Cells reductive chemistry

Electroanalytical techniques are an extension of classical oxidation-reduction chemistry, and indeed oxidation and reduction processes occur at the surface of or within the two electrodes, oxidation at one and reduction at the other. Electrons are consumed by the reduction process at one electrode and generated by the oxidation process at the other. The electrode at which oxidation occurs is termed the anode. The electrode at which reduction occurs is termed the cathode. The complete system, with the anode connected to the cathode via an external conductor, is often called a cell. The individual oxidation and reduction reactions are called half-reactions. The individual electrodes with their half-reactions are called half-cells. As we shall see in this chapter, the half-cells are often in separate containers (mostly to prevent contamination) and are themselves often referred to as electrodes because they are housed in portable glass or plastic tubes. In any case, there must be contact between the half-cells to facilitate ionic diffusion. This contact is called the salt bridge and may take the form of an inverted U-shaped tube filled with an electrolyte solution, as shown in Figure 14.2, or, in most cases, a small fibrous plug at the tip of the portable unit, as we will see later in this chapter. 

One example is the known interference by reducing compounds that affect the chemical conversion of substrate to a colored indicator. This is especially true for the tetrazolium assays (Ulukaya, Colakogullari, and Wood 2004 Chakrabarti et al. 2000 Pagliacci et al. 1993 Collier and Pritsos 2003). The growing list of interfering compounds includes ascorbic acid and sulfhydryl reagents such as glutathione, coenzyme A, dithiothreitol, etc. Similar interferences by compounds that affect the oxidation and reduction chemistry of cells are likely to cause artifacts with the resazurin reduction assay. Assays that measure markers of metabolism also can be influenced by the pH of the culture medium and other factors that may stimulate or stress the metabolic rates of cells. 

There are several parallels in the reduction chemistry of nitroarenes and aromatic N-oxides, such as similar kinetics of electron transfer reactions of the radical-anions and the effects of prototropic equilibria on radical lifetimes in aqueous solution [16]. The benzotriazine di-N-oxide, tirapazamine (Figure 1,16) is currently in Phase III clinical trial as a hypoxic cell cytotoxin in conjunction with cisplatin [132]. The mechanism of its action appears to involve the one-electron reduction product [133] cleaving DNA [134], probably also sensitizing the damage by a radical-addition step [135-138]. 

Recent studies with copper phenanthroline complexes expand on the possibilities for site-directed oxidation-reduction chemistry of copper complexes. Cu(ii)(l,10-phenanthroline)2, alone or tethered to various DNA-binding domains, causes DNA strand scission in vitro in the presence of reductants, which involves the formation of the hydroxyl radical or its equivalent." - Upon reaction of Cu(ii)(Phen)2 with tumor cells, it is likely that the complex binds directly to DNA, acting as a site-directed catalyst for the generation of oxyradi-cals. ... 

Chapter 10 explores oxidation and reduction chemistry. There is a new treatment of fuel cells and hybrid vehicles to illustrate the relevance of this chemistry topic. 

Environment and Life, RSC Publishing, p. i60 As this cytoplasmic (in cell) organic chemistry was reductive of necessity, because the ingredients were made of the oxides of carbon, it was inevitable that oxidizing compounds, which became oxygen, would be released. There followed in the environment an unavoidable and predictable sequence of the oxidation of minerals and non-metal elements in solution, limited by diffusion but generally following sequentially equilibrium constants, redox potentials. ... 

Applying Models Explain how the oxidation-reduction chemistry of both the voltaic cell and the electrolytic cell are combined in the chemistry of rechargeable cells. 

The material prices provided by Gaines et al. (Table 10 [46]) illustrate the high cost of raw materials for lithium-ion cells. Competitive chemistries, such as Pb-acid and Ni/MH, enjoy substantially lower costs for separators (-lOXless) and electrolytes (-100X less). In addition, lithium-ion cells must be assembled in dry rooms to exacting tolerances. However, the dramatic reductions in the price of lithium-ion cells for consumer use is encouraging, as is the recent entry of Chinese producers to the large Li-ion market. 

Chemistry. The alkaline cell derives its power from the reduction of the manganese dioxide cathode and the oxidation of the zinc anode. The reactions... 

Figure 17.7 Electrocatalysis of O2 reduction by Pycnoporus cinnabarinus laccase on a 2-aminoanthracene-modified pyrolytic graphite edge (PGE) electrode and an unmodified PGE electrode at 25 °C in sodium citrate buffer (200 mM, pH 4). Red curves were recorded immediately after spotting laccase solution onto the electrode, while black curves were recorded after exchanging the electrochemical cell solution for enzyme-fiiee buffer solution. Insets show the long-term percentage change in limiting current (at 0.44 V vs. SHE) for electrocatalytic O2 reduction by laccase on an unmodified PGE electrode ( ) or a 2-aminoanthracene modified electrode ( ) after storage at 4 °C, and a cartoon representation of the probable route for electron transfer through the anthracene (shown in blue) to the blue Cu center of laccase. Reproduced by permission of The Royal Society of Chemistry fi om Blanford et al., 2007. (See color insert.)...

In summary, ketoreductases have emerged as valuable catalysts for asymmetric ketone reductions and are preparing to enter the mainstream of synthetic chemistry of chiral alcohols. These biocatalysts are used in three forms wild-type whole-cell microorganism, recombinant... 

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