Assembly of an improved hybrid cascade system for complete ethylene glycol oxidation: Enhanced catalytic performance for an enzymatic biofuel cell.

We report an Enzymatic Fuel Cell (EFC) combining an enzyme that can cleave carbon-carbon bonds (oxalate oxidase (OxOx)) with an organic catalyst (Pyrene-TEMPO (TEMPO = 2,2,6,6-tetramethyl piperidinyl-N-oxyl)) immobilized on the surface of modified carboxylated multi-walled carbon nanotubes (MWCNT-COOH). This combination gave a hybrid bi-catalyst electrode for complete ethylene glycol (EG) oxidation. The hybrid electrode provided ninefold enhanced catalytic activity (0.17 ± 6 × 10-3 mA cm-2) in the presence of EG as compared to the electrode in the absence of EG (0.018 ± 3 × 10-5 mA cm-2), indicating that the enzyme combined with the organic catalyst improved energy generation through deep EG electrooxidation. Electrochemical impedance spectroscopy reveals that the addition of the enzyme in the electrode containing MWCNT-COOH-Pyrene-TEMPO increased the charge transfer resistance (Rct) and the capacitance of the double layer. Long-term electrolysis for 15 h showed that the hybrid electrode presented outstanding current density and stability. The EG oxidation products were identified and quantified by high-performance liquid chromatography (HPLC-UV/RID). The results confirmed complete EG oxidation in the presence of CO2 in the solution, allowing 10 electrons to be collected from the fuel. Overall, this study illustrates the development of a simple and improved hybrid bi-catalyst electrode for promising applications in small electronic devices.

Carbon Nanotube PtSn Nanoparticles for Enhanced Complete Biocatalytic Oxidation of Ethylene Glycol in Biofuel Cells.

We report a hybrid catalytic system containing metallic PtSn nanoparticles deposited on multiwalled carbon nanotubes (Pt65Sn35/MWCNTs), prepared by the microwave-assisted method, coupled to the enzyme oxalate oxidase (OxOx) for complete ethylene glycol (EG) electrooxidation. Pt65Sn35/MWCNTs, without OxOx, showed good electrochemical activity toward EG oxidation and all the byproducts. Pt65Sn35/MWCNTs cleaved the glyoxilic acid C-C bond, producing CO2 and formic acid, which was further oxidized at the electrode. Concerning EG oxidation, the catalytic activity of the hybrid system (Pt65Sn35/MWCNTs+OxOx) was twice the catalytic activity of Pt65Sn35/MWCNTs. Long-term electrolysis revealed that Pt65Sn35/MWCNTs+OxOx was much more active for EG oxidation than Pt65Sn35/MWCNTs: the charge increased by 65%. The chromatographic results proved that Pt65Sn35/MWCNTs+OxOx collected all of the 10 electrons per molecule of the fuel and was able to catalyze EG oxidation to CO2 due to the associative oxidation between the metallic nanoparticles and the enzymatic pathway. Overall, Pt65Sn35/MWCNTs+OxOx proved to be a promising system to enhance the development of enzymatic biofuel cells for further application in the bioelectrochemistry field.

Ethanol Biofuel Cells: Hybrid Catalytic Cascades as a Tool for Biosensor Devices.

Biofuel cells use chemical reactions and biological catalysts (enzymes or microorganisms) to produce electrical energy, providing clean and renewable energy. Enzymatic biofuel cells (EBFCs) have promising characteristics and potential applications as an alternative energy source for low-power electronic devices. Over the last decade, researchers have focused on enhancing the electrocatalytic activity of biosystems and on increasing energy generation and electronic conductivity. Self-powered biosensors can use EBFCs while eliminating the need for an external power source. This review details improvements in EBFC and catalyst arrangements that will help to achieve complete substrate oxidation and to increase the number of collected electrons. It also describes how analytical techniques can be employed to follow the intermediates between the enzymes within the enzymatic cascade. We aim to demonstrate how a high-performance self-powered sensor design based on EBFCs developed for ethanol detection can be adapted and implemented in power devices for biosensing applications.

