Thermally amendable tailor‐made functional polymer by RAFT polymerization and “click reaction”

This investigation reports the preparation and characterization of thermally amendable functional polymer bearing furfuryl functionality via reversible‐addition fragmentation and chain transfer (RAFT) polymerization and Diels‐Alder (DA) reaction. In this case, furfuryl methacrylate (FMA) was polymerized using 4‐cyano‐4‐[(dodecylsulfanylthiocarbonyl)sulfanyl] pentanoic acid as RAFT reagent and 4,4′‐azobis(4‐cyanovaleric acid) as thermal initiator. ¹H NMR, ¹³C NMR, and matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry analysis showed that furfuryl group in poly(furfuryl methacrylate) (PFMA) was not affected during RAFT polymerization and the tailor‐made polymer had RAFT end group. The DA reaction was successfully carried out between the reactive furfuryl functionality of PFMA and different bismaleimides. The thermoreversible property of these DA polymers was characterized by FT‐IR and DSC analysis. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3365–3374     

Chlorotrimethylsilane catalyzed synthesis of 1,3-diphenyl-2-propenones and their antimicrobial activities

The base- or acid-catalyzed Claisen–Schmidt condensation reaction is the common synthetic route for the synthesis of 1,3-diphenyl-2-propenone (known as chalcone). A variety of different synthetic pathways have been used over the decades in the synthesis of chalcone. Microwave irradiation in absence of solvent is employed successfully and presented here with prominent improvement over the existing methods. The reaction is incredibly accelerated in the presence of the catalyst chlorotrimethylsilane (CTMS) and found superior in terms of reaction time, product yield, safer synthetic route, and easy removal of catalyst etc. Products were characterized by elemental analysis and spectroscopy. Single crystal X-ray diffraction was used to determine crystal structures. All compounds were treated for antimicrobial activity. The profound response against bacteria and fungus pathogens by these compounds is impressive and opens up opportunities for further physiological activity studies.     

High-performance polymer electrolyte membranes incorporated with 2D silica nanosheets in high-temperature proton exchange membrane fuel cells

Silica nanosheets(SN)derived from natural vermiculite(Verm)were successfully incorporated into polyethersulfone-polyvinylpyrrolidone(PES-PVP)polymer to fabricate high-temperature proton exchange membranes(HT-PEMs).The content of SN filler was varied(0.1-0.75 wt%)to study its influence on proton conductivity,power density and durability.Benefiting from the hydroxyl groups of SN that enable the formation of additional proton-transferring pathways,the inorganic-organic membrane displayed enhanced proton conductivity of 48.2 mS/cm and power density of 495 mW/cm² at 150℃ without humidification when the content of SN is 0.25 wt%.Furthermore,exfoliated SN(E-SN)and sulfonated SN(S-SN),which were fabricated by a liquid-phase exfoliation method and silane condensation,respectively,were embedded in PES-PVP polymer matrix by a simple blending method.Due to the significant contribution from sulfonic groups in S-SN,the membrane with 0.25 wt%S-SN reached the highest proton conductivity of51.5 mS/cm and peak power density of 546 mW/cm² at150℃,48%higher than the pristine PES-PVP membranes.Compared to unaltered PES-PVP membrane,SN added hybrid composite membrane demonstrated excellent durability for the fuel cell at 150℃.Using a facile method to prepare 2D SN from natural clay minerals,the strategy of exfoliation and functionalization of SN can be potentially used in the production of HT-PEMs.     

Spectrophotometric determination of some pesticides in water samples after preconcentration with Saccharomyces cerevisiae immobilized on sepiolite

A sensitive and selective method for the preconcentration and determination of carbaryl, chlorpyrifos, linuron, and thiram was developed. The column sorption method was used for the preconcentration studies. Several parameters, such as amount of sorbent, pH, flow rate, volume of elution solution, and interferences, that can influence the retention of pesticides on Saccharomyces cerevisiae immobilized on sepiolite were investigated. Results showed that it was possible to achieve quantitative analysis when the sample pH was in the range 4-6 for carbaryl and thiram, 4-8 for linuron and 6 for chlorpyrifos using 100 mL of sample solution containing 20 microg of pesticide and 5 mL of eluent. Recoveries of carbaryl, chlorpyrifos, linuron, and thiram were 93.2 +/- 0.4%, 97.1 -/+ 0.3%, 98.5 +/- 0.4%, and 96.1 +/- 0.2%, respectively, at 95% confidence level under optimum conditions. The capacity of the sorbent was found to be 41, 28, 35, and 46 mg g(-1) for carbaryl, chlorpyrifos, linuron, and thiram, respectively. Saccharomyces cerevisiae immobilized on sepiolite is suitable for repeated use without loss of capacity up to twenty five cycles. The pesticides studied have been determined in river water with high precision and accuracy.     

Palladium-Catalyzed Selective meta-C−H Deuteration of Arenes: Reaction Design and Applications

Deuterium-labeled compounds find wide applications in kinetic studies, and within the pharmaceutical industry. An easily removable pyrimidine-based auxiliary has been employed for the meta-C−H deuteration of arenes. The scope of this Pd-catalyzed deuteration using commercially available [D₁]- and [D₄]-acetic acid has been demonstrated by its application in phenylacetic acid and phenylmethanesulfonate derivatives. A detailed mechanistic study led us to explore the reversibility of the non-rate determining C−H activation step. The present study of meta-deuterium incorporation illustrates the template morphology in terms of selectivity. The applicability of this method has been demonstrated by the selective deuterium incorporation into various pharmaceuticals.     

