Method for determination of radium in seawater using MnO<Subscript>2</Subscript> co-precipitation technique

Radium is considered to be a useful tracer for studying various physical processes of seawater. There are several methods for analysis of radium; however, analysis of radium in seawater by those analytical techniques is a tedious job. Thus a new methodology was optimized for analysis of radium in sea water using MnO₂ co-precipitation followed by gamma spectrometry. The method produced good yield which ranged from 85–98%. The method is simple and requires less amounts of chemicals and no use of acids. Seawater from different western Indian coastal environments viz. Tarapur, Mumbai and Goa were collected and analysed for ²²⁶Ra and ²²⁸Ra using this method.     

Copper-catalyzed enantioselective additions to oxocarbenium ions: alkynylation of isochroman acetals

We have developed an enantioselective, copper(I)-catalyzed addition of terminal alkynes to racemic isochroman acetals. This method is one of the first transition-metal-catalyzed approaches to enantioselective additions to prochiral oxocarbenium ions. In this reaction, TMSOTf is used to form the oxocarbenium ion in situ under conditions compatible with simultaneous formation of the chiral copper acetylide. By using a bis(oxazoline) ligand, good yields and enantioselectivities are observed for a variety of enantioenriched 1-alkynyl isochromans.     

An amyloid-like fibril-forming supramolecular cross-β-structure of a model peptide: a crystallographic insight

The peptide Boc-Val-Phe-OMe 1 bearing sequence similarity with the central hydrophobic cluster (CHC) of Alzheimer's Aβ(18-19) peptide self-assembles to produce amyloid-like straight unbranched fibrils as examined by atomic force microscopy and Congo red assay. Single crystal X-ray diffraction offers the atomic level structure of the supramolecular parallel β-sheet aggregation and antiparallel separation between layers (cross-β-structure).     

Enantioselective O-acetylcyanation/cyanoformylation of aldehydes using catalysts with built-in crown ether-like motif in chiral macrocyclic V(V) salen complexes

Chiral macrocyclic V(V) salen complexes 1a-f derived from macrocyclic ligands obtained by the reaction of 1R,2R-(−) diaminocyclohexane/(1R,2R)-(+)-1,2-diphenylethylenediamine with bis-aldehydes 2 and 3 were synthesized and used as efficient catalysts in asymmetric cyanation reactions. The V(V) catalysts demonstrated excellent performance (product yields and ees up to 99%) with potassium cyanide (KCN) and sodium cyanide (NaCN). The catalytic system also performed very well with a safer source of cyanide-ethyl cyanoformate to give cyanohydrin carbonates in excellent yield and ee (up to 97%). The V(V) macrocyclic salen complex 1b retained its performance at multi-gram level and was conveniently recycled for a number of times.     

Distribution of uranium and thorium in fractionated sediment samples obtained from different locations across Thane Creek area (Mumbai,India)

Uranium concentration varies from 9.01 to 12.7, 8.03 to 11.5, 9.1 to 14.0 and 10.1 to 14.2 mg/kg in grab sediment, coarse sand fraction, fine sand fraction, silt and clay fraction respectively. Thorium concentration varies from 20.0 to 29.4, 17.3 to 28.6, 19.6 to 30.4 and 21.1 to 35.9 in grab sediment, coarse sand fraction, fine sand fraction, silt and clay fraction respectively. Uranium and thorium concentrations vary in different size fractionated sediment samples like silt and clay fraction > fine sand fraction > coarse sand fraction.     

A novel cation induced polymeric chain in Na8[{Cu(gly)2}2]{H2(H2W12O42)}]?·?24H2O: hydrothermal synthesis, spectroscopic characterization and X-ray structure analysis

A novel bis(glycinato)copper(II)paradodecatungstate Na₈[{Cu(gly)₂}₂]-{H₂(H₂W₁₂O₄₂)}] · 24H₂O (1) has been synthesized under hydrothermal conditions. The crystal structure of 1 reveals an infinite one-dimensional chain along the [100] direction and is built from paradodecatungstate (H₂W₁₂O₄₂)¹⁰⁻ clusters joined through [Cu(gly)₂] moieties. Parallel chains are interlinked by NaO₆ octahedra to generate a two-dimensional network.     

