Sugar radical formation

Thus we find that the hole is deeply trapped by two distinctly different mechanisms. One that requires no activation energy, sugar radical formation occurs even at 4 K, and the other that does, HO addition to the guanine radical cation. Similarly, the excess electron is irreversibly trapped by two distinct mechanisms, one that is activated and the other which is not. 

SUGAR RADICAL FORMATION AND EXCITED STATE STUDY... 

Scheme 20-1. Proposed mechanism of sugar radical formation via photo-excitation. (Reprinted with permission from ref.[149], Nucleic Acid Research, (2005), Oxford University Press.)...

The pH (or pD in D2O) was found to have a great effect on sugar radical formation from excited states of one-electron oxidized guanine (in dGuo) but not for one electron oxidized dAdo and its... 

Some time ago, an allyl-like radical was observed in irradiated crystals of 5 -dCMP [26]. This radical was thought to be a sugar radical, although no likely scheme was proposed for its formation. It now appears that this radical is formed on 5-methyl cytosine impurities in these crystals [27]. This radical forms by deprotonation at the methyl group of the cytosine cation, 5meCyt(Me—H) , and may have important consequences in the radiation chemistry of DNA since the ionization potential of 5-methyl cytosine is lower than that of either cytosine or thymine. 

Photolysis of G + leads to the formation of sugar radicals (Adhikary et al. 2005). Product studies from solid state irradiation of Thd are also available (Gromova et al. 1999). As discussed above, the Thd radical cation is expected to deproton-ate at N(3) and at methyl, and the ensuing structural elements indeed dominate the product spectrum parts of which is shown below. 

Hayashi, T. Namiki, M. On the mechanism of free radical formation during browning reaction of sugars with amino compounds. Agric. Biol. Chem. 1981, 45, 933-9. 

A New Mechanism of the Maillard Reaction Involving Sugar Fragmentation and Free Radical Formation... 

Thus we propose the existence of a new pathway to browning in the Maillard reaction, involving sugar fragmentation and free radical formation prior to the Amadori rearrangement. 

Figure 6. Two possible pathways for radical formation in the reaction of a sugar with an amino compound.

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