Mechanism of Decomposition of CuIII(GlyGlyHis): A Pulse Radiolysis Study

Sara Goldstein; Gidon Czapski; Haim Cohen; Dan Meyerstein; Rudi van Eldik

doi:10.1021/ic00093a011

Mechanism of Decomposition of Cu^III(GlyGlyHis): A Pulse Radiolysis Study

Sara Goldstein, Gidon Czapski, Haim Cohen, Dan Meyerstein, Rudi van Eldik

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Abstract

The trivalent copper complexes of GlyGlyHis, Cum^III(H_-2GlyGlyHis) and Cum^III(H_-3GlyGlyHis), prepared via the oxidation of the corresponding Cu(II) complexes by azide radicals, decompose rapidly to yield CO₂, GlyGlyNHCH(OH)CH₂Im (Im = imidazole) and Cu(I) in aqueous solutions. The decomposition of Cu^III(H_-2GlyGlyHis) consists of two consecutive first-order reactions. The first reaction is attributed to a decarboxylation process, where CO₂ and a complex with a Cu^III-carbon σ-bond are formed. This reaction is followed by a heterolytic decomposition of the latter complex to Cu(I) and GlyGlyNHCH(OH)CH₂Im. Cu^III(H_-2GlyGlyHis), which is less stable than Cu^III(H_-3GlyGlyHis), decarboxylates with a rate constant of 38 ± 5 s^-1, whereas the rate of decarboxylation of Cu^III(H_-3GlyGlyHis) is about 2 orders of magnitude slower. The pK_a of the trivalent complex was determined to be 8.6 ± 0.2. A detailed pressure-dependence study of all the mentioned reaction steps was undertaken. The reported volumes of activation support the above outlined assignments for the nature of the rate-determining steps.

Original language	English
Pages (from-to)	3255-3260
Number of pages	6
Journal	Inorganic Chemistry
Volume	33
Issue number	15
DOIs	https://doi.org/10.1021/ic00093a011
State	Published - 1 Jul 1994
Externally published	Yes

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title = "Mechanism of Decomposition of CuIII(GlyGlyHis): A Pulse Radiolysis Study",

abstract = "The trivalent copper complexes of GlyGlyHis, CumIII(H-2GlyGlyHis) and CumIII(H-3GlyGlyHis), prepared via the oxidation of the corresponding Cu(II) complexes by azide radicals, decompose rapidly to yield CO2, GlyGlyNHCH(OH)CH2Im (Im = imidazole) and Cu(I) in aqueous solutions. The decomposition of CuIII(H-2GlyGlyHis) consists of two consecutive first-order reactions. The first reaction is attributed to a decarboxylation process, where CO2 and a complex with a CuIII-carbon σ-bond are formed. This reaction is followed by a heterolytic decomposition of the latter complex to Cu(I) and GlyGlyNHCH(OH)CH2Im. CuIII(H-2GlyGlyHis), which is less stable than CuIII(H-3GlyGlyHis), decarboxylates with a rate constant of 38 ± 5 s-1, whereas the rate of decarboxylation of CuIII(H-3GlyGlyHis) is about 2 orders of magnitude slower. The pKa of the trivalent complex was determined to be 8.6 ± 0.2. A detailed pressure-dependence study of all the mentioned reaction steps was undertaken. The reported volumes of activation support the above outlined assignments for the nature of the rate-determining steps.",

author = "Sara Goldstein and Gidon Czapski and Haim Cohen and Dan Meyerstein and {van Eldik}, Rudi",

year = "1994",

month = jul,

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doi = "10.1021/ic00093a011",

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T1 - Mechanism of Decomposition of CuIII(GlyGlyHis)

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AU - van Eldik, Rudi

PY - 1994/7/1

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N2 - The trivalent copper complexes of GlyGlyHis, CumIII(H-2GlyGlyHis) and CumIII(H-3GlyGlyHis), prepared via the oxidation of the corresponding Cu(II) complexes by azide radicals, decompose rapidly to yield CO2, GlyGlyNHCH(OH)CH2Im (Im = imidazole) and Cu(I) in aqueous solutions. The decomposition of CuIII(H-2GlyGlyHis) consists of two consecutive first-order reactions. The first reaction is attributed to a decarboxylation process, where CO2 and a complex with a CuIII-carbon σ-bond are formed. This reaction is followed by a heterolytic decomposition of the latter complex to Cu(I) and GlyGlyNHCH(OH)CH2Im. CuIII(H-2GlyGlyHis), which is less stable than CuIII(H-3GlyGlyHis), decarboxylates with a rate constant of 38 ± 5 s-1, whereas the rate of decarboxylation of CuIII(H-3GlyGlyHis) is about 2 orders of magnitude slower. The pKa of the trivalent complex was determined to be 8.6 ± 0.2. A detailed pressure-dependence study of all the mentioned reaction steps was undertaken. The reported volumes of activation support the above outlined assignments for the nature of the rate-determining steps.

AB - The trivalent copper complexes of GlyGlyHis, CumIII(H-2GlyGlyHis) and CumIII(H-3GlyGlyHis), prepared via the oxidation of the corresponding Cu(II) complexes by azide radicals, decompose rapidly to yield CO2, GlyGlyNHCH(OH)CH2Im (Im = imidazole) and Cu(I) in aqueous solutions. The decomposition of CuIII(H-2GlyGlyHis) consists of two consecutive first-order reactions. The first reaction is attributed to a decarboxylation process, where CO2 and a complex with a CuIII-carbon σ-bond are formed. This reaction is followed by a heterolytic decomposition of the latter complex to Cu(I) and GlyGlyNHCH(OH)CH2Im. CuIII(H-2GlyGlyHis), which is less stable than CuIII(H-3GlyGlyHis), decarboxylates with a rate constant of 38 ± 5 s-1, whereas the rate of decarboxylation of CuIII(H-3GlyGlyHis) is about 2 orders of magnitude slower. The pKa of the trivalent complex was determined to be 8.6 ± 0.2. A detailed pressure-dependence study of all the mentioned reaction steps was undertaken. The reported volumes of activation support the above outlined assignments for the nature of the rate-determining steps.

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Mechanism of Decomposition of Cu^III(GlyGlyHis): A Pulse Radiolysis Study

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