Measurement of carbon-proton dipolar couplings in liquid crystals using DAPT

Dipolar couplings provide valuable information on order and dynamics in liquid crystals. For measuring heteronuclear dipolar couplings in oriented systems, a new separated local field experiment is presented here. The method is based on the dipolar assisted polarization transfer (DAPT) pulse sequence proposed recently (Chem. Phys. Lett. 2007, 439, 407) for transfer of polarization between two spins I and S. DAPT utilizes the evolution of magnetization of the I and S spins under two blocks of phase shifted BLEW-12 pulses on the I spin separated by a 90 degree pulse on the S spin. Compared to the rotating frame techniques based on Hartmann-Hahn match, this approach is easy to implement and is independent of any matching conditions. DAPT can be utilized either as a proton encoded local field (PELF) technique or as a separated local field (SLF) technique, which means that the heteronuclear dipolar coupling can be obtained by following either the evolution of the abundant spin like proton (PELF) or that of the rare spin such as carbon (SLF). We have demonstrated the use of DAPT both as a PELF and as a SLF technique on an oriented liquid crystalline sample at room temperature and also have compared its performance with PISEMA. We have also incorporated modifications to the original DAPT pulse sequence for (i) improving its sensitivity and (ii) removing carrier offset dependence.     

Supercycled homonuclear dipolar decoupling in solid-state NMR: toward cleaner 1H spectrum and higher spinning rates

A homonuclear dipolar decoupling scheme based on windowed phase-modulated Lee-Goldburg (wPMLG) pulse sequences that causes a"z-rotation" of the spins for high-resolution proton NMR spectroscopy of solids is described and analyzed. This supercycled scheme suppresses the effect of pulse imperfections on the spectra and significantly relaxes the off-resonance dependence of the line-narrowing efficiency and scale factor. This leads to a broad spectral window that is free of artifacts such as zero lines, image peaks, and localized rotor-radio-frequency resonances. High-resolution (1)H spectra and two-dimensional homonuclear (1)H-(1)H correlation spectra of standard amino acids, obtained by a combination of this supercycled scheme with magic angle spinning frequencies up to 25 kHz, are demonstrated.     

Perylene Diimide Based Fluorescent Dyes for Selective Sensing of Nitroaromatic Compounds: Selective Sensing in Aqueous Medium Across Wide pH Range

Water soluble perylenediimide based fluorophore salt, N,N′-bis(ethelenetrimethyl ammoniumiodide)-perylene-3,4,9,10-tetracarboxylicbisimide (PDI-1), has been used for selective fluorescence sensing of picric acid (PA) and 4-nitroaniline (4-NA) in organic as well as aqueous medium across wide pH range (1.0 to 10.0). PDI-1 showed strong fluorescence in dimethylformamide (DMF) (Φf?=?0.26 (DMF) and moderate fluorescence in water. Addition of picric acid (PA) and 4-nitroaniline (4-NA) into PDI-1 in DMF/aqueous solution selectively quenches the fluorescence. The concentration dependent studies showed decrease of fluorescence linearly with increase of PA and 4-NA concentration. The interference studies demonstrate high selectivity for PA and 4-NA. Interestingly, PDI-1 showed selective fluorescence sensing of PA and 4-NA across wide pH range (1.0 to 10.0). Selective fluorescence sensing of PA and 4-NA has also been observed with trifluoroacetate (PDI-2), sulfate (PDI-3) salt of PDI-1 as well as octyl chain substituted PDI (PDI-4) without amine functionality. These studies suggest that PA and 4-NA might be having preferential interaction with PDI aromatic core and quenches the fluorescence. Thus PDI based dyes have been used for selective fluorescent sensing of explosive NACs for the first time to the best our knowledge.

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Graphical Abstract Selective fluorescent sensing of picric acid and 4-nitroaniline nitroaromatic compounds by perylene diimide fluorescent dyes

     

Finely controlled size-selective precipitation and separation of CdSe/ZnS semiconductor nanocrystals using CO2-gas-expanded liquids

A technique was developed to size-selectively separate polydisperse dispersions of CdSe/ZnS nanocrystals into distinct color fractions using only the tunable solvent properties of CO2-expanded hexane. This size-selective precipitation of semiconductor nanoparticles is achieved by finely tuning the solvent strength of the CO2/hexane medium by simply adjusting the applied CO2 pressure. These subtle changes affect the balance between osmotic repulsive and van der Waals attractive forces, thereby allowing fractionation of the nanocrystals into multiple narrow size populations.     

