Optimisation of laboratory arsenic analysis for groundwaters of West Bengal,India and possible water testing strategy

Regular monitoring of arsenic (As) in groundwater is crucial from public health perspectives as millions of people are suffering due to use of contaminated aquifer water for drinking purposes. The routine analyses, especially in developing nations, are mostly done in localised government/non-government laboratories with limited resources, having the target of analysing large number of samples in each run. Thus apart from analytical sensitivity, cost-effectiveness of the method and eco-friendliness of the experimental operation are key surreptitious factors. This demands optimisation of total As measurement methods and finding a method that gives ‘optimum benefit’ considering all these factors together. The present study therefore evaluates four common As (total) measurement methods [iodometric-colorimetric method, silver diethyl dithiocarbamate method, molybdenum blue method and hydride generation atomic absorption spectrophotometric (HG-AAS) method] practised in the Bengal Delta Plain, in view of their analytical sensitivity, related environmental hazard and experimental costs. It was found that the HG-AAS method is analytically more sensitive, whereas the iodometric-colorimetric method and the molybdenum blue method are better choices in terms of eco-friendliness and cost-effectiveness, respectively. However, when all three factors (analytical reliability, environmental hazard and cost) are considered simultaneously, the molybdenum blue method was found to be placed first in the ‘optimum performance rank’ list. It was also found that both environmental hazard and cost play a more crucial role than analytical reliability, although this is case specific and would differ from place to place around the globe. Finally based on the results, we have hypothesised a water testing strategy for developing countries such as India where the molybdenum blue method can be adapted as a screening method and later the HG-AAS method can be used to precisely identify the groundwater samples with As concentration below the WHO drinking water guideline value of 10 μg/L.     

Au(I)/Ag(I)-catalyzed annulation of sugar aldehyde tethered with 3-phenylprop-2-yn-1-yl ether with aryl amines for the pyrano[4,3-b]quinoline derivatives

Aryl amines undergo smooth annulation with O-phenylpropynyl sugar aldehyde in the presence of the Ph₃PAuCl (10 mol %)/AgSbF₆ (10 mol %) catalytic system to afford the corresponding tetrahydro-3aH-spiro[[1,3]dioxolo[4″,5″:4′,5′]furo[3′,2′:5,6]pyrano[4,3-b]quinoline-2,1′-cyclohexane] derivatives in good yields and selectivity.     

Multiphoton ionization and Coulomb explosion of C2H5Br clusters: a mass spectrometric and charge density study

Using time‐of‐flight mass spectrometry (TOFMS), laser‐induced photochemistry of ethyl bromide clusters has been investigated at three different wavelengths (viz. 266, 355 and 532 nm) utilizing nanosecond laser pulses of ~5 × 10⁹ W/cm². An interesting finding of the present work is the observation of multiply charged atomic ions of carbon and bromine at 355 and 532 nm, arising from the Coulomb explosion of (C₂H₅Br)_n clusters. At 266 nm, however, the (C₂H₅Br)_n clusters were found to exhibit the usual multiphoton dissociation/ionization behaviour. The TOFMS studies are complemented by measuring the total charge density of the ionized volume at 266, 355 and 532 nm, using the parallel plate method, and the charge densities were found to be ~2 × 10⁹, 6 × 10⁹ and 2 × 10¹¹ charges/cm³, respectively. The significantly higher charge density and the presence of energetic, multiply charged atomic ions at 532 nm are explained by the higher ponderomotive energy of the 532 nm photon, coupled with the Coulomb stability of the residual multiply charged ethyl bromide clusters generated upon laser irradiation, due to their larger effective cluster size at 532 nm than at 355 and 266 nm. Copyright © 2011 John Wiley & Sons, Ltd.     

