Competition of unsaturated compounds with ethylene for binding and action in plants

The compounds 2,5-norbornadiene, cyclopentadiene, furan, pyrrole, thiophene, 1-methylpyrrole, dicyclopentadiene, methylcyclopentadiene (dimer), and cycloheptatriene have been tested for competition with ethylene for binding and for biological activity using banana fruit. In addition, acetylene, allene, and 1,3-butadiene were tested. All of these compounds competed with ethylene for binding in vitro in a Triton X-100 extract of mung bean sprouts and in vivo in tobacco leaves. Only acetylene, allene, and furan are active in giving an ethylene response in banana. the others all suppress the ethylene response. Only acetylene and allene stimulate ethylene synthesis. Most of the compounds diffuse away from the binding site upon exposure to air.R.J. Reynolds Research Apprentice     

Deep brain stimulation: Challenges at the tissue-electrode interface and current solutions

Deep brain stimulation (DBS) is used to treat the motor symptoms of Parkinson's disease patients by stimulating the subthalamic nucleus. However, optimization of DBS is still needed since the performance of the neural electrodes is limited by the body's response to the implant. This review discusses the issues with DBS, such as placement of electrodes, foreign body response, and electrode degradation. The current solutions to these technical issues include modifications to electrode material, coatings, and geometry.     

Glucose oxidase-polypyrrole electrodes synthesized in p-toluenesulfonic acid and sodium p-toluenesulfonate

Amperometric glucose biosensors have been developed based on entrapment on platinum (Pt) electrode using cyclic voltammetry technique in glucose oxidase (GOD) and pyrrole containing p-toluenesulfonic acid (pTSA) or sodium p-toluenesulfonate (NapTS) as supporting electrolyte solutions. Both of electrolyte solutions were suitable media for the formation and deposition of polypyrrole-GOD (PPy-GOD) layers on Pt substrate. Pt/PPy-GOD electrodes brought about in different morphological properties as well as different electrochemical and biochemical response. The highest responses obtained in pTSA and NapTS electrolytes were observed at pH of 4.5 and 7.0 for Pt/PPy-GOD electrodes, respectively. While linearity was observed between 0.0-1.0 mM glucose substrate for both electrodes, I(max) value of Pt/PPy-GOD(NapTS) electrode was approximately twice as high as that of Pt/PPy-GOD(pTSA) electrode as 25.4 and 14.2 microA, respectively. Five commercial drinks were tested with enzyme electrodes and compared with results obtained spectrophotometrically using glucose kit. Results revealed that Pt/PPy-GOD(NapTS) electrode exhibited better biosensor response.     

Reduction of electrode polarization capacitance in low-frequency impedance spectroscopy by using mesh electrodes

Dielectric measurements of biological samples are obscured by electrode polarization, which at low frequencies dominates over the actual sample response. Reduction of this artifact is especially necessary in studying interactions of electric field with biological systems in the α-dispersion range. We developed a method to reduce the influence of electrode polarization by employing mesh instead of solid electrodes as sensing probes, thereby reducing the area of the double layer. The design decreases the electrode-electrolyte contact area by almost 40% while keeping the bulk sample capacitance the same. Interrogation electric fields away from the electrode surface and sensitivity are unaffected. Electrodes were microfabricated (600μm×50μm, spacing of 100μm) with and without mesh holes 7.5μm×7.5μm in size. Simulations of electric field performed using Comsol Multiphysics showed non-uniformity of the electric field within less than 1.5μm from the electrode surface, which encompasses the double layer region, but at greater distance the solid and mesh electrodes gave the same results. Mesh electrodes reduced capacitance measurements for water and KCl solutions of different concentrations at low frequencies (<10kHz), while higher frequency capacitance remained the same for both electrode types, confirming our hypothesis that this design leaves the electric field mainly unaffected. Impedance measurements at low frequencies for water and mice heart mitochondrial suspension were lower for mesh than for solid electrodes. Comsol simulations confirmed these results by showing that mesh electrodes have a greater charge density than solid electrodes, which affects conductance. These electrodes are being used for mitochondrial membrane potential studies.     

