Effect of Current Density on Preparation and Properties of TF/ß-PbO2 in MSA Media.

The lead-based alloy and DSA anodes have drawbacks, such as poor corrosion resistance, easy peeling of coating, low electrocatalytic activity, and environmental pollution in electrode preparation processes. In this study, titanium foam/ß-PbO2 (TF/ß-PbO2) was prepared by electrodeposition in methanesulfonic acid (MSA) media. The current efficiency and the deposition rate were 89.7% and 5.36 v/(µm·min-1) at the best current density of 80 mA·cm-2, respectively. The TF/ß-PbO2 was characterized by electrochemical tests, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The cyclic voltammetry (CV) test shows that the anodic peak potential of the optimum TF/ß-PbO2 was as low as 2.135 V and anodic voltammetry charge was up to the maximum value of 3.564 × 10-2 C. The linear sweep voltammetry (LSV) test indicates that exchange current density of the optimum TF/ß-PbO2 reached the maximum value of 8.284 × 10-6 A·cm-2. CV and LSV tests indicate that the optimum TF/ß-PbO2 had a high electrocatalytic activity. Electrochemical impedance spectroscopy test Tafel polarization curves show that the optimum TF/ß-PbO2 had better corrosion resistance. The XRD test shows that the crystal was mainly ß-PbO2 of the optimum TF/ß-PbO2 surface and the current density affected the preferential growth of the crystal surface of PbO2. SEM tests show that grains of the optimum TF/ß-PbO2 coating prepared were tightly bound and uniform in size.

From nematic shells to nematic droplets: energetics and defect transitions.

In this work, we investigate the possibility of inducing valence transitions, i.e. transitions between different defect configurations, by transforming a nematic shell into a nematic droplet. Our shells are liquid crystal droplets containing a smaller aqueous droplet inside, which are suspended in an aqueous phase. When osmotically de-swelling the inner droplet, the shell progressively increases its thickness until it eventually becomes a single droplet. During the process, the shell energy landscape evolves, triggering a response in the system. We observe two different scenarios. Either the inner droplet progressively shrinks and disappears, inducing a defect reorganization, or it is expelled from the shell at a critical radius of the inner droplet, abruptly changing the geometry of the system. We use numerical simulations and modeling to investigate the origin of these behaviors. We find that the selected route depends on the defect structure and the energetics of the system as it evolves. The critical inner radius and time for expulsion depend on the osmotic pressure of the outer phase, suggesting that the flow through the shell plays a role in the process.

Geminate labels programmed by two-tone microdroplets combining structural and fluorescent color.

Creating a security label that carries entirely distinct information in reflective and fluorescent states would enhance anti-counterfeiting levels to deter counterfeits ranging from currencies to pharmaceuticals, but has proven extremely challenging. Efforts to tune the reflection color of luminescent materials by modifying inherent chemical structures remain outweighed by substantial trade-offs in fluorescence properties, and vice versa, which destroys the information integrity of labels in either reflection or fluorescent color. Here, a strategy is reported to design geminate labels by programming fluorescent cholesteric liquid crystal microdroplets (two-tone inks), where the luminescent material is 'coated' with the structural color from helical superstructures. These structurally defined microdroplets fabricated by a capillary microfluidic technique contribute to different but intact messages of both reflective and fluorescent patterns in the geminate labels. Such two-tone inks have enormous potential to provide a platform for encryption and protection of valuable authentic information in anti-counterfeiting technology.

Structural transformations in tetravalent nematic shells induced by a magnetic field.

The role of applied fields on the structure of liquid crystals confined to shell geometries has been studied in past theoretical work, providing strategies to produce liquid crystal shells with controlled defect structure or valence. However, the predictions of such studies have not been experimentally explored yet. In this work, we study the structural transformations undergone by tetravalent nematic liquid crystal shells under a strong uniform magnetic field, using both experiments and simulations. We consider two different cases in terms of shell geometry and initial defect symmetry: (i) homogeneous shells with four s = +1/2 defects in a tetrahedral arrangement, and (ii) inhomogeneous shells with four s = +1/2 defects localized in their thinner parts. Consistently with previous theoretical results, we observe that the initial defect structure evolves into a bipolar one, in a process where the defects migrate towards the poles. Interestingly, we find that the defect trajectories and dynamics are controlled by curvature walls that connect the defects by pairs. Based on the angle between Bs, the local projection of the magnetic field on the shell surface, and n+½, a vector describing the defect orientations, we are able to predict the nature and shape of those inversion walls, and therefore, the trajectory and dynamics of the defects. This rule, based on symmetry arguments, is consistent with both experiments and simulations and applies for shells that are either homogeneous or inhomogeneous in thickness. By modifying the angle between Bs and n+½, we are able to induce, in controlled way, complex routes towards the final bipolar state. In the case of inhomogeneous shells, the specific symmetry of the shell allowed us to observe a hybrid splay-bend Helfrich wall for the first time.

Amperometric Determination of Ascorbic Acid on an Au Electrode Modified by a Composite Film of Poly(3,4-ethylenedioxythiophene) and Superconductive Carbon Black.

A new composite film-modified electrode was prepared by the electropolymerisation of poly(3,4-ethylenedioxythiophene) (PEDOT) and superconductive carbon black (SCB) on a gold electrode. The PEDOT-SCB/Au electrode exhibited excellent ability towards the electrocatalytic oxidation of ascorbic acid, in terms of a 480 mV shift of the oxidation potential in the negative direction, and a dramatically enhanced oxidation current. Under the optimum conditions, the amperometric detection of ascorbic acid provided a wide linear detection range from 1.0 × 10(-7) to 8.0 × 10(-4) M, and a detection limit of 5.0 × 10(-8) M (S/N = 2) as well as good reproducibility and stability.

A bicistronic expression strategy for large scale expression and purification of full-length recombinant human parathyroid hormone for osteoporosis therapy.

Parathyroid hormone (PTH) contributes to the increase of trabecular connectivity and is a candidate medication for effective treating osteoporosis. PTH is a protein of 84 amino acids and some studies have suggested that the active site lies within the range from amino acid (aa) 1 to 34. However, a few reports have indicated a causal relationship between PTH (aa 1-34) and osteogenic sarcoma in rats, while some less obvious but important roles of the carboxyl-terminus of PTH were also found. Unfortunately, it is difficult to obtain the active integrated PTH (1-84) in vitro, due to the instability of both the protein and its mRNA. Because an alternative translation start site is located at +25 nucleotides downstream of the true start site, a truncated PTH can be translated. We constructed a rhPTH bicistronic expression plasmid (pTrepth) that could highly express non-fusion soluble rhPTH proteins in Escherichia coli. The BL-21(DE3) containing pTrepth was cultured on a small scale until satisfactory expression and purification results were obtained. We then amplified the transformed cells in a 15-L fermentor and harvested 27g/L cells (wet weight). Extensive rhPTH purification was achieved by a three step chromatography process. Activity tests demonstrated that our purified protein could dramatically increase cAMP in osteosarcoma cells in vitro.