DNA and RNA aptamers: from tools for basic research towards therapeutic applications

The systematic evolution of ligands by exponential enrichment (SELEX) is a combinatorial oligonucleotide library-based in vitro selection approach in which DNA or RNA molecules are selected by their ability to bind their targets with high affinity and specificity, comparable to those of antibodies. Nucleic acids with high affinity for their targets have been selected against a wide variety of compounds, from small molecules, such as ATP, to membrane proteins and even whole organisms. Recently, the use of the SELEX technique was extended to isolate oligonucleotide ligands, also known as aptamers, for a wide range of proteins of importance for therapy and diagnostics, such as growth factors and cell surface antigens. The number of aptamers generated as inhibitors of various target proteins has increased following automatization of the SELEX process. Their diagnostic and therapeutic efficacy can be enhanced by introducing chemical modifications into the oligonucleotides to provide resistance against enzymatic degradation in body fluids. Several aptamers are currently being tested in preclinical and clinical trials, and aptamers are in the process of becoming a new class of therapeutic agents. Recently, the anti-VEGF aptamer pegaptanib received FDA approval for treatment of human ocular vascular disease.     

Multiphoton dissociation/ionisation of dimethyl sulphide (CH3SCH3) at 355 and 532 nm

Multiphoton dissociation/ionization has been studied for CH₃SCH₃ at 355 and 532 nm using a time-of-flight mass spectrometer. The major ion signals observed at 355 nm are C⁺, CH₃ ⁺, HCS⁺, CH₂S⁺, CH₃S⁺ and CH₃SCH₃ ⁺. Power dependence studies at 355 nm show a (2+1) REMPI process for the formation of parent ion. Peaks atm/e = 46, 47 and 61 show two-photon laser power dependence whereasm/e = 15 and 45 peaks show four-photon dependence. However, in 532 nm photo-ionisation, no parent ion signal is observed. A peak atm/e = 35 corresponding to SH₃ ⁺ has been observed. SH₃ ⁺ has been suggested to originate from CH₃SCH₂ ⁺ via a cyclic transition state. Photoionisation results of CH₃SCH₃ have been compared with those of CH₃SSCH₃, at these two wavelengths.     

Root stacks,principal bundles and connections

We investigate principal bundles over a root stack. In case of dimension one, we generalize the criterion of Weil and Atiyah for a principal bundle to have an algebraic connection.     

Intramolecular 1,3-dipolar cycloaddition reactions in the synthesis of complex annelated quinolines, α-carbolines and coumarins

In this study, we report the synthesis of several novel dihydroisoxazole-, tetrahydroisoxazole- and dihydropyrazole-fused pyrido[2,3-b]quinolines, α-carbolines, and pyrido[2,3-c]coumarins, respectively, from simple precursors and by exploring intramolecular 1,3-dipolar cycloaddition reactions involving nitrile oxides, nitrones, and nitrile imines as 1,3-dipoles.     

Anomalous decline of water transport in covalently modified carbon nanotube membranes

Carbon nanotube membranes have been shown to rapidly transport liquids; but progressive hydrophilic modification--contrary to expectations--induces a drastic reduction of water flow. Enhanced electrostatic interaction and the disruption of the mechanically smooth graphitic walls is the determinant of this behavior. These results have critical implications in the design of nanofluidic devices.     

Experimentally Observed Strain Distributions Near Circular Discontinuities of AA6061-T6 Extrusions During Axial Crush

An experimental investigation to determine the strain distribution and collapse behaviour for AA6061-T6 square cross-sectional extrusions with and without circular discontinuities under quasi-static axial compressive loading was completed. Three-dimensional digital image correlation (DIC) was utilized for strain assessment. In order to validate the results of the optical strain measurement system, tensile tests were first conducted employing both the DIC technique and a traditional extensometer. Strain observations from both methods were found to be very consistent prior to strain localization in the test specimen. Quasi-static axial crushing tests were then conducted. Extrusions considered for the present research had a nominal side width, wall thickness and length of 38.1 mm, 3.15 mm, and 200 mm, respectively. A centrally-located circular hole with diameter of either 14.29 mm, 10.72 mm or 7.14 mm was incorporated into the extrusion. Square tubes without any discontinuities were also considered in the experimental testing program. Testing results showed that the collapse mode of the extrusion altered from global bending to a cutting and splitting deformation mode with the presence of the circular discontinuity. Strain localization occurred near the vicinity of the holes for all specimens. For discontinuities sized 14.29 mm and 10.72 mm the location of strain localization and the initiation of material fracture was at the edge of the discontinuity while the location for extrusions with a 7.14 mm hole was found to occur at the intersection of the extrusion side walls. Maximum values of the effective strain were found to vary from approximately 60% to 100%. The region of strain localization was consistent with the location where material fracture initiated.