Determination of rhenium in the URe2 binary compound by differential spectrophotometry

A differential spectrophotometric determination of rhenium in its binary compound with uranium is described; the method is based on the action of tin(II) chloride on perrhenate in the presence of dimethylglyoxime with measurement at 445 nm. Uranium does not interfere. For solutions containing about 1 mg of rhenium, the coefficient of variation was 0.08%.     

Closely stacked oligo(phenylene ethynylene)s: effect of π-stacking on the electronic properties of conjugated chromophores

In this work, a bicyclo[4.4.1]undecane scaffold is used to hold oligo(phenylene ethynylene) units in a cofacially stacked arrangement along the entire length of the conjugated units. We study the impact that the resulting strong interchain interactions have on the photophysical properties. The length of the individual oligomer branches was varied from three to five rings to investigate the effect of conjugation on the electronic properties of the stacked segments. Absorption and fluorescence spectra were recorded and compared to those of the corresponding unstacked analogues. Time-dependent density functional theory calculations were carried out and helped to rationalize the low-energy features present in the fluorescence spectra of the stacked systems. The calculations indicate that the low-energy emissions are due to the presence of excimer-like states. The stronger intensity of the low-energy fluorescence band observed in the five-ring stacked system compared to the three-ring analogue is attributed to the smaller activation barrier that separates the local intrachain state and the excimer-like state in the former compound.     

Alkylation of Unsaturated Aldehyde and Allylic Bisacetate With Organomanganese Reagents in Presence of Tetrakis Acetonitrile Copper(I) Tetrafluroborate

The conjugate addition of organomanganese reagents to α,β‐unsaturated aldehydes and allylic bisacetate in presence of Me₃Si‐Cl and tetrakis acetonitrile copper(I) tetrafluroborate is described.     

ZrOCl2·8H2O: An Efficient Catalyst for One-Pot Synthesis of α-Amino Phosphonates Under Solvent-Free Conditions

A highly efficient protocol has been developed for the three-component reaction of an amine, an aldehyde, and diethyl phopshite catalyzed by ZrOCl₂·8H₂O, an environmentally friendly catalyst, at ambient temperature. The catalyst exhibited remarkable activity and tolerated a wide variety of functional groups, providing the desired amino phosphonates in excellent yields under solvent-free conditions. Alternatively, the reaction rate can be significantly enhanced by carrying out the reaction in a monomode microwave reactor as a promoter.     

Diffraction of sound pulses by a rigid cylinder in an inhomogeneous medium

We consider the problem of scattering of two-dimensional sound pulses by a rigid circular cylinder embedded in a cylindrically stratified inhomogeneous medium. The line source is parallel to the axis of the cylinder. It is assumed that the velocity of soundc is given byc ^?1=pr ^q, wherep andq are real constants andp>0. The method of dual integral transformation developed by Friedlander is used. The solution in terms of pulse propagation modes gives the diffracted pulse and the method of steepest descents yields the geometrical acoustic field.     

Post buckling response of functionally graded materials plate subjected to mechanical and thermal loadings with random material properties

In this paper, the second order statistics of post buckling response of functionally graded materials plate (FGM) subjected to mechanical and thermal loading with nonuniform temperature changes subjected to temperature independent (TID) and dependent (TD) material properties is examined. Material properties such as material properties of each constituent’s materials, volume fraction index are taken as independent random input variables. The basic formulation is based on higher order shear deformation theory (HSDT) with von-Karman nonlinear kinematic using modified C⁰ continuity. A direct iterative based C⁰ nonlinear finite element method (FEM) combined with mean centered first order perturbation technique (FOPT) proposed by last two authors for the composite plate is extended for Functionally Graded Materials (FGMs) plate with reasonable accuracy to compute the second order statistics (mean and coefficient of variation) of the post buckling load response of the FGM plates. The effect of random material properties with amplitude ratios, volume fraction index, plate thickness ratios, aspect ratios, boundary conditions and types of loadings subjected to TID and TD material properties are presented through numerical examples. The performance of outlined present approach is validated with the results available in literatures and independent Monte Carlo simulation (MCS).     

Hyperpolarization of Amino Acids in Water Utilizing Parahydrogen on a Rhodium Nanocatalyst

NMR offers many possibilities in chemical analysis, structural investigations, and medical diagnostics. Although it is broadly used, one of NMR spectroscopies main drawbacks is low sensitivity. Hyperpolarization techniques enhance NMR signals by more than four orders of magnitude allowing the design of new contrast agents. Parahydrogen induced polarization that utilizes the para-hydrogen's singlet state to create enhanced signals is of particular interest since it allows to produce molecular imaging agents within seconds. Herein, we present a strategy for signal enhancement of the carbonyl ¹³C in amino acids by using parahydrogen, as demonstrated for glycine and alanine. Importantly, the hyperpolarization step is carried out in water and chemically unmodified canonical amino acids are obtained. Our approach thus offers a high degree of biocompatibility, which is crucial for further application. The rapid sample hyperpolarization (within seconds) may enable the continuous production of biologically useful probes, such as metabolic contrast agents or probes for structural biology.     

Ultrasound assisted regioselective sulfonation of aromatic compounds with sulfuric acid

A simple and convenient methodology for selective sulfonation of aromatic compounds using sulfuric acid under sonication is described. The present methodology shows a considerable enhancement in the reaction rate along with improved selectivity compared with the reactions performed under silent conditions. The effect of various parameters such as agitation speed, sulfuric acid concentration, and temperature on reaction system have been investigated and are explained on the basis of ultrasonically generated cavitational effects.