Disposable Screen‐Printed Carbon Electrodes for Dual Electrochemiluminescence/Amperometric Detection: Sequential Injection Analysis of Oxalate

This work describes the development and application of an electrochemical cell specifically designed for disposable screen printed carbon electrodes (SPCE) suitable for simultaneous electrochemiluminescence (ECL) and amperometric detection in sequential injection analysis. The flow system with facility for photomultiplier tube via a fiber optic facing the SPCE is user‐friendly and makes the detection process very easy to operate. Instead of the need to constant deliver the chemiluminescence (CL) reagents to the reaction zone, sequential injection analysis allows a considerable reduction in the consumption of the sample and expensive CL reagents (such as Ru(bpy) salts). The utility of the analyzer was demonstrated for the detection of oxalate based on the ECL reaction with Ru(bpy) . Under optimized conditions, in the presence of 100 μM Ru(bpy) , the linear ranges of peak current and ECL light intensity for oxalate distinctly varied from 10 μM to 5 mM and 0.1 μM to 100 μM, respectively. In other words, the linear detection can be covered over a four‐order range with the combination of these two signals.     

Electrocatalytic oxidation of NADH at the self-assembled monolayer of nickel(II) macrocycle on gold electrode

Electroactive self-assembled monolayers (SAMs) of macrocyclic Ni(II) complex (1) were fabricated on gold electrode and its electrochemistry has been studied in different supporting electrolytes. Substantial stabilization of tervalent nickel and a significant negative shift of formal potential of the Ni(3+/2+) couple have been observed when the supporting electrolyte is changed from nitrate to phosphate. Coordination of supporting electrolyte anion with the Ni(III) complex shifts the formal potential and thus tervalent nickel is stabilized. SAM of 1 electrode shows an excellent electrocatalytic activity towards the oxidation of NADH in aqueous NaNO3 solution, whereas it scarcely catalyzes the oxidation of NADH in aqueous phosphate buffer solution. The electrocatalytic oxidation of NADH in Na2SO4 solution is less efficient than that in NaNO3 solution. The anion-dependent electrocatalysis has been discussed on the basis of the difference in the coordinating ability of the anions with the tervalent nickel centers. Steady-state current has been measured for the oxidation of NADH and it was proportional to the concentration of NADH.     

Purification of uranium product from plutonium contamination using acetohydroxamic acid (AHA) based process

Acetohydroxamic acid (AHA) based uranium product purification process to remove plutonium was optimized. For this process, equilibrium data was generated to optimize AHA concentration and acidity of stripping agent/scrubbing agent. Two options namely (i) Pu complexation in aqueous phase followed by extraction and scrubbing ii) extraction followed by scrubbing with AHA were studied. Results of these studies indicate that U product obtained in AHA purification is near to the table top specification and also quantitative Pu recovery from the AHA strip product is possible by oxalate precipitation.     

Comparison of electrical conductivity and thermal properties of borosilicate glass with and without simulated radioactive waste

Electrical conductivity and percentage linear thermal expansion of the borosilicate glass (BSG) and simulated waste-loaded borosilicate glass (BSGW) were measured in the temperature range of 300–780 K and compared. Pronounced increase in electrical conductivity was observed around glass transition temperature (T _g) of BSG and BSGW. The activation energy (E _a) of electrical conduction determined from the measured data for BSG and BSGW is 0.961 ± 0.005 and 0.960 ± 0.005 eV, respectively. The % average linear thermal expansion of BSGW showed a slight decreasing trend compared with pristine BSG. The average coefficient of thermal expansion determined from dilatometry data is 12.87 ± 0.24 × 10^?6 and 11.94 ± 0.23 × 10^?6 K^?1 for BSG and BSGW, respectively. The T _g measured by dilatometry is 806 ± 24 K for BSG and 790 ± 23 K for BSGW, respectively. The T _g measured by DTA was found to be 820 ± 7 and 805 ± 5 K for BSG and BSGW, respectively, for heating cycle. The T _g values obtained from DSC measurements are 805 ± 5 and 803 ± 5 K for BSG and BSGW, respectively. The T _g of BSGW showed a slight decrease compared with that of BSG. The values obtained by DSC examination also showed the lowering of T _g values for the waste-loaded composition. The lowering of T _g may be attributed to the interaction of glass-forming agents and simulated waste elements.     

