A Crystallization Technique For the Enantiomer Resolution of Conglomerates- (+/-)-4-Methoxyphenyl 1-Phenylethyl Ketone

The sorting of crystals of (+/-)-4-methoxyphenyl 1-phenylethyl ketone into its enantiomers is facilitated by crystallisation in a cellular grid made of filter paper.

Crystallization and preliminary X-ray diffraction analysis of a galactose-specific lectin from the seeds of Butea monosperma

The galactose-specific lectin from the seeds of Butea monosperma has been crystallized by the hanging-drop vapour-diffusion technique. The crystals belonged to space group P1, with unit-cell parameters a = 78.45, b = 78.91, c = 101.85 A, alpha = 74.30, beta = 76.65, gamma = 86.88 degrees. X-ray diffraction data were collected to a resolution of 2.44 A under cryoconditions (100 K) using a MAR image-plate detector system mounted on a rotating-anode X-ray generator. Molecular-replacement calculations carried out using the coordinates of several structures of legume lectins as search models indicate that the galactose-specific lectin from B. monosperma forms an octamer.

The concentration dependent cooperative friction coefficient of dilute polymer solutions at the theta point

We combine multiple scattering and renormalization group methods to calculate the leading order dimensionless virial coefficient k(s) for the friction coefficient of dilute polymer solutions under conditions where the osmotic second virial coefficient vanishes (i.e., at the theta point T-theta). Our calculations are formulated in terms of coupled kinetic equations for the polymer and solvent, in which the polymers are modeled as continuous chains whose configurations evolve under the action of random forces in, the velocity field of the solvent. To lowest order in epsilon=4-d, we find that k(s) = 1.06. This result compares satisfactorily with existing experimental estimates of k(s), which are in the range 0.7-0.8. It is also in good agreement with other theoretical results on chains and suspensions at T-theta. Our calculated k(s) is also found to be identical to the leading order virial coefficient of the tracer friction coefficient at the theta point. We discuss possible reasons for the difficulties encountered when attempting to evaluate k(s) by extrapolating prior renormalization group calculations from semidilute concentrations to the infinitely dilute limit. (C) 1996 American Institute of Physics.

Crystallization and preliminary X-ray diffraction analysis of a galactose-specific lectin from the seeds of Butea monosperma

The galactose-specific lectin from the seeds of Butea monosperma has been crystallized by the hanging-drop vapour-diffusion technique. The crystals belonged to space group P1, with unit-cell parameters a = 78.45, b = 78.91, c = 101.85 A, alpha = 74.30, beta = 76.65, gamma = 86.88 degrees. X-ray diffraction data were collected to a resolution of 2.44 A under cryoconditions (100 K) using a MAR image-plate detector system mounted on a rotating-anode X-ray generator. Molecular-replacement calculations carried out using the coordinates of several structures of legume lectins as search models indicate that the galactose-specific lectin from B. monosperma forms an octamer.

Cloning, expression, purification, crystallization and preliminary X-ray studies of the mannose-binding lectin domain of MSMEG_3662 from Mycobacterium smegmatis

The mannose-binding lectin domain of MSMEG_3662 from Mycobacterium smegmatis has been cloned, expressed, purified and crystallized and the crystals have been characterized using X-ray diffraction. The Matthews coefficient suggests the possibility of two lectin domains in the triclinic cell. The amino-acid sequence of the domain indicates structural similarity to well characterized beta-prism II fold lectins.

Effect of substrate on particle arrangement in arrays formed by self-assembly of polymer grafted nanoparticles

We show that the substrate affects the interparticle spacing in monolayer arrays with hexagonal order formed by self-assembly of polymer grafted nanoparticles. Remarkably, arrays with square packing were formed due to convective shearing at a liquid surface induced by miscibility of colloidal solution with the substrate.

