Radical polyanion

Figure 9 The known polyphosphides with radical polyanions P3 and. Atoms connected by thin and thick lines are separated from...

Figure 9 The known polyphosphides with radical polyanions Ps" " and P4 . Atoms connected by thin and thick lines are separated from each other by half a translation period of the projection direction. Small circles are K atoms, large circles P atoms. The unit cells are indicated by thin lines together with the labelled axes...

SOD is a major oxygen free radical scavenging enzyme, which may therefore have beneficial effects in liver fibrosis. Through mannosylation or coupling to the polyanion DIVEMA, SOD was made more liver specific. Both conjugates showed superior inhibition of intrahep-atic ROS production in fibrotic rats as compared to unmodified SOD. DIVEMA-SOD, however, exhibited the most potent inhibitory effects [112]. Although their mode of action is most probably extracellular free radical scavenging, Man-SOD and DIVEMA-SOD are likely to... 

Electro-organic chemistry at the cathode is essentially that of radicals, radical-anions, carbanions, and polyanions (which range from dianions to hexa-anions (Scheme 1). The anions may behave as nucleophiles, bases, and as single electron reductants the factors governing the competition between these roles are not yet fully understood. 

Within the last few years there has been considerable activity directed towards the synthesis of organic and organometallic derivatives of heteropolyanions. Reactions of lacunary polyanions with RMC13, where R is an organic or organometallic radical, provide a simple route to such derivatives.97 Some examples of these reactions are presented in Scheme 5. For the most part the reactions proceed smoothly and the products are remarkably stable towards hydrolysis. Apart from their structural characterization via crystallography and NMR spectroscopy the chemistry of these complexes has not been completely described. 

Since DNA is a highly charged polyanion, it is always hydrated by water molecules [in the dry state (under moist air) it contains 12 water molecules per nucleotide subunit]. In a cellular environment, proteins (histones in eukaryotic cells) are always attached to DNA or are at least surrounded by proteins as in viruses. In order to attack DNA, radicals have to be sufficiently mobile in such a partially hydrophilic environment. For this reason, typical lipid radicals confined to the membranes will not be discussed here, although one must keep in mind that small fragments of free-radical nature maybe able to escape the lipid environment and can, in principle, also react with DNA. 

The first stage of this unusual reaction involves debenzylation of the substrate to form 2-aminobenzimidazole polyaniones. The formation of 2,2 -azobenzimida-zolone is the result of autooxidation of 2-aminobenzimidazole di- and trianiones, when 2-nitrobenzimidazole is formed on oxidizing of radical anions [660]. 

Ring stability might be expected to lessen with increase in size and increasing proportion of SiOj because the silicate polyanions that correspond to compositions approaching 10 mol% of M O, would be very long. The critical 10% composition at which there is a radical change in many properties may be explained as that composition in the region of which a discrete polymerized anion type of structure becomes... 

Numerous anhydrous borate structures can be reduced to various combinations of three types of basic structural units 1) fundamental structural units, 2) combined basic structural units, and 3) full radicals of polyanions. The stability of the FSU, CSU and CRP units in solid and liquid borates is one of the most important issues, and will provide a better understanding of, and control of, phase formation in complex borate systems. 

The rates of reduction of tetrahydrofuran (Curve A), naphthalene in tetrahydrofuran (Curve B), and a mixture of naphthalene and Illinois No. 6 coal in tetrahydrofuran (Curve C) are shown in Figure 1. These preliminary experiments established that potassium reacted only very slowly with tetrahydrofuran under the experimental conditions used for the formation of the coal polyanion. Naphthalene was rapidly converted to a mixture of anion radicals and dianions under the same conditions. The initial reaction between the electron transfer reagent and the Illinois No. 6 coal was quite rapid. However, the reaction slowed to nearly constant rate after about 12 hr. During the last 4 days of reaction the coal molecules acquired about 0.1 negative charge per 100 carbon atoms per hour. 

II. FORMATION OF RADICAL ANIONS, DIANIONS, AND POLYANIONS A. Experimental Aspects... 

Two years later (1989), the same authors reported the oxygenation and oxidation chemistry of the Mn-substituted POMs XMnnWn039"- (X = P, Si, Ge, or B) and a2-P2MnnWi706i8-.316 These POMs undergo reversible oxygenation at low temperature in toluene or benzene solution but irreversible oxidation above 22°C. The 02 adduct can be intercepted by the spin trap 5,5-dimethyl-1-pyrroline A-oxide (DMPO). EPR spectra indicate formation of a polyanion-02-DMP0 intermediate that decomposes to the oxidized POM. The nonpolar organic solutions of these POMs catalyze the oxidation of 2,6- and 2,4,6-substituted phenols to benzoquinones or polyphenyl ethers, and a POM-02-phenoxy radical intermediate can be detected by EPR. 

In the late 20 s, Schlenck and his group demonstrated that the reduction of rc-conjugat-ed systems can be carried out by alkali metals and that the reaction affords dianions 5>. It was also realized that a one electron transfer process occurs in an alternating fashion 1,5) to form radical anions and polyanions. Ever since, this reaction has become the main process of preparation of polycyclic anions 10 13), (Eq. 1) ... 

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 ... 

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