Electrochemical activation of electrodes for amperometric detection of nitric oxide

An open question in the literature of nitric oxide detection was investigated: does electrochemical activation account for the enhanced properties of certain presumed chemically-modified electrodes? Uniform electrodes of graphite, iridium, palladium, platinum, and ruthenium were exposed to potential cycling and then tested for amperometric response to nitric oxide to identify principles that govern electrochemical activation of nitric oxide electrodes. These electrodes were compared to similar electrodes that were not cycled. Only cycled graphite and ruthenium showed significantly increased responses. Graphite demonstrated enhanced performance after exposure to cycling potentials at which oxygen, CO₂, and soluble carbonates form, suggesting that erosion of the electrode enhanced its response by increasing the surface area accessible to nitric oxide. This may explain the performance of carbon fibers cycled to the same potentials in solutions containing metalloporphyrins. The response of ruthenium was enhanced after cycling to less extreme potentials at which soluble species do not form and at which a metallic conductive oxide, RuO₂, could lay down a stable, adherent layer on the electrode surface. Cycled ruthenium also exhibited a much greater increase in capacitance after cycling, consistent with the formation of a conductive surface layer.     

Glucose oxidase-polypyrrole electrodes synthesized in <Emphasis Type="Italic">p</Emphasis>-toluenesulfonic acid and sodium <Emphasis Type="Italic">p</Emphasis>-toluenesulfonate

Amperometric glucose biosensors have been developed based on entrapment on platinum (Pt) electrode using cyclic voltammetry technique in glucose oxidase (GOD) and pyrrole containing p-toluenesulfonic acid (pTSA) or sodium p-toluenesulfonate (NapTS) as supporting electrolyte solutions. Both of electrolyte solutions were suitable media for the formation and deposition of polypyrrole-GOD (PPy-GOD) layers on Pt substrate. Pt/PPy-GOD electrodes brought about in different morphological properties as well as different electrochemical and biochemical response. The highest responses obtained in pTSA and NapTS electrolytes were observed at pH of 4.5 and 7.0 for Pt/PPy-GOD electrodes, respectively. While linearity was observed between 0.0–1.0 mM glucose substrate for both electrodes, I _max value of Pt/PPy-GOD_NapTS electrode was approximately twice as high as that of Pt/PPy-GOD_pTSA electrode as 25.4 and 14.2 μA, respectively. Five commercial drinks were tested with enzyme electrodes and compared with results obtained spectropho-tometrically using glucose kit. Results revealed that Pt/PPy-GOD_NapTS electrode exhibited better biosensor response.     

Problems of the Acetylene Reduction Technique Applied to Water-Saturated Paddy Soils

The acetylene reduction assay for the measurement of N₂ fixation in a water-saturated paddy soil is limited by the slow diffusion of acetylene and ethylene. In laboratory incubation tests, vigorous shaking after the assay period is needed to release ethylene into the gas within the assay vials. Shaking prior to the incubation is also effective for dissolving acetylene in the water-saturated soil. However, a water-saturated soil depth of less than 10 mm during incubation is recommended. In field assays, some amounts of ethylene remain in the water-saturated soil phase of the acetylene reduction assay chamber, but stirring the water-saturated soil before sampling reduces the amount of ethylene remaining in soil. Evidence of a downward movement of acetylene and an upward movement of ethylene through rice plants was obtained. Because of the rapid transfer of acetylene to rice plant roots, an in situ acetylene reduction assay covering a rice hill is likely to detect nitrogen fixation in the proximity of roots where acetylene is easily accessible. Acetylene introduction to the water-saturated soil phase prior to assay did not greatly increase the acetylene reduction rate. Carbon dioxide enrichment in the assay chamber did not enhance nitrogen fixation in a paddy including rice and algae during a 1-day cycle.     

Influence of Acetylene on Growth of Sulfate-Respiring Bacteria

At a concentration of 20% of the atmosphere of the culture flasks, acetylene inhibited growth and carbon dioxide production by Desulfovibrio desulfuricans and Desulfovibrio gigas. The bacteria did not reduce acetylene to ethylene, and neither acetylene dicarboxylic acid nor ethylene was inhibitory. At 10%, acetylene was partially inhibitory for the desulfovibrios. At 5%, acetylene impeded the rate but did not limit the extent of growth and catabolism of the desulfovibrios. Desulfotomaculum ruminis was affected only negligibly, if at all, by acetylene and ethylene at any of these concentrations.     

