Free radical formation effects from

Photopolymerization reactions are widely used for printing and photoresist appHcations (55). Spectral sensitization of cationic polymerization has utilized electron transfer from heteroaromatics, ketones, or dyes to initiators like iodonium or sulfonium salts (60). However, sensitized free-radical polymerization has been the main technology of choice (55). Spectral sensitizers over the wavelength region 300—700 nm are effective. AcryUc monomer polymerization, for example, is sensitized by xanthene, thiazine, acridine, cyanine, and merocyanine dyes. The required free-radical formation via these dyes may be achieved by hydrogen atom-transfer, electron-transfer, or exciplex formation with other initiator components of the photopolymer system. 

Some other examples of free radical formation in various pathologies are discussed below. (Of course, they are only few examples among many others, which can be found in literature.) Mitochondrial diseases are associated with superoxide overproduction [428] and cytochrome c release [429], For example, mitochondrial superoxide production apparently contributes to hippocampal pathology produced by kainate [430]. It has been found that erythrocytes from iron deficiency anemia are more susceptible to oxidative stress than normal cells but have a good capacity for recovery [431]. The beneficial effects of treatment of iron deficiency anemia with iron dextran and iron polymaltose complexes have been shown [432,433]. 

How does UV-induced free radical formation activate immune suppression Some have suggested that UV-induced cytokine production is involved. Because both DNA damage and oxidative stress can activate transcription of the cytokines that activate immune suppression,23>24one of the problems faced by investigators in the field was to divorce the effects of DNA damage from membrane oxidation. One approach was to look at the activation of transcription factors in UV-irradiated enucleated cells. Devary and colleagues25 observed that both NF-kB and AP-1 were activated in enucleated... 

Aliphatic sulfides can be efficient co-initiators for the photoinduced polymerization induced by benzophenone [185, 186]. An exceptionally strong effect was observed for 2,4,6-trimethyl-1,3,5-trithiane (TMT). A model reaction for free-radical formation during photoreduction of an initiator triplet state by a sulfide is the photoreduction of benzophenone by dimethyl sulfide [171, 187-189]. In this process it was established that electron transfer from the sulfur atom to the triplet state of the benzophenone is a primary photochemical step. In this step, radical ions are formed. The overall quantum yields of photoproducts (ketyl radicals and radical anions) are low (Ed) 0.26) in aqueous solution, in the range 0.16-0.20 in mixed water-acetonitrile solution and less then 0.01 in pure acetonitrile. These results suggest that, in organic solvents, back electron transfer within the radical-ion pair to regenerate the reactants is the dominant process. 

Evidence for the activity of some radioprotectors as inhibitors of free radical processes has appeared, and the subject has been reviewed Involvement of MEA as well as of metal ionsf in free radical formation in proteins and bacteria has been observed. It was also found that cysteine and glutathione could accept electrons from irradiated proteins, whereas cystine and non-sulfur compounds did not Presence of metal ions, particularly cupric, had a protective effect for ribo-nuclease, presumably by intercepting electrons and preventing radical formation on the enzymer A protective effect of mucopolysaccharide polyanions and cysteine for trypsin and RHA, however, was not considered to be due to transfer of radiation energy to the protectors " Furthermore, substances known to react with H atoms or the aqueous electron did not protect hydrated E. coll cells from X-rays ... 

C30H21NO9, Mr 539.50, red powder, mp. >350 °C. A very effective cytotoxic antitumor antibiotic with additional activity against Gram-positive bacteria and fungi. F. A and the minor components F. B and f C are isolated from cultures of Streptomyces griseus. The antitumor activity of F. A is assumed to be due to the formation of free radicals which effect DNA strand cleavage. The water-soluble potassium salt of F. A has been developed for cancer therapy. In contrast to other antineoplastic substances F. A does not show any mutagenicity in the Ames test. 

The polymerization rate is directly proportional to the monomer concentration for ideal free radical polymerization kinetics. Deviations from this first-order kinetics can be caused by a whole series of effects which must be checked by separate kinetic experiments. These effects include cage effects during initiator free radical formation, solvation of or complex formation by the initiator free radicals, termination of the kinetic chain by primary free radicals, diffusion controlled termination reactions, and transfer reactions with reduction in the degree of polymerization. Deviations from the square root dependence on initiator concentration are to be primarily expected for termination by primary free radicals and for transfer reactions with reduction in the degree of polymerization. 

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