Single‐Wall Carbon Nanotube Paste Electrodes: a Comparison with Carbon Paste,Platinum and Glassy Carbon Electrodes via Cyclic Voltammetric Data

A new carbon electrode material, obtained by mixing single wall carbon nanotubes (SWNTs) with a mineral oil binder is studied. Carbon nanotube pastes show the special properties of carbon nanotubes combined with the various advantages of composite electrodes such as a very low capacitance (background current) and the possibility of an easy preparation, modification and renewal. A better knowledge of the characteristics of electrode reactions at carbon nanotube paste (CNTP) electrodes was obtained studying the electron transfer rates of various redox couples under different pretreatment conditions. A critical comparison with carbon paste (CP), platinum (Pt) and glassy carbon (GC) electrodes was also carried out. Capacitance and resistance values were also calculated for all electrodes investigated. Both untreated and treated CNTP electrodes showed a low resistance while the capacitance was markedly reduced with CNTP electrodes previously treated with concentrated nitric acid. An electrochemical pretreatment on CNTP electrodes was developed which showed an excellent result towards two‐electron quinonic structure species. After this treatment the heterogeneous standard rate constants for p‐methylaminophenol sulfate (MAP) and dopamine resulted to be significantly higher (2.1×10^?2 cm/s and 2.0×10^?2 cm/s, respectively) than those obtained with the other electrodes studied. Reproducibility, stability and storage characteristics of CNTP electrodes were also reported.     

Evaluation of different mediator-modified screen-printed electrodes used in a flow system as amperometric sensors for NADH

This work presents a comparative study between two different methods for the preparation of mediator-modified screen-printed electrodes, to be used as detectors in a reliable flow injection system for the determination of the nicotinamide adenine dinucleotide (NADH) coenzyme. The best strategy was selected for the final development of compact biosensors based on dehydrogenase enzymes. For the first immobilisation strategy, different redox mediators were electropolymerised onto the SPE surface. The second immobilisation strategy was carried out using polysulfone–graphite composites, which were deposited by screen-printing technology onto the screen-printed electrode (SPE) surface. Both methods achieved an effective and reliable incorporation of redox mediators to the SPE configuration. Finally, a flow system for ammonium determination was developed using a glutamate dehydrogenase (GlDH)-Meldola's Blue (MB)-polysulfone-composite film-based biosensor.

The stability of the redox mediators inside the composite films as well as the negligible fouling effect observed on the electrode surface improve the repeatability and reproducibility of the sensors, important features for continuous analysis in flow systems. Furthermore, the optimised bio/sensors, incorporated in a flow injection system, showed good sensitivities and short response times. Such a good analytical performance together with the simple and fast sensor construction are interesting characteristics to consider the polysulfone-composite films as attractive electrochemical transducer materials for the development of new dehydrogenase-based SPEs.     

The role of adiponectin in the production of IL-6, IL-8, VEGF and MMPs in human endothelial cells and osteoblasts: implications for arthritic joints

This study was performed to evaluate the contribution of adiponectin to the production of interleukin (IL)-6, IL-8, vascular endothelial growth factor (VEGF), matrix metalloproteinase (MMP)-1 and MMP-13 in human endothelial cells and osteoblasts in arthritic joints. Cultured human umbilical vascular endothelial cells (HUVECs) and osteoblasts were stimulated with adiponectin (1 or 10 μg ml⁻¹) or IL-1β (0.1 ng ml⁻¹) in the presence or absence of hypoxia for 24 h. The protein expression patterns were examined by analyzing culture supernatants using the enzyme-linked immunosorbent assay (ELISA). Adiponectin significantly stimulated the production of VEGF, MMP-1 and MMP-13 in osteoblasts but not in endothelial cells, whereas it significantly stimulated the production of IL-6 and IL-8 in both endothelial cells and osteoblasts. The increase in VEGF production induced by adiponectin was significantly greater than that induced by IL-1β. The production of IL-6 and IL-8 in adiponectin-stimulated endothelial cells was approximately 10-fold higher than that in IL-1β-stimulated endothelial cells; in osteoblasts, adiponectin-induced IL-6 and IL-8 secretion was approximately twofold higher than that induced by IL-1β. In addition, IL-8 production in endothelial cells was approximately sevenfold higher than in osteoblasts. However, IL-6 levels were similar between the two cell types, suggesting that adiponectin may be involved in the production of IL-8 in endothelial cells, which may have an important role in neutrophil recruitment to arthritic joints. Furthermore, the increases in protein expression induced by adiponectin were differentially regulated by hypoxia. In conclusion, adiponectin has a more important role than does IL-1β in the production of mediators that drive synovitis and joint destruction in endothelial cells and osteoblasts at physiological concentrations.     

