A lysine dehydrogenase-based electrode for biosensing of L-lysine.

An amperometric biosensor for L-lysine based on the recently isolated enzyme lysine dehydrogenase is described. Immobilization of the enzyme onto a platinum electrode is achieved via entrapment within a gelatin support on a cellulose membrane. Anodic detection (at 0.4 V vs. Ag/AgCl) is facilitated by the presence of a redox-mediating ferricyanide ion. The effect of experimental variables such as pH, enzyme loading, applied potential, cofactor and mediator concentrations were evaluated in order to optimize the analytical performance. A detection limit of 7 x 10(-8) M, and linearity up to 7 x 10(-4) M are reported. The fast response permits adaptation for flow injection operation with good precision (RSD = 1.9%) and high sample throughout (40 samples per hour). The high specificity offered by this new enzyme is indicated by the lack of interference by other L-amino acids, alcohols or carbohydrates.     

Strategies to extend the lifetime of bioelectrochemical enzyme electrodes for biosensing and biofuel cell applications

Enzymes are powerful catalysts for biosensor and biofuel cell electrodes due to their unique substrate specificity. This specificity is defined by the amino acid chain's complex three-dimensional structure based on non-covalent forces, being also responsible for the very limited enzyme lifetime of days to weeks. Many electrochemical applications, however, would benefit from lifetimes over months to years. This mini-review provides a critical overview of strategies and ideas dealing with the problem of short enzyme lifetime, which limits the overall lifetime of bioelectrochemical electrodes. The most common approaches aim to stabilize the enzyme itself. Various immobilization techniques have been used to reduce flexibility of the amino acid chain by introducing covalent or non-covalent binding forces to external molecules. The enzyme can also be stabilized using genetic engineering methods to increase the binding forces within the protein or by optimizing the environment in order to reduce destabilizing interactions. In contrast, renewing the inactivated catalyst decouples overall system lifetime from the limited enzyme lifetime and thereby promises theoretically unlimited electrode lifetimes. Active catalyst can be supplied by exchanging the electrolyte repeatedly. Alternatively, integrated microorganisms can display the enzymes on their surface or secrete them to the electrolyte, allowing unattended power supply for long-term applications.     

A practical method for the analysis of osmotic-and-diffusive energy conversion

A practical method for the study of osmotic- and-diffusive conversion of free energy of solutions with different concentrations is presented. Equations for effective power, dissipative power, total power and energetic efficiency have been derived for fixed membrane systems. These equations allow energetic evaluation of these systems. The significance of the method for biological studies is also suggested.     

Direct electrochemistry of glucose oxidase and biosensing for glucose based on boron-doped carbon nanotubes modified electrode

Due to their unique physicochemical properties, doped carbon nanotubes are now extremely attractive and important nanomaterials in bioanalytical applications. In this work, selecting glucose oxidase (GOD) as a model enzyme, we investigated the direct electrochemistry of GOD based on the B-doped carbon nanotubes/glassy carbon (BCNTs/GC) electrode with cyclic voltammetry. A pair of well-defined, quasi-reversible redox peaks of the immobilized GOD was observed at the BCNTs based enzyme electrode in 0.1M phosphate buffer solution (pH 6.98) by direct electron transfer between the protein and the electrode. As a new platform in glucose analysis, the new glucose biosensor based on the BCNTs/GC electrode has a sensitivity of 111.57 microA mM(-1)cm(-2), a linear range from 0.05 to 0.3mM and a detection limit of 0.01mM (S/N=3). Furthermore, the BCNTs modified electrode exhibits good stability and excellent anti-interferent ability to the commonly co-existed uric acid and ascorbic acid. These indicate that boron-doped carbon nanotubes are the good candidate material for the direct electrochemistry of the redox-active enzyme and the construction of the related enzyme biosensors.     

A structural model of PpoA derived from SAXS-analysis—Implications for substrate conversion

In plants and mammals, oxylipins may be synthesized via multi step processes that consist of dioxygenation and isomerization of the intermediately formed hydroperoxy fatty acid. These processes are typically catalyzed by two distinct enzyme classes: dioxygenases and cytochrome P450 enzymes. In ascomycetes biosynthesis of oxylipins may proceed by a similar two-step pathway. An important difference, however, is that both enzymatic activities may be combined in a single bifunctional enzyme. These types of enzymes are named Psi-factor producing oxygenases (Ppo). Here, the spatial organization of the two domains of PpoA from Aspergillus nidulans was analyzed by small-angle X-ray scattering and the obtained data show that the enzyme exhibits a relatively flat trimeric shape. Atomic structures of the single domains were obtained by template-based structure prediction and docked into the enzyme envelope of the low resolution structure obtained by SAXS. EPR-based distance measurements between the tyrosyl radicals formed in the activated dioxygenase domain of the enzyme supported the trimeric structure obtained from SAXS and the previous assignment of Tyr374 as radical-site in PpoA. Furthermore, two phenylalanine residues in the cytochrome P450 domain were shown to modulate the specificity of hydroperoxy fatty acid rearrangement.     

