Hydrogenic systems,frequency standards and fundamental constants

Hydrogenic (two-body) systems are the only atomic systems for which uncertainties in calculations of the energy levels approach the current state of the art in frequency measurement. This article discusses progress in the theory and measurement of transition frequencies in hydrogenic systems. These studies have relevance to the determination of fundamental constants and the testing of physical theories, especially quantum electrodynamics. A set of high accuracy calculable frequency standards could also be realized by using hydrogenic systems.     

Direct sample fraction deposition using electrospray in narrow-bore size-exclusion chromatography/matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for polymer characterization

A direct sample fraction deposition method was developed for off-line size-exclusion chromatography (SEC)/matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry. By using electrospray, the SEC eluent, together with a suitable matrix solution added coaxially, was directly deposited on the MALDI plate. Owing to the formation of very small droplets in electrospray, solvent evaporation is much faster. The fractionation volume in narrow-bore SEC, which can directly be collected in one MALDI spot, can easily be optimized in the range of a few microlitres. In addition, fairly homogeneous sample spots were obtained. The possible influence of composition variation of the SEC effluent on the analytical results using direct fraction deposition was investigated; no substantial effects were observed. The applicability of the method was demonstrated by characterizing a broad poly(methyl methacrylate) sample. Copyright 2000 John Wiley & Sons, Ltd.     

Applicability of microplate assay coupled to Fiske-Subbarow reducer for the determination of phosphorous produced by in vivo human lymphocytes: PKC is probably cross talking with ecto 5′-nucleotidase

In this research, the phorbol ester, phorbol 12-myristate 13-acetate (PMA), was used to assess the effect of protein kinase C (PKC) activation on the specific activity of ecto-5′-nucleotidase (eNT) in human lymphocytes. PMA mimics the effects of diacylglycerol, a natural compound released by the hydrolysis of the glycosilphosphatidilinositol (GPI) moiety, in activating PKC. In order to evaluate the activity of eNT in living lymphocytes, a micro-assay method was established with a low detection limit for inorganic phosphate (Pi) of 0.94 nmol Pi assay⁻¹. The dephosphorylation of Adenosine monophosphate (AMP) by functional lymphocytes was evaluated and the contribution of the eNT activity was calculated by its inhibition with the specific eNT inhibitor α,β-methylene ADP (MADP) and the use of the broad spectrum phosphatases inhibitor (but not eNT), levamisole. Under the conditions tested, we obtained an AMPase value of 8.05±4.4 nmol Pi million cells⁻¹ h⁻¹. The addition of MADP to the incubation media decreased the AMPase activity to 2.43±0.9 nmol Pi million cells⁻¹ h⁻¹ (p<0.05). On the other hand, when lymphocytes were incubated with PMA, an increase of 182% in the AMPase activity was observed. However, the addition of levamisole inhibited the AMPase activity by about 17%, while the co-incubation of cells with PMA and levamisole reduced only an 8% of the total PMA-increased AMPase activity. These results show that (1) a non-radioactive micro-method can be used to assess the Pi production in living cells; (2) the obtained data strongly suggest that eNT is the main ecto-enzyme present on the surface of circulating lymphocytes responsible for the hydrolysis of extracellular AMP; and (3) that PKC is cross talking with eNT.     

Gold Nanoparticles Obtained by Bio-precipitation from Gold(III) Solutions

The use of metal nanoparticles has shown to be very important in recent industrial applications. Currently gold nanoparticles are being produced by physical methods such as evaporation. Biological processes may be an alternative to physical methods for the production of gold nanoparticles. Alfalfa biomass has shown to be effective at passively binding and reducing gold from solutions containing gold(III) ions and resulting in the formation of gold(0) nanoparticles. High resolution microscopy has shown that five different types of gold particles are present after reaction with gold(III) ions with alfalfa biomass. These particles include: fcc tetrahedral, hexagonal platelet, icosahedral multiple twinned, decahedral multiple twinned, and irregular shaped particles. Further analysis on the frequency of distribution has shown that icosahedral and irregular particles are more frequently formed. In addition, the larger particles observed may be formed through the coalescence of smaller particles. Through modification of the chemical parameters, more uniform particle size distribution may be obtained by the alfalfa bio-reduction of gold(III) from solution.