QUERCETINASE MODEL STUDIES - THE OXYGENATION OF FLAVONOL CATALYZED BYA CATIONIC 2,2'-BIPYRIDINE COPPER(II) FLAVONOLATE COMPLEX

The catalyst [Cu-II(bpy)(fla)]ClO4, 1, was prepared from Cu(CH3CN)(4)C lO4, 2,2'-bipyridine (bpy), flavonol (flaH), and dioxygen in acetonitr ile at ambient conditions. The flavonolato copper complex 1 reacts wit h molecular oxygen slowly at room temperature but reasonably fast at a round 100 degrees C in acetonitrile or DMF to the O-benzoylsalicylato copper complex [Cu-II(bpy)(O-bs)]ClO4 in good yield. Kinetics of the o xygenation of 1 shows that there are two kinetically not interpretable segments of the reaction, however 1 is a good catalyst for the oxygen ation of flavonol to O-benzoylsalicylic acid (O-bsH) at around 100 deg rees C. Kinetic studies of the catalytic reaction resulted in the rate expression -d[flaH]/dt = k(obs)[flaH][catalyst](2)[O-2](2). The react ion constant at 100 degrees C was found to be k(obs) = 7.20 +/- 0.13 X 10(10) mol(-4) dm(12) s(-1), with activation parameters Delta H doubl e dagger = 80.83 +/- 3.14 kJ mol(-1), Delta S double dagger = 179.61 /- 8.82 J mol(-1) K-1. (C) 1998 Elsevier Science B.V.