Interaction of an Antituberculosis Drug with a Nanoscopic Macromolecular Assembly: Temperature-Dependent Förster Resonance Energy Transfer Studies on Rifampicin in an Anionic Sodium Dodecyl Sulfate Micelle

In this contribution, we report studies on the nature of binding of a potent antituberculosis drug, Rifampicin (RF) with a model drug delivery system, sodium dodecyl sulfate (SDS) micelle. Temperature dependent dynamic light scattering (DLS), conductometry, and circular dichroism (CD) spectroscopy have been employed to study the binding interaction of the drug with the micelle. The absorption spectrum of the drug RF in the visible region has been employed to study Förster resonance energy transfer (FRET) from another fluorescent drug Hoechst 33258 (H33258), bound to the micelle. Picosecond-resolved FRET studies at room temperature confirm the simultaneous binding of the two drugs to the micelle and the distance between the donor−acceptor pair is found to be 34 Å. The temperature dependent FRET study also confirms that the location and efficiency of drug binding to the micelle changes significantly at the elevated temperature. The energy transfer efficiency of the donor H33258, as measured from time-resolved studies, decreases significantly from 76% at 20 °C to 60% at 55 °C. This reveals detachment of some amount of the drug molecules from the micelles and increased donor−acceptor distance at elevated temperatures. The estimated donor−acceptor distance increases from a value of 33 Å at 20 °C to 37 Å at 55 °C. The picosecond resolved FRET studies on a synthesized DNA bound H33258 in RF solution have been performed to explore the interaction between the two. Our studies are expected to find relevance in the exploration of a potential vehicle for the vital drug rifampicin

Economic emancipation of the SAARC countries: lessons from ASEAN

Volume 2, Issue 2, July 200

The scanning electron microscope as an accelerator for the undergraduate advanced physics laboratory

Few universities or colleges have an accelerator for use with advanced physics laboratories, but many of these institutions have a scanning electron microscope (SEM) on site, often in the biology department. As an accelerator for the undergraduate, advanced physics laboratory, the SEM is an excellent substitute for an ion accelerator. Although there are no nuclear physics experiments that can be performed with a typical 30 kV SEM, there is an opportunity for experimental work on accelerator physics, atomic physics, electron‐solid interactions, and the basics of modern e‐beam lithography.National Science Foundation (U.S.) (Grant 0823778

Occurrence and characterization of shiga toxin-producing Escherichia coli in raw meat, raw milk, and street vended juices in Bangladesh

The major objective of this study was to investigate the prevalence of Shiga toxin (Stx)–producing Escherichia coli (STEC) in different types of food samples and to compare their genetic relatedness with STEC strains previously isolated from animal sources in Bangladesh. We investigated a total of 213 food samples, including 90 raw meat samples collected from retail butcher shops, 20 raw milk samples from domestic cattle, and 103 fresh juice samples from street vendors in Dhaka city. We found that more than 68% (n=62) of the raw meat samples were positive for the stx gene(s); 34% (n=21) of buffalo meats and 66% (n=41) of beef. Approximately 10% (n=2) of the raw milk and 8% (n=8) of the fresh juice samples were positive for stx. We isolated STEC O157 from seven meat samples (7.8%), of which two were from buffalo meats and five from beef; and no other STEC serotypes could be isolated. We could not isolate STEC from any of the stx-positive raw milk and juice samples. The STEC O157 isolates from raw meats were positive for the stx2, eae, katP, etpD, and enterohemorrhagic E. coli hly virulence genes, and they belonged to three different phage types: 8 (14.3%), 31 (42.8%), and 32 (42.8%). Pulsed-field gel electrophoresis (PFGE) typing revealed six distinct patterns among seven isolates of STEC O157, suggesting a heterogeneous clonal diversity. Of the six PFGE patterns, one was identical and the other two were =90% related to PFGE patterns of STEC O157 strains previously isolated from animal feces, indicating that raw meats are readily contaminated with fecal materials. This study represents the first survey of STEC in the food chain in Bangladesh

Antimicrobial and Cytotoxic Activity of Three Bitter Plants-Enhydra fluctuans, Andrographis Peniculata and Clerodendrum Viscosum.