On the water-induced critical double point in a polymer solution: the role of isotopic substitution

This paper examines the effect of substitution of water by heavy water in a polymer solution of polystyrene (molecular weight = 13000) and acetone. A critical double point (CDP), at which the upper and the lower partially-miscible regions merge, occurs at nearly the same coordinates as for the system [polystyrene + acetone + water]. The shape of the critical line for [polystyrene + acetone + heavy water] is highly asymmetric. An explanation for the occurrence of the water-induced CDP in [polystyrene + acetone] is advanced in terms of the interplay between contact energy dissimilarity and free-volume disparity of the polymer and the solvent. The question of the possible existence of a one-phase hole in an hourglass phase diagram is addressed in [polystyrene + acetone + water]. Our data exclude such a possibility.

Crystallization and preliminary X-ray studies of a galactose-specific lectin from the seeds of Spatholobus parviflorus

A galactose-specific seed lectin was purified from the legume Spatholobus parviflorus and crystallized using the hanging-drop vapour-diffusion technique. The crystals belonged to space group P1, with unit-cell parameters a = 60.998, b = 60.792, c = 78.179 angstrom, alpha = 101.32, beta = 91.38, gamma = 104.32 degrees. X-ray diffraction data were collected under cryoconditions (100 K) to a resolution of 2.04 angstrom using a MAR image-plate detector system mounted on a rotating-anode X-ray (Cu K alpha) generator. Molecular replacement using legume-lectin coordinates as a search model gave a tetrameric structure.

Synthesis of nanodispersed phases during rapid solidification and crystallization of glasses in Ti75Ni25 alloys

The formation of the metallic glass and crystalline phases and related microstructures and the decomposition behavior of rapidly solidified Ti75Ni25 alloys obtained under different processing conditions have been investigated in detail. The competition between glass transition and nucleation of beta-Ti during rapid solidification leads to the possibility of synthesizing the nanocomposites of beta-Ti and glass. Additionally, it is shown that the presence of a small amount of Si also promotes simultaneous nucleation of fine Ti2Ni intermetallic compound. Thermodynamic calculation of the metastable phase diagram indicates the presence of a metastable eutectic reaction between alpha-Ti and Ti2Ni. Evidence of this reaction at lower cooling rates has been presented. On heating, the glass decomposes through this reaction. Finally, on the basis of understanding of the microstructural evolution during decomposition, a new approach has been adopted to synthesize a nanodispersed composite of alpha-Ti in the crystalline Ti2Ni matrix with a narrow size distribution by controlling the devitrification heat treatment of the metallic glass.

Polymer collapse in supercritical solvents

We show analytically that in dilute solutions of high molecular weight polymers, a collapse transition of the chain can be induced by proximity to the critical point of the solvent. The transition is driven by the fluctuations in the medium, which lead to an effective attractive interaction of long range between different parts of the polymer. At the critical point itself, however, the chain adopts the same average conformations that characterize its size in the off-critical limit. In other words, on approach to the critical point, the polymer is found first to contract and collapse, and then subsequently to return to its original dimensions. This behavior has recently been observed in simulations of polymer-solvent mixtures near the lower critical solution temperature of the system, and it is also known to be characteristic of solutions of polymers in bicomponent solvent mixtures near the critical consolute point of the two solvents. (C) 1999 American Institute of Physics. [S0021-9606(99)50431-5].

Reversibility of Mg/Mg2+ couple in a gel polymer electrolyte

Investigations on solid state rechargeable magnesium batteries are considered important similar to lithium batteries. In view of negligible hazards and less reactivity of the magnesium, in comparison with lithium, studies on rechargeable magnesium batteries are expected to have a wide scope in future. Solid polymer electrolytes, which conduct Mg2+ ions and reversibility of a Mg/Mg2+ couple are essential components of the studies. In the present investigations, the existence of reversibility of a Mg/Mg2+ couple in a gel polymer electrolyte (GPE) medium is established for the first time in literature. Results obtained by electrochemical impedance spectroscopy and cyclic voltammetry on Mg/GPE/Mg, SS/GPE/SS symmetrical cells show evidence for the reversibility. (C) 1999 Elsevier Science Ltd. All rights reserved.

