Free radical formation pathways

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. 

Puddephatt et al. (26) noted that irradiation of TiCp2(CH3)2 in the presence of methyl methacrylate (MMA) or styrene gave polymerization of these monomers, a result that can be interpreted as evidence for free radical formation. However, these workers ruled out photoinduced homolysis of the Ti—CH3 bonds mainly on the basis of their observed lack of hydrogen abstraction from solvent. Instead they preferred the pathway... 

The mechanism of action of IL-ip is presently uncharacterized. It is possible that it acts through excitotoxic and iNOS pathways. Inhibition of IL-1 is protective against glutamate neurotoxicity in retinae in vitro (Yoneda et al., 2001). IL-1 inhibition also reduces iNOS expression, free radical formation, and neuronal damage in ischemic brain models (Ohtaki et al., 2003 Osborne et al., 2004) (O Figure 3-7). 

Whereas homolytic ligand dissociation is not commonly observed for inorganic complexes, it has been identified as an important process in organometallic chemistry where it is favored by the characteristic weakness of transition metal-alkyl tr-bonds. Recent determinations yield metal alkyl band dissociation energies for CH3— Mn(CO)s (ca. 120 kJ/mol) and for several alkylcobalt complexes (ca. 80-100 kJ/mol) . Homolytic dissociation of such complexes results in the formation of free radicals and in the opening up of free radical catalytic pathways, e.g., for hydrogenation". Important biochemical examples of free radical catalytic mechanisms, initiated by the homolytic dissociation of a transition metal-carbon bond (i.e., the 5 -deoxyadenosy 1-cobalt bond of coenzyme 8,2) are provided by the coenzyme B,2-promoted rearrangements (see Section... 

Figure 6.37. Proposed mechanistic manifold to account for the formation of other products in the CYP17A catalyzed oxidation of pregnenolone/progesterone. Ionic decomposition (pathway b) of the peroxyhemiacetal competes with free-radical fragmentation (pathway a) to yield the observed mixture of minor products.

Fig. 5. Proposed free-radical pathway attributed to gentamicin-induced ototoxicity. Steps include (1) gentamicin-Fe(III) complex, (2) O2 activation and reduction to lipid peroxide (L-OO radical) and superoxide (ROS) by an electron donor (arachidonic acid), and (3) free-radical formation and damage. Reprinted with permission, Copyright 1997 UMI.

A chemical synthesis of prostaglandins by a free radical pathway through an endoperoxide intermediate showed a strong stereochemical preference for the formation of the endoperoxides having cis alpha and omega appendages. 

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