Comparison of radiometric and non-radiometric methods for uranium determination in groundwater of Punjab,India

Uranium in groundwater samples collected from Punjab state, India was determined using radiometric methods (extractive liquid scintillation and Cerenkov counting). Experimental conditions were optimized by studying the effect of sample pH, quenching and amount of extracting agent added to the scintillation cocktail on recovery of uranium. To ensure the accuracy of results, both radiometric methods were compared with non radiometric method such as adsorptive stripping voltammetry and found to be very good agreement. The distinct advantage of proposed radiometric methods is almost 100 % effective especially extractive liquid scintillation for simultaneous measurement of alpha and beta emitting radionuclides with fast and simple sample preparation.     

Silica-supported polyphosphoric acid (PPA-SiO2): An efficient and reusable heterogeneous catalyst for ecofriendly organic synthesis

This review discusses the advances in the use of silica-supported polyphosphoric acid (PPA-SiO₂) as a green and reusable heterogeneous catalyst in the preparation of various organic compounds and pharmaceutical intermediates. PPA-SiO₂ could be recovered and reused several times without significant loss of their efficiency. In this review, we attempt to give an overview of the applications of PPA-SiO₂ as a catalyst in condensation, cyclization, and addition reactions for the preparation of various organic compounds.     

Wavelength-dependent Coulomb explosion in carbon disulphide (CS2) clusters: generation of energetic multiply charged carbon and sulphur ions

A gigawatt laser-induced Coulomb explosion has been observed in carbon disulphide (CS(2)) clusters generating energetic, multiply charged [C](m+) (m = 1-4) and [S](n+) (n = 1-6) atomic ions of carbon and sulphur. The Coulomb explosion shows wavelength dependence. Comparison of these results with our earlier work shows that the polarizability and dipole moment might help in energy absorption from the laser field but they are not mandatory conditions for this low-intensity Coulomb explosion. The results show that in a field of 10(9) W/cm(2), absorption of 266 and 355 nm laser radiation by CS(2) clusters leads to multiphoton dissociation/ionization whereas at 532 nm the whole cluster explodes generating multiply charged atomic ions.     

Particle Sizing Using Frequency Domain Photon Migration

The transport properties of particulate process streams and their final product quality, are directly affected by critical parameters of particle size distribution, f(x), and volume, mass, or number density of particles or dispersed phase droplets. A method is proposed for the potential on-line monitoring of particle size distribution and volume fraction in real time, using frequency-domain photon migration measurements (FDPM). Theory, experimental measurements, and results for the determination of particle size distributions for both a polystyrene latex and a titanium dioxide suspension determined using the photon migration technique are presented. The critical issues associated with the application of photon migration to particulate and dispersed phase processes are discussed, including the effects of interparticle interactions on the transport of light.     

Quantum interference in the Raman scattering from the silicon nanostructures

We report here microscopic process involved in the photo-excited Fano interaction due to nonlinear process in the silicon nanostructures. Photo-excited Raman line-shapes are investigated to reveal the presence of nonlinear Fano interaction in the silicon nanostructures for three different sizes. The Fano interaction is found to be more prominent due to the phase matching between electronic and phonon Raman scatterings for smaller sized nanostructures. Phase matching is achieved by nonlinear process of two-wave mixing in the silicon nanostructures followed by the formation of electron-phonon bound state.     

B(C6F5)3: an efficient catalyst for reductive alkylation of alkoxy benzenes and for synthesis of triarylmethanes using aldehydes

Tris(pentafluorophenyl)borane [B(C₆F₅)₃] has been used as an efficient catalyst for reductive alkylation of alkoxy benzenes using aldehydes as an alkylating agent in the presence of polymethylhydrosiloxane (PMHS). Various alkylated trimethoxybenzene derivatives have been prepared in good to high yields. In addition, B(C₆F₅)₃ was also used as a catalyst for the reaction of electron-rich arenes with aldehydes to obtain triarylmethanes. The use of reductive alkylation protocol for the synthesis of an isochroman and tetrahydroisoquinoline derivatives has also been demonstrated.     

