Analysis for sulfur as hydrogen sulfide incorporating zirconia pretreatment and preconcentration

The method of analysis for sulfate by reduction of high oxidation state sulfur to hydrogen sulfide, followed by spectrophotometric analysis, has the advantages of allowing small quantities to be measured and some interfering species to be removed. However, it has been found that acid digested samples cannot be analysed by this method due to destruction of the reduction mixture. A column of zirconium(IV) oxide was successfully used to both, remove interfering ions (H(+), Cl(-) and NO(-)(3)) from a sediment digest, as well as perform preconcentration of sulfate. Recoveries from digests of standard sulfur samples were 101 +/- 1%, and from preconcentration solutions 98.8 +/- 1.2%. Comparison of results with independent analyses confirmed that not all sulfur species are detected with the same efficiency by the combined zirconia/reduction-spectrophotometric method.     

X-ray emission from clusters of galaxies and cosmological parameters

Clusters of galaxies are excellent probes of cosmic structure and evolution. X-ray studies of clusters provide some of their key parameters, viz., temperature of the hot intra-cluster gas, its metallicity, X-ray luminosity and surface brightness giving mass distribution and mass-flow rate in the case of cooling flows. X-ray measurements for a large sample of clusters have lead to estimates of the total gravitating mass in them, which can be compared to the virial masses derived from dynamical considerations and gravitational lensing in some of them. X-ray derived total masses are consistent with masses obtained from the other methods after the effects due to the presence of cooling flows are taken into account in the analyses. Estimated virial masses, lack of evolution in X-ray properties, and detection of several very hot clusters at high redshifts indicate a Universe with a low value (≤ 0.3) for the Ω parameter.     

Fluxes in "free" and total zinc are essential for progression of intraerythrocytic stages of Plasmodium falciparum

Dynamic fluxes in the concentration of ions and small molecules are fundamental features of cell signaling, differentiation, and development. Similar roles for fluxes in transition metal concentrations are less well established. Here, we show that massive zinc fluxes are essential in the infection cycle of an intracellular eukaryotic parasite. Using single-cell quantitative imaging, we show that growth of the blood-stage Plasmodium falciparum parasite requires acquisition of 30 million zinc atoms per erythrocyte before host cell rupture, corresponding to a 400% increase in total zinc concentration. Zinc accumulates in a freely available form in parasitophorous compartments outside the food vacuole, including mitochondria. Restriction of zinc availability via small molecule treatment causes a drop in mitochondrial membrane potential and severely inhibits parasite growth. Thus, extraordinary zinc acquisition and trafficking are essential for parasite development.     

Emission ratiometric imaging of intracellular zinc: design of a benzoxazole fluorescent sensor and its application in two-photon microscopy

Zinc and calcium are ubiquitous intracellular metals, and while a variety of quantitative probes have been developed for measuring intracellular changes in calcium concentration, the same is not true of zinc. We describe here the design, synthesis, and properties of the benzoxazole-based, ratiometric zinc probe, Zinbo-5. This bright fluorescent reporter has a quantum yield of 0.1 in the zinc-form, exhibits a Kd for Zn2+ in the nanomolar range, and shows significant changes in both excitation and emission maxima upon zinc binding. The utility of this cell permeable probe is demonstrated in fluorescence microscopy emission ratio imaging experiments on mammalian cells. We further show that Zinbo-5 is well suited for two-photon excitation microscopy ratio imaging and can readily reveal changes in intracellular zinc concentration within optical planes of single cells. To the best of our knowledge, this is the first example of two-photon excitation microscopy applied to ratio imaging of zinc. These methods can be applied to real-time emission or excitation ratio imaging studies of zinc physiology in living cells.     

