A general and efficient CuI/BtH catalyzed coupling of aryl halides with thiols

We report an exceptionally mild, general and efficient copper catalyzed cross coupling reaction of aryl bromides and thiols using 0.5 mol % CuI and 1 mol % benzotriazole. Experimental simplicity, generality, functional group tolerance and low cost of the catalyst are advantages of the protocol.     

Linear sweep voltammetry at the tubular graphite electrode: Part II. Totally irreversible processes

The theory of linear sweep voltammetry at the tubular graphite electrode has been developed for irreversible processes. The convective diffusion differential equations have been transformed into an integral equation which is solved numerically. The current-potential curves have been calculated theoretically and verified experimentally. The dependence of the current-potential curves on velocity has been studied. A procedure for the determination of kinetic parameters, i.e. standard rate constant and transfer coefficient, is presented.     

EPR evidence of possible metastable regions in Mn2+ doped ferroelectric NaNO2

Of the various EPR spectra observed in the ferroelectric phase of NaNO₂, a spectrum designated as spectrum II is observed to have some peculiar properties like dependence of its intensity on growth conditions of the crystal, its disappearance below ≈60°C after heat treatment of the crystal, its reappearance by heating above ≈60°C and also by application of an external dc electric field at ≈30°C. These observations suggest the possible existence, around Mn²⁺-vacancy complex in the ferroelectric phase of NaNO₂, of a metastable structure intermediate to the paraelectric and ferroelectric phase structures.     

m-Aminobenzoic acid inserted β-turn in acyclic tripeptides: a peptidomimetic design

X-ray diffraction studies show that peptides Boc-Leu-Aib-m-ABA-OMe (I) (Aib, α-aminoisobutyric acid; m-ABA, meta-aminobenzoic acid) and Boc-Phe-Aib-m-ABA-OMe (II) adopt a type-II β-turn conformation, solely stabilized by co-operative steric interactions amongst the amino acid residues. This type of β-turn without any intramolecular hydrogen bonding is generally referred to as an open turn. Although there are some examples of constrained cyclic peptides in which o-substituted benzenes have been inserted to mimic the turn region of the neurotrophin, a nerve growth factor, peptides I and II present novel two examples where m-aminobenzoic acid has been incorporated in the β-turn of acyclic tripeptides. The result also demonstrates the first crystallographic evidence of a β-turn structure containing an inserted m-aminobenzoic acid, which can be considered as a rigid γ-aminobutyric acid with an all-trans extended configuration.     

Fabrication and Characterization of Cysteine-Functionalized Zinc Oxide Nanoparticles for Enzyme Immobilization

A green approach is reported for the synthesis of cysteine-functionalized zinc oxide nanoparticles using potato extract as a nontoxic and economical reducing agent. The cysteine-functionalized nanoparticles were used as a support for enzyme immobilization. The structural morphology, crystallinity, and surface functionalization were characterized by scanning electron microscopy, X-ray diffraction, and infrared spectroscopy, respectively. Spherical nanoparticles from 150 to 200?nm were used to evaluate the immobilization efficiency for urease through covalent attachment on the glutaraldehyde-activated amino group of cysteine. In comparison to the unmodified nanoparticles, 62.9% enzyme loading with 72.45% of enzyme specific activity was recovered which was 56% higher than on bare zinc oxide nanoparticles. The point of addition of cysteine during the nanoparticle synthesis had a direct effect on the immobilization efficiency. The immobilized enzyme-specific activity was reduced to 34.32% when cysteine was added following the nanoparticle synthesis. With a facile synthesis procedure and significant immobilization efficiency, cysteine-functionalized zinc oxide nanoparticles were shown to be suitable for various clinical and industrial applications.     

Validated HPTLC method for the simultaneous quantification of diterpenoids in Vitex trifolia L.

Vitex trifolia L. is an important Indian medicinal plant with diverse pharmacological properties. In a recent study, we reported the isolation and antitubercular activity evaluation of three new diterpenoids from its leaves; here we have developed a validated rapid, simple, precise, and accurate high‐performance TLC method for the simultaneous quantification of isolated diterpenoids in V. trifolia. Diterpenoids, 6α,7α‐diacetoxy‐13‐hydroxy‐8(9),14‐labdadien ( A ), 13‐hydroxy‐5(10),14‐halimadien‐6‐one ( B ), and 9‐hydroxy‐13(14)‐labden‐16,15‐olide ( C ) were separated on silica gel 60F₂₅₄ high‐performance TLC plates using chloroform/acetone (98:2, v/v) as mobile phase. The quantitation of diterpenoids was carried out using densitometric reflection/absorption mode at 610 nm after postchromatographic derivatization using a vanillin/sulfuric acid reagent. A precise and accurate quantification can be performed for compounds A and B in the linear working concentration range of 333–1000 ng/band and for C in the range of 670–2000 ng/band with good correlations (r = 0.9984, 0.9991, and 0.9994, respectively). The method was validated for peak purity, precision, accuracy, robustness, LOD, and LOQ, as per the ICH guidelines. The method reported here is simple, reproducible and may be applied for the quantitative analysis of the above diterpenoids in the leaves of V. trifolia.     

Domain decomposition methods for hyperbolic problems

In this paper a method is developed for solving hyperbolic initial boundary value problems in one space dimension using domain decomposition, which can be extended to problems in several space dimensions. We minimize a functional which is the sum of squares of the L ² norms of the residuals and a term which is the sum of the squares of the L ² norms of the jumps in the function across interdomain boundaries. To make the problem well posed the interdomain boundaries are made to move back and forth at alternate time steps with sufficiently high speed. We construct parallel preconditioners and obtain error estimates for the method. The Schwarz waveform relaxation method is often employed to solve hyperbolic problems using domain decomposition but this technique faces difficulties if the system becomes characteristic at the inter-element boundaries. By making the inter-element boundaries move faster than the fastest wave speed associated with the hyperbolic system we are able to overcome this problem.     

Role of halide ions and temperature on the morphology of biologically synthesized gold nanotriangles

In this paper, we demonstrate the effect of halide ions on the formation of biogenically prepared gold nanotriangles using the leaf extract of lemongrass (Cymbopogon flexuosus) plant. We have also studied the effect of halide ions on the morphology of biogenic nanotriangles. It has been shown that iodide ions have a greater propensity to transform flat gold nanotriangles into circular disk-like structures as compared to other halide ions. The study also suggests that the presence of Cl- ions during the synthesis promotes the growth of nanotriangles, whereas the presence of I- ions distorts the nanotriangle morphology and induces the formation of aggregated spherical nanoparticles. The change in the morphology of gold nanotriangles has been explained in terms of the ability of the halide ions to stabilize or inhibit the formation of (111) faces to form [111] oriented gold nanotriangles. Last, we have also shown that the temperature is an important parameter for controlling the aspect ratio and the relative amounts of gold nanotriangles and spherical particles. The results show that, by varying the temperature of reaction condition, the shape, size, and optical properties of anisotropic nanoparticles can be fine-tuned.