Summary Of The Effect Of Metal Ions On Autoxidation Of Dopamine

Table 2 shows the relative effects of metal ion catalysis on the autoxidation of dopamine. It is interesting that copper reacts via a half-order metal dependence [143] and this arises because, although the reaction is triggered by the

Table 2. The effect of metal ions (100 |xM) on the autoxidation of dopamine ([dopamine]T = 10 mM, pH = 7.60).

Metal Ion

104 kobs(s-1)

Fe(II)

5.6

Fe(lII)

6.7

Cu(II)

8.6a

VO2+

10.6

Ni(II)

17.2

Mn(II)

29.1(3.7)a

Co(II)

46.2b

a Half-order rate constant (units 10 5M1/2s 1). b Possible half-order contribution.

a Half-order rate constant (units 10 5M1/2s 1). b Possible half-order contribution.

initial electron transfer within a Cu(II) complex, the resulting Cu(I) does not bind to the catechol function but rather to dioxygen to form CuO+ which is the active species.

Note especially that at the relatively high pH of 7.6 all the metal ion species react considerably slower than at pH < 5. This is because it is mainly the bis-complexes that exist at higher pH.

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