Sol–gel spin coating assisted room temperature operated nanostructured ZnO ethanol sensor with behavior transformation

In this paper, zinc oxide (ZnO) thin film sensor has been fabricated using different sol–gel spin coating route to detect very low concentration (2?ppm) of ethanol vapors at room temperature (RT). The sensor shows appreciable response ~60% for 100?ppm of ethanol (C₂H₅OH) vapors at RT under humidity level ~55% RH. Various sensing parameters viz. % response, selectivity, stability, response/recovery time, repeatability, and reproducibility have been studied successfully. Structural and morphological properties have been studied via X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). XRD reveals the wurtzite structure of polycrystalline ZnO thin film. AFM, SEM, and TEM results confirm the wavy structure of well-shaped and slackly distributed ZnO nanograins with average particle size in range ~15–25?nm. The analyte sensing properties at room temperature can be ascribed to higher specific surface area due to nanograins formation. The significant effect of operating temperature on sensor’s performance is also analysed in order to obtain the optimum temperature (T_opt) of the sensor device. Response reaches to 321.7% for 100?ppm of ethanol vapors at T_opt (175?°C). The transformation in the behavior of sensing layer is observed which is described on the basis of experimental studies.

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Detection of Virulence Genes in Vibrio cholerae Isolated from Aquatic Environment in Kerala, Southern India

Vibrio cholerae is the etiologic agent of cholera. It is an autochthonous inhabitant of all aquatic environments. The virulence of V. cholerae is maintained by the CTX genetic element and tcpA gene. In the present investigation, environmental strains of V. cholerae isolated from different aquatic biotopes in Kerala were identified and serotyped. The antibiotic resistance pattern and presence of virulence and regulatory genes were examined. We found the presence of toxigenic non-O1/non-O139 strains harboring the CTX genetic element, heat-stable enterotoxin, rtxA gene, El Tor hemolysin, and Vibrio pathogenicity island (VPI). The strains also produced the cholera toxin (CT) as determined by monosialoganglioside enzyme-linked immunosorbent assay. A few strains belonging to the O1 serogroup but lacking the CTX genetic element were also observed. The majority of the environmental strains belonged to non-O1/non-O139 serogroup with many possessing toxR, ompU, heat-stable enterotoxin, and rtxA gene. The toxigenic non-O1/non-O139 strains exhibited resistance to trimethoprim, ampicillin, and polymixin B and intermediate resistance to co-trimoxazole. However, all other environmental strains were found resistant to ampicillin and polymixin B. Our findings demonstrate that the virulence genes are dispersed among the environmental strains of V. cholerae and a complex aquatic environment can give rise to pathogenic V. cholerae.     

Organic azide inhibitors of cysteine proteases

Cysteine proteases are crucial regulatory enzymes in human physiology and disease. Inhibitors are usually designed with reactive electrophiles to covalently bond to the catalytic cysteinyl sulfur, and consequently they also indiscriminately interact with biological thiolates and other nucleophiles, leading to toxic side effects in vivo. Here we describe an alternative to using reactive electrophiles, demonstrating the use of a much less reactive azidomethylene substituent (-CH2-N3) that confers potent inhibition of cysteine proteases. This new approach resulted in potent, reversible, competitive inhibitors of caspase-1 (IC50 < 10 nM), with significant advantages over aldehydes such as high stability in vitro to thiols (10 mM dithiothreitol (pH 7.2), 20 mM glutathione (pH 7.2, 9, 11)) and aqueous media, as well as some highly desirable druglike features. It was also demonstrated that azides can be incorporated into inhibitors of other caspases (e.g. 3, 8) and cathepsins (e.g. K, S, B), indicating the versatility of this valuable new approach to cysteine protease inhibition.     

EPR investigation of TiO2 nanoparticles with temperature-dependent properties

An in situ electron paramagnetic resonance (EPR) study has been carried out for anatase (Hombikat UV100) and rutile TiO(2) nanoparticles at liquid helium (He) temperature (4.2 K) under UV irradiation. Rutile titania was synthesized by ultrasonic irradiation with titanium tetrachloride (TiCl(4)) as the precursor. XRD and Raman results evidence the crystallinity of titania phases. The nature of trapped electrons and holes has been investigated by EPR spectroscopy under air and vacuum conditions. Illumination of TiO(2) powder (anatase and rutile) at 4.2 K resulted in the detection of electrons being trapped at Ti(4+) sites within the bulk and holes trapped at lattice oxide ions at the surface. The stability of electron traps was very sensitive to temperature in both phases of TiO(2). The annealing kinetics of the EPR detected radicals has been studied from 4.2 K to ambient temperature and also for calcined titania particles from 523 to 1273 K.     

Conformation-activity relationships in polyketide natural products. Towards the biologically active conformation of epothilone

The conformation-activity relationships for the biologically active polyketide, epothilone, have been determined. Computer-based molecular modeling and high field NMR techniques have provided the solution preferences for epothilones and. For the C1-C8 polypropionate region, two conformational families, conformers 1 and 2, have been identified as having significant populations in polar and non-polar solvents. In the C11-C15 region, additional flexibility was observed and two local conformations have been identified as important, conformers 3 and 4. Epothilone analogues with altered conformational profiles have been designed and synthesized. Conformational analysis and the results of biological assays have been correlated to provide increased understanding of the biologically active conformation for the epothilone class of natural product. Conformation-activity relationships have been shown to be an important complement to structure-activity data.     

Iridium(III) catalyzed oxidation of iodide ions in aqueous acidic medium

Oxidation of iodide ions by K₃Fe(CN)₆, catalyzed by hydrogen ions obtained from hydrochloric acid was found to be further catalyzed by iridium(III) chloride. Rate, when the reaction is catalyzed only by the hydrogen ions, was separated from the rate when iridium(III) and H⁺ions both, catalyze the reaction. Reactions studied separately in the presence as well as in the absence of IrCl₃ under similar conditions were found to follow second order kinetics with respect to [I⁻]. While the rate showed direct proportionality with respect to [K₃Fe(CN)₆] and [IrCl₃]. At low concentrations the reaction shows direct proportionality with respect to [H⁺] which tends to become proportional to the square of hydrogen ions at higher concentrations. Strong retarding affect of externally added hexacyanoferrate(II) ions was observed in the beginning but further addition affects the rate to a little extent. Changes in [Cl⁻] and also ionic strength of the medium have no effect on the rate. With the help of the intercept of catalyst graph, the extent of the reaction, which takes place without adding iridium(III), was calculated and was found to be in accordance with the values obtained from the separately studied reactions in which only H⁺ ions catalyze the reaction. It is proposed that iridium forms a complex, which slowly disproportionates into the rate-determining step. Thermodynamic parameters at four different temperatures were calculated.