Purpose: In this study, three important medicinal plants (Enhydra fluctuans Lour, Clerodendrum viscosum Vent and Andrographis peniculata Wall) of Bangladesh were investigated to analyze their antimicrobial and cytotoxic activities against some pathogenic microorganisms and Artemia salina (brine shrimp nauplii). Methods: The coarse powder material of leaves of each plant was extracted separately with methanol and acetone to yield methanol extracts of leaves of Enhydra fluctuans (MLE), Clerodendrum viscosum (MLC) and Andrographis peniculata (MLA), and acetone extracts of leaves of Enhydra fluctuans (ALE), Clerodendrum viscosum (ALC) and Andrographis peniculata (ALA). The disc diffusion method and the method described by Meyer were used to determine the antimicrobial and cytotoxic activities of each plant extract. Results: Among the test samples, MLE and ALE showed comparatively better antimicrobial activity against a number of bacteria and fungi with inhibition zones in the range of 06-15 mm and according to the intensity of activity, the efficacy against microorganisms were found in the order of Enhydra fluctuans> Andrographi speniculata> Clerodendrum viscosum. In cytotoxicity assay, all samples were found to be active against brine shrimp nauplii (Artemia salina) and ALA produced lowest LC50 value (7.03 μg/ml). Conclusion: Enhydra fluctuans and Andrographi speniculata possesses significant antimicrobial and cytotoxic activities

Characterizing contributions of glacier melt and groundwater during the dry season in a poorly gauged catchment of the Cordillera Blanca (Peru)

The retreat of glaciers in the tropics will have a significant impact on water resources. In order to overcome limitations with discontinuous to nonexistent hydrologic measurements in remote mountain watersheds, a hydrochemical and isotopic mass balance model is used to identify and characterize dry season water origins at the glacier fed Querococha basin located in southern Cordillera Blanca, Peru. Dry season water samples, collected intermittently between 1998 and 2007, were analyzed for major ions and the stable isotopes of water (δ<sup>18</sup>O and δ<sup>2</sup>H). The hydrochemical and isotopic data are analysed using conservative characteristics of selected tracers and relative contributions are calculated based on pre-identified contributing sources at mixing points sampled across the basin. The results show that during the dry-season, groundwater is the largest contributor to basin outflow and that the flux of groundwater is temporally variable. The groundwater contribution significantly correlates (P-value=0.004 to 0.044) to the antecedent precipitation regime at 3 and 18–36 months. Assuming this indicates a maximum of 4 years of precipitation accumulation in groundwater reserves, the Querococha watershed outflows are potentially vulnerable to multi-year droughts and climate related changes in the precipitation regime. The results show that the use of hydrochemical and isotopic data can contribute to hydrologic studies in remote, data poor regions, and that groundwater contribution to tropical proglacial hydrologic systems is a critical component of dry season discharge

Using small-angle X-ray scattering to investigate the compaction behaviour of a granulated clay

The compaction behaviour of a commercial granulated clay (magnesium aluminium smectite, gMgSm) was investigated using macroscopic pressure-density measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray microtomography (XμT) and small-angle X-ray scattering (SAXS). This material was studied as a potential compaction excipient for pharmaceutical tabletting, but also as a model system demonstrating the capabilities of SAXS for investigating compaction in other situations. Bulk compaction measurements showed that the gMgSm was more difficult to compact than polymeric pharmaceutical excipients such as spheronised microcrystalline cellulose (sMCC), corresponding to harder granules. Moreover, in spite of using lubrication (magnesium stearate) on the tooling surfaces, rather high ejection forces were observed, which may cause problems during commercial tabletting, requiring further amelioration. Although the compacted gMgSm specimens were more porous, however, they still exhibited acceptable cohesive strengths, comparable to sMCC. Hence, there may be scope for using granular clay as one component of a tabletting formulation. Following principles established in previous work, SAXS revealed information concerning the intragranular structure of the gMgSm and its response to compaction. The results showed that little compression of the intragranular morphology occurred below a relative density of 0 · 6, suggesting that granule rearrangements or fragmentation were the dominant mechanisms during this stage. By contrast, granule deformation became considerably more important at higher relative density, which also coincided with a significant increase in the cohesive strength of compacted specimens. Spatially-resolved SAXS data was also used to investigate local variations in compaction behaviour within specimens of different shape. The results revealed the expected patterns of density variations within flat-faced cylindrical specimens. Significant variations in density, the magnitude of compressive strain and principal strain direction were also revealed in the vicinity of a debossed feature (a diametral notch) and within bi-convex specimens. The variations in compaction around the debossed notch, with a small region of high density below and low density along the flanks, appeared to be responsible for extensive cracking, which could also cause problems in commercial tabletting

