Multilayer assemblies of polyelectrolyte-gold nanoparticles for the electrocatalytic oxidation and detection of arsenic(III)

Multilayers of poly(diallyldimethylammonium chloride) (PDDA) and citrate capped Au nanoparticles (AuNPs) anchored on sodium 3-mercapto-1-propanesulfonate modified gold electrode by electrostatic layer-by-layer assembly (LbL) technique are shown to be an excellent architecture for the direct electrochemical oxidation of As(III) species. The growth of successive layers in the proposed LbL architecture is followed by atomic force microscopy, UV-vis spectroscopy, quartz crystal microbalance with energy dissipation, and electrochemistry. The first bilayer is found to show rather different physico-chemical characteristics as compared to the subsequent bilayers, and this is attributed to the difference in the adsorption environments. The analytical utility of the architecture with five bilayers is exploited for arsenic sensing via the direct electrocatalytic oxidation of As(III), and the detection limit is found to be well below the WHO guidelines of 10ppb. When the non-redox active PDDA is replaced by the redox-active Os(2,2'-bipyridine)(2)Cl-poly(4-vinylpyridine) polyelectrolyte (PVPOs) in the LbL assembly, the performance is found to be inferior, demonstrating that the redox activity of the polyelectrolyte is futile as far as the direct electro-oxidation of As(III) is concerned.     

Combination of NH2OH·HCl and NaIO4: a new and mild oxidizing agent for selective oxidation of alcohols to carbonyl compounds

A new method for oxidation of alcohols to carbonyl compounds has been developed using NH₂OH·HCl and NaIO₄ under mild reaction conditions at room temperature. Application of the method for the synthesis of diiodo compound from α,β-unsaturated carbonyl compound is also described.     

Highly regio- and stereoselective asymmetric bromoazidation of chiral alpha,beta-unsaturated carboxylic acid derivatives: scope and limitations

Lewis acid catalyzed asymmetric bromoazidation of chiral alpha,beta-unsaturated carboxylic acid derivatives was performed using N-bromosuccinimide (NBS) and trimethylsilyl azide (TMSN3) as the bromine and azide sources. Among the Lewis acids, Yb(OTf)3 was found to be the best catalyst. Regio- and anti-selectivity of 100% and moderate to good diastereoselectivity (up to 89:11) with good yields were obtained when Oppolzer's bornane sultam chiral auxilairy was used. Diastereoselectivity of >95:05 was observed when (2S,5S)-2,5-diphenylpyrrolidine was used as the chiral auxiliary.     

Catalytic application of task specific ionic liquid on the synthesis of benzoquinazolinone derivatives by a multicomponent reaction

Benzoquinazolin-2-one derivatives were synthesized by using a catalytic amount of task specific ionic liquid, [1-methyl-3-(4-sulfobutyl)imidazolium-4-methylbenzenesulfonate] through a one-pot multicomponent Biginelli reaction of α-tetralone, aldehyde, and urea/thiourea in excellent yields within a short reaction time. Mechanism studies suggest that the reaction proceeds through iminium intermediate and C2-H of the TSIL plays a major role on its catalytic activity. The catalyst has been reused four times without any significant loss in catalytic activity. Large scale reaction by using this TSIL suggests the applicability of this methodology for bulk synthesis of quinazolinone derivatives.     

Dielectric,impedance and excitation performance of Aurivillius oxides: Bi4Pb2Zr2TiFeNbO18

The Aurivillius phase-based composition bearing chemical formula Bi₄Pb₂Zr₂TiFeNbO₁₈ (termed as BPZTFNO) was synthesized by a solid-state method. The structural analysis as obtained from the X-ray pattern has depicted an orthorhombic phase. The various size and morphology of grains are distributed throughout the natural surface as revealed from microstructure analysis. The dielectric and electrical study of the BPZTFNO is taken at a various sweep of frequency (1 kHz–1 MHz) and temperatures (25–400 °C). The ferroelectric-paraelectric phase transition is well illustrated from the temperature-dependent dielectric constant. The complex impedance analysis suggests the association of grain effect. The relaxation of non-Debye nature is shown in the impedance study. The formed sample is subjected to an electric field and further its excitation performance is examined suggesting its possible usage in devices.     

Task-specific ionic liquid-catalyzed efficient couplings of indoles with 1,3-dicarbonyl compounds: an efficient synthesis of 3-alkenylated indoles

Direct alkenylation of indoles at the 3-position with 1,3-dicarbonyl compounds under Brønsted acidic ionic liquid catalysis has been developed. The yields were excellent, and the catalyst can be reused at least six times without noticeable loss of catalytic activity.     

Indium triflate-catalyzed one-pot synthesis of 1-substituted-1H-1,2,3,4-tetrazoles under solvent-free conditions

A simple, efficient, and general method has been developed for the synthesis of 1-substituted-1H-1,2,3,4-tetrazoles via a three-component condensation of amine, trimethyl orthoformate, and sodium azide in presence of a catalytic amount of indium triflate under solvent-free conditions. The reaction proceeds smoothly to generate the corresponding 1-substituted tetrazoles in moderate to excellent yields under heating.     

Exchange bias in ferrimagnetic-antiferromagnetic nanocomposite produced by mechanical attrition

Nanoparticles comprising of magnetite (Fe₃O₄) core-hematite (α-Fe₂O₃) shell with mean diameter around 9 nm were synthesized by mechanical grinding. Zero-field-cooled (ZFC) and field-cooled (FC) magnetization and hysteresis loop measurements were carried out over the temperature range 5-300 K. Exchange bias varying from 140 to 10 Oe was observed. This is explained as arising due to ferrimagnetic-antiferromagnetic coupling at the nanointerfaces between the two phases. Analysis of data shows a pronounced increase in the effective anisotropy constant as the milling time is increased.