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METAL IONS AND HYDROGEN PEROXIDE XXIX. On the Kinetics and Mechanism of the Catalase-like Activity of Nickel(II) and Nickel(II)-Amine Complexes
Ist Teil von
Journal of coordination chemistry, 1974-02, Vol.3 (3), p.235-247
Ort / Verlag
Taylor & Francis Group
Erscheinungsjahr
1974
Link zum Volltext
Quelle
Alma/SFX Local Collection
Beschreibungen/Notizen
The disproportionation of H
2
O
2
, catalyzed by Ni
2+
aq
and several Ni
2+
−amine complexes, was investigated. (i) With Ni
2+
aq
in the pH range 6.6-8.2 and without buffer the following rate law holds: μ
0
= d[O
2
/dt = k[Ni
2+
] [H
2
O
2
]
2
/[H
+
] (k = (1.77 ± 0.23) × 10
−9
mol
−1
1. sec
−1
). In the presence of phosphate buffer and in the pH range 6-7 the initial rate, μ
0
, is proportional to 1/[H
+
]. (ii) For the buffer-free Ni
2+
−2,2′-bipyridyl 1:1 system in the pH range 4.5-8 μ
0
= ((k
1
/[H
+
]) + k
2
)[H
2
O
2
]([Ni
2+
]
tot
= [Bipy]
tot
)
0.5
where k
1
= (1.35 ± 0.20) × 10
−12
mol
0.5
l.
−0.5
sec
−1
and k
2
= (2.5 ± 0.5) × 10
−6
mol
−0.5
l.
0.5
sec
−1
. With borate buffer μ
0
is increased, but in the pH-dependent part the given proportionalities between μ
0
and [reactants] are valid. For these conditions the Ni
2+
−2,2′-bipyridyl 1:1 complex is the catalytically most active species. (iii) In the buffer-free system with Ni(ethylenediamine)
2+
2
as catalyst in the pH range 8.2-10 it appears that an analog rate law holds as given above for Ni
2+
aq
(cf. i). Borate buffer has a rate enhancing effect on the catalytic activity of Ni(En)
2+
2
Also there is evidence for μ
0
being proportional to 1/[H
+
]
2
and this means two HOO
−
(or corresponding borate derivatives) are participating in the reaction before the rate determining step. (iv) With 2-picolylamine the 1:1 complex reaches about the activity of Ni
2+
, while with 4-aminomethylimidazole or histamine none of the complex species is as active as Ni
2+
. - As far as possible the reaction laws are given for the mentioned systems. Reaction mechanisms and the structure of the active species, as well as the rate enhancing effect of borate, are discussed.