In vitro testing of a simply constructed, highly stable glucose sensor suitable for implantation in diabetic patients

We have constructed and tested in vitro a potentially implantable, needle-type amperometric enzyme electrode which is suitable for continuous monitoring of glucose concentrations in diabetic patients. The major requirements of stability during operation and ease of manufacture have been met with a sensor design which involves a simple dip-coating procedure for applying to a platinum base electrode an inner membrane of glucose oxidase immobilised in polyhydroxyethyl methacrylate (pHEMA), and an outer membrane composed of a pHEMA/polyurethane mixture. Sensors were operated at 700 mV for detection of hydrogen peroxide. Calibration curves for the sensor were linear to at least 20 mM glucose and were unaffected by a reduction in PO2 from 20 to 5 kPa. During continuous operation in 5 mM buffered glucose solutions in vitro, sensors suffered no significant loss of response over periods of up to 60 h. Such electrodes are, therefore, useful for development as in vivo glucose sensors.     

Acetylene reduction by nitrogen-fixing blue-green algae

Summary Known nitrogen-fixing species of blue-green algae are capable of reducing acetylene to ethylene, but acetylene is not reduced by Anacystis nidulans, which does not fix nitrogen. Cycad root nodules which contain blue-green algae as endophytes reduce acetylene. Acetylene reduction is inhibited by carbon monoxide. Nitrate or ammonium-nitrogen has no immediate effect on algae reducing acetylene, but algae grown on nitrate-nitrogen gradually lose their capacity to reduce acetylene. Nitrate-nitrogen also inhibits heterocyst formation in these algae and there is a fairly direct correlation between the abundance of heterocysts in a particular sample and its capacity to reduce acetylene. Aphanizomenon flosaquae reduces acetylene and fixes nitrogen in unialgal culture and there is strong presumptive evidence that these reductions are carried out by the alga rather than by associated bacteria. The molar ratios of ethylene: ammonia produced vary within the range 1.4–1.8.     

Endogenous ethylene production is a potential problem in the measurement of nitrogenase activity associated with excised corn and sorghum roots

Endogenous ethylene production was evaluated as a source of ethylene during acetylene reduction assays with freshly collected roots of field-grown corn, Zea mays L. cv Funks G-4646, and sorghum, Sorghum bicolor (L.) Moench. cv CK-60A. Ethylene production was not detected when roots were incubated in air without acetylene. The presence of endogenous ethylene production was confirmed when roots were incubated anaerobically and in the presence of 40 millimolar sodium hydrosulfite. Ethylene oxidase activity was also associated with excised roots. The rate of ethylene oxidation was higher than the rates of ethylene accumulation during either acetylene reduction assays or anaerobic incubations. These results indicate that the procedure of incubating roots of grasses in air to monitor endogenous ethylene production is not a valid control in acetylene reduction studies with grasses. The presence of endogenous ethylene production during acetylene reduction assays was demonstrated by using either CO to inhibit nitrogenase activity or chloramphenicol to inhibit nitrogenase synthesis in freshly excised roots.     

The Roles of Poly(Ethylene Oxide) Electrode Buffers in Efficient Polymer Photovoltaics

The role of poly(ethylene oxide) polymer is investigated as an effective buffer with Al electrodes to markedly improve the electrode interface and enhance the open‐circuit voltage (V_OC) and the power conversion efficiency (PCE, η) of poly(3‐hexylthiophene) (P3HT):[6,6]‐phenyl C61‐butyric acid methyl ester (PCBM)‐based bulk‐heterojunction (BHJ) solar cells. A unique process is developed by thermally co‐evaporating the poly(ethylene glycol) dimethyl ether (PEGDE, Mn ca. 2000) polymer with Al metal simultaneously at different ratios in vacuum (10^?6 Torr) to prepare the electrode buffers. The instant formation of a carbide‐like junction at the ethylene oxide/Al interface during the thermal evaporation is of essential importance to the extraction of electrons through the Al electrode. The performance of P3HT:PCBM‐based solar cells can be optimized by modulating the co‐evaporation ratios of the PEGDE polymer with Al metal due to the changes in the work functions of the electrodes. The V_OC and η for devices fabricated with Al electrode are 0.44 V and 1.64%, respectively, and significantly improve to 0.58 V and 4.00% when applying the PEGDE:Al(2:1)/Al electrode. This research leads to a novel electrode design – free of salts, additives, complicated syntheses, and having tunable work function – for fabricating high‐performance photovoltaic cells.     