Immobilization of metallothionein to carbon paste electrode surface via anti-MT antibodies and its use for biosensing of silver

In this paper, heavy metal biosensor based on immobilization of metallothionein (MT) to the surface of carbon paste electrode (CPE) via anti-MT-antibodies is reported. First, the evaluation of MT electroactivity was done. The attention was focused on the capturing of MT to the CPE surface. Antibodies incorporated and mixed into carbon paste were stable; even after two weeks the observed changes in signal height were lower than 5%. Further, the interaction of MT with polyclonal chicken antibodies incorporated in carbon paste electrode was determined by square-wave voltammetry. In the voltammogram, two signals--labelled as cys(MT) and W(a)--were observed. The cys(MT) corresponded to -SH moieties of MT and W(a) corresponded to tryptophan residues of chicken antibodies. Time of interaction (300 s) and MT concentration (125 μg/ml) were optimized to suggest a silver(I) ions biosensor. Biosensor (CPE modified with anti-MT antibody) prepared under the optimized conditions was then used for silver(I) ions detection. The detection limit (3 S/N) for silver(I) ions was estimated as 0.5 nM. The proposed biosensor was tested by detection spiking of silver(I) ions in various water samples (from very pure distilled water to rainwater). Recoveries varied from 74 to 104%.     

N-losses and energy use in a scenario for conversion to organic farming

The aims of organic farming include the recycling of nutrients and organic matter and the minimisation of the environmental impact of agriculture. Reduced nitrogen (N)-losses and energy (E)-use are therefore fundamental objectives of conversion to organic farming. However, the case is not straightforward, and different scenarios for conversion to organic farming might lead to reduced or increased N-losses and E-use. This paper presents a scenario tool that uses a Geographical Information System in association with models for crop rotations, fertilisation practices, N-losses, and E-uses. The scenario tool has been developed within the multidisciplinary research project Land Use and Landscape Development Illustrated with Scenarios (ARLAS). A pilot scenario was carried out, where predicted changes in N-losses and E-uses following conversion to organic farming in areas with special interests in clean groundwater were compared. The N-surplus and E-use were on average reduced by 10 and 54%, respectively. However, these reductions following the predicted changes in crop rotations, livestock densities, and fertilisation practices were not large enough to ensure a statistically significant reduction at the 95% level. We therefore recommend further research in how conversion to organic farming or other changes in the agricultural practice might help to reduce N-surpluses and E-uses. In that context, the presented scenario tool would be useful.     

A review of biomass quality research relevant to the use of poplar and willow for energy conversion

It has been recognized that the chemical and physical properties of biomass feedstocks can play an important role in the efficiency of most energy conversion processes. These properties include the ratio of bark to wood, moisture content, specific gravity, calorific or heating value, and the relative content of extractives, α-cellulose, hemicellulose, and lignin.A review of the literature dealing with the quality of poplar and willow biomass feedstock for energy conversion revealed that considerable variation existed in many of these traits. This variation may make it possible to improve the quality of feedstock through breeding and selection.Little information exists with respect to heritability (both in the broad sense and narrow sense), the genetic correlation between characters, and the presence of genotype-environment interaction. A better understanding of these parameters is essential if the apparent variability is to be used to improve biomass quality.     

Direct electrochemistry and electrocatalysis of hemoglobin on polypyrrole-Fe3O4/dodecyltrimethylammonium bromide-modified carbon paste electrode and its biosensing for hydrogen peroxide

