Radical-cation-based activation

Selenoglycosides are attractive donor species owing to the wide range of reagents that can promote cation- and radical-cation-based processes for their activation and subsequent O-glycosylation (Scheme 4.102) [223,512],... 

The total antioxidant activity of teas and tea polyphenols in aqueous phase oxidation reactions has been deterrnined using an assay based on oxidation of 2,2 -azinobis-(3-ethylbenzothiazoline-sulfonate) (ABTS) by peroxyl radicals (114—117). Black and green tea extracts (2500 ppm) were found to be 8—12 times more effective antioxidants than a 1-mAf solution of the water-soluble form of vitamin E, Trolox. The most potent antioxidants of the tea flavonoids were found to be epicatechin gallate and epigallocatechin gallate. A 1-mAf solution of these flavanols were found respectively to be 4.9 and 4.8 times more potent than a 1-mAf solution of Trolox in scavenging an ABT radical cation. 

Fig. 10 Two schematic representations of a polaron-like species in DNA. In the top drawing, the base pairs of DNA are represented by the horizontal lines the sugar diphosphate backbone is represented by the vertical lines. The polaronic distortion is enclosed in the box and extends over some number of base pairs. This is shown schematically by drawing the base-pair lines closer together. In the lower figure, a specific potential po-laron is identified, AAGGAA, and the radical cation is presented as being delocalized over this sequence. Movement of the polaron from one AAGGAA sequence to the next requires thermal activation...

Tram-anular interactions, which would create an active radical site via hydrogen transfer through 98, cannot be invoked to explain the specific loss of a CH3 radical from the ether side chain. This conclusions is based upon the following experimental observations. The radical cation of the tetrafluoro substituted compound 101 eliminates CH3, but loss of CH3 from the para-isomer 102 is not observed. If a transanuiar process according to 97- 98 were operative, then such a reaction is not expected to be suppressed upon substitution of H by F as is known for many examples from the field of photochemistry of fluoro substituted compounds41 (23). 

These oxidation states attract attention because Fe(IV) and Fe(V) cation radical porphyrins are active intermediates in biological hydroxylation. In strong base, Fe(IV) is produced from Fe(III) by powerful oxidants and Fe(V) arises from radical reduction of Fe(VI)... 

Tandem MS was applied to characterization and differentiation of the connectivity of the 0283 radical cation (mlz = 120) generated by dissociative electron ionization (El) of the l,3,4,6-tetrapentalene-2,5-dione 39. The structural assignment of the radical cation C2S as the C-sulfide ethenedithione, SCCS2 40, was based on the results of ion-molecule reactions of 0283 with nitric oxide, acetonitrile, and methyl isocyanide. The collisional activation spectra of these ion-molecule reaction products recorded on a new type of hybrid tandem mass spectrometer of sectors-quadrupole-sectors configuration allowed the confirmation of the ascribed structure 40 (Scheme 1) <1999PCA3666>. 

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