BACKGROUND Lubricants manufactured conventionally from non‐renewable mineral oil resources are not biodegradable and are liable to cause adverse environmental impacts. Biodegradable vegetable oils present a promising lubricant feedstock alternative. Waste cooking oil (WCO), which otherwise finds no immediate potential utilization can be successfully used to synthesize bio‐lubricant. A novel synthetic method was developed by using the two‐step process of C. rugosa lipase‐mediated hydrolysis of WCO to free fatty acids (FFA) followed by Amberlyst 15H esterification of FFA with octanol. The octyl esters produced was the desired biolubricant. RESULTS The effect of different physico‐chemical parameters like temperature, catalyst loading, agitation speed, molar ratio of octanol:FFA and the presence of different desiccants on the esterification reaction was examined. The optimum conditions to get maximum yield of biolubricant in minimum time were, octanol:FFA molar ratio = 3:1, temperature = 80 °C, catalyst = 2 g and desiccant (preferably silica gel powder) = 50% weight of FFA. Fourier transform infrared spectroscopy confirmed that the product formed was ester. CONCLUSION Biolubricant (octyl esters) was prepared efficiently from WCO by the two‐step process developed. This novel approach represents a viable means of producing lubricants from wastes which are renewable in nature and can be an alternative to non‐renewable mineral oil feedstocks. Copyright © 2012 Society of Chemical Industry

Besides potential surface activity and some beneficial physical properties, biosurfactants express antibacterial activity. Bacterial cell membrane disrupting ability of rhamnolipid produced by Pseudomonas aeruginosa C2 and a lipopeptide type biosurfactant, BS15 produced by Bacillus stratosphericus A15 was examined against Staphylococcus aureus ATCC 25923 and Escherichia coli K8813. Broth dilution technique was followed to examine minimum inhibitory concentration (MIC) of both the biosurfactants. The combined effect of rhamnolipid and BS15 against S. aureus and E. coli showed synergistic activity by expressing fractional inhibitory concentration (FIC) index of 0.43 and 0.5. Survival curve of both the bacteria showed bactericidal activity after treating with biosurfactants at their MIC obtained from FIC index study as it killed >90% of initial population. The lesser value of MIC than minimum bactericidal concentration (MBC) of the biosurfactants also supported their bactericidal activity against both the bacteria. Membrane permeability against both the bacteria was supported by amplifying protein release, increasing of cell surface hydrophobicity, withholding capacity of crystal violet dye and leakage of intracellular materials. Finally cell membrane disruption was confirmed by scanning electron microscopy (SEM). All these experiments expressed synergism and effective bactericidal activity of the combination of rhamnolipid and BS15 by enhancing the bacterial cell membrane permeability. Such effect of the combination of rhamnolipid and BS15 could make them promising alternatives to traditional antibiotic in near future.

We have independently estimated the conduction- and valence-band offsets ΔEc and ΔEv in GaAs/Ga0.51In0.49P quantum wells by measuring the capacitance transient resulting from thermal emission of carriers from the respective wells. The heterostructure samples were grown by low-pressure metalorganic chemical vapor deposition. The band offsets are extrapolated from the emission activation energies with appropriate corrections. The estimated values of ΔEc and ΔEv are 0.198 and 0.285 eV, respectively.

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