Environment, controlled radical

Method I. Addition of RH to H2 + O2 mixtures at about 750 K This approach has been remarkably successful over the last 30 years with a wide variety of organic compounds. It is, however, limited in its use to pressures between 200-600 Torr and temperatures between 720-800 K. Use of small amounts of the additive (RH) and an aged boric-acid-coated Pyrex vessel permits an investigation of the oxidation of alkanes, alkenes, aromatics and related oxygenated compounds in the total absence of surface effects in a constant and controllable radical environment determined almost entirely by the H2 + O2 mixture. Many different RH compounds may then be oxidized under identical conditions. This is in marked contrast to the direct oxidation method where the radical environment is controlled by the oxidant and changes constantly as the intermediates are formed and then oxidized. Two types of experiment are carried out ... 

Many of the problems in polymer chemistry that some years ago appeared irresolvable are, today, state-of-the-art processes. Examples include the formation of block copolymers by controlled radical polymerization, or the increasingly broad application of transition metal-catalyzed polymerization techniques in aqueous environments. Clearly, polymer synthesis is a highly dynamic art form rather than a mature technological field. ... 

The huge variety of defined nanostmctures and materials that can be fabricated via controlled radical polymerization techniques will probably find applications in a wide field of different research directions. The possibility of combining several building units in one device will enable materials scientists to implement multiple levels of stimuli-responsiveness for the construction of smart materials. Research in biomedicine can be expected to benefit from the ability to generate defined nanopattemed surfaces that can play a central role in biophysical investigations. Also, the potential to create precisely defined confined environments could lead to nanocontainers as delivery vehicles, theranostic agents, or artificial enzymes. 

First, in composites with high fiber concentrations, there is little matrix in the system that is not near a fiber surface. Inasmuch as polymerization processes are influenced by the diffusion of free radicals from initiators and from reactive sites, and because free radicals can be deactivated when they are intercepted at solid boundaries, the high interfacial area of a prepolymerized composite represents a radically different environment from a conventional bulk polymerization reactor, where solid boundaries are few and very distant from the regions in which most of the polymerization takes place. The polymer molecular weight distribution and cross-link density produced under such diffusion-controlled conditions will differ appreciably from those in bulk polymerizations. 

Brezonik PL, J Fulkerson-Brekken (1998) Nitrate-induced photoysis in natural waters controls on concentrations of hydroxyl radical photo-intermediates by natural scavenging agents. Environ Sci Technol 32 3004-3010. 

The consecutive reaction will be triggered by too long exposure of already chlorinated product in an environment with a high density of chlorine radicals. Accordingly, controls over residence time, concentration profiles and efficient heat transfer have the potential to cope with such a problem. 

While many biological molecules may be targets for oxidant stress and free radicals, it is clear that the cell membrane and its associated proteins may be particularly vulnerable. The ability of the cell to control its intracellular ionic environment as well as its ability to maintain a polarized membrane potential and electrical excitability depends on the activity of ion-translocating proteins such as channels, pumps and exchangers. Either direct or indirect disturbances of the activity of these ion translocators must ultimately underlie reperfiision and oxidant stress-induced arrhythmias in the heart. A number of studies have therefore investigated the effects of free radicals and oxidant stress on cellular electrophysiology and the activity of key membrane-bound ion translocating proteins. 

For stndying elementary reactions of importance in combnstion, a more controlled environment may be reqnired. Radicals or atoms may be generated by photolysis with UV radiation or with a microwave discharge on a snitable molecniar precursor. 

The imido complex [Mo2(cp)2(/r-SMe)3 (/u.-NFl)]" " 25+ undergoes an irreversible one-electron (EC) reduction [70]. Controlled potential electrolysis afforded the amido analog [Mo2(cp)2(/x-SMe)3(/x-NH2)] 26 almost quantitatively after the transfer of IF mol 25+. The amido complex was not the primary reduction product the latter was assigned as a rearranged imide radical (Sch. 18), which is able to abstract a FI-atom from the environment (supporting electrolyte, solvent, or adventitious water) on the electrolysis timescale. In the presence of protons, the reduction of 25+ became a two-electron (ECE) process. This is consistent with the protonation at the nitrogen lone pair of the primary reduction product, followed by reduction of the resulting amido cation... 

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