Pyrroloquinoline Quinone-Dependent Enzymatic Bioanode: Incorporation of the Substituted Polyaniline Conducting Polymer as a Mediator

One of the main technological issues with enzymatic biofuel cells and biosensors is improving the electron transfer between the enzyme and the current collector to improve current densities. In this study, we show the use of a conducting polymer to mediate pyrroloquinoline quinone-dependent enzymatic bioelectrocatalysis. A self-doped polyaniline (PANi) film is electropolymerized on a Toray carbon paper electrode surface to covalently bond enzymes to this three-dimensional interface. Sulfonic acid groups are introduced into the PANi backbone structure to increase the polymer conductivity at neutral pH via a self-doping process, and the carboxyl groups can be activated to covalently bond to enzymes. The electropolymerization of 2-methoxyaniline-5-sulfonic acid and 3-aminobenzoic acid is optimized with respect to the rate of the bioelectrocatalytic conversion of enzyme substrates. Comparing this PANi conducting copolymer enzyme immobilization technique with the hydrophobically modified Nafion encapsulation-based enzyme immobilization method showed a 9.8-fold increase in current density

Enzymatic Biofuel Cell for Oxidation of Glucose to CO₂

Glucose has been widely studied as a fuel in biofuel cells because it not only is abundant in nature and in the bloodstream but also demonstrates low volatility, is nontoxic, and is inexpensive. Those qualities coupled with its relatively high energy density qualify glucose as a promising fuel. However, one key to efficient use of this substrate as fuel is the ability to oxidize glucose to CO₂ and convert, more efficiently, the chemical energy released upon the redox reactions to electrical power. Most glucose biofuel cells in literature only oxidize glucose to gluconolactone. In this paper, we report the development of a six-enzyme cascade bioanode containing pyrroloquinoline quinone-dependent enzymes extracted from Gluconobacter sp., aldolase from Sulfolobus solfataricus and oxalate oxidase from barley to sequentially oxidize glucose to carbon dioxide through a synthetic minimal metabolic pathway. This bioanode is also capable of performing direct electron transfer to carbon electrode surfaces and eliminates the need for mediators

Mitochondrial Inner Membrane Biomimic for the Investigation of Electron Transport Chain Supercomplex Bioelectrocatalysis

Researchers have proposed that the efficiency of the electron transport chain is due to the synergy among complexes I, III, and IV in the membrane. In this paper, the enzymes of the supercomplex were isolated together, reconstituted into lipids that mimic the inner membrane of mitochondria, and immobilized in a tethered lipid bilayer on a gold electrode. The supercomplex enzymes retained their activity with the addition of their substrates and were inhibited by their respective toxins. The bioelectrocatalytic studies indicate the interdependence of the activity of the different complexes in the bioelectrocatalysis of the electron transport chain supercomplex. These fundamental studies provide a starting point to consider the use of supercomplexes and enzyme cascades for bioenergy conversion applications and biosensing through the regulation of the activity by inhibition

Greener Method to a Manganese Oxygen Reduction Reaction Electrocatalyst: Anion Electrolyte Effects on Electrocatalytic Performance

Efforts to reduce the cost of production and reduce hazards associated with catalyst production, as well as improve catalytic performance of fuel cells, is increasingly gaining attention in chemistry, materials science, and chemical engineering. Costs, particularly of the catalyst system, are incurred in each step of production, including raw materials and their processing, catalyst preparation, and immobilization on electrodes. Here is described a low-temperature neutral pH method of electrodepositing a manganese oxygen-reducing electrocatalyst for alkaline fuel cell systems. The analysis emphasizes the effects of anions used during the deposition process and their effect on catalytic performance

Phenyl Acrylate-Based Cross-Linked Anion Exchange Membranes for Non-aqueous Redox Flow Batteries

Redox flow batteries (RFBs) are of recent interest to store harvested renewable energy for improving grid reliability and utilization. In this study, we synthesized and characterized a series of phenyl acrylate-based UV-cross-linked anion exchange membranes (AEMs) and explored the performance of these AEMs in a model non-aqueous RFB under model conditions. Infrared spectroscopy was utilized to confirm the incorporation of ion carriers in the phenyl acrylate backbone. The electrochemical performance was compared with the commercial Fumasep membrane Fuma-375 based on high stability in non-aqueous solvents, high permeability to the charge-carrying ion, low resistance, low crossover of the redox-active molecules, and low cost. Our results show 55% total capacity retention through 1000 charge/discharge cycles because of low crossover as compared to the Fumasep commercial membrane which retained only 28% capacity. This result is promising in understanding and developing next-generation AEMs for non-aqueous RFBs and other electrochemical systems utilizing organic solvents

Bioelectrocatalytic Oxidation of Glucose in CNT Impregnated Hydrogels: Advantages of Synthetic Enzymatic Metabolon Formation