Amperometric protein sensor - fabricated as a polypyrrole, poly-aminophenylboronic acid bilayer

An approach to the design of electrodes for the production of sensors, which show significant changes to the passage of current in response to the concentration of target protein molecules, is presented. Screen-printed platinum electrodes, modified with two separately applied conducting polymer layers, have been developed as a potential route to forming cheap disposable protein sensors. To achieve a heightened response for the target molecules, an initial layer of polypyrrole was formed on the electrode's surface by electro-deposition. This composite was then employed as a substrate for the subsequent electro-deposition of a relatively thin 'sensing layer' of poly-aminophenylboronic acid. Cyclic voltammetry (CV) of the prepared films revealed an excursion in the current versus potential curve in the anodic phase at approximately 0.0 to +0.2V. It was clearly shown that the introduction of proteins into the CV cell resulted in a measurable decrease in the passage of current in buffered aqueous media. Measured current reductions observed on introducing lysozyme (10ppm) into the test solution were 2.3x10(-6)A for an electrode formed with a poly-aminophenylboronic acid layer on platinum, and 1.75x10(-5)A for a composite electrode formed with poly-aminophenylboronic acid on a polypyrrole coated platinum substrate. The introduction of the competing analytes, dl adrenaline or dopamine, at concentrations typically found in human urine, had little effect on the sensor's response. Additionally, the sensing system was able to maintain a response to added target proteins with as much as 2vol.% urine in the test solution. Using the electrodes in high concentrations of competing physiological analytes, they were able to respond to protein concentrations as low as 0.5ppm in buffered solutions containing urea at a concentration representative of human urine (17,000ppm), which additionally contained glucose (1000ppm).     

Effects of ethylene and acetylene on mango fruit ripening

Mangoes (var. Tommy Atkins) were exposed to ethylene and acetylene over a range of concentrations at high humidity for 24 h at 25°C, then ripened in air alone. Ripeness was assessed after 4 and 8 days by analysis of texture, colour development, soluble solids and acid contents. Ethylene in air at concentrations of 0.01 ml litre^-1 and above or acetylene at 1.0 ml litre^-1 were found to initiate ripening. Treatment with 0.01 ml litre^-1 acetylene resulted in limited softening but had no effect on the other ripening changes analysed. Individual ripening processes responded differently to treatment: texture changes were most rapidly affected, while the rate of acidity losses was often reduced in ethylene treated fruits. Acetylene-treated fruits at concentrations of 0.01 and 0.1 ml litre^-1 showed delayed ripening when compared to those treated with either 1.0 ml litre^-1 acetylene or ethylene. Increased acetylene concentrations of 2.0 ml litre^-1 gave a similar response to 1.0 ml litre^-1, although in some instances there were indications of inhibitory effects.     

Abscission: the role of ethylene, ethylene analogues, carbon dioxide, and oxygen

Ethylene was the most effective abscission accelerant examined, with decreasing activity shown by propene, carbon monoxide, acetylene, vinyl fluoride, 1-butene, and 1,3-butadiene. Carbon dioxide inhibited abscission, but its effect was overcome by ethylene. Oxygen was required for abscission as an electron acceptor for respiration and not as a potentiator or activator of the ethylene attachment site. The molecular requirements for abscission were similar to those shown by other workers for other biological processes under the influence of ethylene.     

Continuous non-destructive determination of nitrogenase activity in microbiol cultures.

The dinitrogen fixing enzyme nitrogenase (nitrogen:(acceptor) oxidoreductase)(EC 1.7.99.2) is monitored by its ability to reduce acetylene to ethylene. Low, non-inhibitory concentrations of acetylene (approximately 10(-7)mol/litre) are mixed with the gas flow aerating microbiol cultures, and acetylene and ethylene in the effluent gas are determined by gas chromatography. The procedure is safe, simple and carried out in situ without disturbing the growing culture. Transient changes in nitrogenase activity are easily detected. The technique may be automated.     

Comparison of colloidal gold electrode fabrication methods: the preparation of a horseradish peroxidase enzyme electrode.

