Title

Reactions of L-cysteine with cobalt(II) and nickel(II)

Document Type

Article

Publication Date

12-1-1968

Abstract

The kinetics of complexation of Co(II) and Ni(II) with L-cysteine have been studied at 20°C and μ = 0.1 M using the temperature jump method. Both anionic forms of this ligand are attacking forms, and the rate constants for the reactions ML +L ⇌ ML , ML +HL ⇌ ML +H , have been determined for n = 1 and 2. For Co(II) they are k = 5.6 × 10 M sec ; k′ = 5.6 × 10 M sec ; k = 2.8 × 10 sec ; k′ = 3.6 × 10 M sec ; k = k′ = 1.5 × 10 M sec ; k = 3.8 × 10 sec ; k′ = 4.9 × 10 M sec ; and for Ni(II) they are k = 1.5 × 10 M sec ; k′ = 1.5 × 10 M sec ; k = 3.4 × 10 sec ; k′ = 4.4 × 10 M sec ; k = k′ = 4.4 × 10 M sec ; k = 1.1 × 10 sec ; k′ = 1.4 × 10 M sec . Differences in forward rate constants for attack of the different ligand species on a given metal ion are related to variations in equilibrium constants for ion-pair formation. The complexes of Co(II) and Ni(II) are probably octahedral and square-planar, respectively. The presence of L-cysteine in the inner co-ordination sphere of these cations seems to cause a greater increase in the rate of loss of remaining water molecules than has been observed with similar ligands. The characteristics of L-cysteine which might account for this effect are discussed. n-1 k-n n n-1 k′-n n 1 1 -1 -1 2 2 -2 -2 1 1 -1 -1 2 2 -2 -2 2(2-n)+ 2- kn 2(n-1)- 2(2-n)+ - k′n 2(n-1)- + 6 -1 -1 5 -1 -1 -3 -1 6 -1 -1 6 -1 -1 -2 -1 8 -1 -1 5 -1 -1 4 -1 -1 -5 -1 4 -1 -1 4 -1 -1 -5 -1 5 -1 -1

Publication Name

Transactions of the Faraday Society

Volume Number

64

First Page

1006

Last Page

1013

DOI

10.1039/TF9686401006

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