Redox controls

Future research should also focus its attention on the factors/mechanisms that regulate free-radical activity in vivo. The complex interrelationship between cellular and extracellular levels of antioxidants needs to be clarified, and factors that govern the synthetic rate of the scavenging enzymes, for example, SOD or catalase will provide further insight into cellular redox control. 

The typical amber color of the hexavalent chromium solution will turn to a pale green once the chromium has been reduced to the trivalent state. Although this color change is a good indicator, redox control is usually employed. 

Liu, C. W. and T. N. Narasimhan, 1989a, Redox-controlled multiple-species reactive chemical transport, 1. Model development. Water Resources Research 25, 869-882. 

Valluzzi, R., Szela, S., Avtges, P., Kirschner, D., and Kaplan, D. (1999). Methionine redox controlled crystallization of biosynthetic silk spidroin. J. Phys. Chem. B 103, 11382-11392. 

Reetz, M.T. and Maase, M., Redox-controlled size-selective fabrication of nanostructured transition metal colloids, Adv. Mater., 11, 773,1999. 

Kaifer, A. E. and Echegoyen, L. (1990). Redox control of cation binding in macrocyclic systems. In Cation Binding by Macrocyclic Systems (ed. Y. Inoue and G. W. Gokel). Marcel Dekker, New York, p. 363... 

An expression predicting treated slurry BODw during treatment with redox control is presented. 

There was no significant effect of aeration rate on the destmction of TS, VS, VFA or COD, thus the only saving in oxygen consumption of using redox control rather than DO control was in the inhibition of nitrification. 

Ehrlich et al. (submitted) measured Cu isotopic fractionation between aqueous Cu(II) and covellite between 2 and 40°C (Fig. 10). The temperature-dependent isotope fraction is fairly large 3%o) and hints at a redox control of Cu isotopic variability in abiotic systems. Marechal and Sheppard (2002) conducted experiments at 30 and 50°C between malachite and a chloride solution for Cu isotope fractionation and between smithsonite and a nitrate solution for Zn. They found that, in this temperature range, Cu in malachite is 0.2 to 0.4%o lighter than in the chloride solution. Replacing the chloride by nitrate ion reduces fractionation which indicates that the coordination of the Cu ion dictates isotopic fractionation. In contrast, Zn isotope fractionation between smithsonite and fluid is extremely small (<0.1%o). 

Ti, or PEEK (polyether ether ketone) to allow measurements under very corrosive conditions. The separated phases pass AMX gadgets for on-line detection (radiometric, spectrophotometric, etc.) or phase sampling for external measurements (atomic absorption, spectrometric, etc.), depending on the system studied. The aqueous phase is also provided with cells for pH measurement, redox control (e.g., by reduction cells using platinum black and hydrogen, metal ion determination, etc.) and temperature control (thermocouples). 

Whitehead (1973) identified Mn halos in the iron formation overlying the Heath Steele B zone and showed that there were both vertical and lateral variations in Mn Fe ratios. This was one of the first demonstrations of redox controlled dispersion that extended laterally on the paleo-seafloor for several km from the sulfide deposit. 

Hart, C.J.R., Mair, J.L, Goldfarb, R.J., Groves, D.I. 2004. Source and redox controls on metallogenic variations in intrusion-related ore systems, Tombstone-Tungsten Belt, Yukon Territory, Canada. Transactions of the Royai Society of Edinburgh Earth Sciences, 95, 339-356. 

NF-kB inhibition. Aqueous extract of mainstream smoke (smoke-bubbled phosphate-buffered saline), in Swiss 3T3 cells, decreased DNA binding of NF-kB during the first 2 hours of exposure and increased more than twofold over controls after 4-6 hours of exposure. There was lack of phosphorylation and degradation of iKB-a and a significant increase in thioredoxin reductase mRNA after 2-6 hours of exposure. Results indicated that the activity of NF-kB in smoke-treated cells was subject mainly to a redox-controlled mechanism dependent on the availability of reduced thioredoxin rather than being controlled by its normal regulator, iKB-a " ". 

Figure 13.35 Redox controlled ring rotation in solution for catenane 404+, which contains the symmetric electron acceptor cyclophane 124+ and a nonsymmetric electron donor ring.

Figure 13.37 Redox controlled movements of the ring components in catenane 42H composed of three interlocked macrocycles. These motions are obtained upon reduction-oxidation of the bipyridinium units of the cyclophane.

The redox-controlled mechanical switching in SAMs of disulfide-functionalized bistable TTF-DMN rotaxanes consisting of cyclophane 124+ and a dumbbell-shaped component containing TTF and DMN stations was also extensively investigated.49... 

Photoinduced electron transfer processes involving electron donor (D) and acceptor (A) components can be tuned via redox reactions. Namely, the excited-state properties of fluorophores can be manipulated by either oxidation of electron donors or reduction of electron acceptors. Also, the oxidized and the reduced species show different properties compared to the respective electron donors and acceptors. By making use of these properties of electron donors and acceptors, a number of molecular switches and logic gates have been described in recent years. In the following, we will introduce these redox-controlled molecular switches according to the redox centers. 

Scheme 15.1 Principle of a switchable, redox-controlled fluorescence in D-A systems (D = TTF).

The efficient on/off switching of fluorescence from substituted zinc porphyrin-ferrocene dyads 16a and 16b is achieved through redox control of the excited-state electron transfer quenching.26 This redox fluorescence switch is based on the switching of the excited-state electron transfer from the ferrocene to the zinc porphyrin through the use of the ferrocene/ferrocenium (Fc/Fc +) redox couple. 

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