Cyclization reactions of 3-hydrazino[1, 2, 4]triazino[5, 6-b]indole

The reaction of 3-hydrazino[1, 2, 4]triazino[5, 6-b]indole I with nitrous acid affords the azide III which could be cyclized with acetic anhydride to 10-acetyl-10H-tetrazolo[5′,1′:3, 4][1, 2, 4]triazino[5, 6-b]indole IIb . Cyclization reactions of I with acetic anhydride, ethyl chloroformate, carbon disulphide and aromatic aldehydes to the corresponding fused triazolo derivatives V–VIII are reported. On the other hand cyclization reactions of I with malononitrile, ethyl cyanoacetate, ethyl acetoacetate and acetylacetone to the corresponding condensed pyrazolino derivatives IX–XI are also reported. The reaction of I with α-dicarbonyl compounds to form mono and dihydrazones are reported. The structure of the compounds prepared and their cyclization mechanisms are reported.     

Synthesis and properties of new tetrazines substituted by heteroatoms: towards the world's smallest organic fluorophores

New tetrazines substituted by heteroatoms have been synthesized and their electrochemical and photochemical properties investigated. All compounds are reversibly electroactive with standard potentials shifting cathodically according to the donor character of the substituent. The tetrazine derivatives are also fluorescent with maximum emission wavelengths in the range 550-575 nm. Some of them show very long fluorescence lifetimes (several tens of ns) and remain fluorescent in the solid state without major changes in the spectral features. The fluorescence of one of the derivatives can be efficiently quenched by the presence of electron-rich compounds such as triphenylamines, phenol or anisole, which make them very promising compounds for sensor applications.     

Structure and catalytic activity of host–guest coordination polymers constructed from copper(I) cyanide nets and 1,4-diaminobutane or 1,5-diaminopentane in the presence of water

The reaction of K₃[Cu(CN)₄] and 1,4-diaminobutane (DAB) or 1,5-diaminopentane (DAP) in the presence of Me₃SnCl affords two monometallic host–guest Cu(I) cyanide polymers: {[H₂DAB][Cu₄(CN)₆]·2H₂O}, 1, and{[H₂DAP][H₃O][Cu₄(CN)₇]·2H₂O}, 2, with exclusion of Me₃Sn⁺ cation. The products were characterized by physicochemical and spectroscopic methods. The structure of 1 consists of two-dimensional hexagonal sheets of (CuCN) _n which stack along the b-axis creating honeycomb-shaped channels capable of encapsulating the protonated DAB and water molecules. The structure of 2 consists of a three-dimensional network of [Cu₄(CN)₇] with large cavities that include H₂DAP and water molecules. The rhombic minicycle [Cu₂(μ-CN)₂] fragments represent the basic building blocks of the network structure of 2. The structures of these compounds are stabilized by hydrogen bonding. The SCP 1 and SCP 2 exhibit good catalytic and photocatalytic activities for the degradation of methylene blue (MB) in the presence of H₂O₂. The efficiency of recycled SCP 1 and SCP 2 and the mechanism of degradation of MB dye were also investigated.     

Size‐dependent spectroscopic,optical, and electrical properties of PbSe nanoparticles

Stable crystalline Lead Selenide nanoparticles (PbSe NPs) were prepared with a cubic (sphalerite) phase in polyvinyl alcohol (PVA) matrix. Moreover, XRD was used to characterize the PbSe NPs in PVA. The size were controlled by Pb:Se ions ratio in which the particle size was found to be inversely proportional to this ratio up to 16:1. FT‐Raman and FT‐IR measurements indicated the decrease of crystallization of PVA due to doping with PbSe NPs as indicated by the appearance of a peak at 1124 cm^‐1 that increases by size reduction of PbSe NPs. The Photoluminescence and electrical measurements monitored the interaction of PbSe NPs with PVA which increased by decreasing the particle size. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A Novel Neutral Carrier for Uranyl Ion Based on a Commercially Available Aminophosphate Derivative: Evaluation in Membrane Electrodes and Nuclear Safeguards Applications

The construction and performance characteristics of uranyl membrane electrodes based on cheap and commercially available amino(trimethyl)phosphate are described. The influence of various membrane constituents on the potentiometric responses of the prepared membrane electrodes has been studied. Optimized membrane electrodes exhibited performance characteristics comparable with those based on high cost and commercially available ionophores. Selectivity studies indicated that the developed membrane electrodes are selective towards uranyl ion over a large number of cations including the well‐known uranyl ion interferents (e.g., Fe³⁺, Th⁺⁴). The analytical utility of the proposed membrane electrode has been demonstrated through its application in nuclear safeguards verification purposes.     

Detection of up-conversion in nano-structure BaTiO<Subscript>3</Subscript> co-doped with Er<Superscript>3+</Superscript> and Yb<Superscript>3+</Superscript> ions

Nano-structure pure barium titanate BaTiO₃ (BT) and (BT) co-doped with constant concentration of Er³⁺ ions and different concentrations of Yb³⁺ ions were prepared using sol–gel method. XRD results confirmed that the pure sample was found to crystallize in tetragonal phase by sintering at 750 °C for 1 h. All major peaks corresponding to perovskite BT phase appeared. Efficient infrared-to-visible up-conversion is reported in the doped samples. The conversion process and results in the generation of visible emissions are discussed. Up-conversion efficiency for red emission predominates in doped samples. Results illustrate the large potential of this class of materials for photonic applications in optoelectronics devices.     

Numerical calculations of erosion in an abrupt pipe contraction of different contraction ratios

Erosion predictions in a pipe with abrupt contraction of different contraction ratios for the special case of two‐phase (liquid and solid) turbulent flow with low particle concentration are presented. A mathematical model based on the time‐averaged governing equations of 2‐D axi‐symmetric turbulent flow is used for the calculations of the fluid velocity field (continuous phase). The particle‐tracking model of the solid particles is based on the solution of the governing equation of each particle motion taking into consideration the effect of particle rebound behaviour. Models of erosion were used to predict the erosion rate in mg/g. The effect of Reynolds number and flow direction with respect to the gravity was investigated for three contraction geometries considering water flow in a carbon steel pipe. The results show that the influence of the contraction ratio on local erosion is very significant. However, this influence becomes insignificant when the average erosion rates over the sudden contraction area are considered. The results also indicate the significant influence of inlet velocity variations. The influence of buoyancy is significant for the cases of low velocity of the continuous flow. A threshold velocity below which erosion may be neglected was indicated. Copyright © 2004 John Wiley & Sons, Ltd.     

Forced convection from a straight elliptical tube

The paper deals with the problem of two-dimensional laminar forced convection heat transfer from a straight isothermal tube of elliptic cross-section placed in a uniform stream. The study is based on numerical solutions of the conservation equations of mass, momentum, and energy which covers the entire flow domain including the wake region. The parameters influencing the heat transfer process are essentially the Reynolds number, Re, the tube geometry represented by its minor to major axis ratio, Ar, and the angle of inclination, λ. The study focuses on the effect of Re, Ar, and λ on the heat transfer process in the range of Re from 20 to 500. The study reveals that the rate of heat transfer reaches its maximum when λ=0^∘ while the minimum occurs when λ=90^∘. The results also show that smaller axis ratio gives higher heat transfer rate when λ=0^∘. The local Nusselt number and surface vorticity distributions are plotted for a number of cases and the effect of vortex shedding on the overall rate of heat transfer is briefly discussed. Received on 20 September, 1997