The Role of Metal Ions and Metallo-Complexes in Luminol Chemiluminescence (Catalysis)
Nekimken, Howard Lewis
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https://hdl.handle.net/2142/70319
Description
Title
The Role of Metal Ions and Metallo-Complexes in Luminol Chemiluminescence (Catalysis)
Author(s)
Nekimken, Howard Lewis
Issue Date
1986
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Analytical
Abstract
Luminol chemiluminescence (CL) has been employed for the sensitive detection of various analytes such as certain transition metal ions and hydrogen peroxide (H(,2)O(,2)). Metal ions and metallo-complexes significantly enhance the light output of the luminol CL reaction (these species are generally referred to as catalysts in the literature). Unfortunately, the mechanism responsible for this enhancement is unknown. This research project studied the metallo-catalyzed liminol CL reaction to improve the understanding of this reaction. Photon emission, extent of reaction, fluorescence efficiency and other related measurements were obtained for the luminol reaction as a function of catalyst identity and concentration. The metallo-catalysts studied were hemin, hemoglobin, horseradish peroxidase (HRP), ferricyanide, Co(II), Cu(II), Cr(III), Fe(II), Fe(III), Ni(II) and Mn(II). In contrast to most reports in the literature, these measurements allowed the direct determination of quantum yield of CL ((PHI)(,CL)) values.
Both the photon emission and extent of reaction for the luminol CL reaction increased with increasing catalyst concentration. The iron porphyrins, hemin, HRP and hemoglobin were found to accelerate the luminol CL reaction most effectively. The next most efficient catalyst was ferricyanide, followed by Co(II), the most effective free metal ion catalyst. Based on data involving the determination of the stoichiometry for the reaction between luminol and catalyst, hemin, hemoglobin, HRP and Co(II) can be classified as true catalysts of this CL reaction (at low enhancer concentrations). Further experiments indicate that the catalytic behavior of the species studied is limited by competing side reactions. A mode of catalytic deactivation is the decomposition or oxidation of the catalyst by H(,2)O(,2). A second mode of deactivation for metal ion catalysts is their precipitation from solution as hydroxides. This research has established a good starting point for further research which ultimately should improve the understanding of the catalyzed luminol, and aqueous solution, CL reactions to the point where these reactions could be utilized much more effectively for the sensitive and routine analysis of various analytes.
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