Assessment of semi-permanent hair dyes in wash water from beauty salons by liquid chromatography-tandem mass spectrometry-selected reaction monitoring (LC-MS/MS-SRM).

Herein, we present an approach for the analytical determination and quantification of semi-permanent hair dyes in wash water samples released during washing of dyed hair employing a liquid chromatography-tandem mass spectrometry-selected reaction monitoring (LC-MS/MS-SRM) method with electrospray ionization detection. Specifically, Basic Blue 99 (BB 99), Basic Brown 16 (BB 16), Basic Red 76 (BR 76), Basic Yellow 57 (BY 57) and Acid Violet 43 (AV 43) are hair dyes with properties known to be harmful to human health and the environment. The hair dyes are present in commercial formulation and are discharged into the effluents without fully effective treatment. The detection and quantification by the LC-MS/MS technique show a linear relationship for each studied hair dye in the concentration range from 1 to 200 ng mL-1 in aqueous solution. The limits of detection and quantification were found from 0.66 to 20 ng mL-1 and from 2.0 to 63 ng mL-1, respectively, values that are compatible with the level required in wash water analysis. The method was applied in samples collected from 5 successive washings of hair dyed with a commercial formulation using the established procedure. BB 99 and BY 57 dyes have lower fixation on the scalp and hair, showing 866 ng mL-1 and 145 ng mL-1 release on the first day of washing, respectively. The accumulation of dye and slow release after washing can lead to future problems for both the environment and living organisms.

Enhanced electrochemical oxidation of ethanol using a hybrid catalyst cascade architecture containing pyrene-TEMPO, oxalate decarboxylase and carboxylated multi-walled carbon nanotube.

The work presented herein demonstrates a hybrid bi-catalytic architecture for the complete electrochemical oxidation of ethanol. The new catalytic system contains pyrene-TEMPO (TEMPO = 2,2,6,6-tetramethylpiperidinyl-N-oxyl) immobilized on the surface of carboxylated multi-walled carbon nanotubes (MWCNT-COOH), and oxalate decarboxylase enzyme (OxDc) immobilized onto a carbon cloth electrode. Electrolysis revealed a stable amperometric curve and an excellent current density value over a duration of 10 h. In addition, the hybrid system immobilized on the carbon electrode exhibits outstanding stability after electrolysis. Nuclear magnetic resonance (NMR) and gas chromatography (GC) demonstrate that the hybrid electrode system is able to oxidize ethanol to CO2 after 10 h of electrolysis. Overall, this study illustrates the enhancement of an enzymatic biofuel cell through the hybrid multi-catalytic systems, which exhibit high oxidation rates for all substrates involved in complete ethanol oxidation, enabling the collection of up to 12 electrons per molecule of ethanol.

Bioinspired architecture of a hybrid bifunctional enzymatic/organic electrocatalyst for complete ethanol oxidation.

Electrochemical ethanol oxidation was performed at an innovative hybrid architecture electrode containing TEMPO-modified linear poly(ethylenimine) (LPEI) and oxalate oxidase (OxOx) immobilized on carboxylated multi-walled carbon nanotubes (MWCNT-COOH). On the basis of chromatographic results, the catalytic hybrid electrode system completely oxidized ethanol to CO2 after 12 h of electrolysis. The fact that the developed system can catalyze ethanol electrooxidation at a carbon electrode confirms that organic oxidation catalysts combined with enzymatic catalysts allow up to 12 electrons to be collected per fuel molecule. The Faradaic efficiency of the hybrid system investigated herein lies above 87%. The combination of OxOx with TEMPO-LPEI to obtain a novel hybrid anode to oxidize ethanol to carbon dioxide constitutes a simple methodology with useful application in the development of enzymatic biofuel cells.

