Redox-sensitive systems

For simpler catechols employed in plant chemical defense we have synthesized and studied more complex analogs into which biological-receptor-site-directing functionality has been integrated to examine the potential of these redox-sensitive systems for inactivating targeted receptors. These modified catechols are models for selective receptor inactivation. 

The efficiency of nucleophilic addition of methanol to the radical cation of arylalkenes can be improved by use of a redox sensitizer system, and also by utilizing solvent and additive effects. Pac and his coworkers found that the aromatic hydrocarbon-electron acceptor sensitizer system, such as phenan-threne-p-dicyanobenzene system, acts as an excellent redox sensitizer for the anti-Markownikoff addition of methanol to 1,1-diphenylethene and indene (Scheme 7) [29]. 

Classification of Redox-Sensitive Systems in Terms of Application. 128... 

ABSTRACT This chapter will focus on three classes of naturally occurring compounds that we have considered as beginning points for mechanistic studies in drug design. Each compound class is dependent for its biological activity on the presence of the redox-sensitive catechol-o-quinone system. 

Elbaz-Poulichet, F., Nagy, A. and Cserny, T. (1997) The distribution of redox sensitive elements (U, As, Sb, V and Mo) along a river-wetland-lake system (Balaton region, Hungary). Aquatic Geochemistry, 3(3), 267-82. 

Kneebone, P.E. and Hering, J.G. (2000) Behavior of arsenic and other redox-sensitive elements in Crowley Lake, CA a reservoir in the Los Angeles aqueduct system. Environmental Science and Technology, 34(20), 4307-12. 

The speciation of redox-sensitive elements (e.g., Cr, Fe, and Mn), redox-sensitive elements that also form organometallic compounds (e.g., As), and redox-sensitive elements that also form organome-tallic and volatile compounds (e.g., Hg) in aquatic systems is discussed in this chapter. Because the scope of this subject is so large, only the dissolved phase in the aquatic system will be considered. 

Table 12 shows some redox sensitive elements in the periodic system of the elements, Table 13 depicts standard potentials for some important redox pairs in aqueous systems. 

Table 12 Redox sensitive elements in the PSE (bold = most common oxidation states in natural aqueous systems) (after Emsley 1992, Merkel and Sperling 1996, 1998)...

Redox processes are important for elements which can exist in more than one oxidation state in natural waters, e.g. Fe and Fe, Mn, and Mn. These are termed redox-sensitive elements. The redox conditions in natural waters often affect the mobility of these elements since the inherent solubility of different oxidation states of an element may vary considerably. For example, Mn is soluble whereas Mn is highly insoluble. In oxic systems, Mn is precipitated in the form of oxyhydr-oxides. In anoxic systems, Mn predominates and is able to diffuse along concentration gradients both upwards and downwards in a water column. This behaviour gives rise to the classic concentration profiles observed for Mn (and Fe) at oxic-anoxic interfaces as illustrated in Figure 2. 

Overall, this refined use of hydrogen concentrations supported the results of the bioassays and the complex system of redox zones inferred from the distribution of dissolved redox-sensitive species. The Grindsted Landfill (DK) plume is host to all of the proposed redox reactions, but also to secondary oxidation-reduction reactions involving ammonium, methane, manganese oxides, ferrous iron, and sulfides. 

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