Title

Reactions of Labile Metal Ions with Oligopeptides. V.1 Copper (II) with Glycylglycine and Glycylsarcosine

Document Type

Article

Publication Date

10-1-1970

Abstract

The complexation reactions of glycylsarcosine and glycylglycine with copper(II) have been studied using the temperature-jump technique. At 25°, the rate constants for the reactions Cu2+ + L– ⇋ CuL+ (k1, k–1) are for glycylsarcosine, k1 = 4.0 X 108 M–1 sec–1, k–1 = 170 sec–1, and for glycylglycine, k1 = 3.5 × 108 M–1 sec–1, k–1 = 960 sec–1. In addition, for the latter ligand, a slower effect appears at pH ~4, which has been ascribed to the reaction Cu(HGG)+ ⇋ CuGG + H+ (kD, kH). The rate constants at 25° are kD = 76 sec–1 and kH = 8.7 × 105 M–1 sec–1. The bonding model for metal ion peptide complexes suggested by Rabin is consistent with these kinetic results. The reactions for glycylglycine were studied at other temperatures and the activation energies were determined. The activation energy for complexation is consistent with the suggestion that the rate-determining step is the removal of a water molecule from an axial position in tetragonally distorted Cu(H2O)62+. The activation energy for the protonation reaction is considerably larger than that usually obtained for reactions of this type and is consistent with structural rearrangement subsequent to proton attack. © 1970, American Chemical Society. All rights reserved.

Publication Name

Journal of the American Chemical Society

Volume Number

92

First Page

5878

Last Page

5882

Issue Number

20

DOI

10.1021/ja00723a011

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