PHOTOINDUCED ELECTRON-TRANSFER REACTIONS BETWEEN EXCITED TRANSITION-METAL COMPLEXES AND REDOX SITES IN ENZYMES

Photogenerated reduced relays act as electron mediators in biocatalyzed photosynthetic biotransformations. Photogenerated N,N'-dimethyl-4,4'-bipyridinium radical cation acts as diffusional electron carrier for the enzymes nitrate reductase and nitrite reductase. In photochemical assemblies that include these biocatalysts, photosensitized reduction of nitrate to nitrite and of nitrite to ammonia proceeds with quantum yields of PHI = 0.08 and 0.06, respectively. In a photochemical system that includes the two biocatalysts, photoreduction of nitrate to ammonia proceeds with a quantum yield of PHI = 0.08. Electrical communication of protein active sites with photoexcited species is also accomplished in organized redox assemblies. Immobilization of nitrate reductase in a functionalized bipyridinium acrylamide-acrylamide copolymer results in an organized assembly exhibiting electrical communication that leads to photosensitized reduction of nitrate to nitrite. Chemical modification of the enzyme glutathione reductase by bipyridinium electron-relay components generates a functionalized protein that acts as an electron-transfer quencher of excited species and is electrically wired toward biocatalyzed reduction of oxidized glutathione.