Calibration and Limits of Camera‐Based Fluorescence Correlation Spectroscopy: A Supported Lipid Bilayer Study

Camera‐based fluorescence correlation spectroscopy (FCS) approaches allow the measurement of thousands of contiguous points yielding excellent statistics and details of sample structure. Imaging total internal reflection FCS (ITIR‐FCS) provides these measurements on lipid membranes. Herein, we determine the influence of the point spread function (PSF) of the optical system, the laser power used, and the time resolution of the camera on the accuracy of diffusion coefficient and concentration measurements. We demonstrate that the PSF can be accurately determined by ITIR‐FCS and that the laser power and time resolution can be varied over a wide range with limited influence on the measurement of the diffusion coefficient whereas the concentration measurements are sensitive to changes in the measurement parameters. One advantage of ITIR‐FCS is that the measurement of the PSF has to be performed only once for a given optical setup, in contrast to confocal FCS in which calibrations have to be performed at least once per measurement day. Using optimized experimental conditions we provide diffusion coefficients for over ten different lipid membranes consisting of one, two and three constituents, measured in over 200000 individual correlation functions. Using software binning and thus the inherent advantage of ITIR‐FCS of providing multiple observation areas in a single measurement we test the FCS diffusion law and show how they can be complemented by the local information provided by the difference in cross‐correlation functions (ΔCCF). With the determination of the PSF by ITIR‐FCS and the optimization of measurement conditions ITIR‐FCS becomes a calibration‐free method. This allows us to provide measurements of absolute diffusion coefficients for bilayers with different compositions, which were stable over many different bilayer preparations over a time of at least one year, using a single PSF calibration.     

Nonlinear wave propagation through a stratified atmosphere

We examine the propagation of sound waves through a stratified atmosphere. The method of multiple scales is employed to obtain an asymptotic equation which describes the evolution of sound waves in an atmosphere with spatially dependant density and entropy fields. The evolution equation is an inviscid Burger-like equation which contains quadratic and cubic nonlinearities, and a curvature term all of which are functions of the space variables. A model equation is derived when the modulations of the signal in a direction transverse to the direction of propagation become significant.     

Enantioconvergent Biohydrolysis of Racemic Styrene Oxide to R-phenyl-1, 2-ethanediol by a Newly Isolated Filamentous Fungus Aspergillus tubingensis TF1

An effort was made to isolate biocatalysts hydrolyzing epoxides from various ecological niches of northeast India, a biodiversity hot spot zone of the world and screened for epoxide hydrolase activity to convert different racemic epoxides to the corresponding 1, 2-vicinal diols. Screening of a total of 450 microorganisms isolated was carried out using NBP colorimetric assay. One of the strains TF1, after internal transcribed spacer sequence analysis, identified as Aspergillus tubingensis, showed promising enantioconvergent epoxide hydrolase activity. The hydrolysis of unsubstituted styrene oxide (1) occurred to give 97 % ee of R-(?)-1-phenylethane-1, 2-diol (6) with more than 99 % conversion within 45 min incubation. It is shown to be a cheap and practical biocatalyst for one step asymmetric synthesis of chiral R-diol. The other representative substrates (2–5), although underwent hydrolysis with more than 99 % conversion beyond 15 h, exhibited poor enantioselectivity.     

OSCILLATION OF SECOND-ORDER NONLINEAR NEUTRAL DIFFERENCE EQUATIONS

In this paper, we consider some kind of second-order nonlinear neutral difference equation and get some sufficient conditions of its oscillation.     

Rhodamine-based probes for metal ion-induced chromo-/fluorogenic dual signaling and their selectivity towards Hg(II) ion

The new signaling probes 2-6, rhodamine-B derivatives of various receptors which contain different donor atoms for effective metal ion coordination, were synthesized and their absorption as well as fluorescence spectral responses were evaluated in the presence of various metal ions. All these probes along with the reference probe 1 have exhibited optimal metal ion-induced absorption and fluorescence enhancement with Hg(II) ion in the longer wavelength region (>500 nm) in MeCN, exploiting the spectral characteristics of metal ion-induced structural transformation of rhodamine. The selectivity and sensitivity towards Hg(II) ion were better pronounced in MeCN-H(2)O (1 : 1 v/v) medium, implying the role of the solvent molecules, water in particular, in the preferential Hg(II) coordination environment. Complexation of Hg(II) to 1-6 not only enhanced the absorption at ~560 nm, which turned the colourless solution into pink to facilitate a naked eye detection, but also amplified the fluorescence intensity simultaneously to offer high sensitivity of detection at lower concentration. The Hg(II)-induced photo-physical spectral responses of 1-6 in presence of other competitive metal ions rendered their high selectivity towards Hg(II). Further, their reversible dual channel signaling pattern under the action of counter anions, exploiting coordination tendency of anions towards Hg(II), which compete with probe-metal interaction, implied the reversibility in their Hg(II) coordination. The selectivity, sensitivity and reversibility, in principle, establishes the potential of these probes as chemosensors for Hg(II) ion detection.