Eco-friendly and facile synthesis of 2-substituted-1H-imidazo[4,5-b]pyridine in aqueous medium by air oxidation

We report a new environmentally-benign, convenient, and facile methodology for the synthesis of 2-substituted-1H-imidazo[4,5-b]pyridine. The reaction of 2,3-diaminopyridine with substituted aryl aldehydes in water under thermal conditions without the use of any oxidative reagent has been studied. The reaction has yielded 1H-imidazo[4,5-b]pyridine derivatives by an air oxidative cyclocondensation reaction in one step in an excellent yield. Furthermore, a series of compounds were synthesized and characterized by melting point, EI-MS, NMR, and IR tools. For comparison, the reference samples were prepared by the reported method. Utilization of aqueous medium, easy reaction conditions, isolation, and purification make this manipulation very interesting from an economic and environmental perspective.     

Releasable luciferin-transporter conjugates: tools for the real-time analysis of cellular uptake and release

The design, synthesis, and evaluation of conjugates of arginine-rich transporters and luciferin are described that release luciferin only after entry into cells that are stably transfected with luciferase. Each molecule of free luciferin that is released after entry generates a photon that can be measured allowing for real-time quantification of uptake and release in cells. The process provides a method to assay uptake and release of free luciferin as a function of variations in the releasable linker and in the transporter.     

Two new glycosides from the soft coral Sinularia firma

Two new glycosides, named Firmacosides A and B, together with known fatty esters, batyl alcohol, Delta(5,20) sterol and sphingosine derivatives have been isolated from the soft coral Sinularia firma TIX-DUR. On the basis of spectroscopic analysis ((1)H-NMR, (13)C-NMR, (1)H-(1)H COSY, HMQC, HMBC and FAB-MS), Firmacoside A was established as hexadecanyl-1-O-alpha-D-arabinopyranosyloxy (1-->4)-alpha-D-arabinopyranosyloxy (1-->4)-alpha-D-arabinopyranoside (1), and firmacoside B was elucidated as docosanyl-1-O-alpha-D-arabinopyranosyloxy (1-->4)-3-O-acetyl-alpha-arabinopyranosyloxy (1-->4)-alpha-D-arabinopyranoside (2).     

Crystal Engineering: A Unique Cyclic Assembly of a 40 Membered Module Composed from Two Alternating Units Each of Benzenehexacarboxylic Acid (Mellitic Acid,MA) and 2,5-Bis-(4-pyridyl)-1,3,4-oxadiazole (4-BPO): Assembly of Modules to Macromolecules by Intermolecular Hydrogen Bonding

Abstract  Individually prepared, equivalent amounts of 2,5-bis-(4-pyridyl)-1,3,4-oxadiazole (4-BPO) and benzenehexacarboxylic acid (mellitic acid, MA) when mixed, deposited long rods, whose X-ray structure showed a unique assembly of 40 membered planar modules composed from two alternating units each of MA and 4-BPO, rather than the anticipated helical profile. Several novel features of complexes of MA with organic molecules are seen here. In almost all cases the intermolecular hydrogen bonding between MA anions is so stable that the MA anions and the complementary cations lie in separate planes. This barrier is overcome in the present case. The basic module associates to form quartets by very simple hydrogen bonding of the carboxylic groups of MA. The quartet assembly is characterized by the rotation of the left hand pair compared to the right hand pair. The mode of the macromolecular assembly is clear, that is, they are layered in alternating planes. Space group: P2₁/c with a = 9.181(1) ?, b = 9.624(1) ?, c = 29.390(2) ?, and β = 94.626(4)°. The modules are embedded in an extensively hydrogen bonded MA network. The assembly profile of MA and 4-BPO is unique and should be a harbinger for the design of novel functional assemblies. The 40-membered module mimics the self-assemblies of peptides and can be important in the design of “Haptens” from simple molecules. Index Abstract  Rod like crystals from water that are formed on mixing MA and 4-BPO are shown to consist of 4-molecule modules (MA–4-BPO–MA–4-BPO–) that contain a 40-membered ring, MA–BPO.