Abstract

A novel hydrogen peroxide (H₂O₂) biosensor was successfully constructed, based on the immobilization of hemoglobin (Hb) on polypyrrole (PPy)-Fe₃O₄ and dodecyltrimethylammonium bromide (DTAB) composite ?lm-modified carbon paste electrodes (CPE). The PPy-Fe₃O₄ composites were synthesized in the suspension solution of Fe₃O₄ nanoparticles via in situ chemical oxidative polymerization under the direction of cationic surfactant cetyl trimethyl ammonium bromide. Spectroscopic and electrochemical examinations illustrated that the PPy-Fe₃O₄/DTAB composites were a biocompatible matrix for immobilizing Hb, which revealed high chemical stability and excellent biocompatibility. The thermodynamic, dynamic, and catalytic performance of the biosensor were analysed using cyclic voltammetry (CV). The results indicated that the PPy-Fe₃O₄/Hb/DTAB/CPE exhibited excellent electrocatalytic activity in the reduction of H₂O₂ with a high sensitivity (104 μA mM^{? 1}). The catalytic reduction currents of H₂O₂ were linearly related to H₂O₂ concentration in the range from 2.5 μM to 60 μM with a detection limit of 0.8 μM (S/N = 3). With such superior characteristics, this biosensor for H₂O₂ can be potentially applied in determination of other reactive oxygen species as well. These results indicated that PPy-Fe₃O₄/DTAB composites are a promising matrix for bioactive molecule immobilization.     

Photoactivation studies of zinc porphyrin-myoglobin system and its application for light-chemical energy conversion

An artificial zinc porphyrin-myoglobin-based photo-chemical energy conversion system, consisting of ZnPP-Mb or ZnPE(1)-Mb as a photosensitizer, NADP(+) as an electron acceptor, and triethanolamine as an electron donor, has been constructed to mimic photosystem I. The photoirradiated product is able to reduce a single-electron acceptor protein cytochrome c, but cannot catalyze the two-electron reduction of acetaldehyde by alcohol dehydrogenase, thus demonstrating a single electron transfer mechanism. Furthermore, the artificial system can bifunctionally promote oxidoredox reactions, depending on the presence or absence of a sacrificial electron donor, thus suggesting its potential application in electrochemical regeneration steps involved in chemical transformation and/or energy conversion.     

Challenges and opportunities for photochemists on the verge of solar energy conversion.

Has photochemistry missed the boat on solar energy conversion? Certainly not, but it is time to reach out and make a difference if we do not want to have to choose between feeding our families or our thirst for fuel. Compared to other initiatives, such as biofuels or nuclear fusion, direct conversion of solar energy into electricity or fuels is lagging behind in terms of funding, and this is slowing progress on overcoming critical bottlenecks. This perspective outlines some of the key fundamental issues in solar energy conversion based on organic photovoltaic devices or artificial photosynthesis where being a photochemist can make a difference.     

A specific enzyme electrode for l-glutamate-development and application

A biosensor for the specific determination of l-glutamate has been developed using l-glutamate oxidase in combination with a hydrogen peroxide indicating electrode. The biosensor response depends linearly on l-glutamate concentration between 0.001 and 1.0 mM. The measuring time is 2 min. The sensor is stable for more than 10 days during which more than 500 assays can be performed. The sensor has been applied to l-glutamate determination in liquid seasonings. Furthermore, transaminase activities have been determined by their catalytic l-glutamate production from alpha-ketoglutarate and l-alanine or l-aspartate. Also, the coimmobilization of glutaminase yielded a bienzyme electrode sensitive to l-glutamine.     

Extraction and conversion pathways for microalgae to biodiesel: a review focused on energy consumption

Numerous life cycle analysis (LCA) studies of microalgae to fuel have been released over the past 3 years in an attempt to determine the environmental sustainability of this novel concept. Despite numerous issues with these LCA studies, they have highlighted that cultivation and dewatering/drying for extraction and conversion are major energy sinks within the process. This paper provides a critical review of extraction and conversion methods discussed in literature and under commercial investigation. The basis of this review is energy consumption, with its purpose to highlight methods that deserve further attention in research and development. This review concludes with an energetic assessment of four conversion processes including pulsed electric field-assisted extraction followed by transesterification, in situ acid catalysed esterification of dry biomass, in situ hydrolysis and esterification of wet biomass and hydrothermal liquefaction. The analysis highlighted that energetically feasible methods do exist for the conversion of microalgal biomass to fuel; however, all require further research to be applied at commercial scale.     

