The oxidation of adrenaline (H2LH+) by molecular oxygen in the presence of catalytic amounts of VO2+ ions has been followed using a Clark-type oxygen electrode. The empirical rate law -d[O2]/dt = kobs.[O2] + p was obtained in which p is a small constant (only observable at low pH) and kobs. is given by the relationship (i), where [VO]T and [L]T are total initial concentrations of kobs. = A[VO]T[L]T/B[H+]2 + C[L]T + D[L]T2 + E/[H+] + F (i) VO2+ and adrenaline respectively. It is demonstrated that this behaviour is consistent with the involvement of both VO2+ and V2+ species and furthermore that it also calls for the presence of a tris(adrenaline) species, V(LH)3+. A kinetically determined equilibrium constant for reaction (ii) is, VO(LH)2 + H2LH+⇌V(LH)3+ + H2O (ii) reported. The necessary proton- and metal-ligand equilibrium constants were obtained by pH- and 1H n.m.r.-titration techniques. All solutions were made up to a constant ionic strength (I = 0.100 mol dm-3) with KNO3 at 25.00 ± 0.02 °C.
|Number of pages||6|
|Journal||Journal of the Chemical Society, Dalton Transactions|
|Publication status||Published - Jan 1 1986|
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