13C NMR investigations of molecular order of rod-like,bent-core,and thiophene mesogens

In this review, methods to obtain the orientational order of topologically variant molecular mesogens using by one- and two-dimensional (2D) solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy are described. Besides ¹³C chemical shifts, the ¹³C─¹H dipolar couplings measured from 2D-separated local field (SLF) technique are used for computing the order parameters of a variety of mesogens. The investigated molecules are composed of a variable number of rings in the core, that is, core ranging from simply one ring to five rings. Among the mesogens investigated, a special focus has been placed on mesogens with thiophene rings, which are gaining popularity as liquid crystalline organic semiconductors. The replacement of a phenyl ring by thiophene in the core has a dramatic influence on molecular topology, as observed from the measured order parameters. The review highlights the advantages of the 2D SLF method for understanding the local dynamics and for mapping the topology of mesogens through the measured order parameters. SLF NMR studies of as many as 24 molecular mesogens that vary in terms of the molecular structure as well as topology are covered in the review. Order parameters of the rings have been estimated from the ¹³C─¹H dipolar couplings in the nematic, smectic A, smectic C, and tilted hexatic phases as well as in B₁ and B₂ mesophases of various mesogens. It is anticipated that, in the years to come, the 2D SLF method would provide advanced molecular information on structurally complex mesogens that are emerging in liquid crystal science through the incessant efforts of synthetic chemists. The mini review covers the orientational order of topologically variant molecular mesogens determined by 1D and 2D solid-state ¹³C NMR spectroscopy. Accordingly, rod-like, bent-core, and thiophene mesogens were subjected to 2D SLF measurements to get the order parameters from which the topology was established. The replacement of phenyl ring by thiophene and its influence on order parameters as well as on molecular topology is also discussed.     

Graphitic nanofillers in PMMA nanocomposites—An investigation of particle size and dispersion and their influence on nanocomposite properties

Mechanical, thermal, and electrical properties of graphite/PMMA composites have been evaluated as functions of particle size and dispersion of the graphitic nanofiller components via the use of three different graphitic nanofillers: “as received graphite” (ARG), “expanded graphite,” (EG) and “graphite nanoplatelets” (GNPs) EG, a graphitic materials with much lower density than ARG, was prepared from ARG flakes via an acid intercalation and thermal expansion. Subsequent sonication of EG in a liquid yielded GNPs as thin stacks of graphitic platelets with thicknesses of ～10 nm. Solution‐based processing was used to prepare PMMA composites with these three fillers. Dynamic mechanical analysis, thermal analysis, and electrical impedance measurements were carried out on the resulting composites, demonstrating that reduced particle size, high surface area, and increased surface roughness can significantly alter the graphite/polymer interface and enhance the mechanical, thermal, and electrical properties of the polymer matrix. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2097–2112, 2007     

Polymerization of acrylamide initiated by peroxomonosulphate and metal ion catalysis

The kinetics of polymerization of acrylamide initiated by potassium peroxomonosulphate, in the presence and absence of Ag⁺, were studied. Rates of polymerization and oxone disappearance were followed. From the rate law for the polymerization, a mechanism has been proposed.     

Coulometric determination of NAD+ and NADH in normal and cancer cells using LDH, RVC and a polymer mediator

An electrochemical method for the measurement of NAD(+) and NADH in normal and cancer tissues using flow injection analysis (FIA) is reported. Reticulated vitreous carbon (RVC) electrodes with entrapped l-lactate dehydrogenase (LDH) and a new redox polymer containing covalently bound toluidine blue O (TBO) were employed for this purpose. Both NAD(+) and NADH were estimated coulometrically based on their reaction with LDH. The latter was immobilized on controlled pore glass (CPG) by cross-linking with glutaraldehyde and packed within the RVC. The concentrations of NAD(+) and NADH in the tissues, estimated using different electron mediators such as ferricyanide (FCN), meldola blue (MB) and TBO have also been compared. The effects of flow rate, pH, applied potential (versus Ag/AgCl reference) and adsorption of the mediators have also been investigated. Based on the measurements of NAD(+) and NADH in normal and cancer tissues it has been concluded that the NADH concentration is lower, while the NAD(+) concentration is higher in cancer tissues. Amongst the electron mediators TBO was found to be a more stable mediator for such measurements.     