High-Capacity and Stable Li-O2 Batteries Enabled by a Trifunctional Soluble Redox Mediator

Li-O₂ batteries with ultrahigh theoretical energy densities usually suffer from low practical discharge capacities and inferior cycling stability owing to the cathode passivation caused by insulating discharge products and by-products. Here, a trifunctional ether-based redox mediator, 2,5-di-tert-butyl-1,4-dimethoxybenzene (DBDMB), is introduced into the electrolyte to capture reactive O₂⁻ and alleviate the rigorous oxidative environment of Li-O₂ batteries. Thanks to the strong solvation effect of DBDMB towards Li⁺ and O₂⁻, it not only reduces the formation of by-products (a high Li₂O₂ yield of 96.6 %), but also promotes the solution growth of large-sized Li₂O₂ particles, avoiding the passivation of cathode as well as enabling a large discharge capacity. Moreover, DBDMB makes the oxidization of Li₂O₂ and the decomposition of main by-products (Li₂CO₃ and LiOH) proceed in a highly effective manner, prolonging the stability of Li-O₂ batteries (243 cycles at 1000 mAh g⁻¹ and 1000 mA g⁻¹).     

Electrochemical oxidation of malonic esters in acetonitrile in the presence of iodides as mediators

Electrochemical oxidation of malonic esters in acetonitrile in the presence of iodides follows two different pathways depending on the nature of the cation. In the presence of Lil, alkyl 1,1,2,2,3,3-propanetetracarboxylates were obtained in 85–98% yields. In the presence of Nal, Kl, or Bu₄NI, the formation of 1,1,2,2-ethanetetracarboxylates and their subsequent dehydrogenation to ethenetetracarboxylates was the main reaction pathway. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 620–623, March, 1997.     

Poly(neutral red): Electrosynthesis,Characterization, and Application as a Redox Mediator

The synthesis by electropolymerization, the characterization, and applications of poly(neutral red) (PNR), including as a redox mediator, are reviewed. PNR's high electrical conductivity and its redox characteristics have led to special applications of the polymer, and it has been used for the development of electrochemical and optical sensors. Moreover, the attractive properties of PNR allow it to be applied in the development of electrochemical biosensors. Future perspectives are indicated.     

A Stereocontrolled Total Synthesis of Lipoxin B4 and its Biological Activity as a Pro-Resolving Lipid Mediator of Neuroinflammation

Two stereocontrolled, efficient, and modular syntheses of eicosanoid lipoxin B4 (LXB₄) are reported. One features a stereoselective reduction followed by an asymmetric epoxidation sequence to set the vicinal diol stereocentres. The dienyne was installed via a one-pot Wittig olefination and base-mediated epoxide ring opening cascade. The other approach installed the diol through an asymmetric dihydroxylation reaction followed by a Horner-Wadsworth-Emmons olefination to afford the common dienyne intermediate. Finally, a Sonogashira coupling and an alkyne hydrosilylation/proto-desilylation protocol furnished LXB₄ in 25 % overall yield in just 10 steps. For the first time, LXB₄ has been fully characterized spectroscopically with its structure confirmed as previously reported. We have demonstrated that the synthesized LXB₄ showed similar biological activity to commercial sources in a cellular neuroprotection model. This synthetic route can be employed to synthesize large quantities of LXB₄, enable synthesis of new analogs, and chemical probes for receptor and pathway characterization.     

Electrochemical oxidation of tetramethyl esters of α,α,ω,ω-alcaneteracarboxylic acids

Cyclization of esters of butane-1,1,4,4- and pentane-1,1,5,5-tetracarboxylic acids during electrolysis in methanol in the presence of Nal produces, with a yield of 95%, the esters of cyclobutane-1,1,2,2- and cyclopentane-1,1,2,2-tetracarboxylic acids. Under similar conditions, esters of the highest ,,,-alkanetetracarboxylic acids undergo iodation and hydroxymethylation due to electrical oxidation of methanol to formaldehyde. During electrolysis in methanol in the presence of NaOAc, the esters of ,,,-alkanetetracarboxylic acids undergo effective hydroxymethylation, followed by cyclization into substituted five- and six-member lactones, or tetrahydrofurans when structurally possible.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2332–2339, October, 1992.     

Catalytic electrooxidation of NADH for dehydrogenase amperometric biosensors

The developments in the techniques of NADH catalytic oxidation relevant for incorporation in amperometric biosensors with dehydrogenase enzymes are reviewed with special emphasis in the years following 1990. The review stresses the direct electro-catalytic methods of NAD⁺ recycling as opposed to enzymatic regeneration of the coenzyme. These developments are viewed and evaluated from a mechanistic perspective of recycling of NADH to enzymatically active NAD⁺, and from the point of view of development of technologically useful reagentless dehydrogenase biosensors. An effort is made to propose a method for the standardization of evaluation of new mediating and direct coenzyme recycling schemes. A perspective is given for the requirements that have to be met for successful biosensor development incorporating dehydrogenase enzymes that open the analytical possibilities to a number of new analytes. The intrinsic limitations of the system are finally discussed and a view of the future of the field is presented.     

Resolving Inflammation: Synthesis,Configurational Assignment,and Biological Evaluations of RvD1n−3 DPA

New drugs that can resolve inflammation without immunosuppressive effects are at the medicinal chemistry frontier. Pro-resolving endogenously formed small molecules, that is, the resolvins, are excellent candidates displaying such bioactions. The first total synthesis of the specialized pro-resolving mediator RvD1_{n−3 DPA} has been achieved using the underutilized sp³–sp³ Negishi cross coupling reaction and an alkyne hydrosilylation–protodesilylation protocol. Biological evaluations revealed that this novel mediator displays low nanomolar pro-resolving properties and potently activates the human DRV1/GPR32 receptor. As such, this endogenous natural product is a lead compound for the development of novel immunoresolvents.