The determination of molybdenum and tungsten by high resolution spectrometry of alpha-induced prompt photon emission

A simple, rapid and non-destructive method is described for determining molybdenum and tungsten in steels over the concentration range 0.07 to about 20% by mass. The method uses high resolution spectrometry of the low energy gamma-rays induced by 5 MeV alpha-particle beams. The precision for molybdenum is 2.7% and for tungsten is 0.55% using respectively the 204 and 100.1 keV gamma-rays. Results obtained by Ge(Li) and intrinsic germanium detectors are compared. The extent of interference from other elements is discussed.     

The Effect of Surface Forces on the Thermal Slip of a Simple Gas

The flow of a simple gas along a plane surface under the action of tangential temperature gradient is considered. The velocity of thermal slip is calculated by the variational method with account of the effect of surface forces. It is shown that, in some situations, surface forces can substantially affect the value of the thermal slip coefficient.     

Molecular dynamics simulations of the mononuclear zinc-beta-lactamase from Bacillus cereus complexed with benzylpenicillin and a quantum chemical study of the reaction mechanism

Herein, we present results from MD simulations of the Michaelis complex formed between the B. cereus zinc-beta-lactamase enzyme and benzylpenicillin. The structural and dynamical effects induced by substrate-binding, the specific role of the conserved residues, and the near attack conformers of the Michaelis complex are discussed. Quantum chemical methods (HF/6-31G* and B3LYP/6-31G*) are also applied to study the hydrolysis reaction of N-methylazetidinone catalyzed by a monozinc system consisting of the side chains of the histidine residues (His86, His88, and His149) complexed with Zn-OH and the side chains of Asp90 and His210. From this model system, we built molecular-mechanics representations of the prereactive complex and transition state configurations docked into the active site. Linear-scaling semiempirical calculations coupled with a continuum solvent model were then performed on these static models. We propose that the experimental rate data for the B. cereus enzyme is compatible with a one-step mechanism for the hydrolysis of beta-lactam substrates in which His210 acts as a proton donor.     

Effect of total percent polyacrylamide in capillary gel electrophoresis for DNA sequencing of short fragments. A phenomenological model.

Polyacrylamide capillary gels were prepared with constant (5% C) cross-linker concentration and with total acrylamide concentration ranging from 2.5 to 6% T. At each acrylamide concentration, peak spacing was constant for DNA sequencing fragments ranging from 25 to 250 nucleotides in length. Peak spacing increased linearly with the total acrylamide concentration. The intercept of the retention time vs. fragment length plot was independent of % T. Ferguson plots were constructed for short DNA fragments; the polyacrylamide pore size falls in the 2.5 to 3.5 nm range for the gels studied. Theoretical plate count is independent of total acrylamide concentration; longitudinal diffusion, and not thermal gradients, limit the plate count. A phenomenological model is presented that predicts retention time, plate count, and resolution for sequencing fragments ranging in size from 25 to 250 bases and gels that range from 2.5 to 6% total acrylamide.     

Photoreduction of benzophenone by dimethylaminoethyl methyacrylate in solutions

The photoreduction of benzophenone by dimethylaminoethyl methacrylate was investigated under the conditions of stationary and pulsed irradiation. With stationary irradiation of this system in benzene an intermediate photoproduct is formed, and its destruction is described by a kinetic equation of second order. By irradiation under pulsed conditions it is possible to detect the formation of the ketyl radicals of benzophenone, the yield and destruction of which depend substantially on the nature of the medium. The relationship between the destruction constant and the concentration of the aminomethacrylate and butyl methacrylate was examined and explained; the constant increases with decrease in the aminomethacrylate concentration and with increase in the butyl methacrylate concentration. The mechanism of the photoreduction of aromatic carbonyl compounds by aminomethacrylates is described.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 1, 56–62, January–February, 1990.     

Surface mixed adsorption films of 2,4,6- trimethylphenol–2,4,6-trichlorophenol at aqueous solution/air interface

 The results of experimental studies of the adsorption at the solution/air interface from an aqueous mixture: 2,4,6-trimethylphenol–2,4,6-trichlorophenol are presented. The surface properties of the above-mentioned mixture were studied by surface potential and surface tension measurements. These measurements were carried out as a function of the concentration of 2,4,6-trimethylphenol aqueous solution at a constant concentration of 2,4,6-trichlorophenol. Using the results obtained and based on the Gibbs equation, Helmholtz formula and Motomura’s method the relative surface excesses of adsorbed substances, effective dipole moments, surface molar fractions of solutes and miscibility of adsorbed films were determined. Received: 7 November 1997 Accepted: 26 February 1998     

Fission track mapping of uranium in black spruce (Picea Mariana) twigs

Fission track analysis (FTA) has been used to investigate the biological uptake of uranium. Examination of fission track maps of black spruce twigs (from areas of uranium mineralization and mill tailings) shows uranium to be concentrated in the inner bark while decreasing in the outer bark of the twigs. Track clusters in the bark, too large to be uraniferous airborne particulate matter, are identified as being associated with resin canals in the twigs. The results of this work help clarify the mechanisms by which uranium is incorporated in black spruce twigs. The observation of decreasing uranium content with the increasing age of black spruce twigs by an earlier worker, can now be explained by the relative reduction in volume of the uranium enriched inner bark with age.     

5,6-dihydroxyindole-2-carboxylic acid by treatment of sepiomelanin with sodium borohydride.

Mild treatment of sepiomelanin and biosynthetic eumelanins with NaBH₄ in 0.1 N NaOH leads to the isolation of 5,6-dihydroxyindole-2-carboxylic acid ($\text{3}$), a component of structural interest which may account for most of the degradation products of melanins so far obtained.     

Zur Spuren-Mitfällung an MnO(OH)2 in NH4F-Lösungen

The co-precipitation of traces of As, W, Sn, Au, Ag, Hg, Co, Fe, Cu, Cd and Zn with MnO(OH)₂ in the concentrated NH₄F solutions was measured by means of their radioactive isotopes. The influence of the starting-concentration (10^?6–10^?3%), of the MnO(OH)₂ amount and of the duration of standing of the sediment in the solution was investigated. The MnO(OH)₂ was formed in situ from Mn⁷⁺ and Mn²⁺ in stoichiometric proportion. This method can be used for an enrichment of traces in analysis as well as for the cleaning of NH₄F solutions.