-dependent kinetics of lipid oxidation was described using Arrhenius equation (lnk vs. 1/T) and activated complex theory (lnk/T vs. 1/T). The calculated kinetic parameters, viz. activation energies, activation enthalpies, and entropies varied from 90.80 to 99.17, 87.58 to 95.94, − 33.28 to − 4.78 J mol⁻¹ K⁻¹, respectively (R²> 0.90, p < 0.05). The optimized blend (OB) consisted of 50.8 and 49.2% of SO and SEO, respectively, and showed the highest synergism (115%) and IP (100 °C) than SO (13.2 vs. 6.1 h). This could be attributed to lignans (6304 vs. 5289 mg kg⁻¹)-induced thermal stability and effective retention of tocopherols (270 vs. 197 mg kg⁻¹). OB possesses balanced composition of ω-fatty acids (ω-9, 34.5 vs. 28.7%; ω-6, 49 vs. 52%) and superior thermal stability (onset temperature, 387 vs. 212 °C; oil induction time, 21.6 vs. 15.7 min) than SO. It could be recommended over SO for culinary applications while ensuing thermal stability and nutritional benefits.

     

Microfluidic production of biopolymer microcapsules with controlled morphology

We report a microfluidic approach to generating capsules of biopolymer hydrogels. Droplets of an aqueous solution of a biopolymer were emulsified in an organic phase comprising a cross-linking agent. Polymer gelation was achieved in situ (on a microfluidic chip) by diffusion-controlled ionic cross-linking of the biopolymer, following the transfer of the cross-linking agent from the continuous phase to the droplets. Gelation was quenched by collecting particles in a large pool of cross-linking agent-free liquid. The structure of microgels (from capsules to gradient microgels to particles with a uniform structure) was controlled by varying the time of residence of droplets on the microfluidic chip and the concentration of the cross-linking agent in the continuous phase. We demonstrated the encapsulation of a controlled number of polystyrene beads in the microgel capsules. The described approach was applied to the preparation of capsules of several polysaccharides such as alginate, kappa-carrageenan, and carboxymethylcellulose.     

A new flavanone, reflexin, from Cuscuta reflexa and its selective sensing of nitric oxide

A new compound, reflexin, 5-hydroxy-7-methoxy-6-(2,3-epoxy-3-methylbutyl)-flavanone, is isolated from the stems of Cuscuta reflexa along with three other known compounds. This new compound has good potential for application especially in the photoactivity of reflexin. It was found to be sensitive to glutathione, forming a fluorescent product that is utilized for sensing nitric oxide (NO). The lowest detection limit of NO analysis was found to be 0.05 μM.     

Biological studies of azadirachtin and its derivatives against polyphagous pest, Spodoptera litura

Azadirachtin-A (Aza-A, figure 1) was subjected to a variety of synthetic transformations and the antifeedant activity and toxicity of the azadirachtin derivatives were assessed against second instar larvae Spodoptera litura on castor leaves in comparison with the crude material containing 9.14% Aza-A, as well as relatively pure 91% Aza-A. A probable mechanism for the base initiated fragmentation of the diketocarbonate into a decalin fragment and a spiroketal moiety has been proposed. The present study indicates that the combination of insect toxicity and antifeedancy of azadirachtin provides good crop protection.