In order to prepare biosensing electrodes which respond to hydrogen peroxide, horseradish peroxidase has been adsorbed to colloidal gold sols and electrodes prepared by deposition of these enzyme-gold sols onto glassy carbon using three methods: evaporation, electrodeposition and electrolyte deposition. In the latter method the enzyme-gold sol is applied to the surface of a glassy carbon disk electrode followed by an equal volume of 2 mM CaCl2. The electrolyte causes the sol to precipitate on the electrode surface, producing an immobilized enzyme electrode. Satisfactory electrodes which gave an electrochemical response to hydrogen peroxide in the presence of the electron transfer mediator ferrocenecarboxylic acid were produced by all three methods. Evaporation of horseradish peroxidase-gold sols produced electrodes with the best reproducibility and the widest linear amperometric response range. These electrodes can also easily be stored in a dry state. Although not as good as evaporation, electrodeposition also produced satisfactory electrodes. Electro-deposition provides the added advantage that it lends itself to the preparation of multi-enzyme/multi-analyte electrodes by the adsorption of different enzymes to separate gold sols, followed by sequential electrodeposition onto discrete areas of a multichannel electrode.     

Comparative effects of acetylene and ethylene gas on initiation of banana ripening

Bananas were exposed to acetylene or ethylene at 0·01, 0·1 and 1 ml/litre, under high humidity, for 24 h at 18 °C. They were then transferred to an atmosphere of air alone for a further 4 days and during this period the respiration rate of three fruit from each treatment was measured. Ripeness was then assessed by colour score and soluble solids content. All levels of ethylene initiated ripening. Treatment with ethylene induced a climacteric rise in respiration, an increase in the soluble solids content of the pulp and degreening of the peel. All levels of acetylene, except 0·01 ml/litre, induced a climacteric rise in respiration. Fruit treated with acetylene at 1 ml/litre had a similar colour score and soluble solids content to those ripened by exposure to ethylene. Fruits treated with acetylene at 0·1 ml/litre had a lower soluble solids content and their peel remained green. Treatment with acetylene at 0·01 ml/litre failed to initiate ripening. Sensory evaluation of fruit ripened by acetylene at 1 ml/litre indicated that the acetylene treated fruit ripened slightly more slowly. When compared at the same stage of ripeness fruits from the two treatments were equally palatable.     

Modeling and analysis of diffusion and reaction in legume nodules

Diffusion of gases through legume nodules is important for nitrogen fixation. A mathematical model is presented for diffusion and enzymatic reaction for legume nodules with a reactive core and an inert shell. The transient model is solved numerically for spherical geometry for acetylene reduction by nitrogenase enzyme. The results are used to estimate the diffusivities of acetylene and ethylene in the nodules by comparing predicted and experimental lag times. The experimental results are also analyzed using an effectiveness factor plot for spherical nodules with inert shells and reactive cores. The results show that the diffusivities are slightly higher than those for acetylene and ethylene in water because of some contribution of gas phase diffusion. Applications to oxygen diffusion through nodule tissue are suggested.     

Preserved enzymatic activity of glucose oxidase immobilized on unmodified electrodes for glucose detection

Glucose sensing electrodes have been realized by immobilizing glucose oxidase (GOx) on unmodified edge plane of highly oriented pyrolytic graphite (epHOPG) and the native oxide of heavily doped silicon (SiO2/Si). Both kinds of electrode show direct interfacial electron transfer due to the redox process of the immobilized GOx. The measured formal potential of the redox process agrees with that of the native enzyme, suggesting that the immobilized GOx has retained its enzymatic activity. The electron transfer rates of the GOx immobilized electrode are 2s(-1) for GOx/epHOPG electrode and 7.9s(-1) for GOx/SiO2/Si electrode, which are greater than those for which GOx is immobilized on modified electrodes, probably due to the fact that the enzyme makes direct contact to electrode surface. The preservation of the enzymatic activity of the immobilized GOx has been confirmed by observing the response of the GOx/epHOPG and GOx/SiO2/Si electrodes to glucose with a detection limit of 0.050 mM. The response signals the catalyzed oxidation of glucose and, therefore, confirms that the immobilized GOx retained its enzymatic activity. The properties of the electrode as a glucose sensor are presented.