Optimum energy intake and gross efficiency of energy conversion for brown trout, Salmo trutta, feeding on invertebrates or fish

1. The chief objectives were to determine the daily optimum energy intake ( C OPT cal day−1) for growth and the gross efficiency ( K G%) for converting energy intake into growth for brown trout, Salmo trutta . Energy budgets for individual fish were obtained from experiments with 292 trout (initial live weight 1–318 g) bred from wild parents, and kept at five constant temperatures (5, 10, 13, 15, 18 °C) and 100% oxygen saturation. Most trout (252) were fed over a period of 42 days on a fixed ration of shrimps, Gammarus pulex , the ration levels varying between zero and maximum, but 40 of the larger trout were fed to satiation on freshly-killed sticklebacks ( Gasterosteus aculeatus ).
2. Energetics models developed in earlier studies on the same data were summarized briefly and were used to predict the relationship between the change in the total energy content of a trout ( C G cal day−1) and its energy intake ( C IN cal day−1), and hence to estimate C OPT. The models were also used to predict the relationship between K G and C IN. In both comparisons, there was good agreement between observed values from the experiments and expected mean values predicted from the models. For trout feeding on invertebrates, C OPT lay closer to the maximum, rather than the maintenance, energy intake. When the diet changed from invertebrates to fish, there was a marked increase in C IN, C G and K G.
3. For trout feeding on invertebrates, K G exceeded 30% within 7–11 °C, with a maximum K G of 31.8% at 8.9 °C. For piscivorous trout, K G exceeded 30% within 4–16 °C and 40% within 6.5–12 °C, with a maximum K G of 41.8% at 9.3 °C. These differences were discussed in relation to the results of previous workers, and the models used in the present study provided a method of exploring the limitations of the ' K -line' hypothesis for the relationship between K G and C IN.     

Photothermal beam deflection: a new method for in vivo measurements of thermal energy dissipation and photochemical energy conversion in intact leaves

A novel photosynthetic technique, photothermal deflection spectroscopy, is presented which is based on the mirage effect and allows the rapid measurement of thermal deactivation of excited pigments in leaf samples placed in an open cell. Modulated heat emission from leaves illuminated with intensity-modulated light was measured via the detection of the periodic deflection of a laser beam parallel to the sample surface. Photothermal deflection signals can be monitored in vivo in leaves placed in various, liquid or gaseous, environments with a satisfactory signal-to-noise ratio close to 60–80 (in distilled water) at low modulation frequencies (below 50 Hz). Using this new and simple photothermal method, it was possible to easily obtain useful information on the leaf photochemical activity and its light-saturation characteristics under normal or stress conditions, suggesting that in vivo deflection signals could be used for assaying the photosynthetic state of health of crop plants. The beam deflection method presented in this paper appears to be a potentially useful photosynthetic tool complementary to the related photoacoustic technique.Abbreviations DCMU dichlorophenyldimethylurea - PD photothermal deflection - PL photochemical energy storage - S/N ratio signal-to-noise ratio     

Vibrational assignments and derived potential energy distributions for tri- and difluoromethyl ketene by density functional calculations

The structures of 3,3,3-trifluoromethyl ketene and 3,3-difluoromethyl ketene were studied by utilizing ab initio calculations with the 6-311++G** basis set at the (B3LYP) Density Functional level. Full optimization was performed for both molecules in their ground and transition states. Energy optimization of the systems under investigation shows that trifluoromethyl ketene exists only in the cis conformation (fluorine atom eclipses the ketene group). Difluoromethyl ketene was predicted to have two stable conformations: the cis (hydrogen atom eclipses the ketene group) and the gauche (fluorine atom eclipses the ketene group) form. The conformational stability of the molecules was found to be governed mainly by electrostatic and molecular orbital interactions. The vibrational frequencies were computed and complete assignments were provided on the basis of normal coordinate calculations and comparison with similar molecules. The potential energy distributions (PED) among symmetry coordinates were derived for the stable conformations of the two molecules.     

A modified active Brownian dynamics model using asymmetric energy conversion and its application to the molecular motor system

We consider a modified energy depot model in the overdamped limit using an asymmetric energy conversion rate, which consists of linear and quadratic terms in an active particle’s velocity. In order to analyze our model, we adopt a system of molecular motors on a microtubule and employ a flashing ratchet potential synchronized to a stochastic energy supply. By performing an active Brownian dynamics simulation, we investigate effects of the active force, thermal noise, external load, and energy-supply rate. Our model yields the stepping and stalling behaviors of the conventional molecular motor. The active force is found to facilitate the forwardly processive stepping motion, while the thermal noise reduces the stall force by enhancing relatively the backward stepping motion under external loads. The stall force in our model decreases as the energy-supply rate is decreased. Hence, assuming the Michaelis–Menten relation between the energy-supply rate and the an ATP concentration, our model describes ATP-dependent stall force in contrast to kinesin-1.