Ionic Liquids Effect on the Stability of 17-Electron Cation Product of the Electrochemical Oxidation of Cymantrene

The oxidative electrochemistry of cymantrene, CpMn(CO)3 (1; Cp = [η5-C5H5]–), was examined in ionic liquids (ILs) composed of anions of varying Lewis base properties. It was observed that the cyclic voltammetric responses strongly depended on the nucleophilic properties of the IL anion. Still, all observations are consistent with the initial formation of 1+ followed by an attack from the IL anion. In bis(trifluoromethylsulfonyl)amide [NTf2]-based ILs, the process shows close to ideal electrochemical reversibility as the reaction between 1+ and [NTf2] anion is very slow. On the other hand, in tetrafluoroborate and trifluoromethanesulfonate-based IL, the oxidation of 1 shows different levels of electrochemical reversibility with a marked sign of anion attack to 1+. In contrast, 1 exhibits an irreversible oxidation process in hexafluorophosphate-based IL. The reaction rate constants for the interaction of 1+ with the different IL anions were estimated by fitting the experimental data to digital simulations of the proposed mechanism. Besides, the use of [NTf2]-based ILs as a supporting electrolyte in CH2Cl2 was also examined. The oxidation process of 1 shows a close to ideal electrochemical reversibility but low to non-chemical reversibility. This study illustrates the wide range of electrochemical environments available with ILs and demonstrates their limited utility for investigating the redox properties of metal carbonyl compounds. It also intends to warn the reader on how the IL media may influence an electrochemical study if care is not exercised

Application of ionic liquids in electrochemical sensing systems

Since 1992, when the room temperature ionic liquids (ILs) based on the 1-alkyl-3-methylimidazolium cation were reported to provide an attractive combination of an electrochemical solvent and electrolyte, ILs have been widely used in electrodeposition, electrosynthesis, electrocatalysis, electrochemical capacitor, and lithium batteries. However, it has only been in the last few years that electrochemical biosensors based on carbon ionic liquid electrodes (CILEs) and IL-modified macrodisk electrodes have been reported. However, there are still a lot of challenges in achieving IL-based sensitive, selective, and reproducible biosensors for high speed analysis of biological and environmental compounds of interest. This review discusses the principles of operation of electrochemical biosensors based on CILEs and IL/composite-modified macrodisk electrodes. Subsequently, recent developments and major strategies for enhancing sensing performance are discussed. Key challenges and opportunities of IL-based biosensors to further development and use are considered. Emphasis is given to direct electron-transfer reaction and electrocatalysis of hemeproteins and enzyme-modified composite electrodes. © 2010 Elsevier B.V. All rights reserve

Biohydrogen—A Green Fuel for Sustainable Energy Solutions

Energy plays a crucial role in the sustainable development of modern nations. Today, hydrogen is considered the most promising alternative fuel as it can be generated from clean and green sources. Moreover, it is an efficient energy carrier because hydrogen burning only generates water as a byproduct. Currently, it is generated from natural gas. However, it can be produced using other methods, i.e., physicochemical, thermal, and biological. The biological method is considered more environmentally friendly and pollution free. This paper aims to provide an updated review of biohydrogen production via photofermentation, dark fermentation, and microbial electrolysis cells using different waste materials as feedstocks. Besides, the role of nanotechnology in enhancing biohydrogen production is examined. Under anaerobic conditions, hydrogen is produced during the conversion of organic substrate into organic acids using fermentative bacteria and during the conversion of organic acids into hydrogen and carbon dioxide using photofermentative bacteria. Different factors that enhance the biohydrogen production of these organisms, either combined or sequentially, using dark and photofermentation processes, are examined, and the effect of each factor on biohydrogen production efficiency is reported. A comparison of hydrogen production efficiency between dark fermentation, photofermentation, and two-stage processes is also presented

Biohydrogen—A Green Fuel for Sustainable Energy Solutions

Energy plays a crucial role in the sustainable development of modern nations. Today, hydrogen is considered the most promising alternative fuel as it can be generated from clean and green sources. Moreover, it is an efficient energy carrier because hydrogen burning only generates water as a byproduct. Currently, it is generated from natural gas. However, it can be produced using other methods, i.e., physicochemical, thermal, and biological. The biological method is considered more environmentally friendly and pollution free. This paper aims to provide an updated review of biohydrogen production via photofermentation, dark fermentation, and microbial electrolysis cells using different waste materials as feedstocks. Besides, the role of nanotechnology in enhancing biohydrogen production is examined. Under anaerobic conditions, hydrogen is produced during the conversion of organic substrate into organic acids using fermentative bacteria and during the conversion of organic acids into hydrogen and carbon dioxide using photofermentative bacteria. Different factors that enhance the biohydrogen production of these organisms, either combined or sequentially, using dark and photofermentation processes, are examined, and the effect of each factor on biohydrogen production efficiency is reported. A comparison of hydrogen production efficiency between dark fermentation, photofermentation, and two-stage processes is also presented

