2-Aminopurine Fluorescence Spectroscopy for Probing a Glucose Binding Aptamer

Glucose is the most important analyte for biosensors. Recently a DNA aptamer was reported allowing binding-based detection. However, due to a relatively weak binding affinity, it is difficult to perform binding assays to understand the property of this aptamer. In this work, we replaced the only adenine base in the aptamer binding pocket with a 2-aminopurine (2AP) and used fluorescence spectroscopy to study glucose binding. In the selection buffer, glucose increased the 2AP fluorescence with a K_d of 15.0 mM glucose, which was comparable with the 10 mM K_d previously reported using the strand displacement assay. The binding required two Na⁺ ions or one Mg²⁺ that cannot be replaced by Li⁺ or K⁺. The binding was weaker at higher temperature and its van't Hoff plot indicated enthalpy-driven binding. While other monosaccharides failed to achieve saturated binding even at high concentrations, two glucose-containing disaccharides, namely trehalose and sucrose, reached a similar fluorescence level as glucose although with over 10-fold higher K_d values. Detection limits in both the selection buffer (0.9 mM) and in artificial interstitial fluids (6.0 mM) were measured.     

Heat extraction methods from salinity-gradient solar ponds and introduction of a novel system of heat extraction for improved efficiency

Heat has generally been successfully extracted from the lower convective zone (LCZ) of solar ponds by two main methods. In the first, hot brine from the LCZ is circulated through an external heat exchanger, as tested and demonstrated in El Paso and elsewhere. In the second method, a heat transfer fluid circulates in a closed cycle through an in-pond heat exchanger, as used in the Pyramid Hill solar pond, in Victoria, Australia. Based on the experiences at the El Paso and Pyramid Hill solar ponds, the technical specifications, material selection, stability control, clarity maintenance, salt management and operating strategies are presented. A novel method of extracting heat from a solar pond is to draw the heat from the gradient layer. This method is analysed theoretically and results of an experimental investigation at Bundoora East, RMIT, are presented. An in-pond heat exchanger made of polyethylene pipe has been used to extract heat for over 2 months. Results indicate that heat extraction from the gradient layer increases the overall energy efficiency of the solar pond by up to 55%, compared with conventional method of heat extraction solely from the LCZ. The experimental results are compared with the theoretical analysis. A close agreement has been found. From this small-scale experimental study, convection currents were found to be localised only and the density profiles were unaffected. An experimental study using an external heat exchanger for brine extraction and re-injection at different levels within the gradient layer still needs to be conducted to determine the effect of the heat extraction from the non-convective zone (NCZ) on the stability of the salinity gradient (both vertically and horizontally) and an economic analysis needs to be conducted to determine the economic gains from increased thermal efficiency.     

Effects of H2O2 addition to the cell balance and self-discharge of Ni/MH batteries with AB5 and A2B7 alloys

In this paper we have compared nickel/metal hydride batteries made from AB₅ and Nd-only A₂B₇ alloys with or without addition of hydrogen peroxide (H₂O₂). The biggest advantages Nd-only A₂B₇ alloys have over AB₅ alloys are: a higher positive electrode utilization rate, lower initial internal resistance and less resistance increase after a 60 °C storage, and higher capacity and resistance degradation during cycling. The hydrogen peroxide was used as an oxidation agent and was added into the electrolyte before closing the cells. The H₂O₂ can oxidize both Co(OH)₂ in the positive electrode and MH alloy in the negative electrode. From the test results, H₂O₂ oxides the MH alloy preferentially over the Co(OH)₂ in the case of AB₅ alloy. This preferential oxidation is reversed in the case of the A₂B₇ alloy in which Co(OH)₂ is oxidized first. In cells made from both alloys, the addition of H₂O₂ prevented the venting of cells during formation, increased the utilization of positive electrode, improved the 60 °C charge retention, and increased the mid-point voltage after 300 cycles. Additionally the H₂O₂ also improved the cell balance for A₂B₇ alloy by decreasing the over-discharge reservoir in the negative electrode and reducing the capacity degradation in A₂B₇ alloy. However, the addition of H₂O₂ in cells made with AB₅ alloy deteriorated the cell balance by increasing the over-discharge reservoir in the negative electrode. The different cell balance and failure mechanisms for the two alloy compositions and H₂O₂ additive were compared and discussed.     

The Effect of Calcium Fluoride on Slag Viscosity

The effect of CaF₂ on the viscosity of high-basicity Al₂O₃-CaO-MgO-SiO₂ (-CaF₂) slags for secondary steelmaking was studied using a Brookfield digital viscometer. The addition of approximately 3 mass pct CaF₂ could decrease the liquidus temperature substantially in the case of high CaO containing slags, leading to good flowability of the slag at the temperature of the ladle treatment. The addition of CaF₂ had the strongest effect on the viscosity of liquid slag with high SiO₂ content.     

Highly dispersed Pd nanoparticles within silica: Synthesis and characterization

Well dispersed and homogeneously distributed Pd nanoparticles within a silica matrix were synthesized by a two stage process: (1) intercalation of palladium tetrammine ions into the layered aluminium-free silicate Na ilerite followed by (2) a self-reduction of the complex through decomposition of the tetrammine ligands by calcination at 550 °C for 5 h under N₂ or air. Samples calcined in N₂ predominantly contained nanoparticles of metallic Pd, while calcination in air led largely to the formation of PdO, as confirmed by XPS and supported by XRD and TGA. Thus, the Pd/PdO loading in the silica can be selectively tuned through this method. The intercalates were characterized by standard methods such as XRD, TGA, ICP and TEM. TGA of the intercalates indicated that the stabilization of the palladium tetrammine complex was enhanced by intercalation into Na ilerite. Based on ICP analysis, the Pd loadings in the intercalates were estimated to be about 18 mass-%, which was also in agreement with the results from TGA. TEM revealed that the Pd/PdO nanoparticles were well dispersed in the silica matrix with an average particle size of approximately 8–10 nm after calcination in air.