Radical‐Cation Dimerization Overwhelms Inclusion in [n]Pseudorotaxanes

Suppression of the dimerization of the viologen radical cation by cucurbit[7]uril ( CB7 ) in water is a well‐known phenomenon. Herein, two counter‐examples are presented. Two viologen‐containing thread molecules were designed, synthesized, and thoroughly characterized by ¹H DOSY NMR spectrometry, UV/Vis absorption spectrophotometry, square‐wave voltammetry, and chronocoulometry: BV ⁴⁺, which contains two viologen subunits, and HV ¹²⁺, which contains six. In both threads, the viologen subunits are covalently bonded to a hexavalent phosphazene core. The corresponding [3]‐ and [7]pseudorotaxanes that form on complexation with CB7 , that is, BV ⁴⁺?( CB 7)₂ and HV ¹²⁺?( CB 7)₆, were also analyzed. The properties of two monomeric control threads, namely, methyl viologen ( MV ²⁺) and benzyl methyl viologen ( BMV ²⁺), as well as their [2]pseudorotaxane complexes with CB7 ( MV ²⁺? CB7 and BMV ²⁺? CB7 ) were also investigated. As expected, the control pseudorotaxanes remained intact after one‐electron reduction of their viologen‐recognition stations. In contrast, analogous reduction of BV ⁴⁺?( CB 7)₂ and HV ¹²⁺?( CB 7)₆ led to host–guest decomplexation and release of the free threads BV ^{2( . +)} and HV ^{6( . +)}, respectively. ¹H DOSY NMR spectrometric and chronocoulometric measurements showed that BV ^{2( . +)} and HV ^{6( . +)} have larger diffusion coefficients than the corresponding [3]‐ and [7]pseudorotaxanes, and UV/Vis absorption studies provided evidence for intramolecular radical‐cation dimerization. These results demonstrate that radical‐cation dimerization, a relatively weak interaction, can be used as a driving force in novel molecular switches.     

DIELECTRIC AND PHASE TRANSITION STUDIES OF 1MC1EPOPB FERROELECTRIC LIQUID CRYSTAL

Abstract

An experimental study for R — 4′-(1 methoxycarbonyl – 1 – ethoxy) phenyl 4 – (4 – octyloxyphenyl) benzoate (1MC1EPOPB) ferroelectric liquid crystal (FLC) using impedance analyzer and differential scanning calorimetric (DSC) technique is reported. The measurements have been done for permittivity, dielectric loss at different frequencies and temperatures. The data have been analyzed for distribution parameters involved in Havriliak-Negami's equation. The relaxation time measured for different relaxation processes is listed. The measurements for static dielectric constants in the parallel(ε_∥) and perpendicular(ε_?) directions at different temperatures have also been taken. The transition temperatures are identified for cooling and heating conditions using DSC technique as well as dielectric measurements. The interesting results have been found and some unknown phases have been monitored, the reason for which needs theoretical interpretation.     

Differential electrochemical behaviour of phytofabricated and chemically synthesized silver nanoparticles towards hydrogen peroxide sensing**

Silver nanoparticles (AgNPs) are one of the most widely used nanomaterials for biomedical applications. However, the impact of its synthesis by chemical and plant-mediated routes on its differential electrochemical behaviour has not been examined till date. Here, we report for the first time the differential study of the electrochemical behaviour of the AgNPs synthesized by different routes. First, the AgNPs were obtained by different routes (chemical and phytofabrication) and extensively characterized to compare their physical properties. Thereafter, a comparison of electron transfer kinetics between chemically synthesized (Ag−C) and phyto-fabricated (Ag-Phy) nanoparticles (NPs) has been studied by electrochemical techniques such as potentiodynamic cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). To further investigate the electrocatalytic properties of both types of AgNPs, we have used the peroxide moieties (H₂O₂), and the Ag−C NPs-based sensor probe has been reported to have four times better sensitivity than the Ag−Phy NPs-based sensor. The AgNPs modified sensor probes have also been tested in real-world environments to explore the consistency of their performance in complex matrices by using clinical urine samples, where we found comparable sensitivity to the standard conditions.     

Synthesis and Characterization of the Adducts of Bis(<Emphasis Type="Italic">O</Emphasis>-butyldithiocarbonato)nickel(II) with Substituted Heterocyclic Amines and X-ray Structure of Bis(<Emphasis Type="Italic">O</Emphasis>-butyldithiocarbonato)bis(4-cyanopyridine)nickel(II)