Electrocatalytic Oxygen and Nitrate Reduction Reactions Using Cu-Based Electrodes

There has been a resurgence of interest in electrocatalysis because interesting chemistry frequently happens at the electrochemical interface between electrodes and electrolytes that are relevant to energy conversion processes. The focus of this dissertation is on the electrocatalytic reduction of oxygen (O 2 ) and nitrate (NO 3 -) to water (H 2 O) and ammonia (NH 3 ), respectively, using molecular- and surface-based Cu electrocatalysts. The oxygen reduction reaction (ORR) is important due to its application in the cathode of fuel cells. The nitrate reduction reaction (NRR) can be used to generate NH 3 as an alternative to the traditional Haber-Bosch process. The first part (chapter 1) of this thesis discusses the importance of electrocatalysis in the field of energy conversion and storage technologies. The second part of this thesis (chapters 2 and 3) focusses on the ORR. Due to the high reduction potential and slow kinetics of the ORR, fuel cells are not being fully commercialized. This part discusses efforts to understand the ORR reaction mechanism and develop new ORR electrocatalysts using Cu tripeptide complexes. Laccase is a well-known Cu-containing ORR enzyme with a low overpotential, but it is only stable in a narrow pH range. Here, we synthesized Cu-tripeptide complexes and investigated their ORR activities in a wide pH range from 2.5 to 10 and determined the effect of peptide aggregation and Cu-peptide binding constant on ORR performance. In the last parts of chapter 2 and 3, we discuss some future prospects of the ORR using non-precious Cu-based electrocatalysts. The third part (chapters 4 and 5) of this thesis discusses the NRR. Here, we fabricated Nafion-modified metals electrodes and tested the activity of theses electrodes for the NRR to produce NH 3 electrochemically. We interrogate the mechanism of NH 3 production from NO 3 - reduction using electrochemical experiments, surface-enhanced Raman spectroscopy, and density functional theory calculations. We also explore this NO 3 - reduction reaction for Nafion-modified electrodeposited Cu electrodes to increase the current density and NH 3 Faradaic efficiency. Lastly, we discuss the future prospect of this electrocatalytic NRR using different fluoropolymers instead of Nafion and propose methods to increase the durability of the catalysts

Humayun Ahmed’s Gouripur Junction: A Saga of Unforgiving Realities and Perpetual Uncertainties of the Marginalized People

Humayun Ahmed in his novel Gouripur Junction attempts to portray the picture of a train station along with the lives of the people depending on it. His sincere efforts are directed mainly towards the marginal people who are fated to be there, somehow eke out a living there and are bound to face the uncertainties and complexities in the struggle for living an unstable life. While the writer has made a comprehensive delineation of their lives along with relationships of different types, love and hatred, strengths and shortcomings, the basic aspect of their life is uncertainty, sufferings and struggle. Humayun Ahmed though commonly considered as a writer having good understanding of and compassion for the middle class, he has another strong but less attended area and that is his unflinching endeavor to portray the marginal people in a comprehensive way. In this novel, his manifest intention is to portray life in totality by a balance attention on the realities as well as the psychosocial aspects of those people and make the readers empathetic towards them. This paper aims at studying this strong but less attended dimension of Humayun Ahmed's fictional works with special attention on his short novel Gouripur Junction. To make the study, the researcher will avail the works of the writer as primary source and major prevailing works on him as the secondary source and hopefully open up a new dimension. Keywords: station, struggle, uncertainty, marginal, dimension