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Complexation of Copper(II) Ion with Tetraglycine as Followed by Electronic Absorption Spectroscopy. A Bioinorganic Chemistry Experiment

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Eugenio Garribba and Giovanni Micera

Department of Chemistry, University of Sassari, I-07100 Sassari, Italy

J. Chem. Educ., 2007, 84 (5), p 832

DOI: 10.1021/ed084p832

Publication Date (Web): May 1, 2007

Section:

History, Education, and Documentation

Abstract

The complexation of Cu(II) ion with tetraglycine (TetraGly) is studied by electronic absorption spectroscopy as a function of pH. In an equimolar solution, tetraglycine forms a sequence of 1:1 chelated species: [CuL]⁺ around pH 5.4, [CuLH_-1] around pH 6.4, [CuLH_-2]^- around pH 8.0, and [CuLH_-3]^2- above pH 11.0. They are characterized, respectively, by the equatorial donor sets [(NH₂, CO); H₂O; H₂O], [(NH₂, N^-, CO); H₂O], [NH₂, N^-, N^-, CO], and [NH₂, N^-, N^-, N^-], where NH₂ is the amino, CO the carbonyl, and N^- the deprotonated amide group. The electronic absorption spectra exhibit a single band in the visible region, which becomes sharper and shifts to higher energy values as the complexation proceeds and the water molecules are replaced by stronger donors. The experimental λ_max value can be calculated through Billo's equation, which assigns a different contribution to the equatorial water, carbonyl-O, carboxylate-O, amino-N, and deprotonated amide-N. Two biological applications, the interaction of Cu(II) with prion and the transport of copper by albumin, are presented.

Keywords (Audience):

Upper-Division Undergraduate

Keywords (Domain):

Biochemistry

Keywords (Pedagogy):

Hands-On Learning / Manipulatives

Keywords (Subject):

Aqueous Solution Chemistry

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This article has been cited by 1 ACS Journal articles (1 most recent appear below).

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- Using Proteins in a Bioinorganic Laboratory Experiment: Iron Loading and Removal from Transferrin
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  Journal of Chemical Education2009 86 (8), 969
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