Surface characterization of WO(3)/ZrO(2) catalysts

A series of WO(3)/ZrO(2) catalysts with tungsten (W) loadings ranging from 0.5 to 11.4 wt% was prepared by incipient wetness impregnation on a preformed ZrO(2) support. The oxidic catalysts were characterized using XRD, Raman spectroscopy, XPS, ISS, and IR spectroscopy. XRD and Raman results showed that the ZrO(2) support was predominantly present in the monoclinic form. XPS and Raman measurements indicated the formation of increasing amounts of W interaction species for catalysts with W loadings up to 8.8 wt% WO(3). In addition to the W interaction species, bulk WO(3) was also observed for catalysts with W loadings > or = 3.0 wt% WO(3). Comparison of the XPS results with coverage measurements by ISS and CO adsorption suggests that the W surface phase is in the form of two-dimensional polymeric patches for catalysts with W loadings 3.0 < or = wt% WO(3) < or = 4.5. For catalysts with W loadings >4.5 wt% WO(3), the results indicated an additional build-up of a bilayer (or multilayer) polymeric W species. Analysis of the hydroxyl region of ZrO(2) by IR spectroscopy showed that initial additions of W occur on the high frequency hydroxyl group. A schematic for the structure of the catalysts has been proposed based on the above observations.     

Iterative computational method for the rapid analysis of iron and plutonium by controlled potential coulometry and some interesting observations on the coulogram of the Pu(III) /Pu(IV/ couple

An iterative computational method for the determination of metal ions in aqueous solutions which form reversible couples such as Fe(II)/Fe(III), Pu(III)/Pu(IV) etc. by controlled potential coulometry has been developed. The method involves carrying out the electrolysis to about 95–97% and calculating the total amount present in the sample by an iterative computational method. The method utilizes the direct application of the Nernst equation. The important criterion to be met is that the coulogram of the couple should strictly obey the Nernst equation. The validity of the method has been checked by analyzing about 50 samples of a standard iron solution. Results of analysis of mixtures of Pu and Fe by the iterative technique show that the interference of Fe can almost entirely be eliminated. However, analysis of Pu samples by this procedure gives results about 2–3% lower than the expected value. A careful examination of the experimental coulograms of Pu in lM HClO₄ indicates a slight deviation from the theoretical coulogram, where as those of Fe match exactly.     

Microwave assisted synthesis of an unusual dinitro phytochemical

A novel dinitro secondary metabolite, 2-nitro-4-(2^′-nitroethenyl)phenol from a marine source, has been prepared via highly accelerated, microwave assisted, nitration reactions using mild reagents. ipso-Substitution of a carboxy group by a nitro group is discussed.     

Role of hadronic dynamics in proton decay

Aspects of hadronic dynamics which play a crucial role in proton decay (exclusive and inclusive) are examined in the context of a comprehensive Bethe-Salpeter (BS) formalism forq \(\bar q\) andqqq systems, under harmonic confinement. The BS model which is characterized by two basic parameters—the universal spring constant \(\tilde \omega \) GeV and the quark massm _q =0.28 GeV, has already provided an impressive set of agreements in respect of a large number and variety of hadronic observables (mass spectra, and an extensive list of e.m. and pionic couplings of both mesons and baryons). TheSU(5) GUT parameters, on the other hand, are kept fixed at the ‘standard’ values, (see e.g. Langacker's review). The absolute normalization of the baryon, which is rather crucial in this case, is fixed with reference to the (topologically equivalent) process of its ‘dissociation’ into three quarks by a hard photon, which makes use of the structure function sum rule \(\int\limits_0^1 {dxF_2^p (x)/x = \sum {Q_i^2 } } \) , instead of the usual BS normalization (which amounts to the conservation of charge). Thee ⁺ inclusive rate, which is about three times that of thee ⁺π⁰ mode, works out at0.54×10 ^?33 yr ^?1 which is smaller than most contemporary calculations by two orders of magnitude. Other exclusive modes are also consistent with the above estimate. The theoretical implications of these results vis a vis contemporary calculations as well as current experimental searches are discussed.