Activated oxygen-derived molecules

There are a number of mechanisms by which ascorbate may facilitate the removal of activated oxygen-derived molecules in vivo-, these include reaction with 0 2, HOj and OH , as well as the reduction of thiyl radicals (see section 5.1),... 

Polyall lene Oxide Block Copolymers. The higher alkylene oxides derived from propjiene, butylene, styrene (qv), and cyclohexene react with active oxygens in a manner analogous to the reaction of ethylene oxide. Because the hydrophilic oxygen constitutes a smaller proportion of these molecules, the net effect is that the oxides, unlike ethylene oxide, are hydrophobic. The higher oxides are not used commercially as surfactant raw materials except for minor quantities that are employed as chain terminators in polyoxyethylene surfactants to lower the foaming tendency. The hydrophobic nature of propylene oxide units, —CH(CH2)CH20—, has been utilized in several ways in the manufacture of surfactants. Manufacture, properties, and uses of poly(oxyethylene- (9-oxypropylene) have been reviewed (98). 

Recent ""Tc-based imaging agents, shown in Figure 5, for hypoxic tissue are in development. These include nitroimidazole derivatives, BSM-181321 and BRU-59-2, based on the "Tc-propyleneamine oxime (PNAO) complexes. Both contain the 2-nitrounidazole functionality, that is the active component of the oxygen mimetic molecule, F-2-nitroimidazole, and have been shown in vivo to localize in ischemic tissue. The BnAO chelate also displays uptake in hypoxic tissue. The mechanism is unknown, however, electrochemical studies show an irreversible reduction at biologically accessible potentials. 

The derivatives usually are produced by aminations, esterifications or etherifications of primary and secondary hydroxyl groups of the CDs. Depending on the substituent, the solubility of the CD derivatives is usually different from that of its parent CDs. Virtually all derivatives have a changed hydrophobic cavity volume and also these modifications can improve solubility, stability against light or oxygen and help to control the chemical activity of guest molecules [2]. 

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