Ionic liquid effects on the redox potential of ferrocene

The ionic liquid, IL, dependence of the mid-point potential of the ferrocene|ferrocenium, Fc0/+, couple versus the decamethylferrocene|decamethylferrocenium, DmFc0/+, couple was studied in eleven ILs and in dichloromethane with added IL as the supporting electrolyte. The difference in mid-point potential between Fc and DmFc indicates that Fc0/+ couple is clearly dependent on the IL structure. A variation of about 0.100 V over the range of ILs studied under neat conditions and by ca. 0.050 V when studied in dichloromethane is reported. Meanwhile, a variable potential shift ranging from 0.014 to 0.082 V was observed when data was compared in these two systems (ILs vs. dichloromethane). The effect of water and lithium ion on the Fc0/+ and DmFc0/+ redox potential was also evaluated and found to be minimal

Mechanistic Aspects of the Electrochemical Oxidation of Aliphatic Amines and Aniline Derivatives

The electrochemical oxidation of amines is an essential alternative to the conventional chemical transformation that provides critical routes for synthesising and modifying a wide range of chemically useful molecules, including pharmaceuticals and agrochemicals. As a result, the anodic reactivity of these compounds has been extensively researched over the past seven decades. However, the different mechanistic aspects of the electrochemical oxidation of amines have never been discussed from a comprehensive and general point of view. This review examines the oxidation mechanism of aliphatic amines, amides, aniline and aniline derivatives, carbamates, and lactams, either directly oxidised at different electrode surfaces or indirectly oxidised by a reversible redox molecule, in which the reactive form was generated in situ. The mechanisms are compared and simplified to understand all possible pathways for the oxidation of amines using only a few general mechanisms. Examples of the application of these oxidation reactions are also provided

Homogeneous electron-transfer reaction between electrochemically generated ferrocenium ions and amine-containing compounds

The homogeneous catalytic oxidation of propylamine (PrA), diethylamine (DEA), pyrrolidine (Pyr), and triethylamine (TEA) has been investigated for the first time in the presence of electrochemically generated ferrocenium ions as the catalyst. Mechanistic details for this electrocatalytic process have been investigated by cyclic voltammetry and other electrochemical techniques. A one-electron oxidative process was observed for all amines. Deviation from this mechanism was only observed during controlled-potential bulk electrolysis of ferrocene in the presence of high concentrations of propylamine, where problems with electrode fouling and catalyst deactivation processes were encountered. The catalytic efficiency and the catalytic oxidation rate constants were estimated and found to follow the order TEA > Pyr > DEA > PrA. Interestingly, the catalytic reaction was not observed when ferrocene was replaced by decamethylferrocene. This observation was analyzed in terms of thermodynamic and structural effects, and a hypothesis is presented. The homogeneous catalytic oxidation reported opens a new avenue to achieve simple, low-cost, and efficient amine oxidation, which is potentially useful in several areas of chemistry

Milk lactate determination with a rotating bioreactor based on an electron transfer mediated by osmium complexes incorporating a continuous-flow/stopped-flow system

The high sensitivity that can be attained using a bienzymatic system and mediated by the redox polymer [Os(bpy)2ClPyCH2NHpoly(allylamine)] (Os-PAA), has been verified by on-line interfacing of a rotating bioreactor and continuous-flow/stopped-flow/continuous-flow processing. When the hydrogen peroxide formed by LOx layer reaches the inner layer, the electronic flow between the immobilized peroxidase and the electrode surface produces a current, proportional to lactate concentration. The determination of lactate was possible with a limit of detection of 5 nmol l&minus;1 in the processing of as many as 30 samples per hour. This arrangement allows working in undiluted milk samples with a good stability and reproducibility. Horseradish peroxidase [EC 1.11.1.7] and Os-PAA were covalently immobilized on the glassy carbon electrode surface (upper cell body), lactate oxidase [EC 1.1.3.x] was immobilized on a disk that can be rotated.<br /