One-pot green synthesis and cytotoxicity of new <Emphasis Type="Italic">α</Emphasis>-aminophosphonates

A novel series of α-aminophosphonates containing the trifluoromethyl aniline moiety were obtained in high yields by condensation of 2-methyl-3-trifluoromethyl aniline, aryl/heteroaryl aldehydes and dimethylphosphite in the presence of chitosan as a catalyst. The molecular modeling studies revealed their important structural features of binding affinities towards the target enzyme. The cytotoxicity of these compounds was evaluated against PC-3(prostate cancer), MCF-7 (breast cancer), HeLa(cCervix Cancer), U973, K562 and HL60 human lLeukemia cell lines. Compound 4k with a pyrene moiety showed high potency against a breast cancer cell line, while compounds 4g and 4k exhibited more promising cytotoxicity against U973, K562 and HL60 cell lines.     

An improvement to double-step Newton method and its multi-step version for solving system of nonlinear equations and its applications

In this work, we have improved the order of the double-step Newton method from four to five using the same number of evaluation of two functions and two first order Fréchet derivatives for each iteration. The multi-step version requires one more function evaluation for each step. The multi-step version converges with order 3r+5, r≥1. Numerical experiments are done comparing the new methods with some existing methods. Our methods are also tested on Chandrasekhar’s problem and the 2-D Bratu problem to illustrate the applications.     

Water-mediated,green, and efficient synthesis of bisquinolones under catalyst-free conditions

Water-mediated, green, and efficient synthesis involving condensation of 4-hydroxy-1-methylquinoline-2(1H)-one (3) with different aromatic and heterocyclic aldehydes (4a–n) leading to 3,3′-(arylmethylene)-bis-(4-hydroxy-1-methylquinolin-2(1H)-one) 5(a–n) under catalyst-free conditions is described. This reaction has an easy workup without using column chromatography and provides excellent yields of the products in shorter reaction times. It does not require any catalyst and uses water as the medium which is the greenest solvent. 3 required in this work was itself obtained by condensation of N-methylaniline (1) with malonic acid (2) in the presence of POCl₃ using a previously reported procedure.     

Synthesis of organic sulfobetaine‐based polymer gel electrolyte for dye‐sensitized solar cell application

We have synthesized eco‐friendly, economic, and equally efficient polysulfobetaine‐based gel electrolyte to the alternative of liquid electrolyte in the fabrication of dye‐sensitized solar cells (DSSCs) for the first time. This nitrogen‐rich and highly conductive polysulfobetaine was synthesized by an easy and facile method without the use of any catalyst and explored for its DSSC application. The synthesized polymer gel electrolyte exhibited good ionic conductivity about 6.8 × 10^?3 Scm^?1 at ambient temperatures. DSSCs were fabricated based on this polysulfobetaine gel electrolyte and studied for their performance based on photovoltaic parameters. The DSSC photovoltaic results were appreciable and are Voc = 0.82 V, Jsc = 11.49 mA/cm², FF = 66%, and PCE = 6.26% at 1 sun intensity. These values are slightly lower than conventional liquid electrolyte‐based DSSC shown as Voc = 0.78 V, Jsc = 12.90 mA/cm², FF = 69%, and PCE = 7.07%, both at 100 mWcm^?2. Conductivity and photovoltaic parameters of the device reveals that as prepared polysulfobetaine‐based polymer gel electrolyte may be useful in the fabrication of DSSC and other electrochemical devices. Copyright © 2017 John Wiley & Sons, Ltd.     

Uniformity analysis in nanocrystalline silver thin films using fuzzy inference system

An automatic and efficient technique to analyze the uniformity of nanoscale images using wavelets, feature similarity index measure (FSIM) and fuzzy inference system is reported. It has been successfully tested on scanning electron micrographs of nanocrystalline silver thin films. Thin films are prepared using on‐axis and off‐axis pulse laser deposition (PLD) technique. It is found that the film prepared using on‐axis PLD is more uniformly distributed and has smoother texture compared with that of the off‐axis technique. In order to analyze the images quantitatively, they are transformed to the wavelet domain to extract the localized frequency variations and a uniformity measure is derived using a fuzzy inference system for quantitatively analyzing the uniformity of each image. The surface plot of the FSIM values of the image is found to be an efficient tool for nanoscientists to evaluate the smoothness of the thin film surfaces. This study is expected to help the nanoscientists to understand these nanostructures in detail. Copyright © 2014 John Wiley & Sons, Ltd.