Seasonal distribution and contamination levels of total PHCs, PAHs and heavy metals in coastal waters of the Alang-Sosiya ship scrapping yard, Gulf of Cambay, India.

Alang-Sosiya situated on the Gulf of Cambay is one of the largest ship breaking yard in the world. The seasonal distribution and contamination levels of dissolved and/or dispersed total petroleum hydrocarbons (PHCs), total polycyclic aromatic hydrocarbons (PAHs) and heavy metals in seawater during high tide are investigated. The concentrations of petroleum hydrocarbons and heavy metals are higher in the winter than in the monsoon and summer. The concentrations of total PHCs and PAHs are about three times higher in the winter and two times in the monsoon or summer at Along-Sosiya and about twice in all seasons at two stations one on either side 5 km away from it as compared to the reference station at Mahuva, 60 km away towards the south. Further, the levels of PHCs are correlated with salinity and compared with those of other regions. The concentration of all metals is the highest in the winter season followed by the monsoon and summer. We carried out the quantitative analysis of the possible relationships among 13 variables such as Al, Fe, Pb, Mn, Cu, Zn, Cd, Cr, Co, pH, NO3-, NO2 and PO4(3-).

Spectrophotometric estimation of bromide ion in excess chloride media.

The redox reaction between bromate and chloride ions in the presence and the absence of two or less equivalents of bromide ion ascertaining the formation of bromine chloride species of type BrCl and BrCl(2)(-) in subsequent reactions in 4% H(2)SO(4), has been studied by spectrophotometry. Calibration graphs for the bromide ion estimation in 0.1% KBrO(3)-4% H(2)SO(4) medium are determined separately in the presence of known amounts of NaCl. The effect of Cl(-) ion percentage on the determination of Br(-) ion is studied and reported herewith a suitable equation for a precise, reliable and quick spectrophotometric estimation.

Distribution, enrichment and accumulation of heavy metals in coastal sediments of Alang-Sosiya ship scrapping yard, India.

Since its inception in 1982, the Alang-Sosiya yard has become the largest ship scrapping works in the world. Several hundreds of ships arrive every year. The degree of heavy metal contamination has been studied in bulk and fine sediments from the intertidal zone of this ship scrapping yard, two stations, one on either side at 5 km distance and one reference station 60 km distance near Mahuva, towards the south. The samples have been subjected to a total digestion technique and analysed for elements: Cd, Co, Cu, Cr, Fe, Mn, Ni, Pb, Zn and Al, and %TOC. The absolute metal concentrations reflected variations in BF and FF sediment samples with organic matter content. Enrichment factors (EF) and geoaccumulation indices (Igeo) have been calculated and the relative contamination levels are assessed at these sites. At Alang-Sosiya, the enrichment of heavy metals has been observed to be relatively high.

Sequence and structural determinants of mannose recognition.

Mannose, an abundant cell surface monosaccharide binds to a diverse set of receptors, which are involved in a variety of important cellular processes. Structural analysis has been carried out on all the proteins containing non-covalently bound mannose as a monosaccharide in the Protein Data Bank, to identify common recognition principles. Proteins, highly specific to mannose, belonging to the super family of bulb lectins, are found to contain a consensus sequence motif QXDXNXVXY, which has been identified to be essential for mannose binding. Analysis of this motif in the crystal structures of bulb lectins has led to the understanding of the contribution of individual residues in mannose recognition. Comparison with other mannose binding proteins, reveals common hydrogen bonding patterns in all of them, despite differences in sequence, overall fold and the substructures at the binding sites of individual proteins. A database analysis also suggests that although the topology of the backbone, as at the binding site in bulb lectins, can generate mannose binding capability in a few other proteins, sequence and disposition of not only the residues in the motif, but also the residues in the neighborhood play a crucial role in allowing that property to be retained.

Solution-Membrane Equilibrium at Metal-Deposited Cation-Exchange Membranes: Chronopotentiometric Characterization of Metal-Modified Membranes.

Copper- and lead-deposited interpolymer cationic membranes have been prepared by electroless plating by an ion-exchange method and characterized by chronopotentiometry and cyclic voltammetry. The parameters such as transition time (tau), Itau1/2, the potential drop (E0) across these membranes immediately after the application of constant current (I), and the height of the potential jump (DeltaE) across the membrane at tau have been measured by chronopotentiometry and compared with those of plain membranes. The approximate percentage of metal coverage and the number of ionic sites masked by the deposited metal in terms of NaCl concentration have been estimated from the differences in Itau1/2 values of plain and metal-deposited membranes. The quantity of metal deposited in a unit area of the membrane surface was measured by differential pulse polarography. The oxidation and reduction peak potentials corresponding to Cu(0)/Cu(II) and Pb(0)/Pb(II) couples were identified by cyclic voltammetry at pH 2.8 and 4.5 of 0.2 M CH3COONa-H2SO4. Copyright 1999 Academic Press.

Kinetics and Mechanism of Two-Electron Reduction of Surfacial Ferric Ions of Colloidal Ferrofluid by l-Ascorbic Acid in Aqueous Acidic Medium.

The kinetics of electron transfer from l-ascorbic acid (H2A) to ferrofluid (FF) in dilute aqueous acidic solutions (pH 2.5-4.0) was investigated spectrophotometrically in detail as a function of [H2A], [FF], [H+], ionic strength, and temperature. FF was found to be reduced and the reduction was first-order dependent on both H2A and FF concentrations. An inverse first order dependence in H+ ion concentration and no dependence on ionic strength were observed. Kinetic, electrochemical, spectrophotometric, and thermodynamic results are interpreted in terms of a mechanism involving a rate-determining outer-sphere one-electron transfer from H2A to FF followed by a subsequent and kinetically rapid transfer of the second electron of H2A to the same molecule of FF, which was already reduced by one electron in rate-determining step. This overall two-electron transfer process from H2A to the same molecule of FF is discussed and compared with other closely related reactions. Copyright 1999 Academic Press.

Crystal structure of a dimeric mannose-specific agglutinin from garlic: quaternary association and carbohydrate specificity.

A mannose-specific agglutinin, isolated from garlic bulbs, has been crystallized in the presence of a large excess of alpha-d-mannose, in space group C2 and cell dimensions, a=203.24, b=43.78, c=79.27 A, beta=112.4 degrees, with two dimers in the asymmetric unit. X-ray diffraction data were collected up to a nominal resolution of 2.4 A and the structure was solved by molecular replacement. The structure, refined to an R-factor of 22.6 % and an Rfree of 27.8 % reveals a beta-prism II fold, similar to that in the snowdrop lectin, comprising three antiparallel four-stranded beta-sheets arranged as a 12-stranded beta-barrel, with an approximate internal 3-fold symmetry. This agglutinin is, however, a dimer unlike snowdrop lectin which exists as a tetramer, despite a high degree of sequence similarity between them. A comparison of the two structures reveals a few substitutions in the garlic lectin which stabilise it into a dimer and prevent tetramer formation. Three mannose molecules have been identified on each subunit. In addition, electron density is observed for another possible mannose molecule per dimer resulting in a total of seven mannose molecules in each dimer. Although the mannose binding sites and the overall structure are similar in the subunits of snowdrop and garlic lectin, their specificities to glycoproteins such as GP120 vary considerably. These differences appear, in part, to be a direct consequence of the differences in oligomerisation, implying that variation in quaternary association may be a mode of achieving oligosaccharide specificity in bulb lectins.