Thermal stability enhancement of Candida rugosa lipase using ionic liquids

The thermal stability of Candida rugosa (C. rugosa) lipase was investigated and compared in n-hexane, benzene, dibutyl-ether as well as [bmim]PF₆ and [omim]PF₆ ionic liquids and the effect of solvent polarity and water activity were evaluated. Deactivation of the enzyme followed a series-type kinetic model. First order deactivation rate constants and the ratios of specific activities were determined and the kinetics of deactivation were studied. Among the organic solvents, the best stability was observed in n-hexane with a half-life of 6.5 h at water activity of 0.51. In ionic liquids, however, even longer half lives were obtained, and the enzyme was stable in these solvents at 50°C. The highest half-life times were obtained in [bmim]PF₆ (12.3 h) and [omim]PF₆ (10.6 h). A direct correlation was found between solvent polarity and thermal stability since the higher the polarity of the solvent, the lower was the stability decrease at 50°C comparing to that at 30°C.     

Tilapia are able to withstand long-term exposure to low environmental pH, judged by their energy status, ionic balance and plasma cortisol

Tilapia Oreochromis mossambicus were exposed to water at pH 4·0 for 37 days. The water was acidified slowly over 6 h enabling the animals to acclimate and preventing damage of the gill epithelium. Additional stressors, e.g. aluminium ions and handling stress, were avoided. No mortality or decreased food consumption was observed during the exposure period. No significant changes were observed between the control and acid exposed groups for the energy rich compounds and related parameters, i.e. the adenylate energy charge, the pool of total adenine nucleotides, and the IMP load of white muscle and liver, indicating maintenance of homeostasis. Moreover, there were no significant differences between control groups and acidified groups at 3, 17 and 37 days for plasma sodium, chloride, cortisol and glucose, implying that ionic balance was maintained and that there was no activation of the pituitary-interrenal axis. It is concluded that tilapia can acclimate to water at pH 4·0 when the acidification rate is slow and additional stressors are avoided.     

Styrene and ethylbenzene absorption in ionic liquids: comparing DFT affinity calculations with experimental data

Styrene is a widely used bulk chemical produced by dehydrogenation of ethylbenzene (EB). Purification of styrene to contain < 100 ppm EB is not cost-effective by conventional separation methods. One separation method is extractive distillation with an ionic liquid (IL) as a binding agent for one of the components, thereby lowering the vapour pressure of this component. In this study, using quantum density functional theory (DFT), we have simulated 22 IL anion–cation pairs, styrene and EB affinities to them, and ion-pair dimer affinities of the ILs. These are compared with experimental liquid–liquid equilibrium studies of M.T.G. Jongmans, B. Schuur, and A.B. de Haan, Ind. Eng. Chem. Res. 50 (2011), pp. 10800–10810. It is shown that experimental selectivity and distribution coefficients of styrene and EB in the ILs are related to computed gas phase anion–cation stabilisation energies and ion-pair–ion-pair dimer affinities. The inverse of molar volume is found to strongly correlate with the selectivity. The computational results also qualitatively correlate with molar volume, and consequently, it is possible to use DFT calculations as a qualitative prediction tool in screening of ILs for this separation process. This tool does not account for effects caused by long alkyl chains, as the length does not seem to affect dimer stabilisation energy beyond ethyl group.     

Chitosan/cellulose-based beads for the affinity purification of histidine-tagged proteins

Chitosan/cellulose-based beads (CCBs) for the affinity purification of histidine-tagged proteins were prepared from chitosan/cellulose dissolved in ionic liquid as a solvent, and their structures were characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, and thermogravimetric analysis. The affinity purification was used to separate hexahistidine-tagged (his-tagged) enhanced green fluorescent protein (EGFP) from Escherichia coli. The results showed that Zn²⁺–CCB exhibited more specific adsorption capacity toward the target protein compared with Ni²⁺–CCB and Cu²⁺–CCB. The maximum adsorption of EGFP was 1.84?mg/g of Zn²⁺–CCB, with 90% purity under the optimized conditions (ionic strength (1.0?M NaCl), pH (7.2) and imidazole concentration (500?mM)). In addition, a regeneration method for the sorbent was further developed by washing with ethylenediaminetetraacetic acid disodium and then reimmobilizing with metal ions. This technique is an alternative method for the purification of his-tagged proteins, making the process more economical, fast, stable, and large batch.     

Purification and characterization of glutathione reductase from Scots pine needles

Changes in the excitability of the liverwort Conocephalum conicum L. caused by inhibitors of ionic channels and phosphorylation uncouplers, were examined. Action potentials were triggered by electrical and light stimuli. Tetraethylammonium chloride, an inhibitor of K⁺ channels, completely blocked the ability to generate action potentials. Excitability also disappeared under the influence of MnCl₂ and LaCl₃, inhibitors of Ca²⁺ channels. The participation of Ca²⁺ and K⁺ in the electrogenesis of action potentials in C. conicum is discussed. Treatment with phosphorylation uncouplers induced a gradual disappearance of the metabolic component of the resting potential. It was accompanied by some series of excitations, numbering from several to over a dozen impulses characterized by decreasing amplitudes, after which the organism became totally unexcitable. Dicyclohexylcarbodiimide an inhibitor of H⁺-ATPase, also caused depolarization of the transmembrane potential and disappearance of excitability. The results indicated the participation of a metabolic component in the generation of action potentials in C. conicum .