Abstract  

We report the synthesis and study of a new series of the adducts of Bis(O-butyldithiocarbonato)nickel(II) with substituted heterocyclic amines such as amino and cyanopyridines. Analytical results show that the adducts have 1:2 stoichiometry with general formula M(Xan)₂ L ₂ (M = Ni(II), Xan = O-butyldithiocarbonate, L = 2-, 3- and 4-aminopyridines, 3- and 4-cyanopyridines). The complexes have been characterized by analytical, magnetic susceptibility measurements, molar conductivity measurements, IR, electronic spectral data and X-ray diffraction analysis. One of the adducts, bis(O-butyldithiocarbonato)bis(4-cyanopyridine)nickel(II), crystallizes in the monoclinic space group P2₁/c with unit cell parameters : a = 12.546(4), b = 11.495(3), c = 9.351(3) ?, β = 102.73(3)o, Z = 2. Crystal structure was solved by direct methods and refined by full matrix least squares procedures to a final R-value of 0.0299 for 2,788 observed reflections. The packing of layers of molecules is stabilized by weak C–H···N and C–H···π hydrogen bonds.     

LC‐MS/MS‐ESI method for simultaneous quantitation of metformin and repaglinidie in rat plasma and its application to pharmacokinetic study in rats

A highly sensitive and specific LC‐MS/MS‐ESI method has been developed for simultaneous quantification of metformin (MFN) and repaglinide (RGN) in rat plasma (50 μL) using phenacetin as an internal standard (IS). Simple protein precipitation was used to extract MFN and RGN from rat plasma. The chromatographic resolution of MFN, RGN and IS was achieved with a mobile phase consisting of 0.2% formic acid in water–acetonitrile (1:1, v/v) with a time program flow gradient on a Chromolith RP‐18e column. The total chromatographic run time was 3.5 min and the elution of MFN, RGN and IS occurred at 1.64, 2.21 and 2.15 min, respectively. A linear response function was established for the range of concentrations 0.855–394 and 0.021–21.7 ng/mL for MFN and RGN, respectively. The intra‐ and inter‐day precision values for MFN and RGN met the acceptance as per FDA guidelines. MFN and RGN were stable in battery of stability studies viz., bench‐top, auto‐sampler and freeze–thaw cycles. The developed assay was applied to a pharmacokinetic study in rats. Copyright © 2012 John Wiley & Sons, Ltd.     

P(i-PrNCH2CH2)3N: an efficient catalyst for TMS-1,3-dithiane addition to aldehydes

Herein we report the use of commercially available P(i-PrNCH₂CH₂)₃N (1a) as an efficient catalyst for 2-trimethylsilyl-1,3-dithiane (TMS-dithiane) addition to aldehydes at room temperature. The catalyst loading required for these reactions (5 mol %) is the lowest recorded in the literature, and the majority of the reaction times for this transformation are the shortest thus far reported. A variety of functional groups are tolerated on the aryl aldehyde substrates.     

Highly sensitive method for the determination of adenosine by LC-MS/MS-ESI: method validation and scope of application to a pharmacokinetic/pharmacodynamic study

A highly sensitive, rapid assay method has been developed and validated for the estimation of adenosine in rat plasma with liquid chromatography coupled to tandem mass spectrometry with electro‐spray ionization in the positive‐ion mode. The assay procedure involves extraction of adenosine and phenacetin (internal standard, IS) from rat plasma with a simple protein precipitation extraction process. The method was validated using rat plasma with extinguished adenosine endogenous levels. Chromatographic separation was achieved using a binary gradient using mobile phase A (acetonitrile) and B (0.2% formic acid in water) at a flow rate of 0.50 mL/min on an Atlantis dC₁₈ column with a total run time of 4.0 min. The MS/MS ion transitions monitored were 268 → 136 for adenosine and 180 → 110 for IS. Method validation was performed as per FDA guidelines and the results met the acceptance criteria. The lower limit of quantitation achieved was 0.48 ng/mL and the linearity range extended from 0.48 to 1210 ng/mL. The intra‐ and inter‐day precisions were in the ranges 2.32–12.7 and 4.01–9.40%, respectively. Copyright © 2011 John Wiley & Sons, Ltd.     

Diffusion of Au and Cu in amorphous Fe80B20 and Fe82B18 alloys

Diffusion rates (D) of Au in two amorphous alloys, Fe₈₀B₂₀ and Fe₈₂B₁₈, and of Cu in amorphous Fe₈₂B₁₈ alloy were measured in the temperature range 546–645 K by using the technique of Rutherford backscattering spectrometry (RBS) and Auger electron spectroscopy (AES), respectively. The diffusion of Au was found to be 3 to 6 times faster in Fe₈₀B₂₀ than in Fe₈₂B₁₈, though both the alloys had almost similar crystallization temperatures. The observed differences in the diffusion rates corroborate the fact that Fe₈₀B₂₀ has a more open structure than Fe₈₂B₁₈ as revealed from the reported values of the metal packing fractions of these two alloys. Also, the diffusivities of smaller sized Cu atoms (radius: 0.128 nm) were found to be higher by more than an order of magnitude than those of larger sized Au atoms (radius: 0.146 nm), suggesting a dependence ofD on the size of the diffusing species.