Enzymatic biofuel cells and bioelectrochemical sensors are often limited in performance because of their inability to utilize all of the energy confined in chemical bonds of complex molecules. Multi-enzyme cascade catalysis provides a means to remedy this limitation, but efficiencies of such electrodes can be further enhanced by improving interenzyme substrate mass transport. This consideration is demonstrated to be advantageous in biological systems, as displayed by nearly ubiquitous organization of sequential enzymes in natural metabolic pathways. This sequential organization, termed a metabolon, is examined in this work for a two-enzyme pentose phosphate pathway bioelectrode for the oxidation of glucose. This two-enzyme electrode is compared with a single enzyme, glucose dehydrogenase, and demonstrates increased performance. In addition, increases in efficiency are demonstrated through the creation of a synthetic two-enzyme metabolon versus randomly suspended enzymes immobilized within a hydrogel matrix

Simplifying Enzymatic Biofuel Cells: Immobilized Naphthoquinone as a Biocathodic Orientational Moiety and Bioanodic Electron Mediator

An elegant method to perform bioelectocatalysis with different oxidoreductases at the cathode and at the anode of an enzymatic biofuel cell is presented. Noncovalent functionalization of multiwalled carbon nanotubes (MWCNTs) was accomplished via π–π interactions of pyrene derivatives. 1-[Bis­(2-naphthoquinonyl)­aminomethyl]­pyrene was synthesized and successfully immobilized on MWCNTs. The incorporation of the quinone-modified MWCNTs within enzymatic bioelectrocatalytic applications was evaluated. The hydrophobic nature of the naphthoquinone aided orientation of laccase and bilirubin oxidase toward the electrode, which enhanced their ability to undergo the direct bioelectrocatalysis of oxygen. In contrast, the electrochemical properties of the quinone were used at the bioanode to mediate electrons from the bioelectrocatalytic oxidation of glucose by pyrroloquinoline quinone-dependent glucose dehydrogenase. This method demonstrates how the smart modification of MWCNTs can develop materials, which can be used simultaneously at both electrodes of enzymatic biofuel cells

Metabolon Catalyzed Pyruvate/Air Biofuel Cell

Metabolon Catalyzed Pyruvate/Air Biofuel Cel

Enhanced Bioelectrocatalysis of <i>Shewanella oneidensis</i> MR‑1 by a Naphthoquinone Redox Polymer

Shewanella oneidensis MR-1 is the model organism used in microbial fuel cells (MFCs). A great deal of research has focused on this bacterium to improve extracellular electron transfer (EET) and subsequently the power output in MFCs. Here, we report on the enhanced bioelectrocatalysis of S. oneidensis MR-1 by using a naphthoquinone redox polymer (NQ-LPEI) on a modified carbon felt electrode. A maximum anodic current of 3.70 ± 0.40 A m^–2 is obtained in a three-electrode setup, a value 15 times higher than that obtained for an anode that did not contain the NQ-LPEI redox polymer (0.24 ± 0.05 A m^–2). Additionally, a maximum power output of 0.53 ± 0.02 W m^–2 was obtained in single-chamber MFCs where the NQ-LPEI modified anode was utilized. The power output was significantly higher than that obtained for MFCs with unmodified anodes (0.19 ± 0.05 W m^–2). These findings suggest that NQ-LPEI could be used with known electrogenic microorganisms to further improve the performances of MFCs

Confocal Raman Microscopy for <i>in Situ</i> Measurement of Phospholipid–Water Partitioning into Model Phospholipid Bilayers within Individual Chromatographic Particles

The phospholipid–water partition coefficient is a commonly measured parameter that correlates with drug efficacy, small-molecule toxicity, and accumulation of molecules in biological systems in the environment. Despite the utility of this parameter, methods for measuring phospholipid–water partition coefficients are limited. This is due to the difficulty of making quantitative measurements in vesicle membranes or supported phospholipid bilayers, both of which are small-volume phases that challenge the sensitivity of many analytical techniques. In this work, we employ <i>in situ</i> confocal Raman microscopy to probe the partitioning of a model membrane-active compound, 2-(4-isobutylphenyl) propionic acid or ibuprofen, into both hybrid- and supported-phospholipid bilayers deposited on the pore walls of individual chromatographic particles. The large surface-area-to-volume ratio of chromatographic silica allows interrogation of a significant lipid bilayer area within a very small volume. The local phospholipid concentration within a confocal probe volume inside the particle can be as high as 0.5 M, which overcomes the sensitivity limitations of making measurements in the limited membrane areas of single vesicles or planar supported bilayers. Quantitative determination of ibuprofen partitioning is achieved by using the phospholipid acyl-chains of the within-particle bilayer as an internal standard. This approach is tested for measurements of pH-dependent partitioning of ibuprofen into both hybrid-lipid and supported-lipid bilayers within silica particles, and the results are compared with octanol–water partitioning and with partitioning into individual optically trapped phospholipid vesicle membranes. Additionally, the impact of ibuprofen partitioning on bilayer structure is evaluated for both within-particle model membranes and compared with the structural impacts of partitioning into vesicle lipid bilayers