Tributyltin Hydride–Mediated Synthesis of Bicyclic Carbocycles Initiated by Et3B/O2

Synthesis of bicyclic carbocycles involving tributyltin hydride–mediated α-carbonyl radical cyclization reaction at room temperature has been reported.     

Internal conrotation and disrotation in H2BCH2BH2 and diborylmethane 1,3 H exchange

The paths of correlated internal disrotation (barrier less than 0.4 kcal/mol) and conrotation (barrier around 1.9 kcal/mol) of the two BH₂ groups in H₂BCH₂BH₂ have been computed employing ab initio [MP2(full)/6–31G**] and density functional theory (Becke3LYP/6–311+G**) methods. Two B(SINGLE BOND)C(DOTTED BOND)B(p) hyperconjugative interactions stabilize the C_s symmetric H₂BCH₂BH₂ isomer ( 1 ). The B(SINGLE BOND)C(DOTTED BOND)B(p) hyperconjugative stabilization, evaluated by homodesmotic reactions and using the orbital deletion procedure (which “deactivates” the “vacant” born p orbital), is less than 6 kcal/mol in diborylmethane. The B(SINGLE BOND)C(DOTTED BOND)B(p) stabilization is shown to be remarkably large in C₄B₆H₁₀ (Td). At MP2(fu)/6–31G**, disproportionation into 1 and methane is only 5.6 kcal/mol exothermic. The 1,3 H exchange in diborylmethane is an asynchronous process and proceeds via a doubly bridged cyclic intermediate with 9.3 kcal/mol barrier. Structures with “planar tetracoordinate” carbon are stabilized considerably by BH₂ substituents, but they are still high in energy. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 1792–1803, 1997     

Dynamics of individual specialization and global diversification in communities

We discuss a model of an economic community consisting of N interacting agents. The state of each agent at any time is characterized, in general, by a mixed strategy profile drawn from a space of s pure strategies. The community evolves as agents update their strategy profiles in response to payoffs received from other agents. The evolution equation is a generalization of the replicator equation. We argue that when N is sufficiently large and the payoff matrix elements satisfy suitable inequalities, the community evolves to retain the full diversity of available strategies even as individual agents specialize to pure strategies. © 1998 John Wiley & Sons, Inc.     

Synthesis and characterization of Li<Subscript>1-x</Subscript>Tb<Subscript>x</Subscript>NiPO<Subscript>4</Subscript> solid solution as cathode materials for lithium ion battery application

Modified Pechini-type polymerizable precursor method has been used to prepare nanosized Li_1-xTb_xNiPO₄ (x = 0, 0.03, 0.05, and 0.07) solid solutions to obtain homogeneous with controlled stoichiometry and smaller particle size. The reaction temperature was determined by thermogravimetric (TG/DTA) analysis. X-ray diffraction analysis reveals the formation of orthorhombic structure and the calculated crystallite sizes are found to be in the range of 75–89 nm. Morphological, compositional, and vibrational properties were performed by SEM, EDAX, and FTIR, respectively. Conductivity measurements were carried out at room temperature by AC impedance analysis. The Li_0.97Tb_0.03Ni_0.99PO₄ sample shows one order of higher conductivity than pure LiNiPO₄. Higher concentration of terbium samples such as Li_0.95Tb_0.05Ni_0.99PO₄ and Li_0.93Tb_0.07Ni_0.99PO₄ lead to decrease of conductivity. The frequency dependency of dielectric permittivity, dielectric loss, and electric modulus of Li_1-x Tb_xNiPO₄ solid solutions are studied. The frequency-dependent plot of modulus reveals that the conductivity relaxation is of non-Debye type.