Adsorption of rhodamine B on Rhizopus oryzae: role of functional groups and cell wall components

The role of different functional groups (i.e. amino, carboxyl, hydroxyl as well as phosphate) and cell wall components (such as chitin, chitosan, glucan and phosphomannan) of Rhizopus oryzae on adsorption of rhodamine B is described. The functional groups were chemically modified to determine their contribution in the present adsorption process. Fourier transformed infrared spectroscopic (FTIR) study was used to characterize the modification of the functional groups due to chemical treatments. Carboxyl and amino groups were identified as most important moieties involved in the binding process. Different cell wall components were also isolated from the cell wall to explore their role involved in the binding process. Phosphomannan fraction adsorbed higher amounts of rhodamine B compared to the other cell wall components. Fluorescence microscopic images also supported the differential adsorption capacity of the various cell wall components.     

Hydrogen‐Bonding Induced Alternate Stacking of Donor (D) and Acceptor (A) Chromophores and their Supramolecular Switching to Segregated States

This paper reports comprehensive studies on the mixed assembly of bis‐(trialkoxybenzamide)‐functionalized dialkoxynaphthalene (DAN) donors and naphthalene‐diimide (NDI) acceptors due the cooperative effects of hydrogen bonding, charge‐transfer (CT) interactions, and solvophobic effects. A series of DAN as well as NDI building blocks have been examined (wherein the relative distance between the two amide groups in a particular chromophore is the variable structural parameter) to understand the structure‐dependent variation in mode of supramolecular assembly and morphology (organogel, reverse vesicle, etc.) of the self‐assembled material. Interestingly, it was observed that when the amide functionalities are introduced to enhance the self‐assembly propensity, the mode of co‐assembly among the DAN and NDI chromophores no longer remained trivial and was dictated by a relatively stronger hydrogen‐bonding interaction instead of a weak CT interaction. Consequently, in a highly non‐polar solvent like methylcyclohexane (MCH), although kinetically controlled CT‐gelation was initially noticed, within a few hours the system sacrificed the CT‐interaction and switched over to the more stable self‐sorted gel to maximize the gain in enthalpy from the hydrogen‐bonding interaction. In contrast, in a relatively less non‐polar solvent such as tetrachloroethylene (TCE), in which the strength of hydrogen bonding is inherently weak, the contribution of the CT interaction also had to be accounted for along with hydrogen bonding leading to a stable CT‐state in the gel or solution phase. The stability and morphology of the CT complex and rate of supramolecular switching (from CT to segregated state) were found to be greatly influenced by subtle structural variation of the building blocks, solvent polarity, and the DAN/NDI ratio. For example, in a given D–A pair, by introducing just one methylene unit in the spacer segment of either of the building blocks a complete change in the mode of co‐assembly (CT state or segregated state) and the morphology (1D fiber to 2D reverse vesicle) was observed. The role of solvent polarity, structural variation, and D/A ratio on the nature of co‐assembly, morphology, and the unprecedented supramolecular‐switching phenomenon have been studied by detail spectroscopic and microscopic experiments in a gel as well as in the solution state and are well supported by DFT calculations.     

Controlled growth of polyaniline fractals on HOPG through potentiodynamic electropolymerization

Polyaniline (PANI) in fractal dimension has been electrodeposited reproducibly on highly oriented pyrolytic graphite (HOPG) from 0.2 M aniline in 1 M aqueous HCl solution by potentiodynamic sweeping in the range of -0.2 to 0.76 V vs Ag/AgCl at room temperature. Fractal growth of PANI dendrimers is affected by diffusion limited polymerization (DLP) at a sweep rate of 15 mV s(-1) for 43 min. This type of PANI dendrimer is prepared for the first time on such large area HOPG substrate by electrochemical technique using rather simple cell setup. The fractal dimension has been determined by chronoamperometry (CA) and box counting technique and is found to vary from 1.4 to 1.9 with the duration of electropolymerization. The sweep rate, terminal oxidation potential, and the diverse surface anisotropy of the HOPG surface are found to be crucial factors in controlling the growth of such PANI fractals.