Synthesis of pyrimido [4,5-c] pyridazine (4-deazafervenulin), pyrazolo[3,4-d] pyrimidine and 6-(pyrazino-1-yl)pyrimidine derivatives

The synthesis of several pyrimido[4,5-c]pyridazine (4-deazafervenulin) ( 1 ), pyrazolo[3,4-d]-pyrimidine ( 2 ) and 6-(pyrazino-1-yl)pyrimidine ( 9 ) analogs has been accomplished from 6-hydrazinouracil ( 3 ). This compound could not be used as starting material for the preparation of indolo[3,2-c]pyridazino[3,4-d]pyrimidine derivatives ( 8 ) because it yielded the corresponding hydrazones ( 7 ).     

Second-harmonic generation of a Gaussian laser beam in a self created magnetized plasma channel

The second-harmonic generation of an intense self-guided right circularly polarized laser beam in a magnetized plasma is investigated. The laser imparts oscillatory velocity to electrons and exerts a radial ponderomotive force on them to create a depleted density channel. The critical power for self-focusing shows huge reduction as electron cyclotron frequency approaches the laser frequency (/spl omega//sub c/ /spl rarr/ /spl omega/). In the presence of the self-created radial density gradient, the laser drives a density perturbation at the fundamental frequency. The density perturbation beats with the oscillatory velocity to produce a second harmonic current density, driving second harmonic radiation copropagating with the laser. The second harmonic, however, is azimuthally asymmetric with /spl theta/-variation as exp(i/spl theta/). Its amplitude shows resonant enhancement as /spl omega//sub c/ /spl rarr/ /spl omega/.     

Thermal and optical study of semiconducting CNTs-doped nematic liquid crystalline material

We report the thermal and spectroscopic analysis of the carbon nanotubes (CNTs)-doped nematic liquid crystal (NLC) material. The CNTs have been oriented in the p-ethoxybenzylidene p-butylaniline NLC. The thermal study of the CNTs doped nematic mixtures shows a significant decrease in the isotropic to nematic phase transition temperature. However higher doping concentration of CNTs has led to the further increase in transition temperature. The UV-Visible spectroscopy has been attempted on the CNTs/NLC mixtures at room temperature. The investigated NLC present one absorption band corresponding to π–π* electronic transition. A red shift of λ_max with the increasing concentration of CNTs in the mixture has been observed. The band gap of NLC has been found to decrease after the doping of CNTs. The absorbance was measured for the UV light, polarized parallel and perpendicular to the LC director in the planar aligned cell.     

Internal pressure,ultrasonic velocity and viscosity of multi-component liquid systems

Ultrasonic velocity, density and viscosity were measured in two ternary liquid systems namely,n-pentane +n-hexane + benzene(I) andn-hexane + cyclohexane + benzene(II) and one quaternary liquid system,n-pentane +n-hexane + benzene + toluene (III). The experimental as well as literature values of thermal expansion coefficient and iso-thermal compressibility of pure liquid components were utilized to deduce the ideal value of internal pressure and excess internal pressure for the above liquid systems at 298·15K using two different approaches. In the conventional approach one needs the experimental values ofα andβ _T of mixtures for computing internal pressure, which was not possible. The second method which is proposed here utilizes only the density, ultrasonic velocity and viscosity data of the mixture. This method is used in computing internal pressure and its excess value for multicomponent liquid systems. A satisfactory agreement has been observed.     

On the flow of a dusty viscous liquid through a circular pipe

Analytical solution of the flow problem of a dusty viscous liquid through a circular pipe in case of axial symmetry is obtained when pressure gradient varies harmonically with time. It is found that the effect of the fine dust is to make the velocity of sedimentation zero and when dust is sufficiently coarse, the effect of the dust is equivalent to an extra frictional force proportional to the fluid velocity.     

L-stable Simpson’s 3/8 rule and Burgers’ equation

In this paper we develop an unconditionally stable third order time integration formula for the diffusion equation with Neumann boundary condition. We use a suitable arithmetic average approximation and explicit backward Euler formula and then develop a third order L-stable Simpson’s 3/8 type formula. We also observe that the arithmetic average approximation is not unique. Then L-stable Simpson’s 3/8 type formula and Hopf-Cole transformation is used to solve Burger’s equation with Dirichlet boundary condition. It is also observed that this numerical method deals efficiently in case of inconsistencies in initial and boundary conditions.     

