Synthesis, NMR Characterization, and a Simple Application of Lithium Borotritide

LiBH(4) is a powerful and selective reagent for regiospecific reduction reactions. A simple synthesis of LiB(3)H(4) at near theoretical specific radioactivity is reported. We have treated Li(3)H synthesized from tritium gas ((3)H(2), approximately 98%) with BBr(3) to produce LiB(3)H(4) (specific activity = 4120 GBq/mmol = 110 Ci/mmol. The maximum theoretical specific activity of LiB(3)H(4) is 4252 GBq/mmol = 115.04 Ci/mmol; 1 matom of (3)H = 1063 GBq = 28.76 Ci.) The tritium labeling performance of the reagent was tested by an exemplary reduction of 2-naphthaldehyde to 2-naphthalenemethanol. LiB(3)H(4) and the reduction products were characterized by a combination of (1)H, (3)H, and (11)B NMR techniques, as appropriate.     

Neutron activation analysis of zeolite catalysts

A new method for the determination of aluminum and silicon has been developed for zeolite catalysts. In contrast to previous methods, thermal neutrons are used for the analysis of both elements, and cadmium absorbers are not needed. The silicon determination utilizes a one-hour irradiation to observe the³¹Si produced by the (n, ) reaction of³⁰Si. A 15-second irradiation is used for the²⁷Al(n, )²⁸Al reaction. The²⁸Al activity is corrected for the contribution from the²⁸Si(n,p)²⁸Al reaction by using the analyzed weight of silicon in the sample and the data for a silicon standard irradiated simultaneously with the zeolite and the aluminum standard. The quantitation limits are 0.012 g for silicon and 3.3×10^–5 g for aluminum. Sodium presents a significant interference, but this element can be removed by taking advantage of the ion exchange properties of these materials.     

Measurement/data-processing method to improve the ruggedness of membrane-based sensors: Application to amperometric oxygen sensor

This paper describes alternative measurement and data-processing approaches that can reduce effects of experimental variables on results obtained with a membrane-based sensor for oxygen. In the new approaches, the membrane-based sensor is first equilibrated with the sample solution, after which a polarizing voltage is applied and current vs. time data are recorded as the response decays toward a steady-state condition. Current vs. time data are then processed by a fixed-time option and an integration option designed to determine the charge corresponding to the total amount of oxygen inside the membrane when a polarizing voltage is applied. The current measured at a fixed time and the total charge varied linearly with oxygen concentration between 0.05 and 0.26 mmol l(-1). Pooled relative standard deviations (N = 35) for the measurement/data-processing step were near 0.4% for the new pre-equilibrium options compared to a value of 0.3% for the steady-state option. Dependencies of the pre-equilibrium options on membrane thickness and stirring rate in the most sensitive regions were at least two orders of magnitude smaller than for the steady-state option.     

Enhancement of the cubic molecular hyperpolarizabilities of nickel benzendithiol by donor and acceptor groups

In this paper the enhancement of the values of the cubic molecular hyperpolarizability of the nickel benzendithiol system, resulting from the selective addition of acceptor and donor groups to the ligand structure, is presented. The polarization of the molecular electronic structure is calculated by the finite field method. Significant increases in the values of are obtained from bridging two p-nitroaniline molecules with the square planar nickel structure. These results show that structures with significant values of x ⁽²⁾ that are derived from the inclusion of donor and acceptor groups might also be included into the ligands of the nickel dithiolene complex to give rise to materials with enhanced values of x ⁽³⁾.