Hybrid catalyst cascade architecture enhancement for complete ethanol electrochemical oxidation.

MWCNT-COOH, TEMPO-modified linear poly(ethylenimine), and alcohol (ADH) and aldehyde (AldDH) dehydrogenase immobilization on electrode surfaces yields a hybrid, tri-catalytic architecture that can catalyze complete ethanol electro-oxidation. The chromatographic results obtained for the tri-catalytic hybrid electrode system show that ethanol is totally oxidized to CO2 after 12 h of electrolysis, confirming that organic oxidation catalysts combined with enzymatic catalysts enable collection of up to 12 electrons from ethanol. The Faradaic efficiency lies above 60% for all of the electrode systems investigated herein. Overall, this study illustrates that surface-immobilized, polymer hydrogel-based hybrid multi-catalytic systems exhibit high oxidation rates and constitute a simple methodology with useful application in the development of enzymatic biofuel cells.

Biotransformation of disperse dyes using nitroreductase immobilized on magnetic particles modified with tosyl group: Identification of products by LC-MS-MS and theoretical studies conducted with DNA.

The present work evaluates the action of nitroreductase enzyme immobilized on Tosylactivated magnetic particles (MP-Tosyl) on three disperse dyes which contain nitro and azo groups. The dyes included Disperse Red 73 (DR 73), Disperse Red 78 (DR 78), and Disperse Red 167 (DR 167). The use of a magnet enabled the rapid and easy removal of the immobilized enzyme after biotransformation; this facilitated the identification of the products generated using high-performance liquid chromatography with diode array detector (HPLC-DAD) and mass spectrometry (LC-MS/MS). The main products formed by the in vitro biotransformation were identified as the product of nitro group reduction to the correspondent amine groups, which were denoted as follows: 50% of 2-(2-(4-((2-cyanoethyl)(ethyl)amino)phenyl)hydrazinyl)-5-nitrobenzonitrile, 98% of 3-((4-((4-amino-2-chlorophenyl) diazenyl)phenyl) (ethyl)amino)propanenitrile and 99% of (3-acetamido-4 - ((4-amino-2-chlorophenyl) diazenyl) phenyl) azanediyl) bis (ethane-2,1-diyl) for DR 73, DR 78 and DR 167, respectively. Based on the docking studies, the dyes investigated were found to be biotransformed by nitroreductase enzyme due to their favorable interaction with the active site of the enzyme. Theoretical results show that DR73 dye exhibits a relatively lower rate of degradation; this is attributed to the cyanide substituent which affects the electron density of the azo group. The docking studies also indicate that all the dyes presented significant reactivity towards DNA. However, Disperse Red 73 was found to exhibit a substantially higher reactivity compared to the other dyes; this implies that the dye possesses a relatively higher mutagenic power. The docking results also show that DR 73, DR 78 and DR 167 may be harmful to both humans and the environment, since the mutagenicity of nitro compounds is associated with the products formed during the reduction of nitro groups. These products can interact with biomolecules, including DNA, causing toxic and mutagenic effects.

Influence of auxochrome group in disperse dyes bearing azo groups as chromophore center in the biotransformation and molecular docking prediction by reductase enzyme: Implications and assessment for environmental toxicity of xenobiotics.