Ferroelectric and paramagnetic properties of Li2Gd4 (MoO4)7 single crystals

Thermal behavior of such fundamental physical properties as polarization, pyroelectric current, dielectric constant and paramagnetic susceptibility are reported for dilithium heptamolybdotetragadolinate, Li₂Gd₄ (MoO₄)₇. The ferroelectric transition point has been determined by various methods and the results compared. The most reliable value of the Curie point has been obtained by the measurement of differential magnetic susceptibility as a function of temperature and is found to be 52±2°C. The room temperature values for the relative dielectric constant and paramagnetic susceptibility are 51.5 and 59.8 x 10^-6 cm³. g^-1, respectively. From the susceptibility measurements the values obtained for the Curie constant, C, and the paramagnetic Curie point, θp, are 1.79 x 10^-2 cm³ . g^-1 . deg and 247°K, respectively. It is believed that Li₂Gd₄ (MoO₄)₇ could be antiferromagnetic between 273 and 325°K.     

The fundamental properties of the direct injection method in the analysis of gaseous reduced sulfur by gas chromatography with a pulsed flame photometric detector

In this study, the fundamental aspects of gas chromatography with a pulsed flame photometric detector were investigated through the calibration of gaseous reduced sulfur compounds based on the direct injection method. Gaseous standards of five reduced sulfur compounds (hydrogen sulfide, methane thiol, dimethyl sulfide, carbon disulfide, and dimethyl disulfide) were calibrated as a function of injection volume and concentration level. The results were evaluated by means of two contrasting calibration approaches: fixed standard concentration method (variable volumetric injection of standard gases prepared at a given concentration) and fixed standard volume method (injection of multiple standards with varying concentrations at a given volume). The optimum detection limit values of reduced sulfur compounds, when estimated at 100 μL of injection volume, ranged from 2.37 pg (carbon disulfide) to 4.89 pg (dimethyl sulfide). Although these detection limit values improved gradually with decreasing injection volume, the minimum detectable concentration (e.g., in nmol mol⁻¹ scale) remained constant due to a balance by the sample volume reduction. The linearity property of pulsed flame photometric detector also appeared to vary dynamically with changes in its sensitivity. According to this study, the performance of pulsed flame photometric detector, when tested by direct injection method, is highly reliable to precisely describe the behavior of reduced sulfur compounds above ∼20 nmol mol⁻¹.     

Dithiomethylether as a ligand in the hydrogenase h-cluster

An X-ray crystallographic refinement of the H-cluster of [FeFe]-hydrogenase from Clostridium pasteurianum has been carried out to close-to atomic resolution and is the highest resolution [FeFe]-hydrogenase presented to date. The 1.39 A, anisotropically refined [FeFe]-hydrogenase structure provides a basis for examining the outstanding issue of the composition of the unique nonprotein dithiolate ligand of the H-cluster. In addition to influencing the electronic structure of the H-cluster, the composition of the ligand has mechanistic implications due to the potential of the bridge-head gamma-group participating in proton transfer during catalysis. In this work, sequential density functional theory optimizations of the dithiolate ligand embedded in a 3.5-3.9 A protein environment provide an unbiased approach to examining the most likely composition of the ligand. Structural, conformational, and energetic considerations indicate a preference for dithiomethylether as an H-cluster ligand and strongly disfavor the dithiomethylammonium as a catalytic base for hydrogen production.     

Determination of molecular configuration by debye length modulation

Silicon nanowire field effect transistors (FETs) have emerged as ultrasensitive, label-free biodetectors that operate by sensing bound surface charge. However, the ionic strength of the environment (i.e., the Debye length of the solution) dictates the effective magnitude of the surface charge. Here, we show that control of the Debye length determines the spatial extent of sensed bound surface charge on the sensor. We apply this technique to different methods of antibody immobilization, demonstrating different effective distances of induced charge from the sensor surface.