Intramolecular charge transfer and biomimetic reaction kinetics in galactose oxidase model complexes.
One-electron oxidation of two structurally similar CuII-diphenolate complexes, 1 and 2, creates EPR-silent CuII-phenoxyl complexes [1]+ and [2]+ that mimic the oxidized form of the enzyme galactose oxidase (GOase). Both model complexes display novel NIR absorptions assigned to phenolate-phenoxyl charge transfer that resemble a tyrosinate-tyrosyl charge-transfer band observed in the enzymatic system. [1]+ and [2]+ react with benzyl alcohol to form 0.5 equivs of benzaldehyde per complex; biomimetic reduction to CuI-phenol complexes is not observed, but such species may exist transiently. Initial kinetic studies show that [2]+ reacts faster with benzyl alcohol than does [1]+, despite being a significantly weaker oxidant (DeltaE degrees = 370 mV). This acceleration is ascribed to mechanistic differences: [2]+ appears to bind substrate prior to the rate-determining step. Large, nonclassical kinetic isotope effects confirm C-H bond cleavage as the rate-determining step in the reactions of both [1]+ and [2]+ with benzyl alcohol, as is the case for GOase.
Pratt
Russell C
RC
Department of Chemistry, Stanford University, Stanford, California 94305-5080, USA.
Stack
T Daniel P
TD
D019905:Benzyl Alcohol / Q000737:chemistry; D040761:Biomimetic Materials / Q000737:chemistry* / Q000378:metabolism; D003300:Copper / Q000737:chemistry* / Q000378:metabolism; D005692:Galactose Oxidase / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D009942:Organometallic Compounds / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D019265:Spectroscopy, Near-Infrared
D009942:Organometallic Compounds; D003300:Copper; D005692:Galactose Oxidase; D019905:Benzyl Alcohol