1.DREAM Assay for Studying Microbial Electron Transfer.
Vishwanathan AS1, Devkota R2, Siva Sankara Sai S3, Rao G4. Appl Biochem Biotechnol. 2015 Dec;177(8):1767-75. doi: 10.1007/s12010-015-1852-3. Epub 2015 Sep 19.
Methylene blue undergoes reduction with an accompanying colour change reaction, from blue to colourless, enabling its use as a metric for estimating reducing power. A dye reduction-based electron-transfer activity monitoring (DREAM) assay is demonstrated as a tool to study and understand the process of microbes sourcing electrons from organic substrates and transferring them to an electron acceptor. The rate at which electrons can be transferred to the thermodynamically most feasible electron acceptor directly depends on the activity of microbes. Nature of available substrate determines the quantum of electrons available. Dissolved oxygen intercepts electrons from the microbes before they can be taken up by the dye. Sodium sulfite can be used to offset the detrimental effects of the presence of dissolved oxygen. This easy-to-perform assay has been demonstrated as a proof-of-concept having potential to be extended to other practical applications.
2.Development of a Photoinduced Chemiluminescent Method for the Determination of the Herbicide Quinmerac in Water.
Catalá-Icardo M1, López-Paz JL, Blázquez-Pérez J. Appl Spectrosc. 2015 Oct;69(10):1199-204. doi: 10.1366/14-07791.
A new, simple, and sensitive method, based on photoinduced chemiluminescence, was developed for the determination of quinmerac. The photoproduct, obtained after ultraviolet irradiation in basic medium, was mixed with sodium sulfite (sensitizer), and Ce(IV) (oxidant) in acid medium. A wide linear dynamic range (2-600 ng mL(-1)) and a limit of detection of 0.6 ng mL(-1) were obtained without any pretreatment (0.08 ng mL(-1) after solid-phase extraction). The determination was performed using a flow-injection manifold, which allowed a high throughput (144 h(-1)). The interday reproducibility was 5.6% (n = 5), and the intraday repeatability was 3.9 and 2.9% for 20 and 200 ng mL(-1) of quinmerac, respectively (n = 21). Finally, the method was applied to surface water and groundwater, with recoveries ranging from 78.1 to 94.5%.
3.Eu(III)-Sensitized Luminescence Probe for Determination of Tolnaftate in Pharmaceuticals and Biological Fluids.
J AOAC Int. 2016 Mar 10. [Epub ahead of print]
A highly selective, sensitive, accurate, and reproducible luminescence procedure for determination of antifungal drug tolnaftate was developed. The introduced method was based on the formation of Europa Universalis III (Eu(III))-tolnaftate complex using sodium sulfite as a deoxygenated agent in the presence of acetate buffer (pH = 6) and micellar solution of anionic surfactant sodium dodecyl sulfate. The optimum conditions (effect of pH, buffer, surfactant, Eu(III), and sodium sulfite concentrations) for the luminescence signal were investigated and optimized. The luminescence signals were recorded at λex = 270 nm and λem = 460 nm. The method has a good linear response(0.2-130 μg/mL-1) between the luminescence intensity and the concentrations of the drug (r = 0.999), with a LOD 0.07 μg/mL-1 and LOQ 0.2 μg/mL-1. The luminescence signals of Eu (III)-tolnaftate-sodium dodecyl sulfate were found to be 200-fold more sensitive without the presence of micelle solution.
4.Kinetic and structural studies reveal a unique binding mode of sulfite to the nickel center in urease.
Mazzei L1, Cianci M2, Benini S3, Bertini L1, Musiani F1, Ciurli S4. J Inorg Biochem. 2016 Jan;154:42-9. doi: 10.1016/j.jinorgbio.2015.11.003. Epub 2015 Nov 5.
Urease is the most efficient enzyme known to date, and catalyzes the hydrolysis of urea using two Ni(II) ions in the active site. Urease is a virulence factor in several human pathogens, while causing severe environmental and agronomic problems. Sporosarcina pasteurii urease has been used extensively in the structural characterization of the enzyme. Sodium sulfite has been widely used as a preservative in urease solutions to prevent oxygen-induced oxidation, but its role as an inhibitor has also been suggested. In the present study, isothermal titration microcalorimetry was used to establish sulfite as a competitive inhibitor for S. pasteurii urease, with an inhibition constant of 0.19mM at pH7. The structure of the urease-sulfite complex, determined at 1.65Å resolution, shows the inhibitor bound to the dinuclear Ni(II) center of urease in a tridentate mode involving bonds between the two Ni(II) ions in the active site and all three oxygen atoms of the inhibitor, supporting the observed competitive inhibition kinetics.