Comparison of three colorimetric methods for the determination of manganese in freshwaters

Three calorimetric methods for the determination of manganese in freshwaters have been investigated and compared with the atomic-absorption spectrometry (AAS) method. Two of the methods, viz. the formaldoxime (FAD) and pyridylazonaphthol (PAN) methods were found to yield poor calibration curves upon standardization, and to have high average errors for the estimation of manganese concentrations in standard solutions. The FAD method, when applied to freshwater samples, was found to be subject to an interfering UV absorbance which could not be negated successfully by a reagent blank; the method thus tended to give high estimations at low concentrations of manganese, but the results obtained also appear to be very sensitive to the nature of the freshwater matrix. On the other hand the PAN method was found to give very high estimations for the concentration of manganese, in both standard solutions and in freshwater samples, owing to the nature of the absorbance of the ligand used for manganese determination. This method also appears to be affected by the freshwater matrix, leading to gross overestimation of manganese levels. A third method, based on a porphyrin ligand [T-(4-CP)P], was found to give results comparable with those of the AAS method in estimating the soluble manganese content in freshwaters.     

Prussian Blue bulk modified screen-printed electrodes for H(2)O(2) detection and for biosensors

A sensor for H(2)O(2) amperometric detection based on a Prussian Blue (PB) bulk modified carbon screen-printed electrode was developed. It has been optimised with respect to the lowest limit of detection achieved. PB was made chemically by the reaction of FeCl(3) with K(4)[Fe(CN)(6)]. The resulting powder, obtained by forced crystallisation induced by acetone, was dried and activated at 150 degrees C for 10 h. PB microparticles (<38 mum) were prepared and mixed with carbon ink. The limit of detection achieved was 0.4 muM with the linear range up to 100 muM of H(2)O(2) with the sensitivity of 137 muA mM(-1) cm(-2), that was comparable with sensors based on electrodeposited PB film. The transducer was applied for a glucose biosensor, that exhibited LOD of 0.22 mM, linear range up to 3 mM, K(M)(app) of 4.6 mM, and the sensitivity of 3.21+/-0.16 muA mM(-1) cm(-2). The peroxide sensor, as well as the glucose biosensor, were totally insensitive to oxygen, ascorbate, urate, and paracetamol.     

The PcoC copper resistance protein coordinates Cu(I) via novel S-methionine interactions

The E. coli copper resistance protein PcoC enhances survival of a bacterium under conditions of extreme copper stress. This small protein has no cysteines, but does have an unusual methionine-rich sequence motif, suggesting that methionine ligation may be important in Cu binding. It is shown that PcoC binds both Cu(I) and Cu(II), in addition to binding Hg(II) and Ag(I). Previously crystallographic studies of PcoC had shown that the apo protein adopts a beta-barrel fold typical of that seen for blue-copper electron-transfer proteins. However, in contrast with electron-transfer proteins, where the Cu(I) and Cu(II) structures are nearly identical, X-ray absorption spectra show that the structures of the Cu site in reduced and oxidized PcoC are dramatically different. Cu(II) PcoC has a tetragonal Cu structure in which the Cu is coordinated to O or N ligands, including at least two histidine ligands. Cu(I) PcoC has a trigonal site with two methionine ligands. This is the first well-characterized example of a methionine-rich protein Cu binding site, demonstrating a new type of biological Cu coordination chemistry.     

Exotic decay in cerium isotopes

Half life for the emission of exotic clusters like ⁸Be, ¹²C, ¹⁶O, ²⁰Ne, ²⁴Mg and ²⁸Si are computed taking Coulomb and proximity potentials as interacting barrier and many of these are found well within the present upper limit of measurement. These results lie very close to those values reported by Shanmugam et al using their cubic plus Yukawa plus exponential model (CYEM). It is found that ¹²C and ¹⁶O emissions from ¹¹⁶Ce and ¹⁶O from ¹¹⁸Ce are most favorable for measurement (T _1/2<10¹⁰ s). Lowest half life time for ¹⁶O emission from ¹¹⁶Ce stress the role of doubly magic ¹⁰⁰Sn daughter in exotic decay. Geiger-Nuttall plots were studied for different clusters and are found to be linear. Inclusion of proximity potential will not produce much deviation to linear nature of Geiger-Nuttall plots. It is observed that neutron excess in the parent nuclei slow down the exotic decay process. These findings support the earlier observations of Gupta and collaborators using their preformed cluster model (PCM).