Spectrofluorometric determination of mercury (II) with murexide

A very sensitive and selective spectrofluorometric method has been developed for Hg(II) determination in pharmaceutical and environmental samples. The method is based on measuring the decrease in fluorescence intensity of murexide after binding Hg(II) . The intensity of the fluorescence emission peak was measured at ex/em 335/435 nm in several buffer solutions (acetic acid/acetate, NaH₂PO₄/Na₂HPO₄, NH₄ ⁺/NH₃) targeting the pH interval 3.0–9.0. The fluorescence intensity decrease was found to be linear in the concentration range of 8 × 10^–7 to 1 × 10^–5 M of Hg(II) by using 5 × 10^–5 M murexide in 0.1 M acetic acid/acetate buffer at pH 4.2. The detection limit was 2 × 10^–7 M. This method was found to be almost free of interference from large excesses of 40 cations and anions. The method was successfully applied to the analysis of Hg(II) in synthetic mixtures, pharmaceutical preparations, and wastewater samples. The recovery was quantitative and the standard deviation for 10 replicates of a sample containing 1 × 10^–6 M Hg(II) was lower than ±4%.     

Euclidean realizations of Mauldin–Williams graphs

“Graph-directed” fractals are collections of metric spaces, each of which can be expressed as a union of several scaled copies of spaces from the collection. They give rise to weighted, directed graphs where the term comes from. We show in this note that any (finite) weighted, directed graph (with weights between 0 and 1) can be realized in a Euclidean space in the sense that, starting from the graph one can define a system of similitudes (with the similarity ratios being the given weights) on an appropriate Euclidean space. The point is that these maps satisfy a certain property (called the open set condition) so that the theory of Mauldin–Williams can be applied to compute the dimension of the emerging fractals. Additionally, we give a novel example of a system of graph-directed fractals.     

Rocket borne instrumentation for the measurement of electron density—height profile in the ionosphere

The present paper describes the construction and working of a high frequency capacitance rocket payload for the measurement of electron concentration in the ionosphere, designed and fabricated mostly with indigenous components. This payload was flight-tested in the first and second Indian Centaure test rocket launched on 26-2-1969 and 7-12-1969 from Thumba Equatorial Rocket Launching Station. The paper also presents the calibration procedures and some of the preliminary results obtained from the first flight to show the capabilities of the instrument.     

The reactions of hexachlorocyclotriphosphazatriene with pyridine derivatives

The reactions of hexachlorocyclotripho‐sphazatriene, N₃P₃Cl₆ ( 1 ), with 2‐hydroxypyridine ( 2 ), 2‐aminopyridine ( 3 ), 2‐amino‐6‐methyl‐pyridine ( 4 ), and 2‐hydroxy‐4‐methylquinoline ( 5 ) have been investigated. The products were identified by elemental analyses, IR, ¹H, ¹³C, and ³¹P NMR spectroscopy. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:57–60, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20185     

Note on the wave equation and tensor products

In this study we apply convolution and tensor products of distribution to solve the non-homogenous wave equation with initial condition and discuss the uniqueness and continuity of solution. We also show that the tensor product can be applied to compute the some singular integrals.     

Nigella sativa extract as a potent antioxidant for petrochemical-induced oxidative stress

Various beneficial properties has been attributed to Nigella sativa, including its antioxidant potential. Previously, it was reported that supercritical fluid extraction (SFE) could be used to obtain N. sativa extract rich in antioxidants. In the present study, N. sativa extracts prepared using the previously optimized SFE as well as the traditional Soxhlet extraction approaches were analyzed for various known antioxidants. N. sativa extracts were found to prevent protein carbonyl formation as well as depletion of intracellular glutathione (GSH) in fibroblasts exposed to toluene. Furthermore, partially purified SFE and Soxhlet fractions could prevent loss of hepatic GSH in toluene-induced oxidative stressed Wistar rats as well as in L929 fibroblasts. The results showed that SFE-produced N. sativa extract is richer in antioxidants than the Soxhlet approach. It was also shown using preparative silica gel and reverse phase chromatography that different fractions of SFE-extracted or Soxhlet-extracted N. sativa had different levels of protective effects with regards to GSH depletion in vivo as well as in cell culture. Although fractions rich in thymoquinone were found to be most potent in terms of antioxidant capacity, the data indicates that the protective effects of N. sativa may not only be due to thymoquinone, but perhaps other antioxidants.     

On distance dependent entropy measures of poly propylene imine and zinc porphyrin dendrimers

A key paradigm in contemporary research is the use of graphs to represent physical systems, molecular structures, or particularly metal frameworks. Graphs are increasingly widely used in a variety of fields, including the study of quantum and molecular systems, macromolecules and their interactions, socioeconomic and ecological systems, and technical and infra-structural systems. Understanding how these systems function, are robust, and are stable begins with structural characterization. The use of entropies and entropy-like measurements of graphs/structures of molecules/networks is crucial from both a mathematical and physical standpoint. Several entropy measures of graphs have been defined and studied extensively during the last few decades. The current paper is devoted to investigation of distance dependent entropy measures of Poly Propylene Imine (PPI) dendrimers and Zinc Porphyrin dendrimers. The analytical formulae of distance dependent entropy measures have been developed and their patterns have been presented through graphical tools.     

A procedure to construct exact solutions of nonlinear evolution equations

In this paper, we implemented the functional variable method for the exact solutions of the Zakharov?CKuznetsov-modified equal-width (ZK-MEW), the modified Benjamin?CBona?CMahony (mBBM) and the modified KdV?CKadomtsev?CPetviashvili (KdV?CKP) equations. By using this scheme, we found some exact solutions of the above-mentioned equations. The obtained solutions include solitary wave solutions, periodic wave solutions and combined formal solutions. The functional variable method presents a wider applicability for handling nonlinear wave equations.     

Refraction-based photonic crystal diode

A system composed of air holes in a dielectric host to form two square photonic crystals, with the same orientation and lattice constant but different scatterer radii, making an interface along their body diagonals, is numerically demonstrated to facilitate unidirectional light transmission. Band structure computations are carried out via the plane wave expansion method, whereas finite-difference time-domain simulations are carried out to investigate the transient behavior. Unidirectional light transmission is achieved over two adjacent stop bands along the ΓX direction, which are circumvented in the forward direction by scaling down the wave vector and rotating the surface normal. Contrast ratios as high as 0.9 are attained within the lower stop band.