Thermal crystallization behaviour of Ge-Te-Se glasses

Ge10Te90-xSex (50 less than or equal to x less than or equal to 70) and Ge20Te80-xSex (x = 30, 50) glasses have been prepared by melt-quenching The thermal crystallization behaviour of these samples has been studied by Differential Scanning Calorimetry (DSC), in order to characterise these glasses for memory-threshold switching applications. It is found that Ge10Te90-xSex glasses have higher thermal stability and are more stable against devitrification. These samples may be suitable for threshold switching devices. Ge20Te80-xSex glasses, on the other hand, phase separate on heating and exhibit a double stage crystallization. Based on this, it can be expected that Ge20Te80-xSex samples will show memory behaviour. The activation energy for thermal crystallization of a representative Ge10Te40-xSe50 glass belonging to the Ge10Te90-xSex series has been found by the Kissinger's method to be 0.92 eV. The value of the activation energy obtained also indicates that Ge10Te90-xSex samples are less prone to devitrification and more suitable for threshold behaviour.

Correlated conformation and charge transport in multiwall carbon nanotube-conducting polymer nanocomposites

The strikingly different charge transport behaviours in nanocomposites of multiwall carbon nanotubes (MWNTs) and conducting polymer polyethylenedioxythiophene-polystyrene-sulfonic-acid (PEDOT-PSS) at low temperatures are explained by probing their conformational properties using small-angle x-ray scattering (SAXS). The SAXS studies indicate the assembly of elongated PEDOT-PSS globules on the walls of nanotubes, coating them partially, thereby limiting the interaction between the nanotubes in the polymer matrix. This results in a charge transport governed mainly by small polarons in the conducting polymer despite the presence of metallic MWNTs. At T > 4 K, hopping of the charge carriers following one-dimensional variable range hopping is evident which also gives rise to a positive magnetoresistance (MR) with an enhanced localization length (similar to 5 nm) due to the presence of MWNTs. However, at T < 4 K, the observation of an unconventional positive temperature coefficient of resistivity is attributed to small polaron tunnelling. The exceptionally large negative MR observed in this temperature regime is conjectured to be due to the presence of quasi-1D MWNTs that can aid in lowering the tunnelling barrier across the nanotube-polymer boundary resulting in large delocalization.

An improved-performance liquid-feed solid-polymer-electrolyte direct methanol fuel cell operating at near-ambient conditions

Results on the performance of a 25 cm(2) liquid-feed solid-polymer-electrolyte direct methanol fuel cell (SPE-DMFC), operating under near-ambient conditions, are reported. The SPE-DMFC can yield a maximum power density of c. 200 mW cm(-2) at 90 C while operating with 1 M aqueous methanol and oxygen under ambient pressure. While operating the SPE-DMFC under similar conditions with air, a maximum power density of ca. 100 mW cm(-2) is achieved. Analysis of the electrode reaction kinetics parameters on the methanol electrode suggests that the reaction mechanism for methanol oxidation remains invariant with temperature. Durability data on the SPE-DMFC at an operational current density of 100 mA cm(-2) have also been obtained.

Electrochemical studies of polyaniline in a gel polymer electrolyte - High energy and high power characteristics of a solid-state redox supercapacitor

Studies on redox supercapacitors employing electronically conducting polymers are of great importance for hybrid power sources and pulse power applications. In the present study, polyaniline (PANI) has been potentiodynamically deposited on stainless steel substrate and characterized in a gel polymer electrolyte (GPE). Use of the GPE facilitates a voltage limit of the capacitor to 1 V, instead of 0.75 V in aqueous electrolytes. From charge-discharge studies of the solid-state PANI capacitors, a specific capacitance of 250 F g(-1) has been obtained at a specific power of 7.5 kW kg(-1) of PANI. The values of specific capacitance and specific power are considerably higher than those reported in the literature. High energy and high power characteristics of the PANI are presented. (C) 2002 The Electrochemical Society.