shweta prasad

Extracellular lipase from Bacillus coagulans BTS-3 was immobilized on activated (alkylated, 2.5% glutaraldehyde) and native (nonactivated) polyethylene powder, and its thermostability and esterification efficiency were studied. Immobilization on activated support was found to enhance thermostability as well as esterification efficiency. The optimum time for immobilization on activated (AS) and nonactivated (NS) polyethylene support was found to be 10 min, and the binding of the lipase was markedly higher on AS. Lipase was more efficiently bound to AS (64%) than to NS (30%) at an optimum temperature of 37°C. The pH and temperature optima for AS- and NS-bound lipase were 9.0 and 55°C and 8.5 and 55°C respectively. At 55°C the free lipase, which had a half-life of 2 h, lost most of its activity at elevated temperatures. In contrast, AS-bound lipase retained 60%–80% of its original activity at 55°C, 60°C, 65°C, and 70°C for 2 h. Exposure to organic solvents resulted in enhanced lipase activity in n-hexane (45%) and ethanol (30%). Both AS- and NS-bound biocatalysts were recyclable and retained more than 85% of their initial activity up to the fourth cycle of hydrolysis of p-nitrophenyl palmitate. The AS-bound lipase efficiently performed maximum esterification (98%) of ethanol and propionic acid (300 mM each, 1 : 1) in n-hexane at 55°C. With free or NS-bound lipase in similar conditions, the conversion of reactants into ester was relatively low (40%). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3986–3993, 2006

Arsenic is present in environment in trace amounts in rocks, soil, water and air but its toxicity effects are highly dependent on its chemical forms; inorganic and organic. There is a direct association between elevated arsenic exposure through drinking water and prevalence of different types of cancers. Present review describes the brief account of arsenic chemistry with reference to water and environment which is relevant to its toxicity arising out of different arsenic species and finally its remediation technologies. The quantification of arsenic species is difficult owing to the low concentration of arsenic in drinking water which is relatively lower than detection limits of modern analytical methods. New hyphenated techniques with more advanced tools have therefore, been discussed in the present paper which are being used in arsenic speciation analysis. The present review also highlights the importance to identify and quantify each chemical species of arsenic as more than 20 arsenic compounds are present in natural environment and in biological systems. Below microgram per liter detection limits are required to quantify arsenic species from these systems and a combination of chromatographic separation with atomic spectroscopy and mass spectroscopic detection is therefore, the most suitable speciation choice. The second important criteria viz. arsenic remediation from contaminated water for supply of safer drinking water is discussed and various remediation technologies are reviewed.