Synthetic azo dyes have increasingly become a matter of great concern as a result of the genotoxic and mutagenic potential of the products derived from azo dye biotransformation. This work evaluates the manner in which reducing enzymes produced by Escherichia coli (E. coli) act on three disperse dyes bearing azo groups, namely Disperse Red 73 (DR 73), Disperse Red 78 (DR 78), and Disperse Red 167 (DR 167). UV-Vis spectrophotometry, high-performance liquid chromatography with diode array detector (HPLC-DAD), and liquid chromatography mass spectrometry (LC-MS/MS) were applied towards the identification of the main products. Seven days of incubation of the azo dyes with the tested enzymes yielded a completely bleached solution. 3-4-Aminophenyl-ethyl-amino-propanitrile was detected following the biotransformation of both DR 73 and DR 78. 4-Nitroaniline and 2-chloro-4-nitroaniline were detected upon the biotransformation of DR 73 and DR 78, respectively. The main products derived from the biotransformation of DR 167 were dimethyl 3,3'-3-acetamido-4-aminophenyl-azanedyl-dipropanoate and 2-chloro-4-nitroaniline. The results imply that DR 73 lost the CN- substituent during the biotransformation. Furthermore, theoretical calculations were also carried out aiming at evaluating the interaction and reactivity of these compounds with DNA. Taken together, the results indicate that DR 73, DR 78, and DR 167 pose health risks and serious threats to both human beings and the environment at large as their biotransformation produces harmful compounds such as amines, which have been widely condemned by the International Agency for Research on Cancer.

Identification of biotransformation products of disperse dyes with rat liver microsomes by LC-MS/MS and theoretical studies with DNA: Structure-mutagenicity relationship using Salmonella/microsome assay.

Azo dyes are known as a group of substances with DNA damage potential that depend on the nature and number of azo groups connected to aromatic rings (benzene and naphthalene), chemical properties, e.g. solubility and reactive functional groups, which significantly affect their toxicological and ecological risks. In this paper, we used in vitro models to evaluate the metabolism of selected textile dyes: Disperse Red 73 (DR 73), Disperse Red 78 (DR 78) and Disperse Red 167 (DR 167). To evaluate the mutagenic potential of the textile dyes, the Salmonella mutagenicity assay (Ames test) with strains TA 98 and TA 100 in the presence and absence of the exogenous metabolic system (S9) was used. DR73 was considered the most mutagenic compound, inducing both replacement base pairs (TA 100) and also changing frameshift (TA 98) mutations that are reduced in the presence of the S9 mixture. Furthermore, we used rat liver microsomes in the same experimental conditions of the S9 mixture to metabolize the dyes and the resultant solutions were analyzed using a liquid chromatography coupled to a quadrupole linear ion trap mass spectrometry (LC-MS/MS) to investigate the metabolites formed by the in vitro biotransformation. Based on this experiment, we detected and identified two biotransformation products for each textile dye substrate analyzed. Furthermore, to evaluate the interaction and reactivity of these compounds with DNA, theoretical calculations were also carried out. The results showed that the chemical reaction occurred preferentially at the azo group and the nitro group, indicating that there was a reduction in these groups by the CYP P450 enzymes presented in the rat microsomal medium. Our results clearly demonstrated that the reduction of these dyes by biological systems is a great environmental concern due to increased genotoxicity for the body of living beings, especially for humans.

Assessment of molecularly imprinted polymers (MIPs) in the preconcentration of disperse red 73 dye prior to photoelectrocatalytic treatment.

Magnetic molecularly imprinted polymers (MMIPs) have become a research hotspot due to their two important characteristics: target recognition and magnetic separation. This paper presents the preparation, characterization, and optimization of an MMIP for the preconcentration of disperse red 73 dye (DR73) and its subsequent efficient degradation by photoelectrocatalytic treatment. The MMIPs were characterized by scanning electron microscopy (SEM), which revealed homogeneous distribution of the particles. Excellent encapsulation of magnetite was confirmed by transmission electron microscopy (TEM). A study of dye binding showed that the dye was retained more selectively in the MIP, compared to the NIP. The release of DR73 from the imprinted polymers into methanol and acetic acid was analyzed by UV-Vis spectrophotometry. The extracts showed higher absorbance values for MMIP, compared to MNIP, confirming greater adsorption of dye in the MMIP material. The extracts were then subjected to photoelectrocatalytic treatment. LC-MS/MS analysis following this treatment showed that the dye was almost completely degraded. Hence, the combination of MMIP extraction and photoelectrocatalysis offers an alternative way of selectively removing an organic contaminant, prior to proceeding with its complete degradation.